The improvement of selective-area growth using plasma assisted molecular beam epitaxy for low ohmic contact resistance

To achieve very low ohmic contact resistance, n+-GaN layer was selectively deposited using plasma assisted molecular beam epitaxy. During this process polycrystalline GaN grew on the patterned SiO2 region which was subsequently removed by a heated KOH solution, resulting in damage on the n⁺-GaN surface. To prevent this damage, an additional SiO2 layer was selectively deposited only on the n⁺-GaN region, producing a specific contact resistance (4.59 × 10^-7 Ω·cm²) much lower than that with the KOH etching damage (4.92 ~ 23.7 × 10^-6 Ω·cm²). Each of KOH etching included large pits (4.08 × 10⁸ cm^-2) and degraded current transport.