Role of intermediate temperature molecular beam epitaxy grown GaAs defects in tunneling and diffusion

Abstract

Current transport in GaAs grown by molecular beam epitaxy in the intermediate temperature (IT-GaAs) range of about 400 °C is investigated. A model is proposed which explains the direct role of deep defects in assisting tunneling from Schottky contacts to semiconductor, where, due to rapidly changing potential, the Wentzel–Kramers–Brillouin approximation cannot be used. The indirect role of defects in diffusion process in the IT-GaAs semiconductor is also investigated. The model is used to explain the dark I–V behavior of metal–semiconductor–metal photodetectors made on unannealed, i.e., as-grown, IT-GaAs. dc responses of annealed and unannealed IT-GaAs are compared showing much smaller values of dark current in low biases in the unannealed device but sharp increase due to defect assisted tunneling at medium bias levels. Since the defect that best fits the model has an activation energy of about 0.5 eV, the annealing behavior suggests that the As interstitial has all the requisite properties of the defect which determines conduction behavior in this material. The observed reduction of dark response by light at high biases, the negative photoresponse, can then be explained based on occupancy of these defects. Device applications include ohmic contacts based on tunneling through IT-GaAs, and, conversely, reduction of tunneling through growth of a barrier layer between Schottky metal and semiconductor.