Crystal quality and surface structure tuning of semi-polar (11–22) GaN on m-plane sapphire via in-situ multiple ammonia treatment

Abstract

The crystal quality and morphological properties of semi-polar (11–22) gallium GaN were enhanced by introducing the In-Situ Multiple Ammonia Treatment (I-SMAT) method. On- and off-axis x-ray rocking curve (XRC) analysis reveals that I-SMAT would reduce several types of crystal defect namely prismatic stacking faults, basal stacking fault type I and II, and partial/perfect dislocations. By implementing an optimized flow of ammonia (NH3) and number of treated GaN pairs, the arrowhead-like features of semi-polar (11–22) GaN was effectively reduced the root mean square roughness from 4.52 to 3.07 nm. High atomic force microscopy (AFM) magnification scan demonstrated the alteration of the grain structure on the surface to become more compact and orderly arranged resulting in narrowing/shallowing of the interfacial valleys between grains. Great influence of employed I-SMAT pairs and NH3 flux was observed from XRC and AFM analysis. Conversely, excessive NH3 flux during this approach would roughen the structural and morphological properties of the semi-polar epilayer whereby the alternating thin GaN epilayer would undergo the selective-area etching to the extreme.