Values for the deep defect density determined from PDS, CPM or ESR may vary significantly on the same sample depending on the method of data analysis used. Experimental conditions under which they yield comparable results are discussed. Procedures for determination of deep defect density from optical spectra are reviewed and compared on samples in light-saturated states. The measurement of the absorption coefficient at E=1.2 eV, with a new range for the calibration factor, is suggested as an easy and generally usable procedure for the determination of deep defect density.

How to reach more precise interpretation of subgap absorption spectra in terms of deep defect density in a-Si:H

Suppression of interference fringes in absorption measurements on thin films

Amorphous Si1−xGex:H films and p‐i‐n diodes were fabricated by decomposition of SiH4/GeH4 mixtures in a triode glow‐discharge reactor The photoconductivity under AM1 illumination in these alloys was constant over a range of band gaps between 18 (x=0) and 15 eV (x=025), while the solar cell conversion efficiency decreased at the same time from 86% to 43% This can be explained by a reduction in the μτ product for holes with rising x in undoped samples as revealed by time‐of‐flight experiments In contrast to μτ, the hole drift mobility μD,h remains constant The opposite behavior is observed for electrons, whose drift mobility μD,e decreases as the mobility activation energy EA increases The relation between EA and μD,e for variable x is suggestive of the Meyer–Neldel rule for the conductivity In conjunction with space‐charge‐limited current and sub‐band‐gap absorption data we conclude that only the conduction‐band tail is widened by the incorporation of Ge while the valence‐band tail remains unaff

Electron and hole transport in a‐Si1−xGex:H alloys

We demonstrated Schottky-barrier solar cell using layer-structured semiconductor tungsten disulfide (WS2) nanofilm (NF) as the photo-active material. WS2 NFs were synthesized by chemical-vapor-deposition initiated on the surface of tungsten. The growth of WS2 NF was confirmed by Raman signature peaks representing active modes of E12g (351.5 cm−1) for in-plane and A1g (420.1 cm−1) for out-of-plane atomic vibrations, respectively. The ITO/WS2/Au Schottky-barrier solar cell was demonstrated by a layer-enabled assembling process, showing a photo-conversion efficiency of 1.7% and effective photon absorption in the wavelength range of 350 nm–950 nm. The Mott-Schottky characteristic suggests low density of bulk and interface defects in WS2 NF attributed to surfaces with negligible amount of dangling bonds which is the essential nature of layered semiconductors.

Schottky-barrier solar cell based on layered semiconductor tungsten disulfide nanofilm

The density of states (DOS) in the mobility gap of a-Si:H is briefly reviewed. Our experimental data on subgap optical absorption, derived by CPM and TM-SCLC results are analyzed and the DOS is obtained by deconvolution. In undoped a-Si:H the energy position of D o -singly occupied Si dangling bond level is approximately at the same position as D − related peak in phosphorus doped a-Si:H and Stokes shift is negligible. Boron doped samples are different, Stokes shift is about 0.4eV and D + related peak is closer to the conduction band. These experimental data together with the results of other authors (DLTS, photocapacitance, luminescence and photoelectric yield) are explained by the idea that doping predominantly creates intimate pairs of silicon dangling bonds with dopant atoms, the energy of which lies deeper in gap compared with the energy of isolated dangling bond. Alternative explanations are also discussed.

a-Si:H gap states investigated by CPM and SCLC

The density of states in amorphous hydrogenated silicon is obtained by deconvolution of the optical absorption coefficient a in the full sub band-gap region. The spectral dependence of the optical absorption coefficient is measured by a constant photocurrent method (CPM) on forward-biased Schottky diodes. The spectral dependence of reflection on the semitransparent Pt electrode is determined. All assumptions used in the deconvolution of a are discussed. The difference in measured value of a (by CPM) in the region below approximately 0.9 eV compared to the measurement of α by photothermal deflection spectroscopy (PDS) is explained by an absorption process seen in PDS and not seen in CPM. This absorption is supposed to be a transition from a deep localized state to a deep localized gap state (two different charge states of the same defect).



[Russian Text Ignored]

A. Abrahám

Papers

Gap states density in a-Si:H deduced from subgap optical absorption measurement on Schottky solar cells