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The behavior of hole polarons in β -gallium oxide (Ga2O3) has attracted significant attention. Depth-resolved cathodoluminescence (CL) was used to investigate the minority carrier dynamics in β -Ga2O3. First, a model describing CL intensity was proposed by considering the depth-dose function and surface recombination. A universal depth-dose function for β -Ga2O3, which has the form of a third-degree polynomial, was presented based on Monte Carlo simulation by introducing a normalized depth, which is the depth normalized by the electron beam range. Second, two experimental approaches, plan-view and cross-sectional CL measurements, were applied to unintentionally doped β -Ga2O3 (âˆ'201) wafers, and the experimental results were compared with those of the proposed model. The hole diffusion length was estimated to be within the range of 200â€"400 nm through the plan-view measurement, whereas a hole diffusion length of 250 nm was obtained through the cross-sectional measurement. The values were consistent with each other, and the model reproduced the experimental results well. This indicates that the nonequilibrium minority hole in the unintentionally doped β -Ga2O3 is mobile and forms a ‘weak’ polaron. The reduced recombination velocity of the (âˆ'201) face was estimated to be approximately ten for the plan-view measurement, whereas that of ten or more was assumed for the cross-sectional measurement. No inconsistency was observed, but the low-energy plan-view measurement is considered more suitable for investigating the surface recombination velocity. [ABSTRACT FROM AUTHOR]

The electrical and passivation properties of alumina layers deposited by the atomic layer deposition (ALD) technique with different precursors at different temperatures are analyzed. Herein, a significantly larger density of the negative fixed charge in alumina layers deposited with ozone in comparison to those prepared with water is observed. A part of this negative charge can be successfully removed by the annealing of the samples already at around 250 °C and this negative charge is tentatively ascribed to oxygen interstitials. The effective surface recombination velocity (seff) is below 2 cm s−1 in all as‐deposited alumina layers independent of the deposition conditions and it is significantly smaller in layers prepared with water. The higher seff in films prepared with ozone can be explained by the higher density of the interface states in these samples as obtained from impedance measurements performed at different ac frequencies and at different biases. The conduction mechanisms in alumina films are also investigated and their difference is discussed. [ABSTRACT FROM AUTHOR]

• The CdTe surface was passivated by the sputtered Al 2 O 3 and V 2 O 5 layers. • The minority carrier lifetime of the CdTe covered with Al 2 O 3 and V 2 O 5 was increased. • There exsits negative fixed charges in V 2 O 5 and Al 2 O 3. • The passivation was ascribed to the electric field effect. In this study, three kinds of metal oxide (MOs), namely, V 2 O 5 , Al 2 O 3 and NiO, were deposited on CdTe thin films to study possible passivation effect on the CdTe surface. Time-resolved photoluminescence (TRPL) measurements were carried out to study the minority carrier lifetime of the MO-coated CdTe and bare CdTe. The results showed that the TRPL decay curves were consisted of a fast and a slow decay process for all samples. For both the bare and NiO-coated CdTe surface, the fast and the slow decay lifetimes were found to be 0.5 and 1.0 ns. While for the Al 2 O 3 - and V 2 O 5 -coated CdTe, the fast decay lifetime was 0.6 and 0.7 ns, and the slow decay lifetime was 2.1 and 2.4 ns, respectively. CdTe surface defect states with high surface recombination velocity, ~106 cm/s, were responsible for the fast decay. The CdTe surface was effectively passivated by a 3-nm-thick V 2 O 5 or Al 2 O 3 coating layer. The simulation and experimental results indicated that the passivation was ascribed to the electric field effect induced by negative fixed charges in V 2 O 5 and Al 2 O 3. [ABSTRACT FROM AUTHOR]

In various types of organic/inorganic solar cells, optical response enhancement is consistently observed within the external quantum efficiency spectra owing to the improvement in interface passivation and the suppression of carrier recombination. In this study, we focused on crystalline silicon solar cells and systematically investigated the impact of interface recombination on the optical response upon dual-side illumination using numerical simulations. The results shed light on the interesting phenomenon that the surface recombination velocity has a significant impact on the external quantum efficiency, and it changes as the illumination direction changes. Moreover, from a practical perspective, the spectra of external quantum efficiency under dual-side illumination conditions can act as a powerful tool for the quick diagnosis of the passivation quality at the top and bottom interfaces. • Numerical simulations were conducted to understand the mechanism behind spectrally dependent surface recombination in silicon solar cells. • Suppressing carrier recombination at the high-low junction interface enhances the optical response across the entire wavelength range upon illumination from the high-low junction side. • Optical response enhancement only occurs in the long-wavelength range by decreasing the surface recombination velocity at the high-low junction interface upon illumination from the p-n junction side. • The spectra of external quantum efficiency under dual-side illumination conditions can act as a powerful tool for the quick diagnosis of the passivation quality at the top and bottom interfaces. [ABSTRACT FROM AUTHOR]

Thermally grown SiO2 is widely used for silicon surface passivation in solar cells and other applications due to excellent interfacial properties. SiO2 films with thickness in the range of 17 nm deposited by industrially viable spray-coating technique on both n- and p-type silicon are reported. Low values of interface state density of 1.4 × 1010 cm−2 eV−1 on n-type and 2.0 × 1010 cm−2 eV−1 on p-type were achieved. Fixed oxide charges in the range of 7.1– 9.4 × 1011 cm−2 and 3.9– 6.5 × 1011 cm−2 on n- and p-type, respectively, are obtained. Excellent passivation results in the effective surface recombination velocity of 0.97 cms−1 and 8.07 cms−1 at minority carrier concentration of 1015 cm−3 on n- and p-type Czochralski silicon, respectively, without the use of capping layer. SiO2 film exhibits dielectric breakdown field strength of 4.3 MV cm−1 and 5.6 MV cm−1 and leakage current density of 2.2 × 10−8 A cm−2 and 1.1 × 10−8 A cm−2 at 1 MV cm−1 on n- and p-type silicon, respectively. These values are superior to sol-gel-based SiO2 films reported previously and are comparable to or better than those reported for other methods for the growth or deposition of SiO2 on silicon. Amorphous nature of the film is validated by high-resolution transmission electron microscopy (TEM). The X-ray photoelectron spectroscopy (XPS) analysis shows nearly stoichiometric SiOx film. [ABSTRACT FROM AUTHOR]

The junction properties at the solution-processed titanium dioxide (TiO2)/n-type crystalline Si(n-Si) interface were studied for poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/n-Si heterojunction solar cells by the steady-state photovoltaic performance and transient reverse recovery characterizations. The power conversion efficiency could be increased from 11.23% to 13.08% by adjusting the layer thickness of TiO2 together with increasing open-circuit voltage and suppressed dark saturation current density. These findings originate from the enhancement of the carrier collection efficiency at the n-Si/cathode interface. The transient reverse recovery characterization revealed that the surface recombination velocity S was ∼375 cm/s for double TiO2 interlayer of ∼2 nm thickness. This value was almost the same as that determined by microwave photoconductance decay measurement. These findings suggest that solution-processed TiO2 has potential as a hole blocking layer for the crystalline Si photovoltaics. [ABSTRACT FROM AUTHOR]

Recombination of the carrier due to the surface state level traps could affect betavoltaic performance. Herein, we employed a theoretical 1-D carrier transport calculation to investigate the surface passivation effect in a planar [147Pm]-Si p-n junction betavoltaic cell and the results were verified using previous studies. In comparison to the ideal condition of the passivated surface, we predict a 10.74% power loss at the device, thus further research concerning the surface passivation layer for betavoltaic batteries might be necessary. • The surface passivation layer influences to battery performance were investigated. • The beta particle interaction with several types of surface passivation layer and p-n junction were simulated using MCNP. • The thickness of Pm2O3 metal source was optimized to reduce the effect of self-absorption. • The thinnest possible SiO2 film was implemented as front-surface passivation layer. [ABSTRACT FROM AUTHOR]

A simple yet reproducible method to deposit high quality aluminium oxide (AlO x) film by spray coating is presented. Excellent thickness and refractive index uniformity is demonstrated. The AlO x film was found to be nearly stoichiometric with an oxygen to aluminium ratio of 1.7 from X-ray photoelectron spectroscopy (XPS) measurements. An interfacial layer with thickness of about 2 nm was observed in transmission electron microscopy analysis. The interfacial layer was determined to be aluminium silicate from XPS data. Electrical characterization of the films on Czochralski (Cz) p-type silicon yielded dielectric constant of 6.5 and mean breakdown field of 4.7 MV cm−1. Interface state density of 8.7 × 10 10 eV−1cm−2 and fixed charge density of − 5.5 × 10 12 cm−2 were obtained from the electrical characterization of metal insulator semiconductor capacitors. The excellent interface quality with low interface state density and high negative charge is suitable for passivation of p-type silicon in solar cell applications. Effective surface recombination velocity of 12 cm s−1 and 48 cm s−1 were obtained for Cz p-type silicon surface for annealing temperature of 750°C and 790°C respectively without the use of capping layer. Image 1 [ABSTRACT FROM AUTHOR]

Surface recombination velocity on mesa sidewalls of SiC p-n diodes with various surface passivation conditions was evaluated from the device-size-dependent preexponential factor of recombination current (${J}_{\text {0rec}}$). The diodes passivated by SiO2 with postoxidation nitridation were dipped into HF to eliminate a shunt current, which is evoked by the nitrided SiO2 layer and disturbs the analysis of the recombination current. For accurate determination of the surface recombination velocity, an effective recombination zone width was precisely derived taking account of the distribution of carrier density in the depletion layer. The surface recombination velocity of the diodes without any passivation and with the postoxidation nitridation (NO annealing at 1250 °C for 70 min) was determined as $\text {1.2}\times \text {10}^{\text {7}}$ and $\text {6.0}\times \text {10}^{\text {5}}$ cm/s, respectively, which indicates that the postoxidation nitridation can reduce the surface recombination by a factor of about 20. We confirmed that TCAD simulation could reproduce the current–voltage characteristics by utilizing the extracted parameters. In addition, an evaluation method was proposed to determine the surface recombination velocity from the high-current region, where diffusion current is dominant. [ABSTRACT FROM AUTHOR]

CdTe-based detectors have the problem of Te-rich surface layers caused by Br etching, which is one of fabrication steps. Te-rich layer acts as a trapping center and serves as an additional source of charge carriers, thereby degrading transport property of charge carriers and enriching leakage current on surface of detector. To solve this problem, we introduced sodium hypochlorite (NaOCl) as a passivant, and investigated its effect on Cd 0.95 Mn 0.05 Te 0.98 Se 0.02 (CMTS), by analyzing chemical state of surface and its performance. After passivation with NaOCl, the results of X-ray photoelectron spectroscopy (XPS) shows the formation of tellurium oxide and elimination of water on CMTS surface, and CMTS presented enhanced performance with Am-241 radioisotope. Consequently, it is demonstrated that the passivation with NaOCl reduces leakage current, compensates defect, and elevates transport of charge carriers, thereby decreasing charge loss of carriers and improving performance of CMTS detector. • The CdMnTeSe(CMTS) was grown with Bridgman method to solve the segregation problems of CdZnTe. • The CMTS also suffered from Br-etching process, resulting in dangling bond and leakage current. • Passivant of sodium hypochlorite on CMTS surface enabled performance improvement of CMTS. [ABSTRACT FROM AUTHOR]

In c-Si solar cells, surface recombination velocity increases as the wafer thickness decreases due to an increase in surface to volume ratio. For high efficiency, in addition to low surface recombination velocity at the rear side, a high internal reflection from the rear surface is also required. The SiO x N y film with low absorbance can act as rear surface reflector. In this study, industrially feasible SiO 2 /SiO x N y stack for rear surface passivation and screen printed local aluminium back surface field were used in the cell structure. A 3 nm thick oxide layer has resulted in low fixed oxide charge density of 1.58 × 10 11 cm −2 without parasitic shunting. The oxide layer capped with SiO x N y layer led to surface recombination velocity of 155 cm/s after firing. Using single layer (SiO 2 ) rear passivation, an efficiency of 18.13% has been obtained with V oc of 625 mV, J sc of 36.4 mA/cm 2 and fill factor of 78.7%. By using double layer (SiO 2 /SiO x N y stack) passivation at the rear side, an efficiency of 18.59% has been achieved with V oc of 632 mV, J sc of 37.6 mA/cm 2 , and fill factor of 78.3%. An improved cell performance was obtained with SiO 2 /SiO x N y rear stack passivation and local BSF. [ABSTRACT FROM AUTHOR]

In this work, we report on the passivation of porous silicon (PS) by tungsten trioxide (WO 3 ) nanostructured thin films deposited via dip-coating of PS in tungsten hexachloride and water/ethanol solution. Structural analysis by Fourier transform infrared spectroscopy showed a partial disappearance of SiH x and Si O Si peaks after WO 3 thin film deposition on the PS due to the replacement of H atoms by WO 3 . Additionally, PS/WO 3 sample revealed weakly intense peaks which can be ascribed to O W O and W O bridging bonds. Morphological analysis by atomic force spectroscopy showed the coverage of the PS surface by a nanostructured thin film of dense WO 3 nanoparticles with a size ranging from 40 to 60 nm. The photoluminescence signal intensity of PS/WO 3 samples presents a continuous increase as a function of the immersion time in the precursor solution. This is attributed to a better decoration of the PS surface by WO 3 nanoplatelets and a decrease of surface recombination velocity (200 × 10 2 cm/s for untreated silicon, 137 × 10 2 cm/s for PS and 99 × 10 2 cm/s for PS/WO 3 samples). Hence, a ~ 50% improvement in the effective lifetime of minority carriers is obtained. Moreover, the deposited WO 3 contributed not only to the passivation of PS, but acted as an antireflection layer which enhanced the optical properties of PS by reducing the reflection of light. These obtained results confirmed the benefits of using WO 3 thin film as passivation/antireflection coating for possible solar cell application. [ABSTRACT FROM AUTHOR]

Surface trap density in silicon nanowires (NWs) plays a key role in the performance of many semiconductor NW-based devices. We use pump-probe microscopy to characterize the surface recombination dynamics on a point-by-point basis in 301 silicon NWs grown using the vapor-liquid-solid (VLS) method. The surface recombination velocity (S), a metric of the surface quality that is directly proportional to trap density, is determined by the relationship S = d/4t from measurements of the recombination lifetime (t) and NW diameter (d) at distinct spatial locations in individual NWs. We find that S varies by as much as 2 orders of magnitude between NWs grown at the same time but varies only by a factor of 2 or three within an individual NW. Although we find that, as expected, smaller-diameter NWs exhibit shorter t, we also find that smaller wires exhibit higher values of S; this indicates that t is shorter both because of the geometrical effect of smaller d and because of a poorer quality surface. These results highlight the need to consider interwire heterogeneity as well as diameter-dependent surface effects when fabricating NW-based devices. [ABSTRACT FROM AUTHOR]

A theoretical approach based on Drift-Diffusion equations is presented to study planar mixed lead halide perovskite solar cells. Updated physical parameters such as permittivity, mobility, effective density of states and doping density is employed in simulations. Current-voltage curve data for two experimental sample is imported and through fitting with the model, density of bulk and interface defects is calculated. We obtain the bulk defect density around 10 16 cm −3 and surface recombination velocities in the range of 10 cm/s. These values which are in good agreement with experimental measurements and considerably deviated from previous theoretical studies, verify the model and adopted constants. Shockley-Queisser limit is also presented as the ideal device and the effect of bulk and interface defects are presented as loss factors that cause departure from this limit. Our simulations conclude that the overall efficiency of perovskite solar cells is mainly governed by the open-circuit voltage and also identify the interface defects as the major loss factor in these devices. [ABSTRACT FROM AUTHOR]

The effects of nanocrystals density on the electron beam induced current are studied by the use of Monte-Carlo simulation. The nanocrystals are considered as recombination centers for captured charges and are distributed randomly at the sample surface. The induced current is collected by a nanocontact. The surface recombination velocity at the free surface is supposed to be zero. For a given electron beam energy, simulated results show a decrease of the carrier collection efficiency and shrinkage of its profile when the nanocrystals density increases. As a consequence, the minority carrier effective diffusion length which is extracted from simulated results is a decreasing function. This is not surprising because it is well known that an increase of recombination centers leads to reduction of the minority carrier lifetime and then a reduction of their diffusion length. These effects are highlighted because of both collecting electrode small size and perpendicular configuration. [ABSTRACT FROM AUTHOR]

Donolato minority carrier collection probability [Sol. Stat. Electron. 28, (1985) 1143–115] is used to describe the surface recombination effects between zero and infinite values of the surface recombination velocity. The probability function is modified for a nano-electrode. An opening angle and a “specific” length are introduced. The opening angle leads to the emerged charge to “see” the electrode, and the “specific” length describes an average distance travelled by the charge at the surface sample before being collected by the nano-contact. Results show that both minority carrier effective diffusion length and collection efficiency maximum increase when the “specific” length is increased. The effective diffusion length varies from 0.3 μm for infinite velocity to 0.9 μm for velocity zero. The latter is 10% smaller than the bulk diffusion Length because of both the nano-scale contact and the bi-dimensional diffusion space which affect the collection probability, and hence the collection efficiency profile. [ABSTRACT FROM AUTHOR]

The III-V semiconductor InGaAs is a key material for photonics because it provides optical emission and absorption in the 1.55 μm telecommunication wavelength window. However, InGaAs suffers from pronounced nonradiative effects associated with its surface states, which affect the performance of nanophotonic devices for optical interconnects, namely nanolasers and nanodetectors. This work reports the strong suppression of surface recombination of undoped InGaAs/InP nanostructured semiconductor pillars using a combination of ammonium sulfide, (NH4)2S, chemical treatment and silicon oxide, SiOx, coating. An 80-fold enhancement in the photoluminescence (PL) intensity of submicrometer pillars at a wavelength of 1550 nm is observed as compared with the unpassivated nanopillars. The PL decay time of ~0.3 μm wide square nanopillars is dramatically increased from ~100 ps to ~25 ns after sulfur treatment and SiOx coating. The extremely long lifetimes reported here, to our knowledge the highest reported to date for undoped InGaAs nanostructures, are associated with a record-low surface recombination velocity of ~260 cm/s. We also conclusively show that the SiOx capping layer plays an active role in the passivation. These results are crucial for the future development of high-performance nanoscale optoelectronic devices for applications in energy-efficient data optical links, single-photon sensing, and photovoltaics. [ABSTRACT FROM AUTHOR]

Sn-based perovskites are promising Pb-free photovoltaic materials with an ideal 1.3 eV bandgap. However, to date, Sn-based thin film perovskite solar cells have yielded relatively low power conversion efficiencies (PCEs). This is traced to their poor photophysical properties (i.e., short diffusion lengths (<30 nm) and two orders of magnitude higher defect densities) than Pb-based systems. Herein, it is revealed that melt-synthesized cesium tin iodide (CsSnI3) ingots containing high-quality large single crystal (SC) grains transcend these fundamental limitations. Through detailed optical spectroscopy, their inherently superior properties are uncovered, with bulk carrier lifetimes reaching 6.6 ns, doping concentrations of around 4.5 × 1017 cm−3, and minority-carrier diffusion lengths approaching 1 µm, as compared to their polycrystalline counterparts having ≈54 ps, ≈9.2 × 1018 cm−3, and ≈16 nm, respectively. CsSnI3 SCs also exhibit very low surface recombination velocity of ≈2 × 103 cm s−1, similar to Pb-based perovskites. Importantly, these key parameters are comparable to high-performance p-type photovoltaic materials (e.g., InP crystals). The findings predict a PCE of ≈23% for optimized CsSnI3 SCs solar cells, highlighting their great potential. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed performance analysis of monolithically integrated dual junction silicon-based tandem solar cells with perovskite as the top cell material, using physics-based model. The perovskite cell is modeled based on four different configurations, namely p-i-n, p-p-n, n-i-p, and n-p-p whereas standard models are considered for the silicon cell. We explore the sensitivity of the tandem cell performance by varying the transport layer properties, namely the minority carrier surface recombination velocities. We also investigate the effect of varying the sub-cell thicknesses on the tandem efficiency. The results illustrate the superior effect of top cell parameters, both surface recombination velocity and thickness, in improving the cell performance. We also demonstrate a range of optimum thickness for the top sub-cell while examining the co-dependence between the absorber layer thickness and minority carrier surface recombination velocities. In closing, we study the effect of series and shunt resistances on the overall tandem cell efficiency. [ABSTRACT FROM AUTHOR]

High efficiency partial rear contact solar cells forms a Metal-Insulator-Semiconductor (MIS) stack in the rear side. Aluminum is used as a local back surface field (localized heavily doped pregion) and a hole contact. The workfunction difference between the aluminum contact and the c-Si(p) causes inversion in the silicon surface of the MIS structure. The surface inversion affects the quality of passivation and hence, the performance of the solar cell which requires further understanding. In this work, we have analysed the influence of aluminum on surface passivation in two passivation stacks namely (i) AlO x /SiN x and (ii) SiO x /SiN x using Sentaurus TCAD simulation. Our simulation result shows that in case of positive dielectric stack (SiO x /SiN x ), aluminum workfunction enhances the passivation (effective surface recombination velocity <15 cm/s) for the injection condition of 2 × 10 13 cm - 3 which is common at the rear side of AlLBSF solar cell. But, in negative dielectric stack (AlO x /SiN x ), aluminum workfunction influence is negligible since it is surpassed by high negative fixed charge density. In addition, we have varied the capping layer (SiN x ) thickness in the dielectric stack to alter the aluminum influence on the crystalline silicon surface. It shows up to 1.0% absolute improvement in the efficiency for reduced SiN x thickness in the SiO x /SiN x stack for the fixed charge density of 2 × 10 11 cm - 2 , interface trap density of 5 × 10 11 cm - 2 , assumed electron and hole capture cross section of 10 - 14 cm 2 and 4 × 10 - 16 cm 2 respectively. This is solely attributed to the aluminum workfunction influence on the rear passivation. [ABSTRACT FROM AUTHOR]

Monte-Carlo simulation is used to study the surface recombination effects on the electron beam induced current technique. The current is collected by a nanoscale electrode. We choose three values for the surface recombination velocity reflecting the sample surface states; zero, infinite value and an intermediate one. From a probabilistic point of view, each of the three surface velocities is described by a collection probability related to the surface effects and to the electrode size. Even if probabilities corresponding to zero and intermediate velocity are chosen to be close one to the other, the results are different. For intermediate velocity the collection efficiency profile is similar to that corresponding to the infinite velocity. Both profiles narrow with diminution of their maximum. At electron beam energies higher than 4 keV the profiles are superimposed because of the large penetration depth, and the smallness of the electrode and its depletion zone. [ABSTRACT FROM AUTHOR]

In the present study the electrical properties of 100 nm and 400 nm alumina films grown by the atomic layer deposition technique on p -type Si before and after a post-deposition annealing at 440 °C and after a dc H plasma treatment at different temperatures are investigated. We show that the density of interface states is below 2 × 10 10 cm −2 in these samples and this value is significantly lower compared to that reported previously in thinner alumina layers (below 50 nm). The effective minority carrier lifetime τ g,eff and the effective surface recombination velocity s eff in untreated p -type Si samples with 100 nm and 400 nm aluminum oxide is comparable with those obtained after thermal oxidation of 90 nm SiO 2 . Both, a post-deposition annealing in forming gas (nitrogen/hydrogen) at elevated temperatures and a dc H-plasma treatment at temperatures close to room temperature lead to the introduction of negatively charged defects in alumina films. The results obtained in samples annealed in different atmospheres at different temperatures or subjected to a dc H plasma treatment allow us to correlate these centers with H-related defects. By comparing with theory we tentatively assign them to negatively charged interstitial H atoms. [ABSTRACT FROM AUTHOR]

We investigate the role of hydrogen content and fixed charges of catalytic chemical vapor deposited (Cat-CVD) SiN x /Si-rich SiN x stacked layers on the quality of crystalline silicon (c-Si) surface passivation. Calculated density of fixed charges is on the order of 10 12 cm − 2 , which is high enough for effective field effect passivation. Hydrogen content in the films is also found to contribute significantly to improvement in passivation quality of the stacked layers. Furthermore, Si-rich SiN x films deposited with H 2 dilution show better passivation quality of SiN x /Si-rich SiN x stacked layers than those prepared without H 2 dilution. Effective minority carrier lifetime ( τ eff ) in c-Si passivated by SiN x /Si-rich SiN x stacked layers is as high as 5.1 ms when H 2 is added during Si-rich SiN x deposition, which is much higher than the case of using Si-rich SiN x films prepared without H 2 dilution showing τ eff of 3.3 ms. [ABSTRACT FROM AUTHOR]

Excellent electrical-passivation of p-type Si (p-Si) in Si solar cells has been achieved by post-deposition rapid annealing of aluminum oxide (AlO x ) films prepared by catalytic chemical vapor deposition (Cat-CVD) using trimethyl aluminum (TMA) and O 2 . Extremely small surface recombination velocity of below 0.1 cm/s has been obtained at post-deposition annealing temperatures in the range of 350–400 °C for an annealing time of 2 min. The reduction of surface recombination velocity has been attributed to band bending induced by a fixed negative charge density of 5 × 1011 charges/cm 2 and an additional small interface trapping density of around 10 10 cm − 2 eV − 1 . [ABSTRACT FROM AUTHOR]

The surface recombination velocity (S 0 ) in n-type Si (n-Si) wafers has been reduced below 0.1 cm/s by dint of positive fixed charges created by alumina (AlOx) films deposited at a film-temperature of 230 °C by catalytic chemical vapor deposition (Cat-CVD) using trimethyl aluminum (TMA) and O 2 . Positive fixed charges of the order of 10 12 charges/cm 2 can be created in AlO x films deposited under O 2 /TMA flow-rate ratios in the range of 3.5–6.5. The extremely small S 0 has been confirmed to be obtainable mainly due to a band bending effect brought about by the positive charges. The polarity and amount of the fixed charges can be determined by the flow-rate ratio of O 2 /TMA. [ABSTRACT FROM AUTHOR]

The effect of charge carrier mobility and surface recombination velocity has been extensively investigated for poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) organic solar cells. We used the effective medium model and the solar cell simulator (SCAPS) to model the current-voltage ( J- V) characteristic and explore the charge carrier transport in P3HT:PCBM devices. We varied the charge carrier mobility for electrons and holes and surface recombination velocity at the contacts for majority and minority charge carriers, and calculated the solar cell characteristics: efficiency ( η), open-circuit-voltage ( Voc), short-circuit current ( Jsc) and fill factor (FF). The significances of surface recombination velocity together with charge carriers mobility are calculated and discussed. We found that in general reduced surface recombination velocities at both contacts are very detrimental for organic solar cell performance especially for devices with low charge mobilities. [ABSTRACT FROM AUTHOR]

Highlights: [•] An analysis was made for some parameters of PERC and standard solar cells. [•] The diffusion length value was enhanced to ∼571μm from ∼218μm. [•] Improvement in J sc and V oc values of PERC solar cell was ∼2.94 and ∼2.61% respectively. [•] The effective back surface recombination velocity of PERC solar cell was ∼67cm/s. [•] The enhancement in relative conversion efficiency was ∼4.73%. [ABSTRACT FROM AUTHOR]

Highlights: [•] The carrier lifetimes of implanted silicon samples were determined with a PTR method. [•] The change of carrier lifetimes for O6+ implanted n type silicon was not observed. [•] The change of carrier lifetimes for Ar8+ implanted p type silicon was not observed. [•] The change of surface recombination velocities was observed in both type the samples. [•] The simplified model of a PTR signal is presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Experiments of photodiodes irradiated by laser at various energy densities are performed in this study. The laser-induced changes in photocurrent and dark current are monitored, the degradation process of responsivity as a function of the laser energy density is obtained. Morphological examinations were done with a scanning electron microscope (SEM), and damaged depth was performed using a step profiler. The results indicate that the relative responsivity of photodiodes for He Ne probe beam gradually reduced with the increase of intense laser energy density. The mechanism of various degradation of responsivity was analyzed. The obvious decrease of responsivity mainly contributes to an increase in the surface recombination velocity caused by defects and thermal breakdown of PN junction. The results were significant for the study of interaction laser with material. [Copyright &y& Elsevier]

Abstract: Photothermal beam deflection technique is an efficient tool for non-destructive evaluation of thin films. Thin films of tin mono sulphide, which find application as absorber layer in photovoltaic cells, were deposited by chemical spray pyrolysis technique and their carrier transport properties were determined using photothermal beam deflection technique. Thermal diffusivity, minority carrier lifetime, mobility and surface recombination velocity of these films fabricated under different spray conditions like varying spray rate, Sn/S ratio and substrate temperature were determined. Photothermal beam deflection technique was also employed for constructing the thermal images of these films to evaluate the film uniformity. [Copyright &y& Elsevier]

Using transient terahertz photoconductivity measurements, we have made noncontact, room temperature measurements of the ultrafast charge carrier dynamics in InP nanowires. InP nanowires exhibited a very long photoconductivity lifetime of over 1 ns, and carrier lifetimes were remarkably insensitive to surface states despite the large nanowire surface area-to-volume ratio. An exceptionally low surface recombination velocity (170 cm/s) was recorded at room temperature. These results suggest that InP nanowires are prime candidates for optoelectronic devices, particularly photovoltaic devices, without the need for surface passivation. We found that the carrier mobility is not limited by nanowire diameter but is strongly limited by the presence of planar crystallographic defects such as stacking faults in these predominantly wurtzite nanowires. These findings show the great potential of very narrow InP nanowires for electronic devices but indicate that improvements in the crystallographic uniformity of InP nanowires will be critical for future nanowire device engineering. [ABSTRACT FROM AUTHOR]

Abstract: High-quality surface passivation is essential for obtaining crystalline silicon (c-Si) solar cells with high energy-conversion efficiency. Silicon-nitride (SiN x )/amorphous-silicon (a-Si) stacked layers prepared by catalytic chemical vapor deposition (Cat-CVD), also referred to as hot-wire CVD, demonstrate excellent performance as surface passivation layers for c-Si and realize a dramatically low surface recombination velocity (SRV). However, the use of a more transparent material than a-Si is required because the a-Si layer absorbs sunlight. Here, Si-rich SiN x films, as a more transparent material, with various atomic ratios of silicon/nitrogen (Si/N) are investigated as a replacement for a-Si films. The use of SiN x /Si-rich-SiN x stacked layers as passivation films on c-Si wafers results in a SRV as low as 5cm/s and 30% improvement of the transparency at the wavelength of 400nm compared to that of the SiN x /a-Si stacked layers. Moreover, after the annealing process, the passivation characteristics of the stacked layer were significantly improved, with a SRV as low as 3cm/s. [Copyright &y& Elsevier]

By combining the doping process of Al alloying with the higher solubility of B in Si, a B/Al co-doped shallow back-surface field (B/Al-BSF) layer was created for fabrication of Si solar cells. The increased carrier concentration in the B/Al-BSF facilitates the modulation of BSF strength. The back-surface recombination velocity exhibits a U-shape function of carrier concentration, and reaches a minimum at a carrier concentration of 1019 cm−3. As a result, the solar cell efficiency can be improved by 0.5%. [Copyright &y& Elsevier]

The off-state source-to-drain leakage current and punchthrough voltage are the quantities that frequently limit the performance of short-channel floating-body silicon-on-sapphire (SOS) n-channel MOSFETs. In this paper, we demonstrate that the high-temperature hydrogen annealing of the SOS film prior to the device fabrication leads to marked improvement in these two parameters. The effect is attributed to the impact of hydrogen on the out-diffused thin alumina layer formed at the silicon–sapphire interface during the anneal. The thin alumina layer acting as a p-type dopant source at the back interface eliminates the back surface depletion of SOS n-MOSFETs. It also acts as a recombination center to eliminate the floating-body effect of floating-body n-MOSFETs. This technique provides a practical and reliable process to build short-channel floating-body SOS n-MOSFETs with off-state leakage as low as the junction leakage and punchthrough voltage as high as 6 V or higher at the gate length of 0.5 \mu\m without any degradation on the inversion layer carrier mobility or increase in the junction leakage current. [ABSTRACT FROM PUBLISHER]

Shallow etch depths may contribute to a reduction in the optical gain of multiple quantum well (MQW) lasers through the lateral diffusion of carriers away from the region of greatest optical intensity. Deeply etched mesas can prevent this lateral diffusion, but this practice may itself contribute to a degradation of optical gain if the sidewalls are not effectively passivated. Simulation results considering the effects of surface recombination velocity (SRV) at the edge of etched active layers indicate that SRV must be reduced below approximately 10cm/s in order for deep etch designs to provide benefit. Very few experimental studies quantify the efficiency of GaN surface passivation in terms of SRV. Further experimental studies are required to better assess the viability of deep etch MQW laser designs. [ABSTRACT FROM AUTHOR]

Abstract: The chemical etch of CdTe surfaces with a mixture of phosphoric and nitric acids is used in research labs in order to enhance the back-contact formation in CdS/CdTe solar cells. However, the possible passivation effect of this approach has not been studied. In this work we report an investigation about the etching effect of nitric/phosphoric acid mixtures with different etching times (0, 30, 40 and 50s) and variable concentrations of the nitric acid upon the surface recombination velocity of CdTe films deposited by close space vapor transport. Surface recombination velocities with values as low as 93cm/s were achieved. [Copyright &y& Elsevier]

Abstract: An n+–p–p+ structure was formed by depositing a thin Al layer on one side and a semitransparent Pd layer on other side of a p–Si wafer, and the diffusion length L was determined from the slope of short circuit current density Jsc vs. illumination intensity Pin characteristics by illuminating the p+ side with a laser light of wavelength λ =789nm, following the photocurrent generation method. The slope was found to decrease after the specimen was exposed to air for a few hours before the measurement. The present investigation revealed that the degradation of slope was owing to increase in surface recombination velocity S significantly, e.g. to 2800cm/s for air exposure of 8h, above its initial value 10cm/s. This resulted from adsorption of moisture on Pd surface which decreases work function of Pd and lowers the accumulation potential barrier. The adsorbed water molecules could be removed from Pd surface by vacuum pumping and then S again became small and the slope regained its original value. The true value of L, smaller or larger than the wafer thickness, can be determined using single monochromatic illumination if S is known or has a negligibly small value, as in our case where the specimen was stored in vacuum. In our specimen we determined L =56μm when S was negligibly small. However, using the experimental slopes of Jsc –Pin curves at two monochromatic illuminations obtained by Sharma et al. we determined both S and L and found their values 1390cm/s and 94μm, respectively. [Copyright &y& Elsevier]

Abstract: The passivation effects of AlOx films were investigated for p-type crystalline Si (c-Si) solar cells. The AlOx films were deposited on 10Ωcm c-Si substrates by catalytic chemical vapor deposition (Cat-CVD) using tri-methyl aluminum (TMA) and O2 at a film temperature of 230°C. The surface recombination velocity (S0) at the AlOx/Si interface was measured to be below 0.5cm/s for AlOx films deposited with O2/TMA gas flow-rate ratios of 15–35. This ultra low S0 was achieved primarily by band bending due to the negative interface fixed-charge density (Nf) of an order of 1012 charges/cm2. The decrease in interface trapping density Dit in the negative fixed charge region assists in decreasing S0. [Copyright &y& Elsevier]

n- and p-type 4H-SiC epilayers were grown on heavily doped SiC substrates. The thickness of the p-type layer was 7 µm and the doping level around 1017 cm³, while the n-type epilayers were 15 lain thick and had a doping concentration of 3-5x1015 cm³ Several different surface treatments were then applied on the epilayers for surface passivation: SiO2 growth, Al203 deposited by atomic layer deposition, and Ar-ion implantation. Using collinear pump - probe technique the effective carrier lifetimes were measured from various places and statistical lifetime distributions were obtained. For surface recombination evaluation, two models are presented. One states that surface recombination velocity (SRV) is equal on both the passivation/epi layer interface (S2) and the deeper interface between the epilayer and the SiC substrate (S1), i.e. (S1=S2). The other model is simulated assuming that SRV in the epilayer/substrate (S1) interface is constant while in the passivation layer/epilayer (S2) interface SRV can be varied (S2) < (S1). Empirical nomograms are presented with various parameters sets to evaluate (S2) values. We found that on the investigated 4H-SiC surfaces (S2) ranges from 3 x 104 to 5 x 104 assuming that the bulk lifetime is 4 µs. In Ar+ implanted surfaces (S2) is between (105 - 106) cm/s. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a novel approach for the extraction of five semiconductor-related parameters, that is, the absorption coefficient α, diffusion length L, normalized surface recombination velocity S, dead layer thickness Zt and the relative quantum efficiency Q directly from any theoretical/experimental steady state cathodoluminescence (CL) signal. The extraction technique, based on genetic algorithms (GA), has many advantages such as the simultaneous obtainment of near-optimum values for the five parameters (α, L, S, Zt, Q). Simulation results for an n-type GaAs defect free semi-infinite semiconductor sample show that the proposed approach is successful and a set of parameter values with error less than 12% from the nominal values, in 95% of the cases, can be obtained. [Copyright &y& Elsevier]

Abstract: Photothermal deflection technique (PTD) is a non-destructive tool for measuring the temperature distribution in and around a sample, due to various non-radiative decay processes occurring within the material. This tool was used to measure the carrier transport properties of CuInS2 and CuInSe2 thin films. Films with thickness <1μm were prepared with different Cu/In ratios to vary the electrical properties. The surface recombination velocity was least for Cu-rich films (5×105 cm/s for CuInS2, 1×103 cm/s for CuInSe2), while stoichiometric films exhibited high mobility (0.6cm2/V s for CuInS2, 32cm2/V s for CuInSe2) and high minority carrier lifetime (0.35µs for CuInS2, 12µs for CuInSe2). [Copyright &y& Elsevier]

Abstract: In this paper, the effect of interface recombination and self-absorption within the light emitting diode (LED) active region on the efficiency of QWIP–HBT–LED integrated device is considered. This device is composed of a quantum well infrared photodetector (QWIP), a heterojunction bipolar transistor (HBT) and an LED. The evaluation is based on solving the continuity equation describing the carrier diffusion within the LED active region. Analytical expression describing the effect of self-absorption and surface recombination on the LED quantum efficiency is derived. In addition, the active region width and all interested device parameters are involved. It is observed that the quantum conversion efficiency of the device under consideration is degraded by the self-absorption and interface recombination within the recombined region of the LED. Also, the quantum conversion efficiency of the device is increased with the increase of the LED active region as long as the recombination velocity is above a specified value, while it is decreased with the increase of the LED active region as long as the recombination velocity is below this specified value. [Copyright &y& Elsevier]

Abstract: Ionizing radiation experiments on gated bipolar transistors used as radiation test structures show a broadening in the peak base current profile after irradiation. The primary mechanism for this effect is identified as the change in the charge state of radiation-induced interface traps in the oxide over the base. From theoretical analysis using Shockley–Reed–Hall (SRH) statistics, a mathematical formulation of effective Fermi level, E f,eff is derived to describe the charge state of interface traps in a gated bipolar transistor under forward bipolar operation as the surface of the transistor is changed from accumulation to inversion by biasing on the gate terminal. [Copyright &y& Elsevier]

This paper proposes an extended 1-D analysis to derive quantum efficiency of various commonly used CMOS photodiodes. The theoretical model of the CMOS photodiode with the n—⁄p—epitaxial⁄p + substrate (n—⁄p—epi⁄p + sub) structure is established from steady-state continuity equations, where most existing boundary conditions are applied. In particular, the minority carrier and current densities are continuous across the interface between two layers with the same dopant type. Models of the other commonly used CMOS photodiodes are also examined. Three CMOS photodiodes with n—⁄p-substrate (n—⁄p—sub), p+⁄n⁄p—substrate (p+⁄n—⁄p—sub), and n—⁄p—epi⁄p + sub structures are fabricated and characterized to validate the proposed model. Additionally, the surface recombination velocity is adequately determined by fitting the simulated quantum efficiency to the measured value. The simulated quantum efficiency of the proposed model for these three photodiodes is quite consistent with the measured values, revealing the feasibility and effectiveness of the proposed model in characterizing various CMOS photodiodes. [ABSTRACT FROM AUTHOR]

Abstract: A method of determination of recombination velocity S f of minority carriers at the front surface of an n+–p–p+(p+–n–n+) silicon solar cell in which the n+(p+) front emitter is made by diffusion of dopant impurity in the p(n) region is presented. This method uses the short-wavelength spectral response of the cell to determine S f and is applicable if the front emitter of the cell has a linearly varying built-in field. It was applied to a p+–n–n+ solar cell that had a Gaussian distribution of the dopant impurity in the p+ front emitter up to a depth of 0.078μm from the surface. Using the spectral response data of cell in 380nm<λ< 500nm range S f was found to have a nearly constant value ∼6×105 cms−1 in 400nm<λ<460nm range. Below and above this wavelength range the value of S f was found to be slightly smaller. For comparison the value of S f was also determined assuming the p+ region to be uniformly doped, and this value was found to be significantly smaller than based on the diffused emitter model. The analysis showed that for a diffused junction cell, the assumption that the front emitter is uniformly doped, ignores the presence of the built-in field in the emitter region and leads to overestimation of minority carrier recombination in the emitter. Consequently for a given contribution of the front emitter region to the spectral response of the cell, this assumption underestimates the front surface recombination and determines a smaller value of S f. On the other hand, the present method can be expected to determine a realistic value of S f independent of λ for most diffused junction silicon solar cells using the spectral response data in a suitable short-wavelength range since each such cell indeed has a built-in electric field in the emitter region. [Copyright &y& Elsevier]

Abstract: Photoluminescence intensity (PLI) measurements of GaAs and InGaAs thin films indicate that InGaAs might be inherently easier to passivate than GaAs. The introduction of just 15% of In leads to a reduction of the surface recombination velocity at native oxide interfaces by an order of magnitude. This is more than the effect expected by a reduced bandgap alone. The PLI method applied to thin films can also be used to determine the surface recombination velocity of other IIIV-oxide interfaces. [Copyright &y& Elsevier]

The carrier lifetime in SiGe planar waveguides with Si cladding was measured with a pump-and-probe technique, using an ultrashort 810 nm laser pulse and a CW 1.55 μm probe, as a function of layer thickness d and Ge concentration x. The measured lifetimes are in the range of 20-90 ns. The obtained interface recombination velocity S is a growing function of both d and x, taking values in the range from 300 to 4000 cm/s. [ABSTRACT FROM AUTHOR]

Abstract: This paper gives an in-depth analysis of the factors affecting the alpha parameter which is used for extracting the surface recombination velocity in electron beam induced current (EBIC) line scan measurements. The analysis shows that the alpha versus normalized surface recombination velocity curve is a function of both the normalized beam depth as well as the normalized scanning range. Variations in the normalized beam depth affect the accuracy only when extracting high surface recombination velocity values. On the other hand, the variation in the normalized scanning range affects the accuracy in extracting the middle range values of the surface recombination velocity only slightly. Conditions for accurate extraction are given in this paper. The analysis was further verified with the use of computer simulation. [Copyright &y& Elsevier]

A new analytical model for the photo-dependent S-parameters of GaAs MESFETs has been presented in this paper. The photo-dependent expressions for the gate-source capacitance, gate-drain capacitance, drain-source resistance, domain capacitance, and domain resistance have been derived and used to study the optical effects on the S-parameters of the MESFET. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 150–155, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21290 [ABSTRACT FROM AUTHOR]

Abstract: Two dimensional device modeling is used to investigate the differential DC current gain in 4H–SiC bipolar junction transistors using surface recombination velocity as one of the physical variables affecting the current gain. The simulated differential gain is compared with the measured experimental DC gain of transistors with two different emitter lengths. The comparison and the analysis made support the trend in modeling the DC gain as a function of surface recombination velocity and show that higher gain can be obtained for transistors with lower surface recombination velocity. [Copyright &y& Elsevier]