EFFECTS OF VACANCIES ON THE ELECTRICAL CHARACTERISTICS OF METAL GAAS SCHOTTKY CONTACTS A QUANTITATIVE MODEL

Abstract

An analytical method, proceeding by solving the Poisson equations both in the metal and in the GaAs substrate, is proposed to study the effects of the vacancies on the electrical characteristics of metal/GaAs contacts. A quantitative model used to calculate the effective charges contributed by the vacancies is developed here for the first time. From this analysis, it is found that the phenomenon of the Fermi level pinning in metal/GaAs contacts can be explained by the existence of vacancies at the metal/GaAs interface. Because of the amphoteric property of the vacancies in GaAs, the Fermi level is pinned at a level, called the ''neutral level'' of the vacancy, at which the effective charge introduced by the vacancies is zero. The change of the Fermi level pinning positions observed in previous experimental results for p and n GaAs can be ascribed to the change of vacancy types due to the nonstoichiometry in the GaAs substrate.