Alias, Mohd Sharizal; Liu, Zhixiong; Alatawi, Abdullah; Ng, Tien Khee; Wu, Tao; Ooi, Boon S.(Conference on Lasers and Electro-Optics, The Optical Society, 2017-05-08)[Conference Paper]
We demonstrate the lasing of a perovskite vertical-cavity surface-emitting laser at green wavelengths, which operates under continuous-wave optical pumping at room-temperature by embedding hybrid perovskite between dielectric mirrors deposited at low-temperature.
Lee, It Ee; Guo, Yong; Ng, Tien Khee; Park, Kihong; Alouini, Mohamed-Slim; Ooi, Boon S.(Conference on Lasers and Electro-Optics, The Optical Society, 2017-05-08)[Conference Paper]
We demonstrate a gigabit near-infrared-based underwater wireless optical communication link using an 808-nm laser diode to mitigate the particle scattering effect in turbid medium. An improvement in the error performance is observed with increasing concentrations.
Janjua, Bilal; Sun, Haiding; Zhao, Chao; Anjum, Dalaver H.; Priante, Davide; Alhamoud, Abdullah; Wu, Feng-Yu; Li, Xiaohang; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Ng, Tien Khee; Ooi, Boon S.(Optics Express, The Optical Society, 2017-01-18)[Article]
Currently the AlGaN-based ultraviolet (UV) solid-state lighting research suffers from numerous challenges. In particular, low internal quantum efficiency, low extraction efficiency, inefficient doping, large polarization fields, and high dislocation density epitaxy constitute bottlenecks in realizing high power devices. Despite the clear advantage of quantum-confinement nanostructure, it has not been widely utilized in AlGaN-based nanowires. Here we utilize the self-assembled nanowires (NWs) with embedding quantum-disks (Qdisks) to mitigate these issues, and achieve UV emission of 337 nm at 32 A/cm (80 mA in 0.5 × 0.5 mm device), a turn-on voltage of ∼5.5 V and droop-free behavior up to 120 A/cm of injection current. The device was grown on a titanium-coated n-type silicon substrate, to improve current injection and heat dissipation. A narrow linewidth of 11.7 nm in the electroluminescence spectrum and a strong wavefunctions overlap factor of 42% confirm strong quantum confinement within uniformly formed AlGaN/AlGaN Qdisks, verified using transmission electron microscopy (TEM). The nitride-based UV nanowires light-emitting diodes (NWs-LEDs) grown on low cost and scalable metal/silicon template substrate, offers a scalable, environment friendly and low cost solution for numerous applications, such as solid-state lighting, spectroscopy, medical science and security.
In this paper, we describe ultraviolet-A (UV-A) light-emitting diodes (LEDs) emitting at 325 nm based on a highly uniform structure of quantum-confined AlGaN quantum-disk nanowires (NWs). By incorporating a 20 nm TaN interlayer between a Ti pre-orienting layer and the silicon substrate, we eliminated the potential barrier for carrier injection and phonon transport, and inhibited the formation of interfacial silicide that led to device failure. Compared to previous reports on metal substrate, we achieved a 16 × reduction in root-mean-square (RMS) roughness, from 24 nm to 1.6 nm, for the samples with the Ti/TaN metal-bilayer, owing to the effective diffusion barrier characteristic of TaN. This was confirmed using energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). We achieved a considerable increase in the injection current density (up to 90 A/cm2) compared to our previous studies, and an optical power of 1.9 μW for the 0.5 × 0.5 mm2 NWs-LED. This work provides a feasible pathway for both a reliable and stable UV-A device operation at elevated current injection, and eventually towards low-cost production of UV devices, leveraging on the scalability of silicon substrates.
Alias, Mohd Sharizal; Liu, Zhixiong; Alatawi, Abdullah; Ng, Tien Khee; Wu, Tao; Ooi, Boon S.(Optics Letters, The Optical Society, 2017-09-11)[Article]
We report an optically pumped green perovskite vertical-cavity surface-emitter operating in continuous-wave (CW) with a power density threshold of ~89 kW/cm2. The device has an active region of CH3NH3PbBr3 embedded in a dielectric microcavity; this feat was achieved with a combination of optimal spectral alignment of the optical cavity modes with the perovskite optical gain, an adequate Q-factor of the microcavity, adequate thermal stability, and improved material quality with a smooth, passivated, and annealed thin active layer. Our results signify a way towards efficient CW perovskite emitter operation and electrical injection using low-cost fabrication methods for addressing monolithic optoelectronic integration and lasing in the green gap.
Tangi, Malleswararao; Shakfa, Mohammad Khaled; Mishra, Pawan; Li, Ming-yang; Chiu, Ming-Hui; Ng, Tien Khee; Li, Lain-Jong; Ooi, Boon S.(Optical Materials Express, The Optical Society, 2017-09-22)[Article]
We report an unusual thermal quenching of the micro-photoluminescence (µ-PL) intensity for a sandwiched single-layer (SL) MoS2. For this study, MoS2 layers were chemical vapor deposited on molecular beam epitaxial grown In0.15Al0.85N lattice matched templates. Later, to accomplish air-stable sandwiched SL-MoS2, a thin In0.15Al0.85N cap layer was deposited on the MoS2/In0.15Al0.85N heterostructure. We confirm that the sandwiched MoS2 is a single layer from optical and structural analyses using µ-Raman spectroscopy and scanning transmission electron microscopy, respectively. By using high-resolution X-ray photoelectron spectroscopy, no structural phase transition of MoS2 is noticed. The recombination processes of bound and free excitons were analyzed by the power-dependent µ-PL studies at 77 K and room temperature (RT). The temperature-dependent micro photoluminescence (TDPL) measurements were carried out in the temperature range of 77 – 400 K. As temperature increases, a significant red-shift is observed for the free-exciton PL peak, revealing the delocalization of carriers. Further, we observe unconventional negative thermal quenching behavior, the enhancement of the µ-PL intensity with increasing temperatures up to 300K, which is explained by carrier hopping transitions that take place between shallow localized states to the band-edges. Thus, this study renders a fundamental insight into understanding the anomalous thermal quenching of µ-PL intensity of sandwiched SL-MoS2.
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