Spectral Dependence of Photoconductivity in Indium-Doped Silicon

Abstract

The spectral dependence of extrinsic photoconductivity over the range 130–700 meV has been measured (mostly at 80°K, with light chopped at 270 Hz) for a variety of indium‐doped silicon crystals. The various samples were characterized by 70–400°K Hall and conductivity measurements, and had indium densities ranging from 7 × 1015 cm−3 to 7 × 1017 cm−3. Crystals of moderately large and extremely small compensation were used. The data were converted into the response per incident photon and per absorbed photon (using, for the latter, data on the photoionization cross section measured on the same group of crystals). The response per absorbed photon is approximately constant from the 150‐meV threshold through the spectral range studied, with no visible evidence of an oscillatory component. The data for one sample were Fourier analyzed in order to detect any latent periodicity in the photoresponse, and a weak periodic component at meV intervals was found and tentatively associated with localized phonon modes.