Publications Details

p- and n-type implantation doping of GaN with Ca and O

Zolper, J.C.

III-N photonic devices have made great advances in recent years following the demonstration of doping of GaN p-type with Mg and n-type with Si. However, the deep ionization energy level of Mg in GaN (approximately 160 meV) limits the ionized of acceptors at room temperature to less than 1.0% of the substitutional Mg. With this in mind, we used ion implantation to characterize the ionization level of Ca in GaN since Ca had been suggested by Strite to be a shallow acceptor in GaN. Ca-implanted GaN converted from n-to-p type after a 1100 °C activation anneal. Variable temperature Hall measurements give an ionization level at 169 meV. Although this level is equivalent to that of Mg, Ca-implantation may have advantages (shallower projected range and less straggle for a given energy) than Mg for electronic devices. In particular, we report the first GaN device using ion implantation doping. This is a GaN junction field effect transistor (JFET) which employed Ca-implantation. A 1.7 μm JFET had a transconductance of 7 mS/mm, a saturation current at 0 V gate bias of 33 mA/mm, a ft of 2.7 GHz, and a fmax of 9.4 GHz. O-implantation was also studied and shown to create a shallow donor level (approximately 25 meV) that is similar to Si. SIMS profiles of as-implanted and annealed samples showed no measurable redistribution of either Ca or O in GaN at 1125 °C.