Monolayer GaN excitonic deep ultraviolet light emitting diodes

Abstract

We report on the molecular beam epitaxy and characterization of monolayer GaN embedded in N-polar AlN nanowire structures. Deep ultraviolet emission from 4.85 to 5.25 eV is measured by varying the AlN barrier thickness. Detailed optical measurements and direct correlation with first-principles calculations based on density functional and many-body perturbation theory suggest that charge carrier recombination occurs predominantly via excitons in the extremely confined monolayer GaN/AlN heterostructures, with exciton binding energy exceeding 200 meV. We have further demonstrated deep ultraviolet light-emitting diodes (LEDs) with the incorporation of single and double monolayer GaN, which operate at 238 and 270 nm, respectively. These unique deep ultraviolet LEDs exhibit highly stable emission and a small turn-on voltage around 5 V.

Monolayer‐Thick GaN/AlN Multilayer Heterostructures for Deep‐Ultraviolet Optoelectronics

“…c-g) Reproduced with permission. [114] Copyright 2020, AIP Publishing. structure, as shown in Figure 18b.…”

“…In contrast to the earlier described 2D structures, alternative nanocolumnar heterostructures comprising GaN/AlN multiple quantum disks with a thickness of several MLs can be realized using PA MBE growth of self-assembled nanocolumns (also called nanorods or nanowires), which occurs practically on any substrate under highly N-enriched conditions at a relatively high T S ¼ 875 C. As a result, individual self-assembled GaN/AlN nanocolumns are formed with a typical density of %10 10 cm À2 , a diameter of %100 nm, and a height up to hundreds of nanometers. [112][113][114] In addition, GaN nanodisks can be fabricated by PA MBE in AlN nanorods grown on top of AlGaN nanorods formed by multistage postgrowth processing of planar AlGaN/AlN/c-Al 2 O 3 heterostructures originally grown using MOCVD. [115] Dry etching in an inductively coupled plasma, using silica nanospheres as masks, followed by wet etching and surface passivation, provides the formation of highly ordered individual nanocolumns with a typical bottom diameter of 500 nm and spacing between nanorods of about 100 nm.…”

“…The nanowires included multiple quantum disks with the nominal thickness of 1 or 2 ML, separated by 5 nm AlN barriers, and demonstrated both photo‐ and electroluminescence in a rather wide spectral range from 240 to 320 nm. In another work, Wu et al [ 114 ] demonstrated UV LEDs based on self‐assembled AlN nanowires including GaN quantum disks with the nominal thickness of 1 or 2 ML, which showed single peaks of electroluminescence at 238 and 270 nm, respectively, as shown in Figure 17c–g. The coincidence of the energies of these luminescence peaks with the exciton recombination energies in a single ML GaN/AlN QW, calculated by Bayerl et al, [ 69 ] allowed the authors to assume the excitonic nature of radiative recombination in these structures.…”

“…g) Normalized PL spectra for 1 ML (black) and 2 ML (red) GaN QW measured at RT. c-g) Reproduced with permission [114]. Copyright 2020, AIP Publishing.…”

Controlling Defect Formation of Nanoscale AlN: Toward Efficient Current Conduction of Ultrawide‐Bandgap Semiconductors

“…Ultrawide‐bandgap semiconductors, including AlN, BN, and diamond, are critical for applications in next‐generation high‐power, high‐frequency electronics, ultraviolet (UV) optoelectronics, high‐power photonics, and quantum devices and systems. [ 1–10 ] Progress in these fields, however, has been severely limited by the lack of scalable substrate, the presence of large densities of defects, and the extremely poor current conduction. [ 3,11,12 ] Moreover, it has remained challenging to achieve a precise control of impurity incorporation and defect formation in these ultrawide‐bandgap semiconductors, severely limiting their structural, electronic, optical, and quantum properties.…”