Effect of Grain Coalescence on Dislocation and Stress Evolution of GaN Films Grown on Nanoscale Patterned Sapphire Substrates

TL;DR

This study investigates how grain coalescence and nucleation layer choice affect dislocation densities and stress in GaN films grown on nanoscale patterned sapphire, revealing that PVD-AlN layers improve grain uniformity and reduce dislocations.

Contribution

It demonstrates that PVD-AlN nucleation layers significantly reduce dislocation densities and influence stress in GaN films compared to LT-GaN layers, advancing understanding of growth mechanisms.

Findings

PVD-AlN layers reduce dislocation densities by over 50%.

Higher 3D growth temperatures decrease edge dislocations.

PVD-AlN layers increase residual compressive stress by ~0.5 GPa.

Abstract

Two types of nucleation layers (NLs), including in-situ low-temperature grown GaN (LT-GaN) and ex-situ sputtered physical vapor deposition AlN (PVD-AlN), are applied on cone-shaped nanoscale patterned sapphire substrate (NPSS). The initial growth process of GaN on these two NLs is comparably investigated by a series of growth interruptions. The coalescence process of GaN grains is modulated by adjusting the three-dimensional (3D) temperatures. The results indicate that higher 3D temperatures reduce the edge dislocation density while increasing the residual compressive stress in GaN films. Compared to the LT-GaN NLs, the PVD-AlN NLs effectively resist Ostwald ripening and facilitate the uniform growth of GaN grains on NPSS. Furthermore, GaN films grown on NPSS with PVD-AlN NLs exhibit a reduction of over 50% in both screw and edge dislocation densities compared to those grown on LT-GaN NLs. Additionally, PVD-AlN NLs result in an increase of about 0.5 GPa in the residual compressive stress observed in GaN films.