Characterization of {11-22} GaN grown using two-step growth technique on shallowly etched r-plane patterned sapphire substrates

Previously, we succeeded in growing flat semipolar (11 22) GaN layers on an r-plane patterned sapphire substrate (r-PSS). However, the GaN layers still contain a dislocation density of over 3 x 10(8)/cm(2) and stacking faults (SFs). To reduce such defects, we employed shallowly etched r-PSSs. The etching depths of the shallowly etched r-PSSs were from 100 to 500 nm, whereas that of a conventional r-PSS was 1 pm. As a result, we found that the threading dislocation density (TDD) decreases as the etching depth decreases. The TDD of the (11 221 GaN layer on r-PSS etched to a depth of 100 nm was 1.3 x 10(8)/cm(2). Moreover, the reduction of the SFs was observed by photoluminescence at cryogenic temperature. The reduction of the defects revealed the growth mechanism; the crystalline quality of)11 22) GaN on an r-PSS depends on the selective growth area of the sapphire sidewall. (C)2014 Elsevier RV. All rights reserved.