Fabrication and characterization of subwavelength nanostructures on freestanding GaN slab

Yongjin Wang,Yoshiaki Kanamori,Fangren Hu,Kazuhiro Hane,Hidehisa Sameshima

doi:10.1364/oe.18.002940

Abstract

We develop a novel way to fabricate subwavelength nanostructures on the freestanding GaN slab using a GaN-on-silicon system by combining self-assemble technique and backside thinning method. Silicon substrate beneath the GaN slab is removed by bulk silicon micromachining, generating the freestanding GaN slab and eliminating silicon absorption of the emitted light. Fast atom beam (FAB) etching is conducted to thin the freestanding GaN slab from the backside, reducing the number of confined modes inside the GaN slab. With self-assembled silica nanospheres acting as an etching mask, subwavelength nanostructures are realized on the GaN surface by FAB etching. The reflection losses at the GaN interfaces are thus suppressed. When the InGaN/GaN multiple quantum wells (MQWs) active layers are excited, the light extraction efficiency is significantly improved for the freestanding nanostructured GaN slab. This work provides a very practical approach to fabricate freestanding nanostructures on the GaN-on-silicon system for further improving the light extraction efficiency.

Highlights

Gallium nitride (GaN) is a relatively new direct band gap III-V semiconductor material for optoelectric applications, especially for light emission
We develop a novel way to fabricate subwavelength nanostructures on the freestanding GaN slab using a GaN-on-silicon system by combining selfassemble technique and backside thinning method
This work provides a very practical approach to fabricate freestanding nanostructures on the Gallium nitride (GaN)-on-silicon system for further improving the light extraction efficiency

Summary

Introduction

Gallium nitride (GaN) is a relatively new direct band gap III-V semiconductor material for optoelectric applications, especially for light emission. In principle it is easy to tune the emission wavelength of the GaN system by changing the indium content [1, 2]. It can fabricate GaNbased light emitting devices that cover the entire visible and near- to deep-UV spectrum. Sapphire and SiC are the most common substrates of choice due to the fact that bulk lattice-matched substrates are not readily available. Both sapphire and SiC are difficult to manufacture. It offers the potential to fabricate optical components on freestanding GaN slabs by combining bulk silicon micromachining and the GaNon-silicon system [7–10]

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