Planarization of GaN by the Etch-Back Method

The planarization of GaN has been mainly addressed by chemo-mechanical polishing methods in the literature. Such techniques were found to be successful in planarizing the nitrogen polar (000-1) surface of GaN. However, planarization of the gallium polar (0001) surface presents a challenge due to its higher degree of chemical inertness. Moreover, studies on the planarization of the remaining crystal orientations remain a topic with sparse representation in the literature. In this paper, we report our planarization studies of GaN films using an etch-back technique. Photoresist is employed as the sacrificial layer and a chlorine inductively coupled plasma (ICP) used for etching. We demonstrate the planarization of rough C-plane and A-plane GaN films grown by hydride vapor phase epitaxy (HVPE). Specifically, an rms roughness of approximately 2.1nm and 4.1nm was realized after iterative etch-back for a representative C-plane and A-plane sample with initial rms roughness of 134nm and 414nm respectively.