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We report on the substrate laser lift-off (LLO) in lateral conduction flip-chip (FC) deep-UV light-emitting diodes (LEDs) with peak emission wavelength at 285 nm. The AlGaN-based LED epilayer structure was grown on a low-defect 2 m-thick AlN/sapphire template and processed into 3 Â 3 small periphery pixel-LED arrays. The total p-contact area of the 9 pixel, single chip devices was 180 Â 180 m 2 . Our results show that the use of FC die assembly with epoxy underfilling the gap between the chip and the submount dramatically increase the yield of damage-free debonding of sapphire and the overlying AlN layer. Equally important, no noticeable degradation of the electrical and optical characteristics of the thin-film light emitters was observed following the LLO process. #

We demonstrate high-external quantum efficiency (∼50%) solar-blind AlGaN p–n junction photodetectors with high-Al content multiple quantum wells (MQWs). A peak responsivity of 0.1 A/W at 250 nm, which falls >103 by 280 nm, indicates that the optical absorption is dominated by the MQW structures. At a reverse bias of 0.5 V, the dark current is <0.1 pA. The readout RC-limited time response is measured as 0.4 µs, and an achievable detector RC-limited time response of 2 ns is estimated. The devices do not show internal gain, which accounts for their high speed.

We report room-temperature to 200 °C operation of n-Al0.65Ga0.35N channel metal semiconductor field effect transistors (MESFET) grown over high-quality AlN/sapphire templates. For this temperature range, the source-drain currents, threshold voltages, and dc-transconductance values remain nearly unchanged with an estimated field-effect mobility of ∼90 cm2/V-s at 200 °C and currents of  &gt;100 mA/mm. The analysis of the temperature dependent current-voltage characteristics of the gate-source Schottky barrier diode reveals that the leakage currents arise from Frenkel-Poole emission. The capacitance-voltage data show no hysteresis, indicating a high quality Schottky barrier interface. These MESFET's have excellent potential for use as a high temperature power electronic or a solar-blind ultraviolet sensing device.

Charge transport in the wide band gap (Al,In)N/GaN heterostructures with high carrier density ~2 10 were investigated over a large range of temperature (280 mK < T < 280 K) and magnetic field (0 < B < 20 T). We observe the first evidences of weak localization in the two-dimensional electron gas in this system. From the Shubnikov-de Haas (SdH) oscillations a relatively light effective mass of ~0.23m e is determined. Furthermore the linear dependence with temperature (T < 20 K) of the inelastic scattering rate () is attributed to the phase breaking by electron-electron scattering. Also in the same temperature range the less than unit ratio of quantum lifetime than Hall transport time ⁄ 1 is taken to signify the dominance of small angle scattering. Above 20 K, with increasing temperature scattering changes from acoustic phonon to optical phonon scattering, resulting in a rapid decrease in carrier mobility and increase in sheet resistance. Suppression of such scatterings will lead to higher mobility and a way forward to high power and high frequency electronics. I.

We report on the fabrication of AlGaN‐based pseudomorphic light‐emitting diodes over sapphire substrate with peak emission at 275 nm. A 0.6 µm thick n‐AlGaN contact layer was grown using a novel pulsed silicon modulation doping technique, which enabled us to achieve a sheet resistance of ∼500Ω/□. In order to mitigate current crowding and Joule heating issues, we implemented the pixel‐LED design with a total p‐active area of 360 µm x 360 µm. Packaged devices exhibited light output powers of ∼7 mW at 100 mA dc pump current. The forward voltage was ∼ 8.8 V. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on AlGaN field effect transistors over AlN/sapphire templates with selective area grown n-Al0.5Ga0.5N channel layers for which a field-effect mobility of 55 cm2/V-sec was measured. Using a pulsed plasma enhanced chemical vapor deposition deposited 100 A thick SiO2 layer as the gate-insulator, the gate-leakage currents were reduced by three orders of magnitude. These devices with or without gate insulators are excellent solar-blind ultraviolet detectors, and they can be operated either in the photoconductive or the photo-voltaic modes. In the photo-conductive mode, gain arising from hole-trapping in the depletion region leads to steady-state photoresponsivity as high as 1.2 × 106A/W at 254 nm, which drops sharply below 290 nm. A hole-trapping limited detector response time of 34 ms, fast enough for real-time flame-detection and imaging applications, was estimated.