Search

The detection of ultraviolet B (UVB) and UVC radiation is of paramount importance, and has expanding applications in industrial, scientific, environmental and biomedical fields. In this work, high-Al-content β-(Al0.4Ga0.6)2O3/Al0.32Ga0.68N films prepared via a thermal oxidation process from AlGaN layers are employed to fabricate UVC/UVB dual-band photodetectors (PDs). The PDs achieve two responsivity peaks at ∼200 nm and 305 nm, and also exhibit tunable dual-band photodetection, which can operate in separate UVB-dominated, UVC/UVB broadband and UVC-dominated detection modes by modulating the bias voltage from 10 V to 25 V. In particular, the PDs exhibit a responsivity (R) of 0.35 A W−1, detectivity of 2.46 × 1012 Jones, UVC/UVA rejection ratio (R200/R365) of 70 and UVC/visible rejection ratio (R200/R500) of 106 with an external quantum efficiency of 219% under 200 nm light illumination at 25 V bias, demonstrating good comprehensive performance over the UVC band. The tunable dual-band detection capability can be ascribed to the effect of increasing bias voltage on lowering the barrier height between electrodes and the (AlxGa1−x)2O3 layer, promoting the photogenerated electrons in (AlxGa1−x)2O3 films to easily cross over the reduced barrier height and contributing to the UVC detection. In addition to providing a facile, economical and feasible way to fabricate UVC/UVB tunable dual-band PDs via bias voltage regulation, this work is also expected to inspire further exploration on developing versatile and high-performance multi-band PDs. [ABSTRACT FROM AUTHOR]

Semipolar AlGaN multiple quantum wells (MQWs) have unique advantages in deep ultraviolet light emitters due to the weak Quantum-Confined Stark Effect. However, their applications are hampered by the poor crystalline quality of semipolar AlGaN thin films. Different treatments were developed to improve the crystal quality of semipolar AlGaN, including a multistep in situ thermal annealing technique proposed by our group. In this work, temperature-dependent and time-resolved photoluminescence characterizations were performed to reveal the carrier localization in the MQW region. The degree of carrier localization in semipolar AlGaN MQWs grown on top of the in situ-annealed AlN is similar to that of conventional ex situ face-to-face annealing, both of which are significantly stronger than that of the c-plane counterpart. Moreover, MQWs on in situ-annealed AlN show drastically reduced dislocation densities, demonstrating its great potential for the future development of high-efficiency optoelectronic devices. [ABSTRACT FROM AUTHOR]

Strain evolution of AlN grown on hole‐type (HT) and pillar‐type (PT) nanopatterned sapphire substrates (NPSSs) during the epitaxial lateral overgrowth process is comparably studied. It is found that, after complete coalescence, the residual strain of AlN on HT‐NPSS is tensile, whereas AlN on PT‐NPSS is almost strain free. The different strain states are associated with different behaviors of crystal merging during the lateral overgrowth process, depending on the type of pattern. Then, ultraviolet‐C (UVC) light‐emitting diode (LED) wafers are grown on two types of AlN templates with the distinctive strain states. It is confirmed that AlN on HT‐NPSS with tensile strain offers the advantage of producing a high‐quality AlGaN layer with a fairly flat surface, which is the key point for fabricating high‐performance UVC LEDs. [ABSTRACT FROM AUTHOR]

An optically pumped AlGaN-based vertical-cavity surface-emitting laser (VCSEL) in the deep ultraviolet (DUV) range (< 280 nm) is demonstrated. The lasing wavelength is 275.91 nm with a threshold power density of 1.21 MW/cm2 and a linewidth of 0.78 nm. The lasing is believed to be benefited from high internal quantum efficiency (IQE) of the AlGaN-based multiple quantum wells (MQWs) and improved fabrication processes. [ABSTRACT FROM AUTHOR]

The world‐wide spreading of coronavirus disease (COVID‐19) has greatly shaken human society, thus effective and fast‐speed methods of non‐daily‐life‐disturbance sterilization have become extremely significant. In this work, by fully benefitting from high‐quality AlN template (with threading dislocation density as low as ≈6×108 cm−2) as well as outstanding deep ultraviolet (UVC‐less than 280 nm) light‐emitting diodes (LEDs) structure design and epitaxy optimization, high power UVC LEDs and ultra‐high‐power sterilization irradiation source are achieved. Moreover, for the first time, a result in which a fast and complete elimination of SARS‐CoV‐2 (the virus causes COVID‐19) within only 1 s is achieved by the nearly whole industry‐chain‐covered product. These results advance the promising potential in UVC‐LED disinfection particularly in the shadow of COVID‐19. [ABSTRACT FROM AUTHOR]

In this work, the influences of thermal annealing and chemical passivation on the optical and electrical properties of ultraviolet light-emitting-diode (UV-LED) were investigated. The electroluminescence (EL) intensities of the LEDs under KOH treatment and thermal annealing increased by 48% and 81%, respectively compared to as-fabricated LED under current level of 10 mA. Cathodoluminescence (CL) mapping of UV-LEDs confirmed no variation of the density of the non-radiative recombination centers after surface treatments, and no obvious change in surface morphology was identified due to lacking of energy for surface atom migration. However, Raman spectroscopy indicates a relaxation of compressive strains inside the thin film after both thermal and chemical treatments, and conductive atomic force microscopy (c-AFM) also illustrated reduced leakage current after KOH passivation, which are responsible for the improved luminescence properties of UV-LEDs. [ABSTRACT FROM AUTHOR]

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, despite the non-uniformity of the thickness and composition of the multiple quantum wells (MQWs) on the sidewall. An efficient carrier confinement and, thus, a high luminescence intensity were demonstrated in the middle of the sidewall through spatial-resolved cathodoluminescence (CL) characterization and were predicted by theoretical simulations. An ultra-high output power density of 1.37 kW/cm2 was obtained from the single μ-LED pyramid, illustrating its great potential for application in high-brightness micro-displays and in virtual reality and augmented reality (VR and AR) applications. [ABSTRACT FROM AUTHOR]

In this Letter, a record modulation bandwidth of 1.31 GHz was achieved by a 10 µm c-plane green micro light emitting diode (micro-LED) at a current density of 41.4 kA/cm 2 . Furthermore, by designing a series-biased 20 µm micro-LED with higher light output power, combined with an orthogonal frequency division multiplexing modulation scheme, a maximum data rate of 5.789 Gbps was achieved at a free-space transmission distance of 0.5 m. This work demonstrates the prospect of c-plane polar green micro-LED in ultrahigh-speed visible light communication, which is expected to realize a high-performance wireless system in the future.

The ${{\rm MoO}&#95;{\rm x}}/{\rm Al}$MoO x /Al electrode was designed and fabricated on p-GaN and sapphire with good ohmic behavior and decent deep ultraviolet (DUV) reflectivity, respectively. The influences of ${{\rm MoO}&#95;{\rm x}}$MoO x thickness and annealing condition on the electrical and optical behaviors of the ${{\rm MoO}&#95;{\rm x}}/{\rm Al}$MoO x /Al structure were investigated. Surface morphology of ${{\rm MoO}&#95;{\rm x}}$MoO x with different thicknesses reveals a 3D growth mode. Partial decomposition of ${{\rm MoO}&#95;{\rm x}}$MoO x was discovered, which helps in the formation of ohmic contact between ${{\rm MoO}&#95;{\rm x}}$MoO x and Al. The potential for application in deep ultraviolet light-emitting-diodes (DUV-LEDs) has also been demonstrated.

The optical properties of hexagonal GaN microdisk arrays grown on sapphire substrates by selective area growth (SAG) technique were investigated both experimentally and theoretically. Whispering-gallery-mode (WGM) lasing is observed from various directions of the GaN pyramids collected at room temperature, with the dominant lasing mode being Transverse-Electric (TE) polarized. A relaxation of compressive strain in the lateral overgrown region of the GaN microdisk is illustrated by photoluminescence (PL) mapping and Raman spectroscopy. A strong correlation between the crystalline quality and lasing behavior of the GaN microdisks was also demonstrated.