Ohmic contacts to n-GaN formed by ion-implanted Si into p-GaN

Abstract

In this paper, we report the ohmic contact to n-GaN fabricated by implanting silicon into Mg-doped GaN using an alloy of Ti/Al/Ti/Au metallization. The used materials were grown on (001) sapphire substrates by metal-organic chemical-vapor deposition (MOCVD). The layer structure was comprised of a GaN buffer layer and followed by a 2 μm thickness Mg-doped GaN (Na=5x10 17 cm -3 ) and then double silicon implantation was performed in order to convert p-type GaN into n-type GaN films. The as-implanted samples were then thermal annealed at 1150 °C for 5 min in N 2 ambient. The carrier concentration and Hall mobility were 3.13x10 18 cm 3 and 112 cm 2 / (V·s) measured by Hall method. Multilayer electrode of Ti (50 nm)/Al (50 nm)/Ti (30 nm)/Au (30 nm) was deposited on n-GaN using an electron-beam evaporation and contacts were formed by a N 2 annealing technique ranging from 600 to 900 °C. After annealing lower than 700 °C, the contacts exhibited a rectifying behavior and became ohmic contact only after high temperature processes (>700 °C). Specific contact resistance was as low as 9.58x10 -4 Ω·cm 2 after annealing at 800 °C for 60 seconds. While annealing temperature is higher than 800 °C, the specific contact resistance becomes worse. This phenomenon is caused by the surface morphology degradation.