An electrically injected AlGaN nanowire laser operating in the ultraviolet-C band

Zhao, Songrui; Liu, X.; Woo, Steffi Y.; Kang, Junjie; Botton, Gianluigi A.; Mi, Zetian

doi:10.1063/1.4927602

Cited by 86 publications

(69 citation statements)

References 32 publications

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“…[18][19][20][21][22] Recent studies have shown that spontaneously formed AlGaN nanowire heterostructures with significantly improved optical and electrical properties can be realized via catalyst-free molecular beam epitaxy (MBE). [23][24][25][26][27][28][29][30][34][35][36][37][38] wavelengths of LEDs and lasers using such spontaneously formed AlGaN nanowires have been limited to 250 nm, or longer. 28,35 In the growth process of such spontaneously formed AlGaN nanowires, it involves the use of highly nitrogen rich conditions to promote the formation and nucleation of nanowire structures.…”

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confidence: 99%

“…[23][24][25][26][27][28][29][30][34][35][36][37][38] wavelengths of LEDs and lasers using such spontaneously formed AlGaN nanowires have been limited to 250 nm, or longer. 28,35 In the growth process of such spontaneously formed AlGaN nanowires, it involves the use of highly nitrogen rich conditions to promote the formation and nucleation of nanowire structures. However, due to the stronger binding energy of Al-N bond compared to Ga-N bond, 39 this nitrogen rich environment significantly reduces the Al adatom diffusion length, leading to highly nonuniform Al and Ga incorporation, which is evidenced by the commonly observed core-shell structures in AlGaN nanowires, 24,27,30,34,38 and the presence of significant compositional nonuniformity at the nano- 24,25,38,40 and atomic-scale.…”

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confidence: 99%

“…However, due to the stronger binding energy of Al-N bond compared to Ga-N bond, 39 this nitrogen rich environment significantly reduces the Al adatom diffusion length, leading to highly nonuniform Al and Ga incorporation, which is evidenced by the commonly observed core-shell structures in AlGaN nanowires, 24,27,30,34,38 and the presence of significant compositional nonuniformity at the nano- 24,25,38,40 and atomic-scale. 34,35 This nonuniform Al and Ga incorporation significantly limits the wavelength tunability of AlGaN ternary nanowires in the UV-C band and prevents the realization of devices operating at a shorter wavelength.…”

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confidence: 99%

“…Figure 1(a) shows the schematic of the growth of AlGaN nanowire segment on such GaN nanowire template. For the growth of AlGaN segment, in order to enhance the Al migration, nitrogen flow rate was reduced to 0.4 standard cubic centimetre per minute (SCCM) compared to the previously reported value of 1 SCCM, 24,25,28,34,35 while both Al and Ga BEPs were kept at 2 × 10 −8 Torr and substrate temperature (thermocouple reading) was in the range of 895-960…”

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Molecular beam epitaxy growth of Al-rich AlGaN nanowires for deep ultraviolet optoelectronics

et al. 2016

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Self-organized AlGaN nanowires by molecular beam epitaxy have attracted significant attention for deep ultraviolet optoelectronics. However, due to the strong compositional modulations under conventional nitrogen rich growth conditions, emission wavelengths less than 250 nm have remained inaccessible. Here we show that Al-rich AlGaN nanowires with much improved compositional uniformity can be achieved in a new growth paradigm, wherein a precise control on the optical bandgap of ternary AlGaN nanowires can be achieved by varying the substrate temperature. AlGaN nanowire LEDs, with emission wavelengths spanning from 236 to 280 nm, are also demonstrated.

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Molecular beam epitaxy growth of Al-rich AlGaN nanowires for deep ultraviolet optoelectronics

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“…By exploiting the light localization effect in randomly arranged AlGaN nanowires, lasing phenomenon by direct electrical injection has been demonstrated for the first time in the deep UV bands [50,[92][93][94]. The layer-by-layer structure in each individual nanowire is shown in Figure 11a, which consists of the n-GaN contact layer, n-AlGaN cladding layer, AlGaN active region, p-AlGaN cladding layer, and p-GaN contact layer.…”

Section: Electrically-injected Deep Uv Lasersmentioning

confidence: 99%

Recent Advances on p-Type III-Nitride Nanowires by Molecular Beam Epitaxy

Zhao

2017

Crystals

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p-Type doping represents a key step towards III-nitride (InN, GaN, AlN) optoelectronic devices. In the past, tremendous efforts have been devoted to obtaining high quality p-type III-nitrides, and extraordinary progress has been made in both materials and device aspects. In this article, we intend to discuss a small portion of these processes, focusing on the molecular beam epitaxy (MBE)-grown p-type InN and AlN-two bottleneck material systems that limit the development of III-nitride near-infrared and deep ultraviolet (UV) optoelectronic devices. We will show that by using MBE-grown nanowire structures, the long-lasting p-type doping challenges of InN and AlN can be largely addressed. New aspects of MBE growth of III-nitride nanostructures are also discussed.

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Carrier Localization at Atomic‐Scale Compositional Fluctuations in Single AlGaN Nanowires with Nano‐Cathodoluminescence

Woo

Tizei

Bugnet

et al. 2016

European Microscopy Congress 2016: Proceedings

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Considerable interest has been generated to develop highly efficient deep ultraviolet (DUV) emitters using AlGaN‐based alloys with direct bandgaps between 3.4 – 6.1 eV for a broad range of applications. Conventional planar AlGaN DUV devices, such as electrically injected solid‐state lasers and light‐emitting diodes, experience limited efficiencies due to the high dislocation density and inefficient p ‐doping with increasing Al‐content using Mg. Nanowire (NW) structures can be a promising alternative to enhance strain relaxation and p ‐doping, both mediated by the additional free surfaces. Exceptionally high internal quantum efficiencies have been reported in high Al‐content AlGaN NWs [1, 2], suggesting strong charge carrier confinement at nanoscale kinetically‐driven alloy inhomogeneities [3] that behave optically as quantum dots [4]. Recently, atomic‐scale compositional modulations have been reported in high Al‐content AlGaN NWs and suggested to act as localization centers to enhance radiative recombination [1, 2]. Comprehensive understanding of emission characteristics in such spontaneously‐formed compositional fluctuations in AlGaN NWs, from directly correlating the localized optical response to structural/chemical properties at relevant lengthscales is still lacking. High and low Al‐content Al x Ga 1‐x N p‐i‐n homojunctions were grown on Si‐doped GaN NW templates on Si(111) substrates by plasma‐assisted molecular beam epitaxy. Characterization on single NWs using nanometer‐scale cathodoluminescence (CL) spectral imaging at 150 K was performed [5], subsequently correlated to structural information obtained with aberration‐corrected scanning transmission electron microscopy (STEM). The low‐Al AlGaN NWs (Sample A, nominally x = 0.11) exhibit an Al‐rich shell that can passivate the surface. A high degree of homogeneity within the AlGaN core region is observed from high‐angle annular dark‐field (HAADF) Z‐contrast imaging, and is further confirmed with electron energy‐loss spectroscopy (EELS) [2]. Individual NWs in Sample A show the presence of up to three emission peaks highly delocalized along the NW length (Fig. 1f–h), two peaks originate from the AlGaN region (sharp 336 nm band‐edge peak, broad and asymmetric peak with 360 nm maximum), and one from the n ‐GaN base (~355 nm). With increased Al concentration (Sample B, nominally x = 0.88), extensive atomic‐scale HAADF intensity fluctuations are present in the AlGaN regions, and these are indicative of strong Ga‐rich/Al‐rich compositional modulations, as validated using EELS elemental mapping at atomic‐resolution [2]. The nature of the laterally discontinuous compositional fluctuations varies between p ‐, i ‐, n ‐doped AlGaN regions (Fig. 2a–e): single atomic layers occurring on c ‐planes along the growth direction in p ‐AlGaN and on semi‐polar {10‐13} planes in i ‐ and n ‐AlGaN. Other nm‐sized modulations and segregation are also observed. NWs in Sample B display a spectrally dense series of narrow lines blue‐shifted (230 – 300 nm), and are drastically more spatially localized within the AlGaN regions in the wavelength‐filtered CL images, relative to Sample A. Subsequent high‐resolution (HR)STEM on these NWs shows that the different spectral behaviors (emission energy) can be correlated to positions along the NW with different types of compositional fluctuations. Specifically, the shortest wavelength peaks (230 – 240 nm) originate from volumes with atomic‐scale Ga‐rich c ‐planes in p ‐AlGaN (Fig. 2c, ROI 1 circled in 2g), while high intensity sharp peaks (250 – 290 nm) can be assigned to regions with atomic‐scale modulations on inclined {10‐13} planes or other nm‐sized segregation (Fig. 2b,d). The presence/absence of extended defects and its role as localization centers will also be discussed [6].

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An electrically injected AlGaN nanowire laser operating in the ultraviolet-C band

Cited by 86 publications

References 32 publications

Molecular beam epitaxy growth of Al-rich AlGaN nanowires for deep ultraviolet optoelectronics

Molecular beam epitaxy growth of Al-rich AlGaN nanowires for deep ultraviolet optoelectronics

Recent Advances on p-Type III-Nitride Nanowires by Molecular Beam Epitaxy

Carrier Localization at Atomic‐Scale Compositional Fluctuations in Single AlGaN Nanowires with Nano‐Cathodoluminescence

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