RF sputtered Ga2O3 thin-films for solar-blind UV-C detection: Investigating effects of crystallinity, stoichiometry, and ambient

The ultraviolet photo-responses of metal–semiconductor–metal (MSM) devices formed on RF sputtered thin film gallium oxide have been investigated as a function of the stoichiometry and crystallinity of the films and the ambient conditions during illumination. Stoichiometry was altered via the oxygen pressure during growth, and crystallinity was altered via the growth surface; amorphous Ga2O3 films were grown on Si3N4, while polycrystalline β-Ga2O3 films were grown on a-plane sapphire. Interdigitated Pt–Ga2O3–Pt MSM photodetectors were fabricated on the Ga2O3 films, and selective UV-C detection was consistently observed. Under an incident optical power of 0.09 mW/cm2, on/off current ratios (IUV-C:Idark) in the best devices exceeded 103:1. Other figures of merit included responsivity as high as 2.0 A/W and detectivity up to 1.2 × 1013 Jones. Operation in air of 90% relative humidity produced the fastest UV-C response times but the highest dark current, attributed to interaction between water and oxygen surface adsorbates, which affected surface band-bending. Comparison with encapsulated devices enabled identification of trap and surface adsorbate limited components of the device response and recovery. Finally, a self-powered (zero bias) interdigitated Pt–Ga2O3–C UV-C photodetector was tested, and this device exhibited a responsivity of 1.1 × 10−2 A/W and a detectivity of 3.7 × 1010 Jones under 0.09 mW/cm2 UV-C illumination.<p></p>