Band fluctuations model for the fundamental absorption of crystalline and amorphous semiconductors a dimensionless joint density of states analysis

We develop a band fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless joint density of states formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p type GaAs and nano crystalline Ga 1 x Mn x N, as examples for direct bandgap materials, as well as amorphous Si H x , SiC H x and SiN x , are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edg

Capacitance voltage curve simulations for different passivation parameters of dielectric layers on silicon

Abstract Surface passivation is a widely used technique to reduce the recombination losses at the semiconductor surface. The passivating layer performance can be mainly characterized by two parameters: The fixed charge density ( Q ox ) and the interface trap density ( D it ) which can be extracted from Capacitance-Voltage measurements (CV). In this paper, simulations of High-Frequency Capacitance-Voltage (HF-CV) curves were developed using simulated passivation parameters in order to examine the reliability of measured results. The D it was modelled by two different sets of functions: First, the sum of Gaussian functions representing different dangling bond types and exponential tails for strained bonds. Second, a simpler U-shape model represented by the sum of exponential tails and a constant value function was employed. These simulations were validated using experimental measurements of a reference sample based on silicon dioxide on crystalline silicon (SiO 2 /c-Si). Additionally, a fitting process of HF-CV curves was proposed using the simple U-shape D it model. A relative error of less than 0.4% was found comparing the average values between the approximated and the experimentally extracted D it ’s. The constant function of the approximated D it represents an average of the experimentally extracted D it for values around the midgap energy where the recombination efficiency is highest

Silicon interface passivation studied by modulated surface photovoltage spectroscopy

We demonstrate that the modulated surface photovoltage spectroscopy modulated SPS technique can be applied to investigate interface states in the bandgap, i.e. interface passivation, of crystalline silicon coated with a downshift layer such as hydrogenated aluminum nitride with embedded terbium ions by suppressing straylight with a cut off filter. Different hydrogen contents influence the surface photovoltage spectra at photon energies below the bandgap of crystalline silicon. Modulated SPS reveals that at higher hydrogen content there is a lower signal and, thus, a lower density of surface defect states. Our experiments show that modulated SPS can become a powerful tool for characterizing defect states at interfaces which cannot be easily studied by other method

Erratum Analysis of the physical and photoelectrochemical properties of c Si p a SiC H p photocathodes for solar water splitting

The photoelectrochemical (PEC) properties of sputtered aluminum doped hydrogenated amorphous silicon carbide thin films grown on p-type crystalline silicon substrates were investigated in 1 M H2SO4<i solution under chopped light illumination. Optical and structural properties of the top absorber layer were systematically assessed after post-deposition isochronical annealing treatments. Samples exhibited a noticeable improvement of the opto-electronic properties after thermal treatments. In addition, an abrupt enhancement of the photocurrent was observed reaching a saturation value of 17 mA cm(-2) at -1.75 V vs. Ag/AgCl (3.5 M KCl). In this research we propose that this enhancement effect is associated to a charge transfer kinetic mechanism influenced by surface states and the p-type substrate. The latter most likely due to the space charge region extending beyond the absorber layer reaching the substrate. Current density-potential and electrochemical impedance spectroscopy measurements in dark revealed a reduction of the SiO2 native layer at cathodic potentials higher than -1 V vs. Ag/AgCl (3.5 M KCl), which contributes to the high charge transfer kinetic of the system. We believe that these results will contribute to understand the substrate influence in the PEC performance of top absorber layers in multilayer structures for solar water splitting.This research was funded by FONDECYT (National Fund for Scientific, Technological Development and Technological Innovation) under the agreement 147-2017. The author M Mejia has been supported by the CONCYTEC Peru (National Council for Science, Technology and Technological Innovation) doctoral scholarship under the Contract Number 236-2015-FONDECYT as well as by the PUCP vicechancellorship for research (VRI, Project No. CAP-2019-3-0041/702). The authors would like to thank the Katholischer Akademischer Auslander-Dienst institution (KAAD) for the short-term grants given to conduct research internships in the Technische Universitat Ilmenau (TU Ilmenau). Finally, the authors would like to thank the German Research Foundation (DFG) (DFG-Gz: INST 273/56-1 FUGG) and the Materials Characterization Center (CAM) at PUCP, for the financial support to conduct the characterization experiments

Hydrogen effects at sputtered Tb doped AlNxOy H c Si p interfaces A transient surface photovoltage spectroscopy study

In the present work, we studied the interface of terbium doped aluminum oxynitride Tb doped AlNxOy H deposited under different hydrogen flows with p type doped crystalline silicon by applying transient surface photovoltage spectroscopy. We observed strong accumulation with concomitant passivation of boron acceptors in the crystalline silicon and defect generation near the interface. With increasing hydrogen flows, the net negative charge in the Tb doped AlNxOy H layer decreased, surface photovoltage signals related to defects increased, surface photovoltage transients decayed faster, and the slowest relaxation of charge carriers separated in space changed from trap limited to hopping transport via an exponential distribution of trap states in energ

Indirect excitation and luminescence activation of Tb doped indium tin oxide and its impact on the host s optical and electrical properties

The effect of adding terbium to indium tin oxide ITO thin films on the electrical, optical and light emission properties was investigated. The films were prepared by radio frequency dual magnetron sputtering, maintaining a high optical transmittance in the ultraviolet and visible spectral regions, and a low electrical resistivity ranging from 5 10 amp; 8722;3 amp; 937; cm to 0.3 amp; 937; cm. Terbium related luminescence is achieved after annealing at 470 amp; 9702;C in air at atmospheric pressure. Electrical resistivity and optical transmittance were measured after each annealing step to evaluate the compromise between the achieved light emission intensity, electrical and optical properties. Additionally, temperature dependence of Tb related luminescence quenching was assessed by temperature dependent photoluminescence measurements, from 83 to 533 K, under non resonant excitation. Thermal quenching activation energies suggest an effective energy transfer mechanism from the ITO host to the rare earth RE ions. This indirect excitation mechanism was modeled using a spherical potential well and a tight binding one band approximation approaches, describing a short range charge trapping process and subsequent formation of bound excitons to RE ion cluster

Analysis of the physical and photoelectrochemical properties of c Si p a SiC H p photocathodes for solar water splitting

The photoelectrochemical PEC properties of sputtered aluminum doped hydrogenated amorphous silicon carbide thin films grown on p type crystalline silicon substrates were investigated in 1 M H2SO4 solution under chopped light illumination. Optical and structural properties of the top absorber layer were systematically assessed after post deposition isochronical annealing treatments. Samples exhibited a noticeable improvement of the opto electronic properties after thermal treatments. In addition, an abrupt enhancement of the photocurrent was observed reaching a saturation value of 17 mA cm amp; 8722;2 at amp; 8722;1.75 V vs. Ag AgCl 3.5 M KCl . In this research we propose that this enhancement effect is associated to a charge transfer kinetic mechanism influenced by surface states and the p type substrate. The latter most likely due to the space charge region extending beyond the absorber layer reaching the substrate. Current density potential and electrochemical impedance spectroscopy measurements in dark revealed a reduction of the SiO2 native layer at cathodic potentials higher than amp; 8722;1 V vs. Ag AgCl 3.5 M KCl , which contributes to the high charge transfer kinetic of the system. We believe that these results will contribute to understand the substrate influence in the PEC performance of top absorber layers in multilayer structures for solar water splittin