Silicon-Rich Si-Ge Alloys For Infrared Detectors - Material Properties

Abstract

Electrical and optical measurements were used to characterize silicon-rich Si-Ge alloys up to 11.3% Ge content. Both high-resistivity p-type material, for use as p-i-n detectors for 1.06-μm radiation, and In-doped material, for use as an extrinsic IR detector beyond 8 μm, were studied. The measurement techniques include Hall-effect measurements versus temperature and photoresponse, photoconductivity, and absorption spectra. A major result is that multiple energy levels were found for acceptors. These energy levels arise from the interaction of the acceptor with its nearest-neighbor shell, and each level corresponds to a different number of Ge atoms in this shell. The concentration of acceptors having a given level corresponds to the probability of the nearest-neighbor shell having the corresponding number of Ge atoms; the probability of a Ge atom occupying a lattice site in the nearest-neighbor shell is from 0.5 to 1.0 times the probability of occupying a random lattice site. These results strongly affect the use of this material for extrinsic IR detectors because an extended response to long wavelengths results. We will also discuss the effects of the disorder in these materials on mobility and on spectral response and diffusion length measurements made on p-i-n detectors fabricated from these materials.