Photoconductivity of Gallium Antimonide

Photoconductivity of n- and p-type GaSb has been investigated. The observed photoresponse extends beyond the threshold of intrinsic absorption. The existence of several levels in the energy gap is deduced from the spectra. With reference to the valence band, one level is located at 0.03 eV, one or two levels in the range 0.060-0.080 eV, and another level at 0.10 eV. The extrinsic photoresponse is produced by electron excitations from these levels to the conduction band. The nature of the centers which give these levels is discussed. It is deduced from the studies that n-type samples with etched surfaces have electron traps in a p-type surface layer. The level of the traps lies ≈0.5 eV below the conduction band, and the density of the traps is estimated to be 3×{}10¹² cm^-2. In addition, the 0.10-eV level in the bulk material traps holes as well as giving the extrinsic photoresponse. The electron capture cross section of this level is ≈2×10^-20 cm². Electron trapping phenomena are observed in the undoped p-type material at low temperatures. Observed quenching, saturation effects, and complicated transient behavior indicate that excited states of the trap have to be taken into account. The traps have a ground-state level at 0.18 eV below the conduction band and a concentration of the order of 10¹⁴ cm^-3.