Electrical Characteristics of Schottky Barriers on 4H-SiC: The Effects of Barrier Height Nonuniformity

摘要

Electrical properties, including current-voltage (I-V0 and capacitance-voltage (C-V) characteristics, have been measured on a large number of Ti, Ni, and Pt-based Schottky barrier diodes on 4H-SiC epilayers. Various nonideal behaviors are frequently observed, including ideality factors greater than one, anomalously low I-V barrier heights, and exceess leakage currents at low forward bias and in reverse bias. The nonidealities are highly nonuniform across individual wafers and from water to water. We find a pronounced linear correlation between I-V barrier height and ideality factor for each metal, while C-V barrier heights remain constant. Electron beam current (EBIC) imaging strongly suggests that the nonidealities result from localized low barrier height patches. These patches are related to discrete crystal defects, which become visible as recombination centers in the EBIC images. Alternative explanations involving generation-recombination current, uniform interfacial layers, and effects related to the periphery are ruled out.