Photocharge Transport and Recombination Measurements in Amorphous Silicon Films and Solar Cells by Photoconductive Frequency Mixing: Annual Subcontract Report, 20 April 1998 - 19 April 1999

Research output: NRELSubcontract Report

Abstract

In the present phase of the program, the transport parameters of a number of amorphous semiconductors prepared by a number of techniques were determined by the photoconductive frequency mixing technique. This technique enabled us to determine the drift mobility, md, and the photomixing lifetime, t. The technique is based on the idea of heterodyne detection for photoconductors. When two similarlypolarized monochromatic optical beams of slightly different frequencies are incident upon a photoconductor, the generation rate of electron-hole pairs will produce a photocurrent, when a dc-bias is applied, which will contain components resulting from the square of the sum of the individual incident fields. Consequently, a photocurrent will be produced, which will consist of a direct current anda microwave current corresponding to the beat frequency. These two currents allow a separate determination of the drift mobility and the photomixing lifetime of the photogenerated carriers. In the present work, the longitudinal modes of a He-Ne laser were employed to generate a beat frequency of 252 MHz; all the measurements were performed at this frequency for the data indicated in theaccompanying figures. The following topics were explored: a) Measurements of the charge transport parameters of homogeneous a-SiGe:H alloys produced by NREL employing the hot-wire technique; b) The change in the charge transport parameters in the transition from hydrogenated amorphous silicon to microcrystalline silicon for material produced by NREL and MVSystems; c) The improvement ininstrumentation of the photomixing measurements; d) Measurements of the hydrostatic dependency of the transport parameters of amorphous silicon; e) Preliminary photomixing measurements on p-i-n devices.
Original languageAmerican English
Number of pages50
StatePublished - 2000

Bibliographical note

Work performed by University of California, Los Angeles, California

NREL Publication Number

  • NREL/SR-520-27931

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