Critical thickness of GaN on AlN: impact of growth temperature and dislocation density

P Sohi,D Martin,N Grandjean

doi:10.1088/1361-6641/aa7248

Abstract

Critical thickness and strain relaxation of c-plane GaN layers grown by molecular beam epitaxy on AlN were studied as a function of growth temperature and threading dislocation density (TDD). For this purpose we used AlN/sapphire templates and AlN single crystals with TDDs of ∼109 cm−2 and ∼103 cm−2, respectively. Whereas at high growth temperature (900 °C) the critical thickness for plastic relaxation is only 3 monolayers (MLs) for both substrates, this value drastically increases when decreasing the growth temperature. It reaches ∼30 MLs when GaN is deposited at 750 °C on AlN single crystals. We also observed that the strain relaxation rate strongly depends on TDD. These results exemplify the lack of efficient gliding planes in III-nitrides when grown along the c-axis, which, combined with low kinetics, allows for plastic relaxation to be frozen out. Achieving pseudomorphic GaN layers on AlN is of interest for two-dimensional electron gases based on AlN/GaN/AlN heterostructures lattice-matched to AlN single crystal substrates.

Highlights

III-nitrides have proven to be promising materials for high power and high frequency electronic devices [1, 2]
Critical thickness and strain relaxation of c-plane GaN layers grown by molecular beam epitaxy on AlN were studied as a function of growth temperature and threading dislocation density (TDD)
Achieving pseudomorphic GaN layers on AlN is of interest for twodimensional electron gases based on AlN/GaN/AlN heterostructures lattice-matched to AlN single crystal substrates

Summary

Introduction

III-nitrides have proven to be promising materials for high power and high frequency electronic devices [1, 2]. Abstract Critical thickness and strain relaxation of c-plane GaN layers grown by molecular beam epitaxy on AlN were studied as a function of growth temperature and threading dislocation density (TDD). In this study we investigate the impact of growth temperature and threading dislocation density (TDD) on the plastic relaxation of c-plane GaN layers grown on AlN.

Results

Conclusion