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In this study, technology computer-aided design (TCAD) was used to investigate carrier selective contact solar cell performance based on the boundary of tunneling oxide and electron selective contact layer properties. The role of tunneling oxide quality in the passivation and inter-diffusion properties of the plasma-enhanced chemical vapor deposition of phosphorus-doped amorphous silicon as an electron selective contact layer is studied for carrier selective contact solar cells. Tunnel oxide quality varies according to the ratio of Si4+ to Si2+ state. For the Si4+/Si2+ ratio of 4, open-circuit voltage of 730 mV and the lowest interface trap density of 5.3 × 1010 cm−2 eV−1 are achieved. The change in diffusion depth of the doped layer with respect to the annealing temperature is analysed by transmission electron microscopy (TEM)/energy dispersive X-ray spectroscopy (EDS) measurement. Carrier selective contact solar cell parameters are optimized by incorporating the experimental values of interface trap density, inter-diffused impurity concentration, and depth in the Quokka 3 TCAD tool. Solar cell conversion efficiency of 24.31% was obtained. To understand the response of carrier selective solar cell to the environmental changes, the output characteristics of the solar cell were studied by varying the illumination temperature by 10% of the standard test conditions (STC) and temperature from 277 K to 377 K (difference of 100 K).

In this study, the contact mechanism between Ag&ndash, Al and Si and the change in contact resistance (Rc) were analyzed by varying the firing profile. The front electrode of an n-type c-Si solar cell was formed through a screen-printing process using Ag&ndash, Al paste. Rc was measured by varying the belt speed and peak temperature of the fast-firing furnace. Rc value of 6.98 m&Omega, cm&minus, 2 was obtained for an optimal fast-firing profile with 865 &deg, C peak temperature and 110 inches per min belt speed. The contact phenomenon and the influence of impurities between the front-electrode&ndash, Si interface and firing conditions were analyzed through scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The EDS analysis revealed that the peak firing temperature at 865 &deg, C exhibited a low atomic weight percentage of Al (0.72 and 0.36%) because Al was involved in the formation of alloy of Si with the front electrode. Based on the optimal results, a solar cell with a conversion efficiency of 19.46% was obtained.

Ga2O3 is a promising wide bandgap semiconductor for applications including power electronics and photodetectors and is available in large diameter, high quality bulk crystalline form. There have been many recent advances on both the materials and processing/device fronts and in this chapter we discuss some developments in Ohmic contacts, plasma etching, understanding of the role of hydrogen and high breakdown rectifier structures. Ga2O3 appears to have a role in expanding applications for high-speed or high-power semiconductor electronic devices. The high-power/high-voltage market is currently primarily served by Si and SiC devices. Ga2O3 is the leading candidate to address the ultra-high power market (>1kW). We will discuss recent progress in developing Ohmic contacts using interlayers of ITO or AZO, high density plasma etching using ICP discharges and the resultant etch rates, morphologies and near-surface damage, behavior of hydrogen incorporated during ion implantation or plasma exposure, measurement of band offsets with dielectrics and application of these processes to vertical and lateral transistor structures.

Tandem-structured amorphous Si solar cells can absorb a broader range of solar spectra than a single-junction device. In a tandem cell, usually a thicker bottom subcell becomes necessary to absorb the required number of photons from long-wavelength light to generate the desired current density. Alternatively, an optoelectronically improved active layer and light-trapping scheme can also be used with a thinner bottom subcell. In this respect, we investigated bottom subcell of tandem solar cells with microcrystalline Si active layer. Three of the primary parameters that were progressively varied for the bottom subcells were the crystalline volume fraction (X c ) of the active layer, buffer layer at the i/n interface, and back reflector (BR). Here, the buffer layer and higher X c are expected to improve respectively the electronic properties of the i/n interface and the active layer of the bottom subcell. Furthermore, a suitable BR can reflect the unabsorbed long-wavelength light back to the cell for further absorption; thereby raising its current density. We have observed that low-power deposition of the microcrystalline Si active layer (150 W), an 8 nm thick buffer layer at the i/n interface, and a zinc oxide BR layer gave best results in a tandem solar cell. An optimized tandem cell exhibited an open-circuit voltage, short-circuit current density, fill factor, and efficiency of 1.445 V, 12.32 mA/cm 2 , 71.56%, and 12.74%, respectively.

AlGaN/GaN high electron mobility transistors (HEMTs) are useful devices for next-generation RF and power electronics systems1,2. Traditional Ni-based Schottky gates in these devices have been shown to degrade when subjected to electrical stress, thermal stress, and radiation due to Ni migration into adjacent metal or semiconductor layers3,4. The instability of these Ni-based gates limits device reliability, rendering the search for replacement gate materials that are electrically- and thermally-stable a topic of tremendous importance. Of the transition metal nitrides, TiN is a particularly promising material, due to its near-metallic conductivity, suitable Schottky barrier heights and ideality factors on GaN and AlGaN, and high temperature stability. This work investigates the performance of atomic layer deposited (ALD) TiN gates and directly compares them to traditional Ni/Au gates. ALD TiN gates (15-75nm thick) were deposited on AlGaN/GaN HEMTs and diodes at 150-350°C using Tetrakis(dimethyamido)titanium (TDMA-Ti) and a 300W N2/H2 plasma as precursors with a growth rate of 0.6 Å/cy. Increasing the growth temperature, while remaining in a linear ALD regime, reduced the oxygen content by a factor of two and eliminated carbon impurities within the film resulting in 7x lower film resistivity. The plasma gas chemistry and pressure (8-80 mTorr) had an even greater impact on the electrical properties of these films. An exponential decrease in resistivity was achieved by increasing the N2/H2 ratio from 0.1-1.6 at a constant temperature. The lowest resistivity (120 µΩ-cm) was attained using a N2-only plasma at 7 mTorr at 350°C. While this resistivity is higher than typical bulk values (10-30 µΩ-cm), it is similar to PVD (30-100 µΩ-cm) and lower than many CVD films, which can vary widely (200-10,000 µΩ-cm). Using this growth parameter knowledge, a series of TiN gates were deposited on GaN diodes with varying oxygen content from 3-12 at%. TiN films with lower oxygen content also exhibited lower barrier heights in Schottky barrier diodes, suggesting a way to tailor the properties for different applications. ALD TiN gates (75nm) also exhibited improved static and dynamic on-state characteristics when directly compared to identical Ni/Au-gated AlGaN/GaN HEMTs. Reverse bias gate stressing indicated a higher critical voltage (VgsTiN = -210V, VgsNi/Au = -120V) and a higher breakdown voltage (VgsTiN = -270 ± 10 V, VgsNi/Au = -240 ± 30V) for the TiN gates. Furthermore, the TiN gates exhibited a decrease in reverse leakage current after stressing suggesting enhanced stability. Gate thermal stability was assessed through sequential device annealing from 400-800°C in 100°C increments. The TiN gated devices exhibited stable DC operation up to 800°C, while the Ni/Au gates showed significant degradation after annealing above 500°C and failed above 700°C. This suggests that ALD TiN gates are a strong candidate for reliable HEMT gate metallization and other applications where increased stability is required at higher temperatures. 1 R.S. Pengelly, et al., IEEE Trans. Microwave Theory Tech. 60 [6], 1764 (2012). 2 S.J. Pearton, et al., J. Vac. Sci. Technol. A 31 [5], 050801 (2013). 3 Y.H. Choi, et al., Materi. Res. Soc. Symp. Proc. 1167, 1167-O05-06 (2009). 4 A.D. Koehler, et al., IEEE Elect. Dev. Lett. 35 [12], 1194 (2014).

$\beta $ -Ga2O3 Schottky barrier diodes were fabricated in a vertical geometry structure consisting of Ni/Au rectifying contacts without edge termination on Si-doped epitaxial layers ( $10~\mu \text{m}$ , $\text{n}\sim 4\times 10^{15}$ cm $^{-3})$ on Sn-doped bulk Ga2O3 substrates with full-area Ti/Au back Ohmic contacts. The reverse breakdown voltage, ${V} _ \text {BR}$ , was a function of rectifying contact area, ranging from 1600 V at $3.1\times 10^{-6}$ cm2 (20- $\mu \text{m}$ diameter) to ~250 V at $2.2{\times }10^{-3}$ cm $^{-2}$ (0.53-mm diameter). The current density near breakdown was not strongly dependent on contact circumference but did scale with contact area, indicating that the bulk current contribution was dominant. The lowest ON-state resistance, ${R} _\text {on}$ , was 1.6 $\text{m}\Omega \cdot $ cm2 for the largest diode and 25 $\text{m}\Omega \cdot $ cm2 for the 1600-V rectifier, leading to a Baliga figure-of-merit ( ${V} _\text {BR}^{2}/{R} _\text {on})$ for the latter of approximately 102.4 MW $\cdot $ cm $^{-2}$ . The ON-OFF ratio was measured at a forward voltage of 1.3 V and ranged from $3\times 10^{7}$ to $2.5\times 10^{6}$ for reverse biases from −5 to −40 V and showed only a small dependence on temperature in the range from 25 °C to 100 °C.

Electron-hole pair (EHP) recombination is a decreasing factor of the efficiency in silicon solar cells. The passivation layer reduces recombination by removing dangling bonds which act as recombination centers. Usually, SiN x , SiO x , SiON x and AlO x layers are used as passivation layer in solar cell applications. Tunnel oxide layer is one of the main issues to achieve high-quality passivation using carrier-selectivity between the silicon wafer and poly-Si layer. In this work, ultra-thin tunnel oxide layer by plasma enhanced chemical vapor deposition using N 2 O plasma is deposited on both sides of the samples. The RF power and substrate temperature are varied. Then phosphorus doped Si layer is deposited. The optimized tunnel oxide layer has low D it (5.3 × 10 10 cm −2 eV −1 ) and high passivation effect (τ eff of 923 μs, iV oc of 739 mV) when deposited with RF power of 200 W and a substrate temperature of 400 °C. This optimized tunnel oxide passivation layer is applied to the n-type c-Si solar cell. The fabricated solar cell showed J sc of 41.04 mA/cm 2 and V OC of 644 mV. Compared to the cell with chemical oxide passivation, J sc and V oc increased by 0.2 mA/cm 2 and 11 mV which were also higher than the cell with SiN x passivation.

The impact of internal irradiation with secondary Compton electrons, generated by gamma-photons, on the characteristics of III-N/GaN-based devices was explored. N-channel AlGaN/GaN high-electron-mobility transistors (HEMTs) were exposed to gamma-radiation from a 60Co source for doses up to 600 Gy. Temperature-dependent electron beam-induced current (EBIC) was employed to measure minority carrier transport properties. For low doses below ∼250 Gy, the minority carrier diffusion length in AlGaN/GaN HEMTs is shown to increase by about 40%. This increase is likely due to longer minority carrier lifetime induced by internal Compton electron irradiation. An associated decrease in activation energy, extracted from temperature-dependent EBIC, was also found. The obtained increase in transconductance and decrease in gate leakage current indicate an improvement in performance of the devices after low doses of irradiation. For high doses of gamma-irradiation, above ∼300 Gy, the performance of HEMTs showed a d...

Deuterium was incorporated in bulk single crystal β-Ga2O3 samples by either ion implantation (100 keV, 1015 cm−2) or plasma exposure (up to 270°C, 30 mins) of single-crystal β-Ga2O3 and then its stability was examined as a function of annealing temperature. The mechanisms in both cases were extracted by fitting the experimental depth profiles using models within the Florida Object Oriented Process Simulator (FLOOPS) code. In the case of incorporation by implantation, annealing causes the deuterium to migrate toward the surface with simultaneous trapping at the residual implant damage. In the case of plasma incorporation where there is no residual damage, annealing causes outgassing of the deuterium from the surface, mediated through molecule formation. Very good fits to the experimental data are achieved by integrating physics of the outdiffusion mechanisms into the FLOOPS code. The rate constants and diffusivities used for the simulation were found to follow an Arrhenius dependence, with an activation energy for outdiffusion of deuterium of 1.22 eV and 2.58 eV for the release rate of deuterium from trap sites in the implanted case.

Schottky diodes were formed on bulk or epitaxial β-Ga2O3 using Ni/Au or Pt/Au and the electrical characteristics measured as a function of temperature in the range 25–200°C. The barrier heights were 1.07 eV (Ni/Au) and 1.04 eV (Pt/Au) at 25°C. The barrier heights increased with temperature, while the on-state resistances (RON) decreased over the same range. The temperature coefficient of reverse breakdown voltage (VB), β, was −4 mV/K for Ni/Au and −0.1 mV/K for Pt/Au. The figure-of-merit (VB2/RON) was above 3 MW.cm−2 at 25°C for Ni/Au diodes and was still ~1 MW.cm−2 at 200°C. The reverse recovery times were also measured as a function of temperature and were of the order of 21–28 ns over the range 25–150°C for both epi and bulk diodes. The results show the already high quality of bulk and epitaxial β-Ga2O3 and the potential of this material for high temperature power electronics.

Thin-film silicon solar cells are promising candidates for the low-cost production of electricity from sunlight. However, their efficiency remains relatively low, which is one of the major issues for their commercialisation. In the thin-film silicon technology, light trapping is an important design consideration for achieving a higher device efficiency. An advanced light-trapping technology is expected to boost the efficiency of solar cells further. Therefore, we investigated the development of an advanced light-trapping scheme in a two-dimensional periodic surface structure produced via inductively coupled plasma reactive-ion etching. The texture of the glass surface was varied under various plasma conditions. For the various shapes and sizes of the obtained surface texture, the increased height and base angle of the individual texture showed an overall increase in the diffused transmission of light. In some cases, the diffused transmission was as high as 89 % of the total light transmitted through the glass. The effect of the textured glass on a solar cell was investigated through simulation. Results show that the efficiency of a single-junction solar cell can be enhanced significantly when such a textured glass is used instead of a non-textured glass.

n-type PERT (passivated emitter, rear totally diffused) bifacial solar cells with boron and phosphorus diffusion as p+ emitter and n+ BSF (back surface field) have attracted significant research interest recently. In this work, the influences of wafer thickness, bulk lifetime, emitter, BSF on the photovoltaic characteristics of solar cells are discussed. The performance of the solar cell is determined by using one-dimensional solar cell simulation software PC1D. The simulation results show that the key role of the BSF is to decrease the surface doping concentration reducing the recombination and thus, increasing the cell efficiency. A lightly phosphorus doped BSF (LD BSF) was experimentally optimized to get low surface dopant concentration for n type bifacial solar cells. Pre-oxidation combined with a multi-plateau drive-in, using limited source diffusion was carried out before pre-deposition. It could reduce the surface dopant concentration with minimal impact on the sheet resistance.

AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated for structures grown on ZrTi metallic alloy buffer layers, which provided lattice matching of the in-plane lattice parameter ("a-parameter") to hexagonal GaN. The quality of the GaN buffer layer and HEMT structure were confirmed with X-ray 2θ and rocking scans as well as cross-section transmission electron microscopy (TEM) images. The X-ray 2θ scans showed full widths at half maximum (FWHM) of 0.06°, 0.05° and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM of the lower section of the HEMT structure containing the GaN buffer layer and the AlN/ZrTi/AlN stack on the Si substrate showed that it was important to grow AlN on the top of ZrTi prior to growing the GaN buffer layer. The estimated threading dislocation (TD) density in the GaN channel layer of the HEMT structure was in the 108 cm−2 range.

AlGaN/GaN high electron mobility transistors (HEMTs) have gained more attention recently because of the superior mobility (~1400 cm2/V-s) and high breakdown voltage. The quality of Ohmic contacts are key characteristics to guarantee the high mobility. During fabrication, Ohmic metals would be exposed to chemicals such as Buffer Oxide Etchant (BOE). BOE is a mixture of HF and NH4F, which is known to be reactive to metals. As a result, it is necessary to understand the effect of BOE treatment on Ohmic metals. The HEMT structures consisted of a 25 nm AlGaN barrier layer, a 0.8 µm C doped GaN buffer layer, a 1.4 µm AlGaN transition layer and a thin AlN nucleation layer on 300 µm Si substrate. HEMT fabrication began with Ti/Al/Ni/Au Ohmic metallization and rapid thermal annealing in N2 at 850ºC for 1 min. Ohmic metals were exposed to BOE for 3 mins. The resistance was monitored every 15 sec by transmission line method (TLM). Scanning electron microscopy (SEM) was used to observe the surface morphology change after BOE exposure. Energy dispersive X-ray spectrum (EDX) and Auger electron analysis was used to characterize the elemental change after BOE exposure. Figure 1 shows the effect of BOE exposure to contact resistance. As shown in Figure 1, the contact resistance increased from 1×10-4 Ω-cm2 to 2×10-4 Ω-cm2 after exposure to BOE for 2 minute. BOE solution is a solution which composed of NH4F and HF. Since the reaction of Ti, Al, and Ni to HF is spontaneous, the increase of contact resistance is expected. The sheet resistance doesn’t change much with BOE treatment time, indicating the GaN is more inert to BOE exposure. Table I shows the elemental change after BOE treatment analyzed by EDX. As shown in TABLE 1, Au decreased by 7% although it supposes to be not reactive to BOE. The content of Ti decreased by 0.1% and the contents for the rest of elements, Al, Ni and N, increased by 0.2, 1.3 and 0.6%, respectively. For EDX, the X-rays are generated in a region about 2 microns in depth of the sample. The thickness of the Ti/Al/Ni/Au Ohmic metallization was around 0.3 µm, and thus the EDX signals of Ga and N should be dominated by the bulk GaN even with some Ga or N out-diffusing through the alloyed Ohmic metallization. Thus, it is reasonable to assume that the Ga and N contents did not change significantly. The percent increases of Ga and N content after BOE treatment were due to the decrease of the Au content. By comparing the increases of percent content of Al, it was less than the percent increase of Ga or N. Therefore, besides Ti and Au, the content of Al also decreased after BOE treatment. However the increase of Ti/Al/Ni/Au Ohmic metallization contact resistance should be mainly caused by the decrease of Au content in the BOE treated sample. Although Au is inert to BOE, Au could be removed by the etching of Al underneath this layer. SEM is also used to observe the surface morphology change after BOE treatment. The Ohmic contacts can be further divided into three different regions, island, ring, and field area. Each island is around 3-5 µm and surrounded by a 1 µm-width Au ring. After BOE treatment, the width became thinner and the island became shorter. With the EDX analysis, Au/Al was found to mainly be distributed in ring area and Ni/Al in the island. Because Al is reactive to BOE, it might be etched and thus peeled off Au in the ring area. The etching of Au might be the reason of thinner width and the increase of contact resistance. In summary, the degradation of Ohmic metallization exposed in BOE was studied. The contact resistance of Ohmic metallization increased significantly after treatment in BOE for 2 minutes. Moreover, after annealing, there were island-like structures surrounded by Au-Al alloy rings and a field area between the islands. The BOE etching occurred mainly at the island and ring areas instead of the field area between the islands. The increase of sheet resistance was due to the etching of surface Al and Ti and the loss of Au in the island and ring areas. Figure 1

AlGaN/GaN high electron mobility transistors (HEMTs) are promising candidates for high power and high current applications with its high mobility and high breakdown field. Epitaxial films for device substrate are typically grown on sapphire or silicon carbide, SiC, with dislocation densities in the order of 108 - 1010cm-2 due to their thermal coefficient and lattice mismatches. The thinner GaN buffer layers on SiC have been reported to have higher threading dislocation density in the GaN, but lead to higher off-state breakdown voltages. However, thick GaN buffer layers on sapphire and their impact on dc performance have not been widely studied. In this study, the impact of GaN buffer layer quality on dc and gate-lag pulse performance of AlGaN/GaN HEMTs was studied. Transmission electron microscopy (TEM) was used to measure the dislocation density in the GaN buffer layer of the HEMT samples. Dc characteristics, including drain I-Vs, transfer characteristics, and gate pulsed drain I-V characteristics of the HEMTs, were measured to establish a correlation between the AlGaN/GaN HEMTs’ dc and gate-pulsed performance and GaN buffer layer quality. AlGaN/GaN HEMT structures grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates were acquired from two different vendors. Both types of wafers had 24% Al concentration in the AlGaN barrier layer. One type of wafer had a 5 µm GaN buffer and the other had a 2 µm GaN buffer layer. HEMT fabrication was started with mesa patterning by conventional optical lithography. The mesa-etching was achieved using a unaxis shuttle-lock reactive ion etcher with inductively coupled plasma module (ICP) for device isolation with a Cl2/Ar plasma. Ohmic metallization of electron-beam evaporated Ti/Al/Ni/Au (25 nm/125 nm/45 nm/100 nm) was patterned by lift-off and subsequently rapid thermally annealed at 850⁰C in a flowing N2 ambient for 45 seconds. Schottky gates of e-beam evaporated Ni/Au (20 nm/80 nm) with 100 μm width and 1 μm length were obtained by standard lift-off patterning. DC current–voltage (I-V) characteristics were measured using an HP4156 parameter analyzer, and gate-lag pulse measurements were measured using an Agilent 8114A pulse generator. Figure 1 shows the bright field cross-sectional transmission electron microscopy (BF-XTEM) pictures of AlGaN/GaN surface for the top layers of (a) HEMT structure with 2 µm GaN buffer layer, (b) HEMT structure with 5 μm GaN buffer layer as well as the GaN/sapphire interface for the (c) HEMT structure with 2 μm GaN buffer layer, and (d) HEMT structure with 5 μm GaN buffer layer. Dislocations are seen to originate near the GaN/sapphire interface and propagate up through the AlGaN/GaN interface to the surface of both HEMT wafers. However, it is clear that the HEMT structure with 2 μm GaN buffer layer exhibited a much higher defect density. The calculated defect density for 2 μm GaN buffer layer substrate had an order of magnitude higher defect density. However, 5μm GaN buffer layer wafer showed that it was under high strain with larger height difference across the 2 inch with lower radius of curvature. There was no major difference in HEMTs’ dc performance was observed. In the other hand, Figure 2 (a) and (b) shows that gate lag measurement on fabricated HEMTs on 5 μm GaN buffer layer wafer showed no degradation and on 2 μm GaN buffer layer wafer showed the otherwise. The effects of defect density on HEMT dc and radio frequency performance were studied. HEMTs were fabricated on 2 and 5 μm of GaN buffer layers with the same composition of active layers. Despite there was no significant difference was seen in dc characteristics, significant reduction in pulse measurements was observed on thinner GaN layer HEMTs. These results suggest that the defects created in GaN buffer layer do not largely influence device dc performance but are closely related to high frequency performance. Figure 1

AlGaN/GaN high electron mobility transistors (HEMTs) showed its promising features in high power and high frequency applications such as inverter units in hybrid electric vehicles, advanced radar systems, and satellite-based communication networks with its high density of sheet carrier concentration, high electron mobility, and radiation hardness. However, the high gate leakage and current collapse limits the reliability and performance of the HEMTs. In the other hand, using oxide as gate dielectric solves the problems at the same time not degrading the device performances. In this paper, we investigated the effect of the proton energy dependency on dc characteristics of atomic layer deposition (ALD) deposited Al2O3 gate dielectric AlGaN/GaN MOS-HEMTs. AlGaN/GaN MOS-HEMTs were irradiation with fixed proton dose of 5 × 1015 cm-2 at 5MeV, 10MeV, and 15MeV. The MOS-HEMTs’ dc characteristics were compared before and after the irradiation to assess the damage done by irradiation. AlGaN/GaN epilayer were grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD), consisting of 5 μm GaN buffer, 21 nm of undoped Al0.24Ga0.76N, and a 5 nm undoped GaN cap. On-wafer Hall measurement was used to measure sheet resistance, sheet carrier concentration, and mobility of 479 Ω/□, 9.55 × 1012 cm-2, and 1363 cm2/V·s respectively. Mesa isolation process was achieved by Unaxis Shuttlelock Reactive Ion Etcher with Inductively Coupled Plasma Module (ICP) with Cl2/Ar plasma. Consisting of Ti/Al/Ni/Au (25 nm/125 nm/45 nm/100 nm), 5 μm distance of source to drain Ohmic metallization was achieved by lift-off process of electron-beam evaporator deposited Ohmic metal. Rapid thermal annealing at 850ºC with N2 ambient for 45 seconds was followed by Ohmic metallization. A 10 nm Al2O3 layer was deposited by ALD at 300ºC. Ni/Au (20nm/80nm) gate metal with 100 μm width and 1 μm length was deposited by liftoff of e-beam evaporator. After fabricating MOS-HEMT, proton irradiation was projected at the Korean Institute of Radiological & Medical Sciences (KIRAMS) using a MC 50 (Scanditronix) cyclotron with proton fluence of 5 × 1015 cm-2 at 5MeV. MOS-HEMT’s dc characteristics were measured by 4156 HP parameter analyzer. Transmission line measurement (TLM) was used to measure sheet resistance (RS), transfer resistance (RT), and contact resistance (RC) before and after proton irradiation. Stopping and range of ions in matter simulations (SRIMS) was used to simulate the penetration depth of the protons into AlGaN/GaN MOS-HEMTs at different proton energies. Figure 1 shows the effect of 5 × 1015 cm-2 proton irradiation at 10MeV on drain I-V characteristics before and after. The saturation current, IDSS, was reduced by 68.3% and mobility, which was calculated from linear region of drain I-V curve using charge control model, was reduced by 69.3%. These reductions were due to the displacement damage induced by ion bombardment from proton irradiation. Table 1 shows the summary of MOS-HEMTs device degradation in IDSS, transconductance, threshold voltage shift, mobility, and sheet carrier concentration. In conclusion, irradiation-induced damage causes the reductions of carrier mobility and carrier concentration. The severe degradation in lower irradiation energy is observed due to the more acceptor type defects generated near the 2 dimensional electron gas channel. Figure 1

Highly oriented crystalline aluminum doped zinc oxide (AZO) films were sputter deposited on glass substrates and a systematic investigation on the as deposited and etched films was reported for its further application in silicon thin film solar cell. Influence of the deposition pressure (from 2 to 8 mTorr) and post-annealing temperature (at 400 °C for 5 min) on the structural, optical and electrical properties of the as-deposited and etched samples were analyzed. The optimum condition for its reproducibility and large area deposition is determined and found that the depositions made at 8 mTorr at 200 W having the distance from source to substrate of 9 cm. All the AZO films exhibited a c -axis preferred orientation perpendicular to the substrate and their crystallinity was improved after annealing. From the XRD pattern the grain size, stress and strain of the films were evaluated and there is no drastic variation. Optical transmittance, resistivity, Hall mobility and carrier concentration for the as deposited and etched-annealed films were found to improve from 79 to 82%; 2.97 to 3.14×10 −4 Ω cm; 25 to 38 cm 2 /V s; 8.39 to 5.96×10 20 /cm 3 respectively. Based on the triangle diagram between figure of merit and Hall mobility, we obtained a balance of point between the electrical and optical properties to select the deposition condition of film for device application.

We present low cost hydrothermally deposited uniform zinc oxide (ZnO) nanorods with high haze ratios for the a-Si thin film solar cells. The problem of low transmittance and conductivity of hydrothermally deposited ZnO nanorods was overcome by using RF magnetron sputtered aluminum doped zinc oxide (ZnO:Al ~300 nm) films as a seed layer. The length and diameters of the ZnO nanorods were controlled by varying growth times from 1 to 4 h. The length of the ZnO nanorods was varied from 1 to 1.5 µm, while the diameter was kept larger than 300 nm to obtain various aspect ratios. The uniform ZnO nanorods showed higher transmittance (~89.07%) and haze ratio in the visible wavelength region. We also observed that the large diameters (>300 nm) and average aspect ratio (3–4) of ZnO nanorods favored the light scattering in the longer wavelength region. Therefore, we proposed uniformly deposited ZnO nanorods with high haze ratio for the future low cost and large area amorphous silicon thin film solar cells.

Various SF6/Ar plasma-textured periodic glass surface morphologies for high transmittance, haze ratio and low sheet resistance of ITO:Zr films are reported. The SF6/Ar plasma-textured glass surface morphologies were changed from low aspect ratio to high aspect ratio with the increase in RF power from 500 to 600 W. The micro- and nano-size features of textured glass surface morphologies enhanced the haze ratio in visible as well as NIR wavelength region. Micro-size textured features also influenced the sheet resistance and electrical characteristics of ITO:Zr films due to step coverage. The ITO:Zr/AZO bilayer was used as front TCO electrode for p-i-n amorphous silicon thin film solar cells with current density–voltage characteristics as: V oc = 875 mV, FF = 70.90 %, J sc = 11.31 mA/cm2, η = 7.02 %.

We report various SF6/Ar plasma textured periodic glass surface morphologies with high transmittance, haze ratio, and root mean square (rms) roughness of ITO:Zr films for amorphous silicon thin film solar cells (a-Si TFSCs). SF6/Ar plasma textured glass surface morphologies contain micro- and nano-textured features that help to scatter the light in visible and near infra-red (NIR) wavelength regions. We designed the textured glass surface morphologies with big square craters to smaller pyramids for various glass etching times from 30 to 75 min. Magnetron sputtered ITO:Zr (∼210 nm) films were deposited on textured glass surface morphologies and showed higher transmittance and haze ratio of 88.48% and 77.61%, respectively, in the visible-NIR (400–1100 nm) wavelength region. The sheet resistance and resistivity of ITO:Zr films decreased with the increase of etching time, due to high rms roughness and better step coverage. A passivation AZO (30 nm) layer was added to the ITO:Zr films, due to its better stability against hydrogen plasma exposure. The ITO:Zr/AZO films were employed as a front TCO layer and the current density–voltage (J–V) characteristics of a-Si TFSCs increased by light scattering effect, without any reduction in either the open circuit voltage (VOC) or the fill factor (FF). Relative to flat glass substrate, JSC and the efficiency of a-Si TFSCs were enhanced by 7.51% and 19.39%, respectively, for textured glass surface morphology.

Wide band gap p-type nano crystalline silicon oxide (p-nc-SiO:H) window layer is useful for multi junction solar cells. We prepared such a material by using high hydrogen dilution and low plasma power that shows high optical gap as well as high conductivity. By varying CO2 flow rates of from 0.3 to 2.5 sccm we obtained the films with crystallite volume fraction (Xc) ranging from 43.7% to 4.5%, while by decreasing the plasma power density from 426, to 28 mW/cm2 the Xc was observed to increase from 14.0% to 45.8%. At a high plasma power the hydrogen dilution did not show significant change in film properties. The electrical conductivity and activation energy was observed to be favorable at low plasma power density, which was 3.4 × 10−2 S cm−1 and 0.102 eV respectively at 28 mW/cm2 plasma power density. It is expected that at a low plasma power a large number of SiH3 radicals actively take part in film deposition, leading to an improved film properties. Solar cells fabricated with the selected p-nc-SiO:H, shows improved short wavelength response of the quantum efficiency, indicating the advantage of using such p-type materials. The optical gap of these p-nc-SiO:H films were in the range of 1.784 to 2.130 eV.

AlGaN/GaN HEMTs have gained more attention recently because of the superior mobility (~1400 cm2/V-s) and high breakdown voltage. However, the reported breakdown voltage (~2000V at Lds=40µm) was still below GaN limit. The reason might be due to surface traps, defects in GaN buffer layer, etc. Methods to improve breakdown voltage include acceptor doping in buffer layer, insulator passivation or field plate over dielectric passivation. In this paper, we propose a new structure, which opened a via through the substrate as a backside gate and a field plate, and demonstrate the improvement of device performance such as transport characteristics and breakdown voltage. The HEMT structures consisted of a 25 nm AlGaN barrier layer, a 0.8 µm C doped GaN buffer layer, a 1.4µm AlGaN transition layer and a thin AlN nucleation layer on 300µm Si substrate. HEMT fabrication began with Ti/Al/Ni/Au Ohmic metallization and rapid thermal annealing in N2 at 825ºC. Isolation was accomplished by use of multiple energy N+ implantations. After implantation, the devices were passivated with 70-nm-thick SiNx by PECVD at 300ºC. Gate definition was achieved by patterning the gate and selectively removing the SiNx layer. The contact windows to the Ohmic contact pads were also opened simultaneously as defining the gate. After SiNx etching, wider gate patterns and Ohmic contact pads were opened. Ni/Au-based gate metallization was deposited on the gate and Ohmic contact pads simultaneously. The devices were then passivated with another 400-nm SiNx layer at 300ºC. The contact windows were opened by dry etching. The LDS was 4 µm. The LG was 0.45 and WG was 100 µm, respectively. There was an additional metal deposition for source field plate (FP). It was connected to the source and extended by 1 µm out over the gate to the gate-to-drain region. Above process flows are our standard process flow for reference. For our new structure, to drill via holes on the backside of the devices, the wafers were first polished to 150µm. Photoresist AZ9260 were used to pattern the via holes on the backside of the samples and aligned to the front side by Aligner MJB3. The high aspect ratio of the via holes were fabricated by BOSCH process. After forming via holes, Ti/Au was sputtered to form the backside gate (BG). Figure 1 showed effect of backside voltage (VBG) to drain I-V characteristics. As shown in Figure 1, the drain saturation current decreased and the channel resistance became higher after applying VBG at -10 V. Also, the drain current at pinch off region get decreased. This is due to the introduction of another depletion region from the backside of the device. In other words, the BG provided an additional control of the device, which made the device more robust. Figure 2 showed the transfer characteristics of device with and without applying VBG. As shown in Figure 2, both of the on current and off current became lower. Besides, the sub-threshold slope became steeper after applying -10 V at the BG, which meant better modulation of the device. Due to the better pinch off of the device, the breakdown voltage (VBD) was significantly improved. Table 1 showed the summary of the effect of VBG. As shown in TABLE 1, although IDS was slightly decreased, but the more reduction of gate current improved on/off ratio for one order, sub-threshold swing from 204 to 137 mV/dec, and VBD for 40%. These improvements were all achieved because of the backside gate. Besides applying VBG to improve VBD, the BG could be used as a FP, too. Studies have shown that FP can redistribute the electric field, and thus increase the VBD. In this study, we demonstrate the similar result. When connecting the BG to front-side gate, the VBD could be increased around 8 % as shown in Figure 3. When connecting the BG to front-side source, VBD didn’t have noticeable improvement. The reason that source FP didn’t have obvious effect in our study might be the existence of front-side FP. On the other hand, drain FP actually decrease the VBD. For drain FP, the backside FP was at positive bias. This positive bias along with the front-side positive bias would generate hot electrons and enhance the tunneling. In summary, VBD could be improved by simply connecting the backside gate to front-side gate. In conclusion, we demonstrate a new structure for AlGaN/GaN HEMT. This structure could improve the on/off ratio, sub-threshold swing, and breakdown voltage. It is worth to see if it could improve short channel effect, self-heating effect, or current collapse. Figure 1

Front transparent conductive oxide (TCO) films play a vital role in amorphous silicon based thin film solar cells due to their high transparency, conductivity and excellent light scattering properties. The precise surface morphology with better step coverage for the front TCO films is a hot research topic now a days. Since the low step coverage of TCO films suffered non uniformity and hence low performance of amorphous silicon thin film solar cells (a-Si TFSCs). We report novel multi-textured periodic textured glass surface morphologies with high transmittance and better step coverage of AZO films for the a-Si TFSCs. The SF 6 /Ar plasma etching of glass substrates was used for the high roughness and haze ratio while wet (Buffered Hydro Fluoric acid (BHF)) chemical etching was performed for the better step coverage by controlling the shape of textured glass surface morphology. The pyramid shaped textured glass surface morphologies offered the lowest sheet resistance, high transmittance and roughness for the RF magnetron sputtered AZO films. The AZO films showed the highest total transmittance and haze ratio of 90.19% and 54.29% in the visible wavelength region with lowest sheet resistance of 6.242 Ω/□ for 800 nm thickness. The AZO films deposited on the pyramid glass surface showed the better step coverage. The minor variation in sheet resistance and resistivity of the AZO films was related to the step coverage of the AZO films that is closely related with the shape and angle of the surface morphology. The AZO films with low sheet resistance, high transmittance and step coverage can be employed to improve the performance of future a-Si thin film solar cells.

Recently 3D scenes are used in medical fields. We developed a medical 3D microscope with a HMD. We mounted two cameras on the 3D microscope. Incoming images through an object lens of an optical microscope are projected on sensors of mounted cameras by using reflector mirrors. These are processed in a computer and sent to HMD by wireless communications. However, there is the problem about 3D imaging display. Two camera images are easily distorted due to the defect in the 3D microscope and the color of the images are also a little changed because of the color characteristics of the cameras. In this paper, we suggested the method to correct the geometric and color distortion of the stereo camera image and real time implementation of these methods using GPU. We used a wireless HMD for ease of use by doctors. This system would be helpful for doctors to operate more comfortably.

Pulsed DC magnetron sputtered indium tin oxide (ITO) films deposited on glass substrates with lowest resistivity of 2.62 x 10(-4) Ω x cm and high transmittance of about 89% in the visible wavelength region. We report the enhancement of ITO work function (Φ(ITO)) by the variation of oxygen (O2) flow rate and N2O surface plasma treatment. The Φ(ITO) increased from 4.43 to 4.56 eV with the increase in O2 flow rate from 0 to 4 sccm while surface treatment of N2O plasma further enhanced the ITO work function to 4.65 eV. The crystallinity of the ITO films improved with increasing O2 flow rate, as revealed by XRD analysis. The ITO work function was increased by the interfacial dipole resulting from the surface rich in O- ions and by the dipole moment formed at the ITO surface during N2O plasma treatment. The ITO films with high work functions can be used to modify the front barrier height in heterojunction with intrinsic thin layer (HIT) solar cells.

In heterojunction silicon with intrinsic thin layer (HIT) solar cells, the excellent opto-electrical properties of indium tin oxide (ITO) front contact play a critical role in attaining high efficiency. Therefore, in this study, we present and demonstrate an effective statistic approach based on combining Taguchi method and Grey relational analysis for the optimization of ITO films. A reduction in the number of experiments by approximately 90% is obtained by the Taguchi method through an orthogonal array. The reproduction of the effect of process parameters on single performance characteristic, however, is still ensured. In addition, an excellent trade-off between electrical and optical properties of ITO films was attained within the selected range of parameters by Grey relational analysis at power density of 0.685 W/cm 2 , working pressure of 0.4 Pa, substrate temperature of 200 °C, and post-annealing temperature of 200 °C in 30 min. Under optimal condition, the ITO films showed lowest electrical resistivity of 1.978 × 10 −4 Ω cm, and highest transmittance of 90.322%. The HIT solar cells using these ITO films as a front contact show highest efficiency of 16.616%, yielding a 1.750% absolute increase in efficiency compared to using ITO films with the initial condition. Furthermore, the analysis of variance (ANOVA) is determined to define the process parameters which have a dominant effect on the electrical and optical properties of ITO films. Based on ANOVA, we found that the substrate temperature was a key parameter which critically affects the opto-electrical properties of ITO films.

The high work function transparent conductive oxide films can be use to modify the front barrier height of amorphous/crystalline silicon heterojunction solar cells. We report the implementation of double ITO/In 2 O 3 films as a front anti-reflection electrode in amorphous/crystalline silicon heterojunction solar cells. The In 2 O 3 and ITO films were deposited by in-situ radio frequency (RF) magnetron sputtering system. The thin In 2 O 3 films were used to modify the front contact barrier height of amorphous/crystalline silicon heterojunction solar cell due to their high work function while the ITO films were used to improve the conductivity of front transparent conductive oxide layer. We investigated the electrical and optical properties of double ITO/In 2 O 3 layer with the variation of film thickness. In order to satisfy the requirement of solar cell applications, the optimum combination of thickness in terms of sheet resistance, resistivity, transmittance, etc. was sought. The double ITO/In 2 O 3 layer with the thickness of 80/20 nm were applied as front anti-reflection electrode and the best performance of the device was found to be; V oc = 670 mV, J sc = 37.42 mA/cm 2 , FF = 71.16% and η = 17.84%.

In this study, a cost effective and low temperature approach to fabricate a shallow-emitter crystalline silicon (c-Si) solar cell using a low sheet resistance, and highly transparent indium tin oxide (ITO) as an antireflection layer is presented. Deposited films with either (400) or (222) predominant planes were obtained by varying the substrate temperature. Better crystallization, good electrical properties, higher optical gap, and higher work function were observed for the films with (400) predominant planes; however, the transmittance in the near-infrared region suffered from free-carrier absorption effect. These ITO films were applied to replace the conventional SiNx film, as an antireflection coating for a c-Si solar cell with shallow-emitter having a sheet resistance of 100 Ω/⎕. Using the optimal condition, the photovoltaic parameter of the device yielded an open-circuit voltage and fill factor of up to 604 mV and 81.59%, respectively, resulting in an efficiency of 17.27%. This photovoltaic conversion efficiency, based on the c-Si solar cell with shallow-emitter, is relatively higher than that of the current reports.

Effects of the carrier concentration on the dielectric function of indium tin oxide (ITO) films were investigated by spectroscopic ellipsometry using Tauc–Lorentz and Drude oscillator terms. The real and imaginary parts of dielectric function values increased with increasing carrier concentration. Samples with lower refractive indices had (440) preferable crystallographic orientations. A more significant Burstein–Moss (B–M) effect leads to a lower extinction coefficient ( k ) value in the short-wavelength regions, while more Free-carrier absorption (FCA) leads to a higher k value in the near-infrared region. The electrical properties obtained from optical studies, such as the carrier concentration and the carrier mobility, were compared with those obtained by van der Pauw measurements. The observed discrepancies between optically and electrically obtained values were due to carrier transport and grain boundaries. ITO films with a widened band gap energy due to the B–M shift are key to improve quantum efficiency (QE) at short-wavelengths in heterojunction silicon (HJ) solar cells. The reduced QE at long-wavelengths is attributed to optical scattering in the ITO films due to FCA. Despite widening the band gap, the short-circuit current density ( J sc ) decreased from 36.27 mA/cm 2 to 34.17 mA/cm 2 with increasing carrier concentration from 6.15 × 10 20 cm −3 to 9.84 × 10 20 cm −3 . This result demonstrates that the FCA effect may affect J sc more in HJ solar cells. The ITO film, prepared at the lowest carrier concentration, was used as an antireflection layer to fabricate HJ solar cells via optimization of the passivated layer. It resulted in a cell efficiency of 19.12% and an open-circuit voltage of 702 mV.

We prepared highly transparent magnetron-sputtered indium tin oxide (ITO) films deposited at various RF powers for a-Si:H(p)/c-Si heterojunction solar cell applications. The surface morphology of ITO films improved in terms of an increase in grain size as the RF power increased. Rapid growth of the (400) plane was observed with increasing RF power, while the (222) plane remain unchanged. The ITO film deposited at 100 W showed the lowest resistivity of 3.8 � 10 � 4 Ω cm and highest visible transmittance of 90.19%. The deposition rate and optical bandgap of ITO films were varied from 20 to 100 nm/min and from 3.68 to 3.77 eV for RF power from 50 to 250 W, respectively. Highly transparent ITO films were utilized as the front anti-reflection layer in heterojunctions with intrinsic thinlayer (HIT) solar cells showed the efficiency of 16.3% for RF power of 100 W. The HIT solar cells deposited at RF power of 100 W also exhibited higher carrier lifetime and implied voltage.

We showed well-aligned zinc oxide (ZnO) nanorod arrays synthesized using hydrothermal method at atmospheric pressure. The influence of fabrication conditions such as Zn2+/hexamethylentriamin concentration ratio, and growth temperature on the formation of ZnO nanorods was investigated. Scanning Electron Microscope (SEM) images and X-ray Diffraction (XRD) analysis were used to confirm the single crystal of ZnO nanorods, which showed wurtzite structure with growth direction of [0001] (the c-axis). Photoluminescence (PL) measurements of ZnO nanorods revealed an intense ultraviolet peak at 388.5 nm (3.19 eV) at room temperature. The results showed that the ZnO seed layers had strong influence on the growth of vertically aligned ZnO nanorods. The gas sensor based on ZnO nanorod arrays had the most selectivity with n-butanol gas (within 2 surveyed gas: ethanol and n-butanol) and showed a higher sensitivity of 222, fast response time of 15 seconds, recovery time of 110 seconds and lower operating temperature of 200-250 °C than the sensor based on the ZnO film in the same detecting conditions.

In this study, we propose a statistical approach based on Taguchi method and Grey relational analysis for effective optimization of indium tin oxide (ITO) films which are used as front contact for shallow emitter based crystalline silicon (c-Si) solar cells. The experiments were designed by the Taguchi method through an orthogonal array, resulting in the reduction of the number of experiments by approximately 90%; the reproduction effect of process parameters on performance characteristics, however, is still ensured. Excellent compromise between electrical and optical properties of ITO films was obtained by Grey relational analysis at power density of 0.685 W/cm 2 , working pressure of 0.4 Pa, substrate temperature of 250 °C, and post-annealing temperature of 300 °C in 30 min. The ITO films exhibited lowest electrical resistivity of 1.316×10 −4 Ω cm, and highest transmittance of 91.251% under optimal condition. The shallow emitter based c-Si solar cells using the optimal ITO films showed highest efficiency of 17.555%, yielding a 1.375% absolute increase in efficiency compared to using ITO films with initial condition. Furthermore, using analysis of variance, we found that the substrate temperature was a key parameter which critically affected the opto-electrical properties of ITO films.

ITO and ITO:Zr films with various thicknesses were prepared on glass substrates by RF magnetron sputtering. We observed a decrease in sheet resistance with increasing film thickness that in good agreement with Fuchs-Sondheimer theory. The ITO films doped with ZrO2 (∼0.2 wt%) showed improvement in some of the electrical and optical properties of ITO films. The surface roughness of ITO:Zr films increased with increasing film thickness. ITO:Zr films with thickness of 120 nm showed highest work function of 5.13 eV, as estimated from XPS data. The ITO:Zr films were employed as front electrodes in HIT solar cells; the best device performance was found to be: Voc = 710 mV, Jsc = 34.44 mA/cm2, FF = 74.8%, η = 18.30% at a thickness of 120 nm. A maximum quantum efficiency (QE) of 89% was recorded for HIT solar cells at a wavelength of 700 nm for 120 nm thick ITO:Zr films.

We report the influence of magnetron sputtered zirconium-doped indium tin oxide (ITO:Zr) films with high mobility and work function on the heterojunction with intrinsic thin layer (HIT) solar cell. The addition of oxygen (O2) to argon (Ar) flow ratio during the deposition process improves the Hall mobility of the ITO:Zr films while the carrier concentration decreased. The small amount of oxygen resulted in an enhancement of work function while excess amount of O2 was not suitable for the electrical and surface properties of ITO:Zr films. The increase of O2/Ar flow ratio from 0% to 0.4% improved the work function from 5.03 to 5.13 eV while the conductivity of ITO:Zr films remained about the same. The ITO:Zr films were employed as a front anti-reflection layer in a HIT solar cell and the best photo-voltage parameters were found to be Voc=710 mV, Jsc=33.66 mA/cm2, FF=72.4%, and η=17.31% for the O2/Ar flow ratio of 0.4%. The increase of ITO:Zr work function leads to an increase in open circuit voltage (Voc) and fill factor (FF) of the device. Therefore, the ITO:Zr films with high work function can be used to modify the front barrier height in the HIT solar cell.

The RF magnetron sputtered indium tin oxide (ITO) films were deposited on glass substrates with low resistivity, high transmittance and work function for various oxygen (O2) flow rates. The addition of small O2 contents during the sputtering process increased the Hall mobility of ITO films while carrier concentration was decreased. The work function of ITO films was enhanced from 4.31 to 4.81 eV through the growth of (222) plane having relatively low surface energy. The highly transparent ITO films were employed as front anti-reflection layer in heterojunction with intrinsic thin layer (HIT) solar cells and the best photo-voltage parameters were found to be; Voc = 665 mV, Jsc = 35.1 mA/cm2, FF = 73.2% and η = 17.1% for the O2 flow rate of 0.1 sccm. The high work function ITO films play an important role for barrier height modification in HIT solar cell.

An indium tin oxide (ITO) film with low carrier concentration (n), high mobility (μ) and high work function (ΦITO) is a beneficial material for the front electrode in heterojunction silicon (HJ) solar cells due to its low free-carrier absorption in the near-infrared wavelength and low Schottky barrier height at the ITO/emitter-layer front contact. This low free-carrier absorption as well as the low Schottky barrier height increase the open-circuit voltage (Voc) and the short-circuit current density (Jsc), which in turn increases the overall cell efficiency (η). Hence, ITO films with lower n, higher μ and higher ΦITO were prepared by controlling the density of the interstitial oxygen [Oi] in the films and used as anti-reflection electrodes in HJ solar cells. With increasing [Oi] in the ITO, the preferential orientation of the (222) crystalline plane became more dominant. The ΦITO and μ increased from 4.87 eV and 38.9 cm2 V− 1 s− 1 to 5.04 eV and 48.79 cm2 V− 1 s− 1, respectively, whereas n decreased from 4.7 × 1020 cm− 3 to 2.8 × 1020 cm− 3. We attribute these changes to the chemisorbed oxygen into the ITO films, while the decrease of n is due to the ability of interstitial oxygen to capture electron, and the increase of μ is due to the reduction in free-carrier scattering. These ITO films were used to fabricate HJ solar cells. As [Oi] in the ITO film increased, the device performance improved and the best cell performance was obtained with Voc of 714 mV, Jsc 34.79 mA/cm2 and η of 17.82%. By computer simulation, we found that the higher ΦITO and μ but lower n were responsible for the enhanced cell performance. The cell performance, however, deteriorated due to poor film properties when [Oi] exceeded concentration limit from 3.2 × 1020 cm− 3.

Inductive coupled plasma-reactive ion etching (ICP-RIE) offers an anisotropic texturing with superiorsurface structure of glass substrate. We report light trapping scheme of ICP-RIE glass texturing by SF 6 /Arplasma. We observed that surface structure is an important factor to improve the diffused transmittanceand haze ratio of textured glass. The presence of metal elements like Al, B, F and Na are responsible forlow etching rate (22.66e27.33 nm/min) of textured glass. The total transmittance remains high whereasthe diffused transmittance increased with the pattern size due to the variation of surface morphology ofglass. Our textured glass substrates showed the high diffused transmittance and haze ratio in the visible-NIR wavelength region. The electrical properties of the ITO lms are independent of glass surfacestructure that may be suitable for high performance of thin lm solar cells. 2013 Elsevier Ltd. All rights reserved. Light trapping is an important phenomenon for improving theperformance of amorphous silicon (a-Si) based thin lm solar cells.The front transparent conductive oxide (TCO) lms in p-i-n solarcell should exhibit good transparency, low resistivity and excellentlight scattering properties[1,2]. It is well known that the front TCO lms with textured surface can scatter more light at the TCO/a-Si:H(p) interface and haze ratio is strongly in uenced by the sur-face morphology of glass substrates. Therefore, the surface struc-ture of glass substrate plays avital role to improve the performanceof thin lm solar cell[3,4].Several light trapping schemes being used related to TCO andglass substrates like wet chemical etching, dry etching and plas-monic effect of metal nano-particles[5e7]. Eventhough wetchemical etching is simple and inexpensive but surface structure ofglass is textured in an isotropic manner. Therefore the surfacemorphologyofwettexturedglassisnotmuchsuitableforthea-Si:Hthin lm solar cells. The texturing of glass substrate by ICP-RIE canimprove the rms roughness, surface morphology and haze ratio asobservedbyA.HongsingthongandI.A.Yunazetal.[8,9].Recently,J.Achtelik et al. reported the nanosphere lithography combined withRIE to improve the glass surface for solar cells[10]. The surfacemorphology and haze ratio are the key parameters to improve theperformance of a-Si:H thin lm solar cells. The ICP-RIE texturing ofglass substrates had long been used for the anisotropic etching inmicro-electromechanicalsystem(MEMs)devices[11e13] .Althoughthere are several reports related to the dry etching of glass sub-strates, but ICP-RIE texturing of patterned glass by photo-lithography for high haze ratio in thin lm solar cells are rarelyreported.In this article, we report the ICP-RIE texturing of patterned glasssubstrates for the better surface structure and high haze ratio. Theultra-violet (UV) photo-lithography process was used for the pat-terningofcorningandsodalimeglasssubstrateswithAl(w 200nm)hard mask. The surface morphologyof the texturedglass substrateshas been discussed. The etching mechanism and X-ray photo-electron spectroscopic (XPS) analysis of ICP-RIE textured glass isexplained. The total, diffused transmittance and haze ratio ofcorning and soda lime glass substrates is also discussed. The elec-trical properties of ITO lms deposited on as deposit and texturedglass substrates are also described.

To improve the quantum efficiency (QE) and hence the efficiency of the amorphous/crystalline silicon heterojunction solar cell, we have employed a LiF dielectric layer on the rear side. The high dipole moment of the LiF reduces the aluminum electrode's work–function and then lowers the energy barrier at back contact. This lower energy barrier height helps to enhance both the operating voltage and the QE at longer wavelength region, in turn improves the open-circuit voltage (Voc), short-circuit current density (Jsc), and then overall cell efficiency. With optimized LiF layer thickness of 20 nm, 1 cm2 heterojunction with intrinsic thin layer (HIT) solar cells were produced with industry-compatible process, yielding Voc of 690 mV, Jsc of 33.62 mA/cm2, and cell efficiencies of 17.13%. Therefore LiF/Al electrode on rear side is proposed as an alternate back electrode for high efficiency HIT solar cells.