Defect Capture Cross Sections Research Articles

Theoretical simulation of mixed organic–inorganic perovskite solar cell using SCAPS-1D simulator

In this work, a triple cation mix halide perovskite solar cell is explored to improve its stability and efficiency. FTO/SnO2/perovskite/CuSCN/carbon the device structure is simulated using SCAPS-1D and outcomes and found in good agreements with experimental results. Furthermore, the effect of various parameters like absorbance coefficient, reflection of front surface, defect capture cross section and defect position on device performance are examined. This optimized device exhibits high PCE, 27.10 % with Voc = 1.24 V, Jsc = 25.37 mA/cm2 and FF = 85.70 %. Finally, the effects of temperature, absorber defect density and interface defect density are computed on optimised structure and observed degradation in device performance with increase in these factors. Lastly, the results are concluded using J-V and EQE curves. This study may be vital in the development of stable and highly efficient triple cation perovskite solar cell technology.

Proton induced radiation effect of SiC MOSFET under different bias

Radiation effects of silicon carbide metal–oxide–semiconductor field-effect transistors (SiC MOSFETs) induced by 20 MeV proton under drain bias (V D = 800 V, V G = 0 V), gate bias (V D = 0 V, V G = 10 V), turn-on bias (V D = 0.5 V, V G = 4 V) and static bias (V D = 0 V, V G = 0 V) are investigated. The drain current of SiC MOSFET under turn-on bias increases linearly with the increase of proton fluence during the proton irradiation. When the cumulative proton fluence reaches 2 × 1011 p⋅cm−2, the threshold voltage of SiC MOSFETs with four bias conditions shifts to the left, and the degradation of electrical characteristics of SiC MOSFETs with gate bias is the most serious. In the deep level transient spectrum test, it is found that the defect energy level of SiC MOSFET is mainly the ON2 (E c – 1.1 eV) defect center, and the defect concentration and defect capture cross section of SiC MOSFET with proton radiation under gate bias increase most. By comparing the degradation of SiC MOSFET under proton cumulative irradiation, equivalent 1 MeV neutron irradiation and gamma irradiation, and combining with the defect change of SiC MOSFET under gamma irradiation and the non-ionizing energy loss induced by equivalent 1 MeV neutron in SiC MOSFET, the degradation of SiC MOSFET induced by proton is mainly caused by ionizing radiation damage. The results of TCAD analysis show that the ionizing radiation damage of SiC MOSFET is affected by the intensity and direction of the electric field in the oxide layer and epitaxial layer.

Defect spectroscopy and non-ionizing energy loss analysis of proton and electron irradiated p-type GaAs solar cells

Admittance spectroscopy combined with non-ionizing energy loss (NIEL) analysis is shown to be a powerful tool for analyzing solar cell radiation degradation, not relying on the change of macroscopic cell parameters. GaAs component cells, representative of the middle sub-cell in Ga0.5In0.5P/GaAs/Ge solar cells, were irradiated with protons and electrons in the 0.5–3 MeV energy range. Four irradiation-induced defects are identified in the p-type base layer. The nature of each defect is assessed by analyzing the dependence of its introduction rate on the NIEL deposited by electrons in the semiconductor. The expected linear relationship is only achieved if a unique threshold energy Ed is ascribed to each defect, which ranges from 9 to 38 eV. An electron NIEL with Ed=21eV, customarily used for GaAs-based solar cell degradation analysis, is an approximation of the relative abundance of these four defects. The 21 eV value is thus a GaAs material-specific parameter, independent of the electrical device design. In addition, the type and energy of the incident particle is correlated with the relative abundance of high Ed defects. The impact of each defect on the macroscopic electrical parameters of the cell, namely, the open-circuit voltage VOC, the short-circuit current density JSC, and the recombination current density J02, is assessed with the help of a Pearson analysis. The different effectiveness of electron and proton irradiation on parameters dominated by recombination in the depleted region, such as VOC or J02, is attributed in part to the influence of the particle recoil spectra on the defect capture cross section.

Evolution of LeTID defects in industrial multi-crystalline silicon wafers under laser illumination - Dependency of wafer position in brick and temperature

In the past few years, a hot topic in both research and industrialization of p-type multi-crystalline silicon (mc-Si) solar cells is to investigate the mechanism, measurement and mitigation of the light- and elevated temperature-induced degradation (LeTID), which has been found to be a bulk-sensitive degradation behavior and is dependent on the degradation condition. In this paper, we study the influence of silicon bulk property on LeTID from five representative positions along a relative low resistivity (0.82–1.33 Ω cm) p-type mc-Si brick. The evolution of degradation and regeneration under different laser illumination conditions are investigated. Identical defect capture cross section ratio k values of ~35 at mid-gap along the brick height are found. For the first time, the activation energy for degradation (Ea,deg) and regeneration (Ea,reg) along the brick are studied, which shows Ea,deg = Ea,reg and a tendency of larger values towards the brick bottom. These results indicate that the LeTID in the whole brick might be induced by a single defect and thus mitigated in a single manner. Besides, a laser illumination of 45 kW/m2 at 142 °C for 100 s is able to induce over 90% degradation for all wafers, which could be used as a universal and fast LeTID test condition.

Hydrogen induced degradation: A possible mechanism for light- and elevated temperature- induced degradation in n-type silicon

In this work, we demonstrate a form of minority carrier degradation on n-type Cz silicon that affects both the bulk and surface related lifetimes. We identify three key behaviors of the degradation mechanism; 1) a firing dependence for the extent of degradation, 2) the appearance of bulk degradation when wafers are fired in the presence of a diffused emitter and 3) a firing related apparent surface degradation when wafers are fired in the absence of an emitter. We further report a defect capture cross-section ratio of σn/σp = 0.028 ± 0.003 for the defect in n-type. Utilizing our understanding of light and elevated temperature induced degradation (LeTID) in p-type silicon, we demonstrate that the degradation behaviors in both n-type and p-type silicon are closely correlated. In light of numerous reports on the involvement of hydrogen, the potential role of a hydrogen-induced degradation mechanism is discussed in both p- and n-type silicon, particularly in relation to the diffusion of hydrogen and influence of hydrogen-dopant interactions.

Alpha radiation induced space charge stability effects in semi-insulating silicon carbide semiconductors compared to diamond

Although the use of semi-insulating silicon carbide material for radiation detection purposes has been previously demonstrated, its use in practical applications has been inhibited by space charge stability issues caused by defect concentrations within the material, the so called polarisation effect, by which the count rate and resultant spectrum changes with irradiation time.This is a result of the charge carriers generated during irradiation filling deep level defects within the material, causing space charge buildup and de-activating that trap level until the trapped charge is re-emitted. Consequently, the time dependence of the polarisation effect has been determined by a combination of parameters that can be influenced during operation, namely the incident radiation intensity, ambient light, temperature and bias. The material properties have also been considered through the use of materials with different defect capture cross sections, concentrations and energy level.A thorough characterisation of the alpha irradiation induced polarisation phenomenon in semi-insulating silicon carbide has been conducted to demonstrate that stable operation detectors are in fact possible with this material. The effects were compared to single crystal diamond and polycrystalline diamond, which are known to exhibit similar polarisation issues.The polarisation rate as an effect of incident flux, bias and temperature was determined, with the depolarisation rate as a function of ambient light and bias also demonstrated. Consequently it has been shown that stable operation can be maintained for detectors made from semi-insulating SiC material of active thickness 350μm at incident alpha radiation fluxes of <0.7 alphas per second per mm2 with high operating biases (>±400V). Furthermore, polarisation can be suitably managed or reduced through the use of light illumination and elevated temperatures (373K).

A 3-state defect model for light-induced degradation in boron-doped float-zone silicon

We report on a light-induced bulk defect activation and subsequent deactivation in boron doped float-zone silicon that can be described by a 3-state model. During treatment at elevated temperature and illumination, a sample first converts from an initial high lifetime state into a degraded low lifetime state and then shows a recovery reaction leading to a third high lifetime state that is then stable under degradation conditions. Furthermore, it is shown that reverse reactions into the initial state appear to be possible both from the degraded as well as the regenerated state. An injection dependent analysis of lifetime data yields a defect capture cross section ratio of ∼20 suggesting a positively charged defect. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Photo-Induced Current Transient Spectroscopy of Semi-insulating Single Crystal Cs2Hg6S7

The ternary compound Cs2Hg6S7 has shown considerable promise as a wide gap semiconductor for hard radiation detection at room temperature. We report on the measurement of defect levels in Cs2Hg6S7 using photo-induced current transient spectroscopy. We observe a series of defect levels with mean activation energies of 0.053, 0.052, 0.34, 0.35, and 0.46 eV. The defects are attributed to Cs vacancies and Cs and Hg antisite defects. Defect capture cross-sections are in the range 10−20–10−15 cm2.

Photo-induced current transient spectroscopy of single crystal Tl6I4Se

The compound Tl6I4Se is a promising wide band gap semiconductor for hard radiation detection at room temperature. To further improve its detection efficiency, native defects have been investigated using photo-induced current transient spectroscopy (PICTS). We observe two shallow acceptor levels with mean activation energies of 76, 175 meV, and two shallow donor defects 62, and 96 meV, respectively. No deeper donor levels are observed. The levels are attributed to native point defects. Defect capture cross sections in the range 10−21 to 10−18 cm2 were measured. The small capture cross sections are attributed to the effective screening of the defects due to a large static dielectric constant.

Fill Factor Limitation of Silicon Heterojunction Solar Cells by Junction Recombination

In this work we experimentally investigate the influence of the chemical and field effect passivation of a-Si:H films on the junction recombination at maximum power point conditions of silicon heterojunction solar cells. By simulating the charge of doped a-Si:H films with external corona charges, chemical and field effect passivation are investigated independent of each other. If we apply a negative corona charge to a lifetime test structure inversion conditions are obtained which corresponds to a p/n junction. With positive charges we can create accumulation i.e. a high/low junction (for an n-type wafer). From injection level dependent lifetime measurements the implied solar cell parameters iVoc and iFF are extracted. Especially the implied fill factor is influenced by the recombination characteristics at the injection level at maximum power point conditions. It is shown that under inversion conditions the implied solar cell parameters are lower compared to accumulation conditions. The main reason for this seems to be the asymmetry in defect capture cross sections for electrons and holes. As this defect characteristic at the c-Si/a-Si:H interface cannot be altered, a considerable reduction of the defect density is required to further decrease junction recombination at M PP conditions and thus increase the FF of SHJ cells.

&gt;21% Efficient Silicon Heterojunction Solar Cells on n- and p-Type Wafers Compared

The properties and high-efficiency potential of front- and rear-emitter silicon heterojunction solar cells on n- and p-type wafers were experimentally investigated. In the low-carrier-injection range, cells on p-type wafers suffer from reduced minority carrier lifetime, mainly due to the asymmetry in interface defect capture cross sections. This leads to slightly lower fill factors than for n-type cells. By using high-quality passivation layers, however, these losses can be minimized. High open-circuit voltages (Vocs) were obtained on both types of float zone (FZ) wafers: up to 735 mV on n-type and 726 mV on p-type. The best Voc measured on Czochralski (CZ) p-type wafers was only 692 mV, whereas it reached 732 mV on CZ n-type. The highest aperture-area certified efficiencies obtained on 4 cm2 cells were 22.14% (Voc = 727 mV , FF = 78.4%) and 21.38% (Voc = 722 mV, FF = 77.1%) on n- and p-type FZ wafers, respectively, proving that heterojunction schemes can perform almost as well on high-quality p-type as on n-type wafers. To our knowledge, this is the highest efficiency ever reported for a full silicon heterojunction solar cell on a p-type wafer, and the highest Voc on any p-type crystalline silicon device with reasonable FF.

Probing bulk defect energy bands using generalized charge pumping method

The multifrequency charge pumping (CP) technique has long been used to probe the density of defects at the substrate-oxide interface, as well as in the bulk of the oxide of MOS transistors. However, profiling the energy levels of the defects has been more difficult due to the narrow scanning range of the voltage of a typical CP signal, and the uncertainty associated with the defect capture cross-section. In this paper, we discuss a generalized CP method that can identify defect energy bands within a bulk oxide, without requiring separate characterization of the defect capture cross-section. We use the new technique to characterize defects in both fresh and stressed samples of various dielectric compositions. By quantifying the way defects are generated as a function of time, we gain insight into the nature of defect generation in a particular gate dielectric. We also discuss the relative merits of voltage, time, and other variables of CP to probe bulk defect density, and compare the technique with related characterization approaches.

Analysis of defect capture cross sections using non-radiative multiphonon-assisted trapping model

A multiphonon-assisted model included in a Poisson–Schroedinger solver has been applied to the calculation of the capture/emission trapping rates of CMOS oxide interface defects. The dependencies of trap capture cross-sections with trap energy, depth, applied bias and temperature have been extracted, with the purpose of evaluating the accuracy of constant cross-section models adopted in compact and empirical approaches. The model has been applied to the extraction of interface trap concentrations and to the accurate AC analysis of the trap frequency response.

Effects of deep defect concentration on junction space charge capacitance measurements

Expressions for the small signal capacitance and pulse bias-induced large signal capacitance transient of an abrupt n+-p junction in the presence of one or more deep traps of arbitrary concentrations are presented. The expressions show that a simple inverse relationship between the measured small signal capacitance and the junction’s space charge depletion width is not expected. Unexpected effects on defect capture cross section and defect concentration determination, when applied to deep level transient spectroscopy simulations, are also reported. Experimental results of both temperature dependent capacitance and transient capacitance measurements performed on electron irradiated Si n+-p junctions are presented and analyzed in the context of these expressions. Modeling of the measured signals using these expressions is shown to be in good agreement with the experiment.

Dislocation-related deep levels in carbon rich p-type polycrystalline silicon

We present a study of dislocation-related defects in boron-doped p-type silicon crystals grown by the edge-defined film-fed growth (EFG) and float-zone (FZ) method. Deep level transient spectroscopy (DLTS) was used to identify electrically active defects. We have observed a E v+0.33 eV level in EFG silicon and a E v+0.39 eV in FZ silicon. In order to measure defect capture cross sections, we examined the intensity of the DLTS signal and peak position as a function of filling-pulse duration. The traps, both in EFG and FZ silicon, exhibit a logarithmic capture kinetics, a feature typical for extended defects such as dislocations. However, the complex behavior of defects in EFG material suggests that either the dislocations are decorated with clouds of carbon related or metallic defects, or its close spacing produces overlap of space charge regions, affecting therefore, its electrical activity.

A comprehensive analysis of irradiated silicon detectors at cryogenic temperatures

The effect of particle irradiation on high-resistivity silicon detectors has been extensively studied with the goal of engineering devices able to survive the very challenging radiation environment at the CERN Large Hadron Collider (LHC). The main aspect under investigation has been the changes observed in detector effective doping concentration (N/sub eff/). We have previously proposed a mechanism to explain the evolution of N/sub eff/, whereby charge is exchanged directly between closely-spaced defect centres in the dense terminal clusters formed by hadron irradiation. This model has been implemented in both a commercial finite-element device simulator (ISE-TCAD) and a purpose-built simulation of interdefect charge exchange. To control the risk of breakdown due to the high leakage currents foreseen during ten years of LHC operation, silicon detectors will be operated below room temperature (around -10/spl deg/C). This, and more general current interest in the field of cryogenic operation, has led us to investigate the behavior of our model over a wide range of temperatures. We present charge collection spectra from 1064 nm laser pulses as a function of detector bias between temperatures of 115 K and 290 K, using devices irradiated with 23 GeV protons in the range 10/sup 13/-4/spl times/10/sup 14/ protons/spl middot/cm/sup -2/. These data allow a deeper investigation of the influence of defect capture cross sections on N/sub eff/. The model prediction for the reversion to n-type of heavily-irradiated detectors at low temperature is investigated and deviations from the model are explored.

Density of states and capture cross-sections in annealed and light-soaked hydrogenated amorphous silicon layers

The density of states of a lightly p-doped hydrogenated amorphous silicon sample and the related transport behaviours were extensively studied and compared with those of intrinsic samples both in the annealed and light-soaked states. It is observed that p-doping increases the density of positively charged dangling bonds in the annealed samples, in agreement with the predictions of the defect-pool model. After light-soaking, a decrease of positively charged dangling bonds and an increase of neutral ones in the p-doped sample are observed, which is still in qualitative agreement with the predictions of the model. However, quantitatively, the results of modulated photocurrent experiments cannot be reproduced on the basis of this model. It is proposed that light-soaking either induces a variation of the defect capture cross-sections or creates a distribution of states in the gap for which the defect-pool model does not account.

Observation and electronic characterization of two E′ center charge traps in conventionally processed thermal SiO2 on Si

We demonstrate that at least two varieties of E′ defect precursors exist in a wide variety of conventionally processed thermal SiO2 thin films. We provisionally label the defects EP and E′γp. We find that EP defect capture cross sections exceed the corresponding E′γp values by an order of magnitude, that EP centers are distributed far more broadly throughout the oxides than are the E′γp defects, and that the EP resonance, unlike the E′γp resonance is not stable at room temperature.

Evaluation of a defect capture cross section for minority carriers: Application to GaAs

The majority-carrier trapping cross section for a majority-carrier trap can be obtained using capacitance spectroscopy by monitoring the kinetics of trap filling. This method cannot be applied for the determination of the trapping cross section of minority carrier by this majority-carrier trap because the capture or emission kinetics cannot be observed. Here we propose a method to measure the minority-carrier trapping cross section for majority-carrier trap. It is not a general method but limited to defects which have the property to anneal under minority-carrier injection, a rather common feature in III-V and II-VI semiconductor compounds. For such defects, the annealing rate induced by injection is proportional to the rate of minority carrier trapping. As a result, the study of the annealing rate versus the density of injection and versus the temperature allows us to obtain the minority-carrier trapping cross section and its variation with temperature. The method is illustrated by a study of the so-called E3 defects, created by electron irradiation at room temperature in n-type GaAs. For this defect, we find a minority-carrier cross section which is thermally activated with an activation energy of ∼0.35 eV, implying that the capture of minority carriers, like the capture of majority carriers, occurs through multiphonon emission. A discussion of this result in terms of configuration coordinate diagram shows the limitation of this model.