Microwave plasma etching of GaN in nitrogen atmosphere

Effects of microwave nitrogen plasma etching of gallium nitride epilayers grown on sapphire were studied. The samples were etched with different supplied power ranging from 400 up to 800 W. High resolution X-ray diffraction, atomic force microscopy and infrared reflectivity were used to characterize epilayers after the treatment in the nitrogen plasma. We show that the application of low power (400 to 500 W) plasma is not an efficient way of GaN etching. Moreover, for these powers, the nitrogen plasma induced serious damage into the layer that led to its roughening and amorphisation. On the contrary, at higher powers, we observed etching with a rate of about 0.7 mu m/h, a smaller surface roughening and less subsurface layer amorphisation. We explain these phenomena by a temperature increase (over 600 degrees C) caused by the high power plasma.