D.R. Bapat

Bio: D.R. Bapat is an academic researcher from Tata Institute of Fundamental Research. The author has contributed to research in topics: Space charge & Silicon. The author has an hindex of 2, co-authored 7 publications receiving 32 citations.

Space‐charge limited conduction in n+nn+ amorphous hydrogenated silicon films

Abstract: High field conduction in n+nn+ amorphous hydrogenated silicon (α‐Si:H) films has been investigated at different temperatures. The results can be explained by assuming space‐charge limited conduction (SCLC) with a uniform density of traps. The value of density of states at the Fermi level, g(EF), obtained from the SCLC measurements ranges between 7−9×1016 cm−3 eV−1. Similar values are obtained by measurements of field effect and frequency and temperature dependence of Schottky barrier capacitance on material grown under identical conditions.

Efficient phosphorus doping of amorphous silicon carbide films

Abstract: In this letter we report on improved phosphorus incorporation in amorphous SiC films as measured by the dc conductivity and activation energy. In this process, we show that preheating of the gas mixture is an important process parameter which leads to improved impurity incorporation.

ac field effect in amorphous silicon

Abstract: We have measured the frequency dependence of the field effect in amorphous silicon. We show that the frequency dependence allows us to separate out the effects of mobile charges and slow states in a field effect measurement. For a‐Si on 7059 substrates, the value deduced from ac field effect for g(EF) differs only by a factor of two from that deduced from dc field effect measurements. We show from a study of the Nb2O5/a‐Si interface that the ac field effect is not as sensitive to the nature of the interface as the dc field effect.

Space‐charge‐limited currents: Refinements in analysis and applications to a‐Si1−xGex: H alloys

Abstract: A new algorithm is described for deriving the density of states N(E) from the Fermi energy EF upwards toward the conduction band edge. This refinement in the analysis of space‐charge‐limited currents (SCLC) enables the accurate determination of N(E) by implicitly accounting for the spatial variations of physical quantities across the thickness of the diode. SCLC is measured in NiCr/n+/a‐Si1−xGex: H/Pt diode structures. For a‐Si:H samples, SCLC values for N(EF) are compared to those derived from admittance measurements on the same diodes. The two determinations agree in samples where 1016

Density of states and mobility—lifetime product in hydrogenated amorphous silicon, from thermostimulated conductivity and photoconductivity measurements

Abstract: By combining thermostimulated conductivity and photoconductivity measurements, the density of gap states g(E) as well as the product of the microscopic mobility μ and the recombination lifetime τ of various samples containing hydrogenated amorphous silicon (a-Si:H) have been determined. The results obtained on pure a-Si: H are compared with those of nitrogen-doped a-Si: H films and of multi-layer structures consisting of alternating layers of 570 A thick a-Si: H and 30 A thick a-SiNx: H. A large density of states in the latter material is attributed to interface states. The μτ products measured are several orders of magnitude larger than the product of drift mobility and deep trapping time obtained from time-of-flight and charge-collection experiments. The results suggest that in addition to dangling bonds there are other recombination centres.

Single and double carrier injection in A-Si:H

Abstract: The far forward current in α-Si:H Schottky diodes has been compared with the current in nin devices with identical i-layers. The former is about one order of magnitude larger and has to be described by double injection, while the latter is governed by single-carrier space-charge-limited conduction. The transient behaviour of the diodes is also different from that in nin devices and confirms the occurrence of double injection. Metastable changes in α-Si:H (the Staebler-Wronski effect) are obtained after current-soaking in pip samples, but not after current-soaking in nin samples. To explain this, a model is suggested which is based on SiSi bond weakening by hole trapping in valence band tail states.

Dominant recombination process in amorphous silicon alloys

Abstract: We have critically examined experimental results on photoconductivity in hydrogenated amorphous silicon alloys to ascertain whether recombination at a single defect site (namely, the dangling bonds) or a continuous distribution of centers (dangling bonds together with other defects) provides a realistic model to explain the available experimental data. We find from both these results and from additional experimental data that, for good quality, low defect density material, room temperature recombination is controlled by a continuous distribution of states located between the trap‐quasi‐Fermi levels.

Density of states study of sputtered and evaporated a-Si: H by space-charge-limited current technique

Abstract: The density of states (DOS) in sputtered and evaporated a-Si: H has been determined from space-charge-limited current (SCLC) measurements on samples with a Cr/a-Si/a-Si: H/a-Si/Cr sandwich configuration. In the current-voltage characteristics of sputtered films, a non-Ohmic region due to one-carrier SCLC conduction is followed by a sharp increase in current at higher fields. This increase is attributed to switching phenomena caused by the formation of a current filament in the film. The DOS near the Fermi level of sp-a-Si: H films varies between 7 × 1015 and 1 × 1017 cm−3 eV−1, and, as observed in gd-a-Si: H, depends strongly on the film thickness in the measured range of 0·6-2·0 μm. The DOS for evaporated films is comparatively low–around 1017 cm−3 eV-−1 –showing that dangling bonds can be saturated by incorporation of sufficient atomic hydrogen into the films.