Monolayer-Scale GaN/AlN Multiple Quantum Wells for High Power e-Beam Pumped UV-Emitters in the 240–270 nm Spectral Range

Abstract

Monolayer (ML)-scale GaN/AlN multiple quantum well (MQW) structures for electron-beam-pumped ultraviolet (UV) emitters are grown on c-sapphire substrates by using plasma-assisted molecular beam epitaxy under controllable metal-rich conditions, which provides the spiral growth of densely packed atomically smooth hillocks without metal droplets. These structures have ML-stepped terrace-like surface topology in the entire QW thickness range from 0.75–7 ML and absence of stress at the well thickness below 2 ML. Satisfactory quantum confinement and mitigating the quantum-confined Stark effect in the stress-free MQW structures enable one to achieve the relatively bright UV cathodoluminescence with a narrow-line (~15 nm) in the sub-250-nm spectral range. The structures with many QWs (up to 400) exhibit the output optical power of ~1 W at 240 nm, when pumped by a standard thermionic-cathode (LaB6) electron gun at an electron energy of 20 keV and a current of 65 mA. This power is increased up to 11.8 W at an average excitation energy of 5 µJ per pulse, generated by the electron gun with a ferroelectric plasma cathode at an electron-beam energy of 12.5 keV and a current of 450 mA.

High‐Efficiency E‐Beam Pumped Deep‐Ultraviolet Surface Emitter Based on AlGaN Ultra‐Thin Staggered Quantum Wells

“…In order to disregard the above‐mentioned issues, the electron beam‐pumped deep‐ultraviolet surface emitter (DUVSE) is proposed to increase the output power and avoid the conventional carrier injection layers. [ 22–28 ] The device merely consists of a carbon nanotube (CNT) field emitter and AlGaN multiple quantum wells (MQWs). This DUVSE announces plenty of advantages such as low emitted light re‐absorption, [ 24 ] simple epitaxial structure, [ 23 ] and solo‐device fabrication at wafer‐scale.…”

“…Many reports have suggested that the utilization of AlGaN-delta-GaN MQWs or ultra-thin AlN/GaN MQWs is beneficial for mitigating QCSE, raising electron-hole wavefunction overlap, and accordingly increasing internal quantum efficiency (IQE). [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] The performance of e-beam pumped light source and laser-based on these structures is also optimized. [24][25][26][27][28][29][30] Whereas, an over-thin QW structure at the monolayer (ML) level sometimes weakens carrier confinement capacity and contrarily decreases WPE.…”

“…[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] The performance of e-beam pumped light source and laser-based on these structures is also optimized. [24][25][26][27][28][29][30] Whereas, an over-thin QW structure at the monolayer (ML) level sometimes weakens carrier confinement capacity and contrarily decreases WPE. [25,32] Therefore, exploring a strategy to trade-off the carrier confinement capacity and electron-hole wavefunction overlap in ultra-thin MQW structure would be of significance to increase the WPE of wafer-sized DUVSE.…”

“…[17][18][19][20][21] Moreover, such low WPE results in a huge amount of heat at a large injection current and hinders the device's reliability, thus obstructing the fabrication of a highpower-density integrated UV light source.In order to disregard the above-mentioned issues, the electron beam-pumped deep-ultraviolet surface emitter (DUVSE) is proposed to increase the output power and avoid the conventional carrier injection layers. [22][23][24][25][26][27][28] The device merely consists of a carbon nanotube (CNT) field emitter and AlGaN multiple quantum wells (MQWs). This DUVSE announces plenty of advantages such as low emitted light re-absorption, [24] simple epitaxial structure, [23] and solo-device fabrication at wafer-scale.…”

Special Issue: Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices)

“…In the last article of this Special Issue [ 7 ], the authors demonstrated the possibility of plasma-assisted molecular beam epitaxy to fabricate multiple GaN/AlN quantum wells (MQWs) with heterostructures that can be used in high-power ultraviolet (UV) emitters pumped by an electron beam. The main feature of these heterostructures, which can emit in the sub-250 nm UVC spectral range, is the ultra-thin quantum wells with a nominal thickness of less than 2 mL.…”