Ultraviolet-sensitive AlGaN-based surface acoustic wave devices

Abstract

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-

Surface acoustic wave-based ultraviolet photodetectors: a review

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