Influence of the reactor environment on the selective area thermal etching of GaN nanohole arrays

Pierre-Marie Coulon,Peng Feng,Tao Wang,Stéphane Vézian,Philip A Shields,Benjamin Damilano

doi:10.1038/s41598-020-62539-1

Abstract

Selective area thermal etching (SATE) of gallium nitride is a simple subtractive process for creating novel device architectures and improving the structural and optical quality of III-nitride-based devices. In contrast to plasma etching, it allows, for example, the creation of enclosed features with extremely high aspect ratios without introducing ion-related etch damage. We report how SATE can create uniform and organized GaN nanohole arrays from c-plane and (11–22) semi-polar GaN in a conventional MOVPE reactor. The morphology, etching anisotropy and etch depth of the nanoholes were investigated by scanning electron microscopy for a broad range of etching parameters, including the temperature, the pressure, the NH3 flow rate and the carrier gas mixture. The supply of NH3 during SATE plays a crucial role in obtaining a highly anisotropic thermal etching process with the formation of hexagonal non-polar-faceted nanoholes. Changing other parameters affects the formation, or not, of non-polar sidewalls, the uniformity of the nanohole diameter, and the etch rate, which reaches 6 µm per hour. Finally, the paper discusses the SATE mechanism within a MOVPE environment, which can be applied to other mask configurations, such as dots, rings or lines, along with other crystallographic orientations.

Highlights

Selective area thermal etching (SATE) of gallium nitride is a simple subtractive process for creating novel device architectures and improving the structural and optical quality of III-nitride-based devices
The parameters of the inductively coupled plasma (ICP) chamber can be optimized to reach fairly straight nanohole sidewalls for an etch depth up to hundreds of nanometers[21,30], deeper etching over a micron will be inevitably limited by the selectivity, the thickness of the mask and aspect ratio dependent etching, which induces a dramatic reduction in etch rate for deep holes
To create GaN nanoholes, a SiNx mask having circular nano-openings was fabricated by Displacement Talbot Lithography (DTL)[34] and inductively coupled plasma etching on GaN templates

Summary

Introduction

Selective area thermal etching (SATE) of gallium nitride is a simple subtractive process for creating novel device architectures and improving the structural and optical quality of III-nitride-based devices. Damilano and co-authors reported several works on the selective area sublimation (SAS) of nanorods and nanoholes having a straight sidewall profile, achieved in a molecular beam epitaxy (MBE) chamber either from a SiNx self-organized mask[15,31], or a SiNx nanopatterned mask[32,33]. With their conditions, nanorods and nanoholes with a high organization and fairly uniform dimensions were successfully achieved[32,33]. The etching mechanism behind the SATE of GaN nanohole arrays within a MOVPE environment is discussed

Methods

Results

Conclusion