We describe the photoresponse of GaN-based surface acoustic wave (SAW) delay-line oscillator operating in the 200 MHz range. The decrease in oscillator frequency under ultraviolet illumination of GaN transducer is caused by the SAW velocity decrease due to the acoustoelectronic interaction with photoconductivity electrons. The oscillator frequency shift reaches its maximum value at 365 nm and drops to zero above 400 nm with visible/ultraviolet rejection ratio more than 100. The optical quenching of the photoconductivity in GaN was observed. These results demonstrate the potential of the GaN-based SAW oscillators for applications as visible–blind remote UV sensors.

We present a study on the time evolution of the electroluminescence (EL) spectra of AlGaN-based deep ultraviolet light-emitting diodes (LEDs) under pulsed current pumping. The EL spectra peaks at 285 nm and 330 nm are found to result from recombination involving band-to-band and free carriers to deep acceptor level transitions. The 330 nm long-wavelength transitions to deep acceptor levels in the p-AlGaN layer as well as the nonradiative processes significantly influence the LED internal quantum efficiency.

We report on AlGaN single-quantum-well light-emitting diodes (LEDs) on sapphire with peak emission at 285 nm. A study is presented to identify the key material parameters controlling the device quantum efficiency. At room temperature, for a 200 μm×200 μm square geometry mesa type device, we obtain a power as high as 0.25 mW for 650 mA pulsed pumping. The LEDs show significantly higher output powers at temperatures below 100 K.

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Two types of novel ultraviolet-sensitive III-nitride based surface acoustic wave devices are presented. We demonstrate the Al x Ga 1-x N-based surface acoustic wave delay-line oscillator, which is applied as an ultraviolet sensor capable of solar-blind operation with remote wireless pickup of the output signal. Also, we report on the SAW-induced high-frequency resistance modulation effect, which is dramatically increased under ultraviolet illumination. Key wordsSurface acoustic waves; ultraviolet sensor; aluminum gallium nitride. INTRODUCTIONDue to the wide energy band gap, AlN, GaN, and their alloys are well suited for applications in near-visible and ultraviolet (UV) range optical sensors. These III-nitride group materials also possess strong piezoelectric properties, which make them attractive for surface acoustic wave (SAW) device applications. The SAW propagation properties in III-nitrides appear to be sensitive to UV radiation thus enabling the implementation of novel types of SAWbased UV sensors. The GaN-based SAW oscillator as a sensor for wavelengths 365 nm was previously demonstrated [1]. Such a SAW-based sensor has an advantage of the output signal in the radio-frequency format that makes the remote wireless pickup of the signal possible. There is a great interest in developing the solar-blind UV sensors, i.e. those with a reduced response at optical wavelengths longer than 300 nm. Using aluminum-gallium nitride, which allows one to control the band-gap energy by varying the compound composition, the spectral characteristic of the sensor response can be correspondingly adjusted. In this paper, we report on the Al x Ga 1-x N-based SAW oscillator and demonstrate differences in its responsivity at optical wavelengths above and below 300 nm. A perturbation by the SAW of photogenerated charge carrier system in III-nitride semiconductors lead to a variety of interesting effects, which have a potential for applications in UV sensors of new types. The remote collection and electrical measurement of photogenerated carriers swept by a SAW in GaN have been recently reported [2]. We have observed the high-frequency resistance modulation (HFRM) by surface acoustic wave under UV illumination [3]. Here we present a more detailed descrip-