Deep-state-controlled minority-carrier lifetime in n-type gallium phosphide

Details of a method for the characterization of deep levels with large capture cross sections for minority carriers are presented. This technique has been used to investigate centers in gallium phosphide. Two defects at EV+0.75 eV and EV+0.95 eV are described in detail. Evidence is presented that shows that the shallower of these defects can control the minority-carrier lifetime in n-type gallium phosphide and in fact is the dominant recombination center in most epitaxial layers of this material. The technique uses capacitance as a measure of the charge state of the deep levels in the depletion region of a Schottky barrier. This charge state is perturbed by the capture and subsequent thermal emission of minority carriers. The carriers are generated by irradiation of the semiconductor with low-intensity light at a wavelength near the absorption edge. Minority carriers generated in the neutral material within about a diffusion length of the barrier region are extracted by the depletion field. Majority carriers are excluded by the field and consequently the current through the barrier is due predominantly to minority carriers. These are captured by the defects, the fastest capture being into the levels with the largest capture cross sections. As a result, the technique can in many cases be used selectively to detect the most important recombination centers in a semiconductor and to determine their capture cross sections, concentrations, and energy depths.