Smooth GaN membranes by polarization-assisted electrochemical etching

J Ciers,N Grandjean,F Hjort,J.-F Carlin,Å Haglund,M A Bergmann

doi:10.1063/5.0034898

Abstract

III-nitride membranes offer promising perspectives and improved device designs in photonics, electronics, and optomechanics. However, the removal of the growth substrate often leads to a rough membrane surface, which increases scattering losses in optical devices. In this work, we demonstrate membranes with etched surface roughness comparable to that of the as-grown epitaxial material, accomplished by the implementation of a properly designed built-in polarization field near the top of the sacrificial layer from an AlInN interlayer, which is polarization-mismatched to GaN. This leads to a steeper reduction in free carrier density during the electrochemical etching of the sacrificial layer, limiting the etching current and thus causing an abrupter etch stop. As a result, the root mean square roughness is reduced to 0.4 nm over 5 × 5 μm2. These smooth membranes open attractive pathways for the fabrication of high-quality optical cavities and waveguides operating in the ultraviolet and visible spectral regions.

Highlights

N requires a large number of pairs, which might be detrimental for practical use.6,7 The issues with heterogeneous epitaxy of III-Ns can be circumvented by lifting-off III-N membranes from the growth substrate and bonding them to the material of choice
We demonstrate membranes with etched surface roughness comparable to that of the as-grown epitaxial material, accomplished by the implementation of a properly designed built-in polarization field near the top of the sacrificial layer from an AlInN interlayer, which is polarization-mismatched to GaN
Only EC etching simultaneously allows for the fabrication of membranes with low dislocation density, precisely controlled thickness, smooth surfaces, and etching rates up to 1 lm/s, while being compatible with electrical contacts [the thermal decomposition of GaN is not, due to the high temperatures required, >1000 C (Ref. 8)]

Summary

Introduction

N requires a large number of pairs, which might be detrimental for practical use.6,7 The issues with heterogeneous epitaxy of III-Ns can be circumvented by lifting-off III-N membranes from the growth substrate and bonding them to the material of choice. We demonstrate membranes with etched surface roughness comparable to that of the as-grown epitaxial material, accomplished by the implementation of a properly designed built-in polarization field near the top of the sacrificial layer from an AlInN interlayer, which is polarization-mismatched to GaN.

Results

Conclusion