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Dislocation Reduction and Stress Relaxation of GaN and InGaN Multiple Quantum Wells with Improved Performance via Serpentine Channel Patterned Mask
The
existence of high threading dislocation density (TDD) in GaN-based
epilayers is a long unsolved problem, which hinders further applications
of defect-sensitive GaN-based devices. Multiple-modulation of epitaxial
lateral overgrowth (ELOG) is used to achieve high-quality GaN template
on a novel serpentine channel patterned sapphire substrate (SCPSS).
The dislocation blocking brought by the serpentine channel patterned
mask, coupled with repeated dislocation bending, can reduce the dislocation
density to a yet-to-be-optimized level of ∼2 × 10<sup>5</sup> to 2 × 10<sup>6</sup> cm<sup>–2</sup>. About
80% area utilization rate of GaN with low TDD and stress relaxation
is obtained. The periodical variations of dislocation density, optical
properties and residual stress in GaN-based epilayers on SCPSS are
analyzed. The quantum efficiency of InGaN/GaN multiple quantum wells
(MQWs) on it can be increased by 52% compared with the conventional
sapphire substrate. The reduced nonradiative recombination centers,
the enhanced carrier localization, and the suppressed quantum confined
Stark effect, are the main determinants of improved luminous performance
in MQWs on SCPSS. This developed ELOG on serpentine shaped mask needs
no interruption and regrowth, which can be a promising candidate for
the heteroepitaxy of semipolar/nonpolar GaN and GaAs with high quality