Reactive ion etch damage on GaN and its recovery

Abstract

Surface properties of GaN subjected to reactive ion etching and their impact on device performance have been investigated by transport, optical, and surface potential measurements. Different etching conditions were studied to minimize plasma-induced damage. Higher etch rates could be obtained at high powers and low pressures, with the accompanying roughening of the surface. Surface potential for the as-grown samples was found to be in the range of 0.5–0.7V using scanning Kevin probe microscopy. However, after etching at a power level of 300W, the surface potential decreased to 0.1–0.2V. An almost linear reduction was observed with increasing power. Additionally, the intensity of the near band edge photoluminescence decreased and the free carrier density increased after etching. These results suggest that the changes in the surface potential may originate from the formation of possible nitrogen vacancies and other surface oriented defects. To recover the etched surface, N2 plasma, rapid thermal annealing, and etching in wet potassium hydroxide were performed. For each of these methods, the surface potential was found to increase by 0.1–0.3V, also the reverse leakage current in Schottky diodes, fabricated on treated samples, was reduced considerably compared with as-etched samples, which implies a partial to complete recovery from the plasma-induced damage.