th  - 1987 - 51st ENC Conference

MF23 - POSTERS
NMR INVESTIGATIONS OF ATOMIC MICROSTRUCTURE
IN AMORPHOUS SEMICONDUCTORS
Q
Karen K. Gleason , Mark A. Petrich, and Jeffrey A. Reimer,
.Department of Chemical Engineering, University of California,
Berkeley, CA 94720-9989.
The microstructure of amorphous semiconductors has important
implications for their electronic properties. Nuclear magnetic
resonance (NMR) can examine the microstructure of these materials
on an atomic scale. Previous NMR results have indicated that the
hydrogen in these materials exists both as isolated hydrogen atoms
and as clusters of hydrogen. Using Multiple Quantum NMR, a
technique which is able to "count" the number of hydrogen atoms in a
cluster, we have studied the effects of deposition temperature,
dopant atoms, and annealing on the clustering of hydrogen in
amorphous silicon. Our results indicate that electronic device
quality amorphous silicon films contain small clusters of
approximately six hydrogen atoms, while nondevice quality films
contain larger hydrogen atom clusters. We have also extended the
multiple quantum NMR technique to study a series of amorphous
silicon carbide alloys, systematically varied in carbon content. We
have found that small amounts of carbon decrease the total hydrogen
content of the alloy, but increase hydrogen clustering. Carbon-13
and silicon-29 magic-angle spinning NMR spectra, taken with and
without proton decoupling, allow us to probe local bonding
configurations. These studies have shown that both sp 2 and sp 3
carbon bonding environments are important in these materials. It is
especially interesting that nearly all the hydrogenated carbon are
in the sp 3 bonding configuration.
By comparing our NMR results with data from other analytical
techniques such as infrared and optical absorption spectroscopy,
Rutherford backscattering, and conductivity measurements, we hope
to elucidate the relationships between deposition chemistry, atomic
microstructure, and optoelectronic properties of this
technologically important class of materials.
Supported by NSF grant DMR-8304163.