Effect of oxygen plasma modification on Pd/Al/Au Ohmic contacts on undoped AlN

Abstract

The influence of surface modification of undoped AlN by oxygen plasma on the Pd/Al/Au Ohmic contacts was studied. Pd/Al/Au alloys were deposited on undoped AlN films by electron beam evaporation and annealed from 750 °C to 900 °C for 30 s to form metal–semiconductor contacts. All the samples without oxygen plasma treatment were Schottky contacts. After oxygen plasma treatment, the contacts below annealing temperature of 850 °C were Schottky type. However, the contacts changed to be Ohmic type with specific contact resistivity of 3.01 Ω · cm2 when the annealing temperature was 900 °C. The samples were characterized by scanning electron microscopy and x-ray diffraction, which indicated that the formation of AlPd alloy was believed to play a key role for the formation of low Ohmic contacts. The first-principle calculation indicated that the surface modification by oxygen plasma could increase the work function of AlN and therefore benefit the formation of Ohmic contacts. This result can promote the application prospects of AlN in deep ultraviolet optoelectronic devices and high frequency and high power RF devices.