Rapid advancement of wide-bandgap AlGaN semiconductor materials offers tremendous opportunities in the field of ultraviolet (UV) optoelectronics for a wide range of advanced applications. ...Additionally, SiC has large bandgap and excellent material properties, also making itself a suitable material for UV photodetection. More importantly, high-quality AlGaN alloys can be epitaxially grown on SiC substrates because of the very small lattice mismatch between them (less than 1%), which enables a possible monolithic integration of those two materials and allows us to take advantage of their material and physical properties to realize high-performance UV optoelectronics and eventually the integrated UV photonics systems. Herein, we review the recent progress in the development of UV optoelectronics based on AlGaN-SiC platform, mainly focusing on: (1) the growth strategies and material characterizations of AlGaN epilayers on SiC; (2) the fabrication and performance evaluation of UV optoelectronic devices built on the platform, including UV LEDs/lasers and UV photodetectors. Thereafter, we briefly discuss the initial efforts in the pursuit of monolithic integration of those UV optoelectronic devices. Finally, the challenges and potential advances associated with individual UV optoelectronic components as well as UV integrated photonics system on the prosperous AlGaN-SiC platform are outlined, providing insights and perspectives for possible device- and system-level innovation in future.
The recent advances in the development of ultraviolet light emitters (LED, lasers) and photodetectors on the AlGaN-SiC platform are reviewed. By taking advantage of the extreme small lattice mismatch between the two wide bandgap semiconductors - AlGaN and SiC, together with their compatible physical and material properties, a monolithic ultraviolet photonics integration system can be built on the AlGaN-SiC platform. Display omitted
•AlGaN and SiC are recognized as two most promising wide bandgap semiconductors for UV optoelectronics applications.•AlGaN and SiC can be integrated to form AlGaN-SiC platform for the monolithic UV photonics integration system.•This review provides a comprehensive summary of the recent advancement of UV optoelectronics based on the AlGaN-SiC platform.•The outlooks and challenges in device- and system-level innovation of UV optoelectronics on AlGaN-SiC platform are discussed.
Flexible electronic and photonic devices have received broad interest in the past, due to their compact size, new functionalities, and other merits which devices on rigid substrates do not possess. ...In this context, the author review recent progresses on flexible III‐nitride nanowire photonic devices, focusing on LEDs and lasers. The formation of III‐nitride nanowire LEDs and lasers directly on various foreign substrates is firstly described, paving the way to flexible III‐nitride nanowire photonic devices through either direct growth on or transfer to flexible substrates. The realization of flexible III‐nitride nanowire LEDs through various transfer processes is further detailed. In the end, the challenges of III‐nitride nanowire technology for flexible integrated photonics are discussed.
Group III‐nitrides and their alloys possess a tunable energy bandgap from 0.65 to 6.1 eV, enabling various light emitting devices. Dislocation‐free nitride nanowires can be formed virtually on any unconventional substrates, not only on rigid substrates but also flexible substrates like metal foil and 2D materials. Thus, those direct growth approaches or nanowire transfer techniques represent a viable path towards III‐nitride nanowire‐based flexible photonics.
High‐quality epitaxy consisting of Al1−xGaxN/Al1−yGayN multiple quantum wells (MQWs) with sharp interfaces and emitting at ≈280 nm is successfully grown on sapphire with a misorientation angle as ...large as 4°. Wavy MQWs are observed due to step bunching formed at the step edges. A thicker QW width accompanied by a greater accumulation of gallium near the macrostep edge than that on the flat‐terrace is observed on 4° misoriented sapphire, leading to the generation of potential minima with respect to their neighboring QWs. Consequently, a significantly enhanced photoluminescence intensity (at least ten times higher), improved internal quantum efficiency (six times higher at low excitation laser power), and a much longer carrier lifetime are achieved. Importantly, the wafer‐level output‐power of the ultraviolet light emitting diodes on 4° misoriented substrate is nearly increased by 2–3 times. This gain is attributed to the introduction of compositional inhomogeneities in AlGaN alloys induced by gallium accumulation at the step‐bunched region thus forming a lateral potential well for carrier localization. The experimental results are further confirmed by a numerical modeling in which a 3D carrier confinement mechanism is proposed. Herein, the compositional modulation in active region arising from the substrate misorientation provides a promising approach in the pursuit of high‐efficient ultraviolet emitters.
Enhanced ultraviolet luminescence of AlGaN wavy‐quantum‐wells grown on large misoriented sapphires is demonstrated, enabled by the successful introduction of compositional inhomogeneities in AlGaN alloys induced by gallium accumulation and thus forming a 3D carrier confinement for radiative recombination. Herein, the compositional modulation in active region arising from large misoriented‐substrate offers a promising approach in the pursuit of high‐efficient ultraviolet emitters.
Mercury-free semiconductor deep ultraviolet light-emitting diodes (DUV-LEDs) still suffer from low power efficiencies due to extremely poor light extraction efficiency. In this paper, a ...high-reflective electrode is proposed and carefully optimized for making an ohmic contact with the n-type AlGaN layer in the DUV-LEDs (~280 nm). The electrode is made of Cr/120-nm Al metal stack with a different thickness of the Cr layer in a range of 1-20 nm followed by the complete LED fabrication process. We found that the DUV-LED with a 1-nm Cr/120-nm Al electrode obtains maximum light output power and the highest external quantum efficiency, showing an enhancement factor of 40.9% and 25.4%, respectively, in comparison to a conventional LED with an electrode made of 20-nm Cr/120-nm Al. This enhancement is mainly attributed to a higher UV reflectivity of the 1-nm Cr/120-nm Al electrode. Furthermore, a better ohmic contact was achieved in such electrode due to the formation of higher quality Al-Cr and Cr-N alloys in such metal/n-AlGaN junction.
Abstract
III–V semiconductor nanowires are indispensable building blocks for nanoscale electronic and optoelectronic devices. However, solely relying on their intrinsic physical and material ...properties sometimes limits device functionalities to meet the increasing demands in versatile and complex electronic world. By leveraging the distinctive nature of the one-dimensional geometry and large surface-to-volume ratio of the nanowires, new properties can be attained through monolithic integration of conventional nanowires with other easy-synthesized functional materials. Herein, we combine high-crystal-quality III-nitride nanowires with amorphous molybdenum sulfides (a-MoS
x
) to construct III-nitride/a-MoS
x
core-shell nanostructures. Upon light illumination, such nanostructures exhibit striking spectrally distinctive photodetection characteristic in photoelectrochemical environment, demonstrating a negative photoresponsivity of −100.42 mA W
−1
under 254 nm illumination, and a positive photoresponsivity of 29.5 mA W
−1
under 365 nm illumination. Density functional theory calculations reveal that the successful surface modification of the nanowires via a-MoS
x
decoration accelerates the reaction process at the electrolyte/nanowire interface, leading to the generation of opposite photocurrent signals under different photon illumination. Most importantly, such polarity-switchable photoconductivity can be further tuned for multiple wavelength bands photodetection by simply adjusting the surrounding environment and/or tailoring the nanowire composition, showing great promise to build light-wavelength controllable sensing devices in the future.
Aluminum‐gallium‐nitride alloys (Al
x
Ga1–
x
N, 0 ≤ x ≤ 1) can emit light covering the ultraviolet spectrum from 210 to 360 nm. However, these emitters have not fulfilled their full promise to ...replace the toxic and fragile mercury UV lamps due to their low efficiencies. This study demonstrates a promising approach to enhancing the luminescence efficiency of AlGaN multiple quantum wells (MQWs) via the introduction of a lateral‐polarity structure (LPS) comprising both III and N‐polar domains. The enhanced luminescence in LPS is attributed to the surface roughening, and compositional inhomogeneities in the N‐polar domain. The space‐resolved internal quantum efficiency (IQE) mapping shows a higher relative IQE in N‐polar domains and near inversion domain boundaries, providing strong evidence of enhanced radiative recombination efficiency in the LPS. These experimental observations are in good agreement with the theoretical calculations, where both lateral and vertical band diagrams are investigated. This work suggests that the introduction of the LPS in AlGaN‐based MQWs can provide unprecedented tunability in achieving higher luminescence performance in the development of solid state light sources.
The micro‐photoluminescence (µ‐PL) mapping of the lateral‐polarity structure samples with a color bar (left) represents the integrated emission intensity from multiple AlGaN quantum wells. N‐polar wells shows higher PL intensity than III‐polar wells. Right: Atomic resolution scanning transmission electron microscopy images in the N‐polar and III‐polar domains, where polarity can be clearly identified.
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