An ε -Ga₂O₃-Based Surface Acoustic Wave Resonator for Deep Ultraviolet Detection

<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula>-phase gallium oxide (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula>-Ga2O<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{3}}$ </tex-math></inline-formula>) semiconductor offers an excellent potential for fabricating surface acoustic wave photodetectors (SAW PDs) to detect deep ultraviolet (deep-UV) light, taking advantage of its combination of an ultra-wide bandgap of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~4.9$ </tex-math></inline-formula> eV and a strong piezoelectric property. In this letter, we developed SAW deep-UV PDs in a single-port resonator topology using an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula>- Ga2O3 thin film grown on sapphire substrates. The device exhibited two resonate frequencies at 1.39 and 2.33 GHz, corresponding to the propagation of Rayleigh and Sezawa waves. The frequency shifts of the Rayleigh mode signal to a 254-nm wavelength UV illumination were investigated and discussed. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula>-Ga2O3 SAW PDs in our study, yielding a competitive responsivity of 5.4 ppm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot (\mu $ </tex-math></inline-formula>W/cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}})^{\text {-1}}$ </tex-math></inline-formula>, were demonstrated to be suitable for deep-UV detection.