Photothermal and photoconductive determination of surface and bulk defect densities in amorphous silicon films

The sub-band-gap optical absorption spectra of high-quality hydrogenated amorphous silicon (a-Si:H) films are shown to be dominated by surface and interface state absorption when measured by photothermal deflection spectroscopy (PDS), while spectra determined using the constant photocurrent method (...

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Bibliographic Details
Published in:Applied physics letters 1987-05, Vol.50 (21), p.1521-1523
Main Authors: SMITH, Z. E, CHU, V, SHEPARD, K, ALJISHI, S, SLOBODIN, D, KOLODZEY, J, WAGNER, S, CHU, T. L
Format: Article
Language:English
Subjects:
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Exact sciences and technology
Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation
Optical properties of specific thin films
Physics
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Summary:The sub-band-gap optical absorption spectra of high-quality hydrogenated amorphous silicon (a-Si:H) films are shown to be dominated by surface and interface state absorption when measured by photothermal deflection spectroscopy (PDS), while spectra determined using the constant photocurrent method (CPM) are not. For bulk defect states (both as-deposited and light-induced), the integrated subgap absorption is approximately twice as large for PDS as for CPM. Similarly, the conversion factor relating integrated subgap absorption with neutral dangling bond density is twice as large for CPM as PDS. This factor of 2 results from CPM seeing only transitions from below midgap into the conduction band while PDS sees transitions from the valence band into states above midgap as well.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.97819