Arsenic and Cadmium Implantations into n-Type Gallium Arsenide

Abstract

Electrical properties of cadmium-implanted layers in n-type GaAs substrates and effects of arsenic preimplantations have been investigated. The implant conditions were energy 20 keV, dose 1014–1016/cm2, and substrate temperature 500°C for cadmium implants and 25°C for arsenic preimplants. The measured carrier-concentration profile shows that a heavily doped p-type layer exists within 1000 Å of the surface for cadmium-implanted specimens. However, current-voltage and capacitance-voltage characteristics of the diodes fabricated by implantations of 1015 and 1016 Cd/cm2 indicate that these junctions have a p-π-n structure. Thicknesses of the π layers are about 3 μ for the dose of 1016 Cd/cm2 and 1.5 μ for 1015 Cd/cm2. On the other hand, diodes fabricated by arsenic and cadmium implants have characteristics of normal p-n junctions. Arsenic preimplantation reveals the fact that high-dose implantation into a hot substrate produces a large number of arsenic vacancies, which diffuse deeply into the substrate. Arsenic vacancy-donor silicon complex acts as a deep-level compensating center and forms a thick high-resistance layer.