• Special Issue
  • Semiconductor UV Photonics
  • 11 Article (s)
MOVPE-grown AlGaN-based tunnel heterojunctions enabling fully transparent UVC LEDs
Christian Kuhn, Luca Sulmoni, Martin Guttmann, Johannes Glaab, Norman Susilo, Tim Wernicke, Markus Weyers, and Michael Kneissl
We report on AlGaN-based tunnel heterojunctions grown by metalorganic vapor phase epitaxy enabling fully transparent UVC LEDs by eliminating the absorbing p-AlGaN and p-GaN layers. Furthermore, the electrical characteristics can be improved by exploiting the higher conductivity of n-AlGaN layers as well as a lower resistance of n-contacts. UVC LEDs with AlGaN:Mg/AlGaN:Si tunnel junctions exhibiting single peak emission at 268 nm have been realized, demonstrating effective carrier injection into the AlGaN multiple quantum well active region. The incorporation of a low band gap interlayer enables effective tunneling and strong voltage reduction. Therefore, the interlayer thickness is systematically varied. Tunnel heterojunction LEDs with an 8 nm thick GaN interlayer exhibit continuous-wave emission powers >3 mW near thermal rollover. External quantum efficiencies of 1.4% at a DC current of 5 mA and operating voltages of 20 V are measured on-wafer. Laterally homogeneous emission is demonstrated by UV-sensitive electroluminescence microscopy images. The complete UVC LED heterostructure is grown in a single epitaxy process including in situ activation of the magnesium acceptors.
Photonics Research
  • Publication Date: Apr. 29, 2019
  • Vol.7 Issue, 5 050000B7 (2019)
Visible- and solar-blind photodetectors using AlGaN high electron mobility transistors with nanodot-based floating gate
Andrew M. Armstrong, Brianna A. Klein, Andrew A. Allerman, Albert G. Baca, Mary H. Crawford, Jacob Podkaminer, Carlos R. Perez, Michael P. Siegal, Erica A. Douglas, Vincent M. Abate, and Francois Leonard
AlGaN-channel high electron mobility transistors (HEMTs) were operated as visible- and solar-blind photodetectors by using GaN nanodots as an optically active floating gate. The effect of the floating gate was large enough to switch an HEMT from the off-state in the dark to an on-state under illumination. This opto-electronic response achieved responsivity >108 A/W at room temperature while allowing HEMTs to be electrically biased in the off-state for low dark current and low DC power dissipation. The influence of GaN nanodot distance from the HEMT channel on the dynamic range of the photodetector was investigated, along with the responsivity and temporal response of the floating gate HEMT as a function of optical intensity. The absorption threshold was shown to be controlled by the AlN mole fraction of the HEMT channel layer, thus enabling the same device design to be tuned for either visible- or solar-blind detection.
Photonics Research
  • Publication Date: May. 20, 2019
  • Vol.7 Issue, 6 06000B24 (2019)
GaN-based ultraviolet microdisk laser diode grown on Si
Jin Wang, Meixin Feng, Rui Zhou, Qian Sun, Jianxun Liu, Yingnan Huang, Yu Zhou, Hongwei Gao, Xinhe Zheng, Masao Ikeda, and Hui Yang
This work reports a demonstration of electrically injected GaN-based near-ultraviolet microdisk laser diodes with a lasing wavelength of 386.3 nm at room temperature. The crack-free laser structure was epitaxially grown on Si substrates using an Al-composed down-graded AlN/AlGaN multilayer buffer to mitigate the mismatches in the lattice constant and coefficient of thermal expansion, and processed into “sandwich-like” microdisk structures with a radius of 12 μm. Air-bridge electrodes were successfully fabricated to enable the device electrical characterization. The electrically pumped lasing of the as-fabricated microdisk laser diodes was evidenced by the rapid narrowing down of electroluminescence spectra and dramatic increase in the light output power, as the current exceeded the threshold of 248 mA.
Photonics Research
  • Publication Date: May. 22, 2019
  • Vol.7 Issue, 6 06000B32 (2019)
Current-induced degradation and lifetime prediction of 310  nm ultraviolet light-emitting diodes
Jan Ruschel, Johannes Glaab, Batoul Beidoun, Neysha Lobo Ploch, Jens Rass, Tim Kolbe, Arne Knauer, Markus Weyers, Sven Einfeldt, and Michael Kneissl
Photonics Research
  • Publication Date: Jun. 24, 2019
  • Vol.7 Issue, 7 07000B36 (2019)
1 Gbps free-space deep-ultraviolet communications based on III-nitride micro-LEDs emitting at 262 nm|On the Cover
Xiangyu He, Enyuan Xie, Mohamed Sufyan Islim, Ardimas Andi Purwita, Jonathan J. D. McKendry, Erdan Gu, Harald Haas, and Martin D. Dawson
The low modulation bandwidth of deep-ultraviolet (UV) light sources is considered as the main reason limiting the data transmission rate of deep-UV communications. Here, we present high-bandwidth III-nitride micro-light-emitting diodes (μLEDs) emitting in the UV-C region and their applications in deep-UV communication systems. The fabricated UV-C μLEDs with 566 μm2 emission area produce an optical power of 196 μW at the 3400 A/cm2 current density. The measured 3 dB modulation bandwidth of these μLEDs initially increases linearly with the driving current density and then saturates as 438 MHz at a current density of 71 A/cm2, which is limited by the cutoff frequency of the commercial avalanche photodiode used for the measurement. A deep-UV communication system is further demonstrated. By using the UV-C μLED, up to 800 Mbps and 1.1 Gbps data transmission rates at bit error ratio of 3.8×10 3 are achieved assuming on-off keying and orthogonal frequency-division multiplexing modulation schemes, respectively.
Photonics Research
  • Publication Date: Jun. 24, 2019
  • Vol.7 Issue, 7 07000B41 (2019)
Magnesium ion-implantation-based gallium nitride p-i-n photodiode for visible-blind ultraviolet detection
Weizong Xu, Yating Shi, Fangfang Ren, Dong Zhou, Linlin Su, Qing Liu, Liang Cheng, Jiandong Ye, Dunjun Chen, Rong Zhang, Youdou Zheng, and Hai Lu
In this work, a GaN p-i-n diode based on Mg ion implantation for visible-blind UV detection is demonstrated. With an optimized implantation and annealing process, a p-GaN layer and corresponding GaN p-i-n photodiode are achieved via Mg implantation. As revealed in the UV detection characterizations, these diodes exhibit a sharp wavelength cutoff at 365 nm, high UV/visible rejection ratio of 1.2×104, and high photoresponsivity of 0.35 A/W, and are proved to be comparable with commercially available GaN p-n photodiodes. Additionally, a localized states-related gain mechanism is systematically investigated, and a relevant physics model of electric-field-assisted photocarrier hopping is proposed. The demonstrated Mg ion-implantation-based approach is believed to be an applicable and CMOS-process-compatible technology for GaN-based p-i-n photodiodes.
Photonics Research
  • Publication Date: Jul. 15, 2019
  • Vol.7 Issue, 8 08000B48 (2019)
Review of encapsulation materials for AlGaN-based deep-ultraviolet light-emitting diodes
Yosuke Nagasawa, and Akira Hirano
This paper reviews and introduces the techniques for boosting the light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet (DUV: λ<300 nm) light-emitting diodes (LEDs) on the basis of the discussion of their molecular structures and optical characteristics, focusing on organoencapsulation materials. Comparisons of various fluororesins, silicone resin, and nonorgano materials are described. The only usable organomaterial for encapsulating DUV-LEDs is currently considered to be polymerized perfluoro(4-vinyloxy-1-butene) (p-BVE) terminated with a ─CF3 end group. By forming hemispherical lenses on DUV-LED dies using p-BVE having a ─CF3 end group with a refractive index of about 1.35, the LEE was improved by 1.5-fold, demonstrating a cost-feasible packaging technique.
Photonics Research
  • Publication Date: Aug. 01, 2019
  • Vol.7 Issue, 8 08000B55 (2019)
Deep ultraviolet light-emitting diodes based on well-ordered AlGaN nanorod array
Liang Zhang, Yanan Guo, Jianchang Yan, Qingqing Wu, Yi Lu, Zhuohui Wu, Wen Gu, Xuecheng Wei, Junxi Wang, and Jinmin Li
The nanorod structure is an alternative scheme to develop high-efficiency deep ultraviolet light-emitting diodes (DUV LEDs). In this paper, we first report the electrically injected 274-nm AlGaN nanorod array DUV LEDs fabricated by the nanosphere lithography and dry-etching technique. Nanorod DUV LED devices with good electrical properties are successfully realized. Compared to planar DUV LEDs, nanorod DUV LEDs present >2.5 times improvement in light output power and external quantum efficiency. The internal quantum efficiency of nanorod LEDs increases by 1.2 times due to the transformation of carriers from the exciton to the free electron–hole, possibly driven by the interface state effect of the nanorod sidewall surface. In addition, the nanorod array significantly facilitates photons escaping from the interior of LEDs along the vertical direction, contributing to improving light extraction efficiency. The three-dimensional finite-different time-domain simulation is performed to further analyze in detail the TE- and TM-polarized photons extraction mechanisms of the nanostructure. Our results demonstrate the nanorod structure is a good candidate for high-efficiency DUV emitters.
Photonics Research
  • Publication Date: Aug. 15, 2019
  • Vol.7 Issue, 9 09000B66 (2019)

UV light has been utilized by people in numerous critical applications for over 100 years. However, mainstream UV emitters and detectors are often bulky and inefficient. Recently, large investment and progress have been made by institutions and companies around the world to create and improve semiconductor materials, structures, and devices for more efficient generation and manipulation of UV light with a much smaller footprint and better reliability. This feature issue will cover modeling, experimentation, and applications related to UV photonics research and its applications.

This feature issue in Photonics Research will serve as a venue for the most recent publications in the increasingly popular research area of semiconductor ultraviolet (UV) photonics, which has found broad applications in sterilization, communication, sensing, curing, medical treatment, and national security.