Assessment of AlGaN/AlN superlattices on GaN nanowires as active region of electron-pumped ultraviolet sources

TL;DR

This study designs and characterizes AlGaN/AlN superlattices on GaN nanowires, demonstrating high efficiency and tunable ultraviolet emission for electron-pumped UV sources, with improved stability over planar structures.

Contribution

It introduces a novel nanowire-based superlattice structure with enhanced efficiency and tunability for UV emission, outperforming traditional planar devices.

Findings

Nanowire superlattices achieve over 60% IQE at room temperature.

Emission wavelength tunable from 340 to 258 nm by adjusting composition.

Stable emission under electron beam excitation with no quenching observed.

Abstract

In this paper, we describe the design and characterization of 400-nm-long (88 periods) AlxGa1-xN/AlN (0 < x < 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN superlattices with the same periodicity and thickness grown on bulk GaN substrates along the N-polar and metal-polar crystallographic axes. The nanowire samples are less sensitive to nonradiative recombination than planar layers, attaining internal quantum efficiencies (IQE) in excess of 60% at room temperature even under low injection conditions. The IQE remains stable for higher excitation power densities, up to 50 kW/cm2. We demonstrate that the nanowire superlattice is long enough to collect the electron-hole pairs generated by an electron beam with an acceleration voltage VA = 5 kV. At such VA, the light emitted from the nanowire ensemble does not show any sign of quenching under constant electron beam excitation (tested for an excitation power density around 8 kW/cm2 over the scale of minutes). Varying the dot/barrier thickness ratio and the Al content in the dots, the nanowire peak emission can be tuned in the range from 340 to 258 nm. Keywords: GaN, AlN, nanowire, ultraviolet