Increased electrical activation in the near-surface region of sulfur and nitrogen coimplanted GaAs

Abstract

A large increase in the electrical activation of sulfur coimplanted with nitrogen in GaAs is observed within a thin (<500 Å) near-surface region. A free electron concentration as high as 1.5×1019 cm−3 is observed in this layer, which is a factor of 5 higher than in a GaAs sample implanted with S only. The high free electron concentration in this thin layer is the result of the incorporation of N on the As site which forms a thin dilute GaNxAs1−x alloy layer. The increased electrical activity of S in this layer is explained by the N-induced modifications of the conduction band as predicted by the band anticrossing model. The measured free electron concentration is consistent with a GaNxAs1−x alloy layer with x∼0.3%. The results have important practical implications on the fabrication of low-resistance, nonalloyed ohmic contacts to n-type GaAs.