Polarity Control and Nanoscale Optical Characterization of AlGaN-Based Multiple-Quantum-Wells for Ultraviolet C Emitters

Abstract

Optical properties of AlGaN UVC multiple-quantum-wells (MQWs) with nanoscale inverted polarity domains are strongly related to polar surfaces and nanoscale structures. In this work, the impact of pregrowth nitridation of the sapphire substrate on the polarity control of UVC MQW is highlighted, and the optical properties of III- and N-polar domains were distinguished. Nanoscale cathodoluminescence peak separation of more than 30 nm is observed in lateral-polarity-structure (LPS) UVC MQWs, which is ascribed to the potential minima induced by the local variation of QW thickness and Ga enrichment inside N-polar domains. After an AlGaN/AlN superlattice is inserted and the V/III ratio is enhanced during growth, the surface morphology of the N-polar domain is greatly improved, leading to a single-peak emission at a wavelength of 275 nm in both the III- and N-polar domains, and a 10-fold stronger peak intensity at the inversion domain boundary. Such understandings on the polar surface optimization and underlying reasons of peak separation enable rational design for efficient UVC emitters with improved performance.

Coherent-interface-induced strain in large lattice-mismatched materials: A new approach for modeling Raman shift

“…( 7) with R GaN = 6.5 ± 0.3 and R AlN = 7.7 ± 0.4 can be used to correctly estimate the biaxial strain in IIInitrides via Raman spectroscopy. The considerable application potential of the present findings could benefit a broad readership interested in III-nitride-based optoelectronics and power electronics devices [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][85][86][87][88]].…”

“…Research in wide-bandgap III-nitride semiconductors continues to progress rapidly, especially for the materials with bandgap exceeding that of gallium nitride (3.4 eV). Specifically, III-nitride based heterostructures provide new opportunities for a wide range of research and device applications, such as piezotronics and piezophototronics [1], self-powered photoelectrochemical-type photodetectors [2], room-temperature quantum emitters [3], single photon emitters [4][5][6], resonant tunneling diodes [7], highelectron-mobility transistors [8,9], efficient photoelectrocatalysts for solar water splitting [10], multi-wavelength light-emitting diodes (LEDs) [11,12], and deep ultraviolet (DUV)-LEDs [13][14][15][16][17]. AlGaN-based DUV-LEDs represent a sustainable alternative to replace the environmentally harmful conventional mercury lamps [18] and thus, are becoming crucial for many applications such as water purification and/or inactivation of microorganisms, including bacteria, fungi, and viruses [19,20].…”

Si‐Doping Effects in AlGaN Channel Layer on Performance of N‐Polar AlGaN/AlN FETs

“…The carrier-transport properties of N-polar nitride semiconductors demonstrate emission enhancement of light-emitting diodes and other optical devices. [8,9] Previous simulations have shown that the N-polar AlGaN/AlN structure can be assumed to have a higher carrier density than conventional metal-polar AlGaN/GaN electronic devices. [10] In electronic devices, HEMTs using Al-polar AlN require an AlN cap layer owing to their polarization characteristics, making it difficult to reduce the contact resistance.…”

Evidence of Carrier Localization in AlGaN/GaN‐Based UV Multiple Quantum Wells with Opposite Polarity Domains Provided by Nanoscale Imaging

“…[19] Higher luminescence intensity was observed in N-polar than in III-polar domains, which can be ascribed to thickness fluctuations in N-polar domains as previously demonstrated by transmission electron microscopy (TEM). [20,21] However, it must be noted that in addition to that, composition fluctuation and strain variation also play critical roles in the carrier localization effect, which has never been investigated before and, thus, requires in-depth investigations, especially from the perspective of nanoscale mapping.…”