Low resistivity contacts to plasma etched Mg-doped GaN using very low power inductively coupled plasma etching

The electrical characteristics of contacts to p-type GaN etched using inductively coupled plasma-reactive ion etching at low radio-frequency (RF) and inductively coupled plasma (ICP) powers were studied via current–voltage characteristics and transfer length method analysis. Although the quality of ohmic contacts to p-GaN is generally degraded by plasma etching, the results indicate that the specific contact resistance improves significantly both for the same etch depth and for the same etch time when the power is reduced from RF/ICP power of 75/150 W to very low RF/ICP power of 20/40 W. The use of a two step approach using a combination of higher power (75/150 W) followed by very low power (20/40 W) etches on the same sample also show improvement compared to the standard etch. Finally, etching with low power to a shallow etch depth of 60 nm achieved a very low specific contact resistance of 0.035 Ωcm2, while a deeper etch of more than 500 nm resulted in a contact resistance of 0.153 Ωcm2, both lower than any previously published values for ohmic contacts made to etched p-GaN.