Dependence of the electrical properties of Zn contacts to GaAs on the structural properties of the Zn–GaAs interface

Ohmic contacts to p‐type GaAs are extremely important in the fabrication of heterojunction lasers, integrated optical devices, and solar cells. The importance of the metallurgical properties of the Zn–GaAs interface in determining the contact resistance is described here. The contacts were formed by the deposition of several thousand angstroms of zinc onto p‐type GaAs (N_a=4×10¹⁸ cm⁻³) substrates by evaporation in an ultrahigh vacuum system. The nonlinear current–voltage characteristics of as‐deposited samples changed to linear characteristics after annealing the samples up to 300 °C. The specific contact resistivities (ρ_c) as determined by four‐point probe were typically 2×10⁻⁴ Ω cm². Further annealing of the samples beyond 300 °C changed the linear current–voltage characteristics to nonlinear. The Auger depth profiles on samples which were as‐deposited, annealed at 300 °C and annealed up to 500 °C explain the variations in the electrical characteristics. If preferential Zn diffusion into GaAs at 300 °C caused the Ohmic behavior, further heating up to 500 °C resulted in ZnO formation degrading both the electrical and structural properties.