Deep-UV LED controlled AlGaN-based SAW oscillator

Abstract

We have demonstrated the possibility of controlling the frequency of an AlGaN-based SAW delay-line oscillator by LEDs emitting in deep UV range. The energy bandgap of AlGaN corresponded to the cutoff wavelength of 270 nm. The deep UV LEDs used in these experiments were supplied by Sensor Electronic Technology, Inc. and had the photon energies 265 nm and 305 nm. We also used 375 nm LED from Ni-chia Corporation. The SAW delay-line oscillator had the SAW delay line between the output and input of an RF wide-band amplifier. Illumination of the SAW propagation path by a UV LED resulted in the downshift of the oscillator frequency. We attribute this shift to the interaction of the SAW with photoexcited carriers in the AlGaN layer. The responsivity of the SAW oscillator significantly varied with the LED wavelength and was slightly dependent on the incident optical power. At optical powers within 15-40 μW the responsivities were 0.5 kHz/μW at 265 nm, 0.18 kHz/μW at 305 nm, and 0.03 kHz/μW at 375 nm. No response was observed from the green (560 nm) LED with a similar optical power. The comparatively strong response at 305 nm wavelength (below the energy bandgap of AlGaN) indicated the importance of trapping effects.