Search

Abstract The extraction of trap-limited mobility information using photoconductivity relaxation dynamics in thin-film amorphous semiconductors is evaluated. Simulated photoconductivity dynamics suggest that free carrier decay is characterised by a spectrum of recombination lifetimes, where the spectra are sensitive to the underlying distribution of shallow trap densities and the experimental photoconductivity generation conditions employed. Weighted averaging of the spectral lifetimes is found to return trap-limited lifetime estimates which agree to within 5% of the lifetime values expected from free-to-trapped carrier ratios established under steady-state photoconductivity conditions. The averaged spectral lifetimes may consequently be used with mobility-lifetime magnitudes to determine the associated trap-limited mobility. The analysis procedure is evaluated using photoconductivity data obtained from a set of a-Si:H films deposited over a range of substrate temperatures. Highlights • Photocurrent recovery dynamics yield a spectrum of free-carrier recombination times • Trap-limited mobility values may be determined from the recombination time spectra • Intervals to achieve 1/3 photocurrent recovery approximate the recombination time • a-Si:H recovery data suggests potential fluctuations suppress mobility magnitudes [ABSTRACT FROM AUTHOR]

Abstract This work reports on transparent semiconducting indium sulfide fluoride (ISF) thin-films exhibiting high sensitivity to ultraviolet radiation. The films were deposited on fused silica and silicon substrates using a radio-frequency plasma-enhanced reactive thermal evaporation system. The deposition was performed evaporating pure indium in SF 6 plasma at a substrate temperature of 423 K. Rutherford backscattering measurements were used to determine the chemical composition of the films deposited on silicon substrates. The surface morphology was studied using scanning electron microscopy technique. The film characterization includes electrical, optical, and photoconductivity measurements. The synthesized compound is highly-resistive (~700 MΩ-cm at 300 K) and exhibits an evident semiconducting behavior. The activation energy of 0.88 eV is deduced from the temperature dependence of electrical resistivity. The indirect band energy gap of 2.8 eV is determined from transmittance spectra of the ISF films. The photoconductivity band is centered at 345 nm wavelength. The photoconductivity spectrum also shows the Urbach tail with a characteristic energy of 166 meV. ISF is a promising candidate for a buffer layer in chalcogenide-based solar cells. Highlights • Indium Sulfide Fluoride (ISF) films by plasma-enhanced reactive thermal evaporation • Chemical composition by Rutherford backscattering spectrometry • ISF is an amorphous semiconductor with 2.8 eV indirect bandgap. • ISF films are highly sensitive to UV radiation. • ISF is a wide-gap semiconductor suitable for photovoltaic and UV-sensing applications. [ABSTRACT FROM AUTHOR]

• A realistic optical model for thin-films photodiodes based on the transfer matrix method. • Boron-doped protocrystalline silicon as a low-absorption p-layer material. • An analytic optical-constant model for each semiconductor in the multilayer optical stack. • Analysis of absorption and reflection losses in the photodiode, device optimization. • 92% peak efficiency at 510 nm wavelength and 66%@400 nm have been achieved. This article reports on blue-enhanced a-Si:H-based n-i-p photodiodes with protocrystalline silicon (pc-Si:H) p-layers by plasma-enhanced chemical vapor deposition. Microstructure of p-layers was studied by Raman spectroscopy. An optical model has been developed to analyze the device performance. The Transfer Matrix Method was applied to simulate light propagation in the glass/Cr/n-i-p/ZnO:Al stack, while modified Tauc-Lorentz model including the Urbach tail was used to obtain the dispersive optical constants for each semiconductor layer. Two photodiodes with a-Si:H and pc-Si:H p-layers were fabricated, characterized, and modeled for comparison. The deduced optical gaps are 1.8 and 2.33 eV for p-type a-Si:H and pc-Si:H, respectively. Observed band gap widening is the quantum confinement effect due to Si nanocrystals in pc-Si:H. Modeling reveals that incorporation of pc-Si:H leads to a significant reduction of absorption and reflection losses. The optimized heterojunction photodiode exhibits a quantum efficiency up to 92% at 510 nm wavelength. The achieved quantum efficiency of 66% at 400 nm wavelength almost triples that for the homojunction photodiode. [ABSTRACT FROM AUTHOR]

Abstract High-k amorphous SrTa 2 O 6 (STA) thin films were successfully deposited by rf magnetron sputtering for gate insulators in thin-film transistor (TFT). Practical STA thin films with high dielectric constant of 41.8, wide band gap of 4.58 eV, and low leakage current of ~10−8 A/cm2 were obtained through by optimal sputtering condition. The TFTs with amorphous InGaZnO (IGZO) as a channel and STA as a gate insulator were fabricated and investigated for thinning effects of gate insulator on transfer characteristic. The IGZO-TFT with 70-nm-thick STA achieved high performance switching properties; (mobility of 14.9 cm2/(V·s), threshold voltage of 0.6 V, sub-threshold swing of 111 mV/decade, and on/off ratio of 1.0 × 1010). These characteristics are due to the large gate capacitance of 4.6 × 10−7 F/cm2 and low gate leakage current from use of STA. Highlights • The SrTa 2 O 6 thin films were successfully deposited by sputtering method. • Amorphous SrTa 2 O 6 showed high dielectric constant with low leakage current. • InGaZnO thin-film transistor with SrTa 2 O 6 achieved low voltage operation. [ABSTRACT FROM AUTHOR]

The effect of vacuum annealing on the amorphous oxide semiconductor Cd–Ga–O system with a tunable band gap was examined. While the amorphous halo peak in XRD patterns of the films with Cd concentration of ~ 70% started sharpening after annealing at a temperature ≥ 200 °C. In contrast, the films with Cd content of ~ 50% and ~ 20% were not crystallized for annealing temperatures up to 700 °C. Carrier concentrations and Hall mobilities of ~ 70% and ~ 50% films were maximized by annealing at 400 °C and 500 °C, respectively, regardless of the properties of the as-deposited films, which were varied because of the unintended variation of deposition conditions such as the residual water vapor pressure in the deposition chamber. The initial electrical conductivity of ~ 20% films widely varied from < 10 − 8 to 11 S·cm − 1 , and annealing at 500 °C was required for obtaining conductive films from the insulating as-deposited films. The maximum Hall mobility for films with Cd content of ~ 70% and ~ 50% films was ≥ 10 cm 2 V − 1 s − 1 and that for the film with ~ 20% Cd content was ≥ 3 cm 2 V − 1 s − 1 . [ABSTRACT FROM AUTHOR]

Reactive pulsed laser deposition is a technique suitable for producing homogenous thin layers of silicon or germanium with high concentration of embedded manganese atoms. Linear calibration of EDS (Energy Dispersive X-ray Spectroscopy) was utilized for an elemental analysis of thin layers. MnSi and MnGe (manganese-silicon and manganese-germanium) layers containing non-oxidized Mn were obtained for Mn molar concentration in the range from 15 to 50%. Electron diffraction showed an amorphous character of MnSi layers. MnGe layers contained two different types of nanoparticles incorporated inside an amorphous matrix. The layers were semiconducting with resistivities from 10 − 3 to 10 − 5 Ω m. [ABSTRACT FROM AUTHOR]

Amorphous Ge 30.5 Se 69.5 and Ge 39.5 Se 60.5 films were prepared by thermal evaporation from previously synthetized bulk glasses. We did not observe a shift in the optical band gap values associated with the change in film thickness for the virgin and annealed states of the thin films. Certain minor changes in the optical band gap values were explained by the change in the chemical composition and by the change in the sample disorder. Both ultraviolet and visible and far infrared spectra indicate that annealed Ge 39.5 Se 60.5 thin films are practically insensitive to the illumination while Ge 30.5 Se 69.5 thin films show a reversible photodarkening. The observed reversible changes of the optical band gap for Ge 30.5 Se 69.5 thin films were also not dependent on the film thickness. The network structural rigidity, which can be combined with a quick relaxation of the light induced excitation directly back to the ground state, was suggested as the reason for the absence of reversible photodarkening in Ge 39.5 Se 60.5 thin films. [ABSTRACT FROM AUTHOR]

We fabricated amorphous oxide semiconductor films, a-(Ga 1– x Zn x )O y , at room temperature on glass, which have widely tunable band gaps ( E g ) ranging from 3.47–4.12 eV. The highest electron Hall mobility ~ 7 cm 2 V − 1 s − 1 was obtained for E g = ~ 3.8 eV. Ultraviolet photoemission spectroscopy revealed that the increase in E g with increasing the Ga content comes mostly from the deepening of the valence band maximum level while the conduction band minimum level remains almost unchanged. These characteristics are explained by their electronic structures. As these films can be fabricated at room temperature on plastic, this achievement extends the applications of flexible electronics to opto-electronic integrated circuits associated with deep ultraviolet region. [ABSTRACT FROM AUTHOR]

Amorphous zinc oxide–silica ( a -ZnO–SiO 2 ) nanocomposite has been synthesized using a sol–gel process. X-ray diffraction patterns show a broad diffraction peak of amorphous SiO 2 with no peaks related to ZnO wurtzite structure. ZnO–SiO 2 nanocomposite posses uniformly spherical particles and large surface area 462 m 2 /g. The prepared a -ZnO–SiO 2 nanocomposite was used as a chemical sensor to detect phenyl hydrazine via a simple electrochemical technique by measuring the current–potential ( I – V ) characteristics. The calibration curve exhibits good linearity over all concentration range from 390 μM to 50 mM (r 2 = 0.9986) and the limit of detection was estimated to be 1.42 μM. The sensitivity was calculated to be 10.80 μA cm − 2 mM − 1 as a result of good adsorption ability and large surface area of the prepared sensor. Interestingly, the modified ZnO–SiO 2 nanocomposite sensor electrode was extremely stable during the sensing runs, since no significant sensitivity decrease was observed after being re-used for five times. Furthermore, no deterioration in the I – V characteristics was detected after being stored in ambient conditions for three months, indicating the fabricated sensor exhibited long term stability. [ABSTRACT FROM AUTHOR]

We reviewed studies reporting the applications of the Tauc–Lorentz (TL) parameterization for the complex dielectric function in spectroscopic ellipsometry. Since this model became very popular for representation of the dielectric functions of amorphous semiconductors and dielectrics, there is a need for an improved multi-oscillator TL model with a constraint on the band-gap parameter E g , which forces it to be common for all TL oscillators, and possibility to represent weak absorption features below the bandgap which previously very often were associated with the exponential Urbach tail. In this paper we propose an extended TL model by inclusion of additional unbounded Lorentz and/or Gaussian oscillators with transition energies located below the bandgap. We conclude that the proposed model is the most appropriate for the characterization of various materials with sub-band absorption features and gives meaningful value for the energy bandgap. A few examples to illustrate practical use of modified model have been provided. [ABSTRACT FROM AUTHOR]

The fabrication of ultra-thin SiNx (< 2 nm) is a necessary step in third generation photovoltaics, memory, or light-emitting diode applications. Using the low temperature, cheap, scaleable synthesis technique of hot-wire chemical vapor deposition (HWCVD) for this purpose poses many challenges. Here, an approach of fabricating ultra thin SiNx of thickness ~ 1.9 nm in a superlattice (SL) structure via nitridation of a-Si layers in-situ HWCVD at 250 °C is reported. Quantum well SL and quantum dot (QD) SL films are realized, wherein SiNx layers are formed by nitriding a-Si. Both these films investigated by Raman spectroscopy and high resolution transmission electron microscopy, reveal the formation of ultra-thin SiNx in a SL structure with a-Si, accompanied by sharp interfaces. In addition, annealing of the SL structures, results in QDs of crystalline Si in the a-Si layers, maintaining the SiNx layer as well as the sharp interface between the SiNx and a-Si layers of the as-deposited SL structure. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism for instability against positive bias stress (PBS) in amorphous Si–In–Zn–O (SIZO) thin-film transistors has been investigated by analyzing the subgap density of states (DOSs), which was extracted from multi-frequency method using direct capacitance–voltage measurements. It was found that DOSs including shallow tail states and deep trap states are constant in density as PBS time increases. It indicates that the bulk traps in the SIZO channel layer and the channel/dielectric interfacial traps are not created during the PBS duration. Therefore, the instability against PBS in SIZO thin-film transistors is attributed to the charge trapping by the acceptor-like DOSs. [Copyright &y& Elsevier]

Abstract: This study used powders containing various In2O3–Ga2O3–ZnO (IGZO) chemical compositions to manufacture targets by using a metallurgical process. The resulting targets were used to deposit amorphous In–Ga–Zn–O (a-IGZO) channel films using a radio frequency (r.f.) magnetron sputtering process. The average transmittance increased and achieved saturation; the resistivity increased in conjunction with the O2 flow ratio of less than 6%; and subsequently, the resistivity decreased with increasing the O2 flow ratio larger than 6%. This study examined the effects of compositions on electrical characteristics and optical properties of a-IGZO films at varied O2 flow rates. The effects of composition on optical and electrical characteristics of a-IGZO films indicate that the average transmittance of a-IGZO films with more zinc atoms (approximately 50%) had more than 80% at various O2 flow ratios because of the higher oxygen absorption of the zinc atoms. However, the average transmittance of a-IGZO film with a lower zinc atomic ratio (approximately 20%) without an O2 flow ratio decreased to below 10% because of the indium and indium oxide crystalline precipitation in the indium-rich a-IGZO films. The results revealed that the resistivity increased when the gallium atomic ratio increased and the indium atomic ratio decreased. [Copyright &y& Elsevier]

Abstract: Quantitative estimation of the specific contact resistivity and energy barrier at the interface between transparent conducting oxide (TCO) and hydrogenated p-type amorphous silicon carbide (a-Si1−xCx:H(p)) was carried out by inserting an interfacial buffer layer of hydrogenated p-type microcrystalline silicon (μc-Si:H(p)) or hydrogenated p-type amorphous silicon (a-Si:H(p)). In addition, superstrate configuration p–i–n hydrogenated amorphous silicon (a-Si:H) solar cells were fabricated by plasma enhanced chemical vapor deposition to investigate the effect of the inserted buffer layer on the solar cell device. Ultraviolet photoelectron spectroscopy was employed to measure the work functions of the TCO and a-Si1−xCx:H(p) layers and to allow direct calculations of the energy barriers at the interfaces. Especially interface structures were compared with/without a buffer which is either highly doped μc-Si:H(p) layer or low doped a-Si:H(p) layer, to improve the contact properties of aluminum-doped zinc oxide and a-Si1−xCx:H(p). Out of the two buffers, the superior contact properties of μc-Si:H(p) buffer could be expected due to its higher conductivity and slightly lower specific contact resistivity. However, the overall solar cell conversion efficiencies were almost the same for both of the buffered structures and the resultant similar efficiencies were attributed to the difference between the fill factors of the solar cells. The effects of the energy barrier heights of the two buffered structures and their influence on solar cell device performances were intensively investigated and discussed with comparisons. [Copyright &y& Elsevier]

Abstract: We report the study of dielectric properties of amorphous semiconducting YBCO thin films measured in a broad frequency range, from 40Hz to 2GHz and in the 210 to 430K temperature range, using a coaxial discontinuity technique. At all temperatures, dielectric permittivity and conductivity spectra exhibit typical features of dielectric relaxation processes. A first relaxation at low frequency (300Hz–2kHz), observed only at high temperature, might be attributed to interfacial effects. Polarization in the grains of the YBCO thin films could lead to the second relaxation observed at higher frequency (800Hz–660kHz). The relaxation frequencies increase with temperature and follow a thermally activated behavior of the Arrhenius-type. Optical near-infrared response of YBCO bolometers exhibits a corner frequency around 40kHz. Above this frequency, the thermal diffusion is localized inside the YBCO thin film. This frequency is in good agreement with the relaxation frequency attributed to YBCO grains in the thin film, i.e. around 40kHz at 300K. [Copyright &y& Elsevier]

Abstract: YBa2Cu3O6+ x (YBCO) compounds are well known to exhibit superconducting properties for x >0.5 and semiconducting properties for lower oxygen content. In this work, YBCO oxide thin films of the semiconducting phase were deposited by direct-current (DC) hollow cathode sputtering at low temperature in the 100 to 400°C range. Structural, electrical and optical properties are investigated and discussed in relation with the envisaged bolometric detection application. Structural characterizations show that films are amorphous, with a granular structure of low roughness (3nm rms). DC electrical measurements both reveal that films grown at 100°C exhibit a high temperature coefficient of resistance (TCR~−3%K−1 to −4%K−1 at 300K) and an optimized low resistivity value of 345Ω·cm at 300K. Consequently, this material is suitable for uncooled infrared bolometer application and can be deposited at 100°C in a complementary metal-oxide-semiconductor compatible technological process for co-integration with readout circuitry. In addition, optical measurements performed in the 0.5 to 2.2μm wavelength range on films grown at 100°C highlight optical conductivity values in line with those expected for YBCO material, as well as the presence of two optical band gaps that are discussed with respect to the film nanostructure. [Copyright &y& Elsevier]

Abstract: The paper presents the optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films with various In/(In+Zn) ratios obtained by Pulsed Laser Deposition. Thickness results obtained from simulations of X-ray Reflectivity and Spectroscopic Ellipsometry data were very similar. The dependence of density on stoichiometry resembles the corresponding dependence of the refractive index in the transparency range. A free carrier absorption was noted in the visible spectral range, leading to a weak absorbing thin transparent conductive oxide. On the other hand, the refractive index is smaller than those of based oxides (ZnO and In2 O 3), and counterbalance therefore the weak light absorption. [Copyright &y& Elsevier]

Abstract: Thin films of amorphous indium tin oxide were deposited by soft sputtering. The film was gradually annealed in air at temperatures from 110°C to 150°C. Its structural and electrical properties were monitored in order to get a better understanding of the annealing process. Firstly, carrier density decreases by oxygen intake. Crystallization speeds up at 150°C, with a 2.5 D growth of crystallites. The preferred orientations come from sputtering induced seeds. Then, the carrier density increases again due to tin activation. Meanwhile, the carrier mobility is more damaged by the low temperature annealing in air than by a standard annealing in a reducing atmosphere. Thus, tin oxide segregation is suspected at grain boundaries. [Copyright &y& Elsevier]

Abstract: Photovoltaic properties and electronic structures of n-type amorphous In–Ga x –Zn–O/p-type Si heterojunction solar cells (x =1, 2, and 3) were investigated focusing on the effects of Ga content based on expectation that Ga-rich films have larger band gaps and improve open circuit voltages (VOC) of solar cells. To know the electronic structures such as the conduction band minimums (CBMs) and the valence band maximums (VBMs) of these materials, hard x-ray photoemission spectroscopy (HX-PES) was performed. Contrary to the above expectation, the best result was obtained for x =1 with an energy conversion efficiency of 5.3%. Although the Ga-rich films had larger optical band gaps and higher CBMs, VOC were remained low and poorer fill factors were obtained due to larger densities of defects. The low VOCwere partly resulted from the deep VBM levels of the Ga-rich films. The defect densities are discussed in relation also to near-VBM states and near-CBM states observed in HX-PES and subgap optical absorptions. [Copyright &y& Elsevier]

Abstract: Thermally induced instability of amorphous Si–In–Zn–O (SIZO) with 1wt.% silicon (Si) concentration and Ga–In–Zn–O (GIZO) with gallium (Ga) of 30wt.% thin film transistors (TFTs) has been investigated, by comparing the density of states extracted from multi-frequency method. It was observed that the density of state of SIZO-TFT was lower than that of GIZO-TFT, in spite of low processing temperature of SIZO-TFT and thermally induced instability of SIZO- and GIZO-TFT was strongly related with the total trap density. We report that Si of only 1wt.% in SIZO can improve thermal stability of threshold voltage of In–Zn–O based TFTs more effectively than Ga of 30wt.% in GIZO. [Copyright &y& Elsevier]

Abstract: An operation model for an amorphous In–Ga–Zn–O (a-IGZO) based thin film transistor (TFT) is studied. The model is not based on the exponential tail states employed in hydrogenated amorphous Si (a-Si:H) TFT, but on a power function of the carrier density which is observed in the TFT and Hall mobilities of a-IGZO. A 2D numerical simulator employing this model reproduced current–voltage characteristics under on operation of coplanar homojunction a-IGZO TFTs. Although the mathematical expression of the mobility is similar to the field effect mobility of a-Si:H TFT, the present model explains the temperature dependence of the on characteristics of a-IGZO TFT. [Copyright &y& Elsevier]

Abstract: Effects of low-temperature annealing were examined for amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs). In a previous study, we reported that O2 annealing is effective to improve performances of a-IGZO TFTs when annealed at ≥300°C, but causes large negative threshold voltage shift when annealed at ≤ 200°C. Here, we examined effects of ozone (O3) annealing on physical properties and TFT characteristics of a-IGZO in comparison with conventional O2 annealing. We found little differences in chemical composition, band gap and photoemission spectra between the O2 and the O3 annealed films. On the other hand, free electron density was suppressed well by the O3 annealing even at low temperatures ≤200°C. Moreover, even at 150°C, the TFTs characteristics were improved to the subthreshold voltage swing of 217mV/decade, the saturation mobility of ~11.4cm2(Vs)−1 and the threshold voltage of 0.1V by the O3 annealing. It was also found that the effects of the O3 annealing is more effective for thicker channel TFTs, which would be due to stronger oxidation power and the larger diffusion constant of oxygen atoms produced from O3 molecules than those of O2. These results substantiate that the O3 annealing is more effective to improve TFT characteristics in particular for low-temperature processes at ≤200°C. [Copyright &y& Elsevier]

Abstract: Effect of hygroscopic magnesium oxide (MgO) passivation layer on the stability of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) under positive bias stress and positive bias temperature stress has been investigated. The effect of MgO passivation has been observed by comparing the shift of the positive threshold voltage (Vth) after constant bias temperature stress, which were 8.2V for the unpassivated TFTs and 1.88V for the passivated TFTs. In addition, MgO passivated a-IGZO TFTs show also excellent stability under a humidity test since MgO passivation layer can prevent the penetration of water into back channel. In order to investigate the origin of humidity test result, we have measured X-ray photoelectron spectroscopy depth profile of both unpassivated and MgO passivated TFTs with a-IGZO back channel layers after N2 wet annealing. [Copyright &y& Elsevier]

Abstract: The stability of amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) was investigated focusing on the effects of passivation layer materials (Y2O3, Al2O3, HfO2, and SiO2) and thermal annealing. Positive bias constant current stress (CCS), negative bias stress without light illumination (NBS), and negative bias light illumination stress (NBLS) were examined. It was found that Y2O3 was the best passivation layer material in this study in terms of all the stability tests if the channel was annealed prior to the passivation formation (post-deposition annealing) and the passivation layer was annealed at ≥250°C (post-fabrication annealing). Post-fabrication thermal annealing of the Y2O3 passivation layer produced very stable TFTs against the CCS and NBS stresses and eliminated subgap photoresponse up to the photon energy of 2.9eV. Even for NBLS with 2.7eV photons, the threshold voltage shift is suppressed well to −4.4V after 3h of test. These results provide the following information; (i) passivation removes the surface deep subgap defects in a-IGZO and eliminates the subgap photoresponse, but (ii) the bulk defects in a-IGZO should be removed prior to the passivation process. The Y2O3-passivated TFT is not only stable for these stress conditions, but is also compatible with high-frequency operation with the current gain cut-off frequency of 91kHz, which is consistent with the static characteristics. [Copyright &y& Elsevier]

Abstract: The effect of contact resistance on the measurement of the field effect mobility of compositionally homogeneous channel indium zinc oxide (IZO)/IZO metallization thin film transistors (TFTs) is reported. The TFTs studied in this work operate in depletion mode as n-channel field effect devices with a field effect mobility calculated in the linear regime (μ FE) of 20±1.9cm2/Vs and similar of 18±1.3cm2/Vs when calculated in the saturation regime (μ FE sat). These values, however, significantly underestimate the channel mobility since a large part of the applied drain voltage is dropped across the source/drain contact interface. The transmission line method was employed to characterize the contact resistance and it was found that the conducting-IZO/semiconducting-IZO channel contact is highly resistive (specific contact resistance, ρ C >100 Ωcm2) and, further, this contact resistance is modulated with applied gate voltage. Accounting for the contact resistance (which is large and modulated by gate voltage), the corrected μ FE is shown to be 39±2.6cm2/Vs which is consistent with Hall mobility measurements of high carrier density IZO. [Copyright &y& Elsevier]

Abstract: The effect of low-temperature (200°C) annealing on the threshold voltage, carrier density, and interface defect density of amorphous indium zinc oxide (a-IZO) thin film transistors (TFTs) is reported. Transmission electron microscopy and x-ray diffraction analysis show that the amorphous structure is retained after 1h at 200°C. The TFTs fabricated from as-deposited IZO operate in the depletion mode with on–off ratio of >106, sub-threshold slope (S) of ~1.5V/decade, field effect mobility (μFE) of 18±1.6cm2/Vs, and threshold voltage (V Th) of −3±0.7V. Low-temperature annealing at 200°C in air improves the on-current, decreases the sub-threshold slope (1.56 vs. 1.18V/decade), and increases the field effect mobility (μFE) from 18.2 to 23.3cm2/Vs but also results in a V Th shift of −15±1.1V. The carrier density in the channel of the as-deposited (4.3×1016 /cm3) and annealed at 200°C (8.1×1017 /cm3) devices were estimated from test-TFT structures using the transmission line measurement methods to find channel resistivity at zero gate voltage and the TFT structures to estimate carrier mobility. [Copyright &y& Elsevier]

Abstract: The solid phase epitaxy (SPE) of undoped amorphous Si (a-Si) deposited on SiO2 patterned Si(001) wafers by reduced pressure chemical vapor deposition (RPCVD) using a H2–Si2H6 gas system was investigated. The SPE was performed by applying in-situ postannealing directly after deposition process. By transmission electron microscopy (TEM) and scanning electron microscopy, we studied the lateral SPE (L-SPE) length on sidewall and mask for various postannealing times, temperatures and a-Si thicknesses. We observed an increase in L-SPE growth for longer postannealing times, temperatures and larger Si thicknesses on mask. TEM defect studies revealed that by SPE crystallized epi-Si exhibits a higher defect density on the mask than at the inside of the mask window. By introducing SiO2-cap on the sample with 180nm Si thickness following postannealing at 570°C for 5 h, the crystallization of up to 450nm epi-Si from a-Si is achieved. We demonstrated the possibility to use this technique for SiGe:C heterojunction bipolar transistor (HBT) base layer stack to crystallize Si-buffer layer to widen the monocrystalline region around the bipolar window and to improve base link resistivity of the HBT. [Copyright &y& Elsevier]

Abstract: In this work, digermane (Ge2H6) is investigated as low temperature Ge precursor for Chemical Vapor Deposition. High quality Ge epitaxial growth on Si substrates is reported at temperatures as low as 275°C and a specific Ge2H6 surface reaction is proposed to explain the growth mechanism at those very low temperatures. In addition, we highlight that Ge2H6 provides solutions, not covered by conventional GeH4, for various original Ge-based materials: direct deposition of amorphous Ge layers directly on dielectric or metallic surfaces, as well as the epitaxial growth of smooth, fully strained, monocrystalline GeSn layers on Ge substrates. [Copyright &y& Elsevier]

Abstract: We present a catalyst enhanced etch process with high etch rates for amorphous Si based alloys (e.g. α-Si, α-Si:C, α-Si:P, α-SiCP) and low etch rates for crystalline Si (e.g. c-Si, c-Si:C, c-Si:P, c-SiCP) with etch rate ratios up to ~200. The addition of a suitable surface catalyst such as Ge (e.g. from GeH4) during HCl based etch processes increases both, the etch rate of amorphous Si alloys and the etch rate selectivity against c-Si alloys. The Ge source dynamically forms a SiGe surface layer during the etch process. Ge penetrates fast into α-Si through diffusion, forming an α-SiGe film with high [Ge] concentration. Ge diffusion into c-Si however is very limited; a rather slow surface-sub-surface exchange reaction (segregation) causes a penetration depth of only one monolayer. Repeated cycles of a selective chemical vapor etch process following a non-selective deposition process enable effective selective epitaxial growth. [Copyright &y& Elsevier]

Abstract: In this work, a concept to mitigate light-induced degradation of thin film silicon solar cells is systematically demonstrated. To overcome the light-induced degradation of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells, conventional p-type hydrogenated amorphous silicon-carbide (p-a-SiC:H) layer is replaced by the p-type nanocrystalline silicon carbide (p-nc-SiC:H). Current–voltage characteristics of solar cells fabricated with p-nc-SiC:H layers are evaluated. The introduction of a p-nc-SiC:H layer as a window layer for a-Si:H solar cells improves the light soaking degradation ratio from 24.6% to 15.9% compared to a-Si:H solar cells with a conventional p-a-SiC:H layers. Although the initial efficiency with p-nc-SiC:H layers is not as high as the standard a-Si:H solar cell with p-a-SiC:H layers, the stabilized efficiency of a-Si:H solar cell with p-nc-SiC:H window layer (8.0%) still exceeds that of the standard a-Si:H cell (7.7%). [Copyright &y& Elsevier]

Abstract: In2O3 thin films were prepared by the thermal oxidation of amorphous InSe films in air atmosphere. The structure, morphology and composition of the thermal annealed products were characterized by X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive spectroscopy, respectively. The XRD patterns indicate that the as-deposited InSe films were amorphous and they fully transformed into polycrystalline In2O3 films with a cubic crystal structure in the preferential (222) orientation at a temperature around 600°C. The optical energy gap of 3.66eV was determined at room temperature by transmittance and reflectance measurements using UV–vis–NIR spectroscopy. A preliminary characterization shows that these films have a promising response towards NO2 gas at a working temperature around 180°C. [Copyright &y& Elsevier]

Abstract: The electrical switching behavior of amorphous GexSe35−xTe65 thin film samples has been studied in sandwich geometry of electrodes. It is found that these samples exhibit memory switching behavior, which is similar to that of bulk Ge–Se–Te glasses. As expected, the switching voltages of GexSe35−xTe65 thin film samples are lower compared to those of bulk samples. In both thin film amorphous and bulk glassy samples, the switching voltages are found to increase with the increase in Ge concentration, which is consistent with the increase in network connectivity with the addition of higher coordinated Ge atoms. A sharp increase is seen in the composition dependence of the switching fields of amorphous GexSe35−xTe65 films above x=21, which can be associated with the stiffness transition. Further, the optical band gap of a-GexSe35−xTe65 thin film samples, calculated from the absorption spectra, is found to show an increasing trend with the increase in Ge concentration, which is consistent with the variation of switching fields with composition. The increase in structural cross-linking with progressive addition of 4-fold coordinated Ge atoms is one of the main reasons for the observed increase in switching fields as well as band gaps of GexSe35−xTe65 samples. [Copyright &y& Elsevier]

Abstract: The properties of hydrogenated amorphous germanium (a-Ge:H) are studied as a function of near-substrate plasma density and hydrogen partial pressure at fixed temperature. Near substrate plasma density is varied by using an unbalanced magnetron and an external magnetic field, and characterized using a guard ring flat probe and a cylindrical Langmuir probe. Films are characterized by infrared absorption, optical transmission, dark conductivity, activation energy, and photoconductivity. A major effect of increasing the near-substrate plasma density is to increase the dihydride component content of the films. The photoconductivity of these films is lower than those whose hydrogen content is increased by increasing the hydrogen partial pressure during deposition, implying a degradation in film properties with increasing near-substrate plasma density. These results show that chemical effects, as well as ion bombardment effects, need to be considered in the plasma-based deposition of a-Ge:H. [Copyright &y& Elsevier]

Abstract: Thin films of Sn10Sb20Se70-XTeX (0≤X≤14) composition were deposited using thermal evaporation technique. As-prepared films were amorphous as studied by X-ray diffraction. Surface morphology studies revealed that films have surface roughness ~2nm and av. grain size ~30nm. Optical band gap Eg showed a sharp decrease for initial substitution of Se with Te upto 2at.%. A broad hump in the optical band gap is observed for further substitution of Se with Te. The trend of optical band gap variation with tellurium content has been qualitatively explained using band model given by Kastner. The dc-conductivity measurements showed thermally activated conduction with single activation energy for the measured temperature regime and followed Meyer–Neldel rule. The dc-activation energy has nearly half the value as that of optical band gap that revealed the intrinsic nature of semiconductor. The annealing below glass transition Tg led to decrease in optical band gap as well as dc-activation energy that might be related to increase of disorder in material with annealing. [Copyright &y& Elsevier]

Abstract: The present article is a review of the recent progress and major trends in the field of thin-film transistor (TFT) research involving the use of amorphous oxide semiconductors (AOS). First, an overview is provided on how electrical performance may be enhanced by the adoption of specific device structures and process schemes, the combination of various oxide semiconductor materials, and the appropriate selection of gate dielectrics and electrode metals in contact with the semiconductor. As metal oxide TFT devices are excellent candidates for switching or driving transistors in next generation active matrix liquid crystal displays (AMLCD) or active matrix organic light emitting diode (AMOLED) displays, the major parameters of interest in the electrical characteristics involve the field effect mobility (μFE), threshold voltage (Vth), and subthreshold swing (SS). A study of the stability of amorphous oxide TFT devices is presented next. Switching or driving transistors in AMLCD or AMOLED displays inevitably involves voltage bias or constant current stress upon prolonged operation, and in this regard many research groups have examined and proposed device degradation mechanisms under various stress conditions. The most recent studies involve stress experiments in the presence of visible light irradiating the semiconductor, and different degradation mechanisms have been proposed with respect to photon radiation. The last part of this review consists of a description of methods other than conventional vacuum deposition techniques regarding the formation of oxide semiconductor films, along with some potential application fields including flexible displays and information storage. [Copyright &y& Elsevier]

Abstract: A novel nanoplate-structured thin-film solar cell was investigated that could solve the conflict between light absorption and carrier transport in a p-type amorphous silicon carbide (a-SiC)/i-type amorphous silicon germanide (a-SiGe)/n-type amorphous silicon (a-Si) thin-film solar cell. This structure has an n-type a-Si nanoplate array on the substrate, a-SiC p-layer, and an a-SiGe i-layer which are sequentially grown along the surface of each n-type a-Si nanoplate. Under illumination by sunlight, light is absorbed along the vertical direction of the nanoplate, while the carrier transport is along the horizontal direction. The nanoplate structure may absorb most of the sunlight and provide a thinner film for the effective transport of photon-generated carriers as compared to the conventional planar structure. [Copyright &y& Elsevier]

Abstract: Creating micro-/nano-scale topography on material surfaces to change their wetting properties has been a subject of much interest in recent years. Wenzel in 1936 and Cassie and Baxter in 1944 proposed that by microscopically increasing the surface roughness of a substrate, it is possible to increase its hydrophobicity. This paper reports the fabrication of micro-textured surfaces and nano-textured surfaces, and the combination of both on stainless steel substrates by sandblasting, thermal evaporation of aluminum, and aluminum-induced crystallization (AIC) of amorphous silicon (a-Si). Meanwhile, fluorinated carbon films were used to change the chemical composition of the surfaces to render the surfaces more hydrophobic. These surface modifications were investigated to create superhydrophobic surfaces on stainless steel substrates. The topography resulting from these surface modifications was analyzed by scanning electron microscopy and surface profilometry. The wetting properties of these surfaces were characterized by water contact angle measurement. The results of this study show that superhydrophobic surfaces can be produced by either micro-scale surface texturing or nano-scale surface texturing, or the combination of both, after fluorinated carbon film deposition. [Copyright &y& Elsevier]

Abstract: The structure of molybdenum layers deposited by direct current magnetron sputtering onto the amorphous silicon (a-Si) layers as function of nominal layer thickness was studied by methods of transmission electron microscopy. Molybdenum layers with nominal thickness 1.5

Abstract: Amorphous carbon layers (ACL) were deposited on Si (100) wafers by plasma enhanced chemical vapor deposition (PECVD) by using 1-hexene (C6H12) as a carbon source for dry etch hard mask of semiconductor devices manufacturing process. The deposition characteristics and film properties were investigated by means of ellipsometry, Raman spectroscopy, X-ray photo electron spectroscopy (XPS) and stress analysis. Hardness, Young''s modulus, and surface roughness of ACL deposited at 550°C were investigated by using nano-indentation and AFM. The deposition rate was decreased from 5050Å/min to 2160Å/min, and dry etch rate was decreased from 2090Å/min to 1770Å/min, and extinction coefficient was increased from 0.1 to 0.5. Raman analysis revealed a higher shift of the G-peak and a lower shift of the D-peak and the increase of I(D)/I(G) ratio as the deposition temperature was increased from 350°C to 550°C. XPS results of ACL deposited at 550°C revealed a carbon 1s binding energy of 284.4eV. The compressive film stress was decreased from 2.95GPa to 1.28GPa with increasing deposition temperature. The hardness and Young''s modulus of ACL deposited at 550°C were 5.8GPa and 48.7GPa respectively. The surface roughness RMS of ACL deposited at 550°C was 2.24Å, and that after cleaning in diluted HF solution (H2O:HF=200:1), SC1 (NH4OH:H2O2:H2O=1:4:20) solution, and sulfuric acid solution (H2SO4:H2O2 =6:1) was 2.28Å, 2.30Å and 7.34Å, respectively. The removal amount of ACL deposited at 550°C in diluted HF solution, SC1 solution and sulfuric acid solution was 6Å, 36Å and 110Å, respectively. These results demonstrated the viability of ACL deposited by PECVD from C6H12 at 550°C for application as the dry etch hard mask in fabrication of semiconductor devices. [Copyright &y& Elsevier]

Abstract: Amorphous and microcrystalline silicon thin films are used in solar cells as a multi-junction photovoltaic device. Plasma enhanced chemical vapor deposition is used and high deposition rate of a few nm/s is required while keeping film quality. SiH4 is used as a precursor diluted with H2. Electron impact processes give complex interdependent plasma chemical reactions. Many researchers suggest keeping high H/SiHx ratio is important. Numerical modeling of this process for capacitively coupled plasma and inductively coupled plasma is done to investigate which process parameters are playing key roles in determining it. A full set of 67 volume reactions and reduced set are used. Under most of conditions, CCP shows 100 times higher H/SiH3 ratio over ICP case due to its spatially localized two electron temperature distribution. Multi hollow cathode type CCP is also modeled as a 2×2 hole array. For Ar, the discharge is well localized at the neck of the hole at a few Torr of gas pressure. H2 and SiH4 +H2 needed higher gas pressure and power density to get a multi hole localized density profile. H/SiH3 was calculated to be about 1/10. [Copyright &y& Elsevier]

Abstract: A new route for obtaining very small, spheroid glass powders is demonstrated using an RF (radio frequency) thermal plasma system. During the process, four kinds of chemicals, here SiO2, B2O3, BaCO3, and K2CO3, were mixed at pre-set weight ratios, spray-dried, calcined at 250°C for 3h, and crushed into fragments. Then, they were successfully reformed into nano-sized amorphous powders (<200nm) with spherical shape by injecting them along the centerline of an RF thermal plasma reactor at ~24kW. The as-synthesized powders show negligible (<1%) composition changes when compared with the injected precursors of raw material compounds. [Copyright &y& Elsevier]

Abstract: In this study, we compared the line edge roughnesses (LER) and profile angles of chemical vapor deposited (CVD) amorphous carbon (a-C) patterns etched in an inductively coupled plasma (ICP) etcher produced by varying process parameters such as the N2 gas flow ratio, Q (N2), and dc self-bias voltage (Vdc) in O2/N2/Ar and H2/N2/Ar plasmas. The tendencies of the LER and profile angle values of the etched CVD a-C pattern were similar in both plasmas. The LER was smaller in the O2/N2/Ar than in the H2/N2/Ar plasmas, and the profile angle was larger in the O2/N2/Ar than in the H2/N2/Ar plasmas under the same processes conditions. The use of O2/N2/Ar plasma was more advantageous than the H2/N2/Ar plasma for controlling LER and profile angle. [Copyright &y& Elsevier]

Abstract: Amorphous carbon layers (ACLs) were prepared by plasma enhanced chemical vapor deposition (PECVD) from 1-hexene (C6H12) and propylene (C3H6) as a carbon source at different temperatures for dry etch hard mask of semiconductor devices manufacturing process. The deposition rate of ACL deposited at 550°C from C6H12 and C3H6 was 5050Å/min and 6360Å/min. Although the deposition rate of ACL deposited from C6H6 was lower than that from C3H6, normalized deposition rate of ACL deposited from C6H12 was 1.64 times higher than that from C3H6. The relative amount of hydrocarbon contents measured by FTIR (Fourier transformation infrared) and TDS (thermal desorption spectroscopy) was decreased with the increase of deposition temperature. Raman results showed that the numbers and size of graphite cluster of ACLs deposited from each source were increased with the increase of deposition temperature. The extinction coefficient of ACL deposited at 550°C from C6H12 was 0.51 and that from C3H6 was 0.48. The density of ACL deposited at 550°C from C6H12 was 1.48g/cm3 and that from C3H6 was 1.45g/cm3. The dry etching rate of ACL deposited at 550°C from C6H12 was 1770Å/min and that from C3H6 was 1840Å/min. The deposition rate, dry etch rate and the amount of hydrocarbon contents of ACLs deposited from each carbon source were decreased with the increase of deposition temperature but extinction coefficient and density were increased with the increase of deposition temperature. We concluded that the variation behavior of the deposition characteristics and film properties of ACLs from C6H12 with the increase of deposition temperature was the same as those of ACLs from C3H6. The high density and low dry etch rate of ACL from C6H12 can be explained by less hydrocarbon incorporation during deposition and these properties are more favorable for the dry etch hard mask application in semiconductor device fabrication. [Copyright &y& Elsevier]

Abstract: Characteristics of amorphous silicon (a-Si) etching using atmospheric pressure plasma discharge had been studied. Dielectric barrier discharge (DBD) plasma with nitrogen gas was employed for the study. The active chemical agent for etching was generated by mixing a small quantity of sulfur hexafluoride (SF6) gas into the plasma. The two distinguishable plasma zones are generated with the specially designed DBD plasma generator. The one is the main discharge zone generated between the two parallel plate electrodes. And the other one is downstream plasma zone extracted from the main discharge zone through the holes perforated on the bottom electrode. A test specimen was etched located at the plasma zone and moved the zone several times for etching on a temperature controlled stage. The etch rate of a-Si and the selectivity to silicon nitride (SiNx) were improved by addition of hydrogen (H2) or methane (CH4) gas into the plasma. However, when the specimen temperature was lower than 100°C with H2 or CH4 gas added plasma condition, a-Si layer was not etched at all, but in the range of 100–140°C of specimen temperature, the a-Si layer started to be etched while the influence of the specimen temperature on etching of a-Si was ignorable in that temperature range. At the optimized condition, the a-Si etch rate was up to 3000A/min in the downstream plasma zone with the 3mm of the distance between the surface of the specimen and the bottom side of the DBD plasma generator module. And the etch rate ratio between a-Si and SiNx was more than 100:1. [Copyright &y& Elsevier]

Abstract: The effects of argon neutral beam (NB) energy on amorphous carbon (a-C) films were investigated, the a-C films were deposited by a neutral particle beam assisted sputtering (NBAS) system. The energy of the neutral particle beam can be directly controlled by a reflector bias voltage as a unique operating parameter of the system. The results from the analysis by Raman spectra, Fourier transform infrared (FT-IR), UV–visible spectroscopy and electrical conductivity indicate the properties of the amorphous carbon films can be manipulated by simply adjusting the NB energy (or reflector bias voltage) without changing any other process parameters. By increasing the reflector bias voltage, the amount of cross-linked sp2 clusters as well as the sp3 bonding in the a-C film coating from the NBAS system can be increased effectively and the composition of carbon thin films can be changed from a nano-crystalline graphite phase to an amorphous carbon phase. In addition, the deposition rate increases with reflector bias voltage due to additional sputtering at the carbon reflector without any variation of physical and electrical properties of the a-C film. [Copyright &y& Elsevier]

Abstract: A pulse-modulated direct-current methane plasma is used to deposit amorphous hydrogenated carbon (a-C:H) films on Si and polymethyl methacrylate (PMMA) substrates. The structure and mechanical properties of the films are examined by applying a negative pulse bias voltage of 0.5 to 3kV to the substrate at a pulse bias period of 100 to 200μs. The deposition rate on both Si and PMMA increases with increasing the net input power, independent of the pulse period. The Raman spectra demonstrate that the films on Si are diamond-like carbon (DLC), while those on PMMA are polymer-like or soft amorphous carbon because of higher crystallinity of the sp2 phase and lower nanoscale hardness. The residual compressive stress of the films on PMMA is constantly low ranging from 0 to 2GPa due exclusively to high flexibility of PMMA, which causes the easy relief of the stress and thus the density decrease in the films. [Copyright &y& Elsevier]

Abstract: In this study, we investigated the electrical characteristics and the stability of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) from the viewpoint of active layer composition. Active layers of TFTs were deposited by r.f. sputtering. Two kinds of sputtering targets, which have different compositional ratios of In:Ga:Zn, were used to make variations in the active layer composition. All the fabricated IGZO TFTs showed more excellent characteristics than conventional amorphous silicon TFTs. However, in accordance with the Ga content, IGZO TFTs showed somewhat different electrical characteristics in values such as the threshold voltage and the field effect mobility. The device stability was also dependent on the Ga content, but had trade-off relation with the electrical characteristics. [Copyright &y& Elsevier]

Abstract: Amorphous hydrogenated silicon films were deposited on glass substrates at room temperature. This cold deposition process was operated in a dielectric barrier discharge CVD reactor with a fixed strip-shaped plasma matched with a moving substrate holder. The maximum film area was 300×600mm2. The film deposition rate as a function of applied peak voltage of DBD power was investigated under different hydrogen-diluted silane concentrations, and the film surface smoothness, continuity, and film/glass adherence were also studied. The maximum deposition rate was 12.2Å/s, which was performed under the applied peak voltage of 16kV and a hydrogen-diluted silane concentration of 50%. IR measurements reveal that the silane concentration plays a key role in determining the hydrogen-silicon bonding configurations. With increasing hydrogen-diluted silane concentration, the H–Si bonding configurations shift gradually from Si–H3 to Si–H. The variation of photo/dark conductivity ratio and optical bandgap versus hydrogen-diluted silane concentration were investigated. The use of DBD-CVD for deposition of a-Si:H films offers certain advantages, such as colder substrate, faster film growth rate, and larger deposition area. However, the consumption of silane for the DBD-PECVD procedure is much greater than for the RF-PECVD process. [Copyright &y& Elsevier]

Abstract: In this study, smooth and conformal hydrogenated silicon thin films are examined and analyzed on various multi-walled carbon nanotube (MWCNT) substrates. The films are deposited using radio-frequency plasma-enhanced chemical vapor deposition with He dilution and parameters that are heavily in the γ regime. It is proposed that high-energy plasmas with limited penetration depth can induce crystallization to occur on MWCNT substrates of varying active surface areas. The samples presented exhibit properties that are promising for energy applications, including photovoltaics and lithium-ion batteries and have been studied using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, UV–Vis spectrophotometry, four-point probe measurements, and Fourier transform infrared spectroscopy. [Copyright &y& Elsevier]

Abstract: Crystallization of amorphous silicon (a-Si:H) film is extremely important in many aspects of electronic devices and has been heavily explored. We demonstrate that microwave irradiation, 200W, is able to fast-crystallize a-Si:H film using as susceptor carbon-overcoat which contains graphite and carbon nano-tube. X-ray diffraction and Raman spectra reveal that nearly full crystallization is reached within 90s. Microwave absorption by the carbon-overcoat generates thermal energy which heats up a-Si:H film to a threshold temperature 440±10°C required for initiation of microwave crystallization. Dielectric properties of a-Si:H film facilitate its self-heating and nucleation of Si crystallites at above the threshold temperature. This method is extendable to fast-crystallize a-Si:H film on a remote and large-area basis. [Copyright &y& Elsevier]