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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.

We report on the effect of dry etching and the combination of metal stacks used to form ohmic contacts on silicon-doped high-Al-content (>60%) n-AlGaN layers for deep-ultraviolet light-emitting diodes. The contact characteristics are compared for as-grown and plasma-etched n-AlGaN samples. The Ti/Al/Ti/ Au contacts to as-grown n-AlGaN were linear, with a specific contact resistivity of 5 9 10 À5 X-cm 2 . The same metallic layer combinations yielded nonlinear contacts on the plasma-etched surface of the n-AlGaN layers. However, when Ni was used as the barrier layer instead of titanium, the contacts to plasma-etched AlGaN surfaces became linear, with a specific contact resistivity of 5 9 10 À4 X-cm 2 .

We propose and demonstrate a vertical-cavity surface-emitting laser structure that operates predominantly in the single fundamental transverse mode over a wide operation current range. In this laser structure, a microlens is integrated on top of an otherwise ordinary surface-emitting laser so that a small portion of laser output is fed back into the cavity, forcing the lasing to occur in the fundamental mode. Model calculations reproduce the observed mode selection effect.