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

• We succeeded in the selective area growth of a semipolar {11–22} GaN layer on a shallowly etched r-PSS.
• Selective area growth was achieved by applying a two-step growth process.
• The shallowly etched r-PSS was effective in reducing the dislocation density of {11–22} GaN.
• The adoption of shallowly etched r-PSS and two-step growth technique enabled suppression of the defect such as SFs.

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 3×108/cm2 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 μm. As a result, we found that the threading dislocation density (TDD) decreases as the etching depth decreases. The TDD of the {11−22} GaN layer on r-PSS etched to a depth of 100 nm was 1.3×108/cm2. 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.