Electrical characterization of HVPE GaN containing different concentrations of carbon dopants

Abstract

A comprehensive study of the electrical characteristics in Schottky diodes made of GaN:C grown by hydride vapour phase epitaxy (HVPE) technology has been reported. The Schottky junctions were made of an Ni/Au (25/200 nm) metal stack and ohmic contacts were fabricated by Ti/Al/Ni/Au (30/90/20/100 nm) e-beam deposition of the metal thin-films followed by rapid thermal annealing. A good quality of the fabricated Schottky diodes has been proved by considering the transient shape using a pulsed technique of barrier evaluation under linearly increasing voltage (BELIV). The concentrations of equilibrium carriers of 1 × 1011 cm−3 and of 2 × 1010 cm−3 have been evaluated for relatively low and high carbon density doped samples, respectively, using photo-capacitance characteristics dependent on excitation intensity. The effective mobility of carriers of μeff = 610 cm2/Vs has been estimated by considering the serial resistance variations dependent on excitation density, through analysis of delay times that appeared in the formation of peaks within BELIV transients. Optical deep level transient spectroscopy has shown that thermal emission from the rather shallow centres prevails. The centres, ascribed to vacancies as well as to carbon on Ga sites, have been identified. It has been demonstrated that Schottky junctions made of heavy carbon doped (NC ≥ 1018 cm−3) HVPE GaN material are able to withstand voltages of ≥300 V.