Relations between Structure and the Optical and Electrical Properties of Amorphous Si and Ge Films

Abstract

A review of recent structural, electrical, and optical experiments on amorphous Ge and Si films is given. Amorphous Ge and Si have no long-range periodic ordering but do have a short-range order with nearly the same tetrahedral arrangements as the corresponding crystals. SiC and the III–V compounds probably retain a similar structure in the amorphous phase. Electron spin resonance and small-angle diffraction studies on amorphous Ge and Si give indications of a large number of dangling bonds and internal surfaces distributed throughout the volume of the films. Strong correlations exist between the annealing out of the dangling bonds and accompanying decreases in the electrical conductivity, optical absorption, and refractive index. Structural models have been formulated which agree with the data on density, radial distribution function, and dangling bonds. These models indicate what features should be incorporated into the interpretation of the conduction and absorption experiments. Some promising areas of further research are indicated.