Low resistance NiO/β-Ga_{2}O_{3} heterojunction diodes grown via molecular beam epitaxy

Abstract

NiO is one of the most important p-type oxide contact materials used in many semiconductor technologies. However, current NiO growth methods can induce interfacial damage that diminishes device performance. Fine control of interfaces is especially important in implementing NiO heterojunction diodes and transistors based on ultra wide band gap (UWBG) semiconductors such as AlGaN and Ga_{2}O_{3} used for power electronic applications. Here, we report on how molecular beam epitaxy can be used to achieve low-defect, lightly doped NiO contact layers for a β-Ga_{2}O_{3} diodes. Although high-temperature growth does not measurably decrease the on-state resistance of the diode, increased growth rates up to 600 nm/hr lower on-state resistance in p-- NiO / β-Ga_{2}O_{3} heterojunction diodes without reducing film quality. At a NiO growth rate of 380 nm/hr, unoptimized diodes with 35 nm thick p-- NiO layers demonstrate a device-average specific on-state resistance of 1.46 Ω-cm^{2} and an ideality factor of 1.46. Individual devices grown at this condition show specific on-state resistance as low as 25 mΩ-cm2 with a rectification ratio of 2.7x106. Scanning transmission electron microscopy imaging reveals the (100) NiO/ (100) β-Ga_{2}O_{3} interface is coherent and atomically abrupt. These results open a new avenue to optimizing the NiO interface to produce robust, competitive kV-class power electronic devices based on β-Ga_{2}O_{3} and other UWBG semiconductors.