Near- and mid-infrared intersubband absorption in top-down GaN/AlN nano- and micropillars

TL;DR

This study explores how top-down etching of GaN/AlN heterostructures into nano- and micropillars affects intersubband absorption and emission, revealing that small spacing preserves absorption even with significant material removal, advancing group-III nitride device development.

Contribution

It provides a systematic analysis of the effects of nano- and micropillar structuring on intersubband properties in GaN/AlN heterostructures, highlighting the preservation of absorption at small spacings.

Findings

Inter- and intra-band absorption remains strong at small pillar spacings.

Large pillar spacings cause masking effects due to photonic modes.

Significant material removal does not diminish intersubband absorption at small spacings.

Abstract

We present a systematic study of top-down processed GaN/AlN heterostructures for intersubband optoelectronic applications. Samples containing quantum well superlattices that display either near- or mid-infrared intersubband absorption were etched into nano- and micropillar arrays in an inductively coupled plasma. We investigate the influence of this process on the structure and strain-state, on the interband emission and on the intersubband absorption. Notably, for pillar spacings significantly smaller ($\leq1/3$) than the intersubband wavelength, the magnitude of the intersubband absorption is not reduced even when 90\% of the material is etched away and a similar linewidth is obtained. The same holds for the interband emission. In contrast, for pillar spacings on the order of the intersubband absorption wavelength, the intersubband absorption is masked by refraction effects and photonic crystal modes. The presented results are a first step towards micro- and nanostructured group-III nitride devices relying on intersubband transitions.