Comparison Study of β -Ga2O3Photodetectors on Bulk Substrate and Sapphire

We fabricated β-Ga2O3photodetectors on bulk substrate and sapphire. Bulk Ga2O3photodetector demonstrates the improved responsivity compared with the device on sapphire, due to the higher crystal quality in bulk material. Optical gain is achieved in both the devices. For the first time, we report that the Ga2O3photodetector epitaxially grown on sapphire achieves a blueshift of bandgap in comparison with bulk device. Based on the measured responsivity characteristics, the direct and indirect EGof bulk Ga2O3are 4.78 and 4.59 eV, respectively. The Ga2O3photodetector on sapphire exhibits a maximum cutoff wavelength at 253 nm, corresponding to the direct EGof 4.90 eV. The increment of EGin Ga2O3on sapphire over bulk material is attributed to the residual strain in the film. The time-dependent photoresponse of the devices suggests that Ga2O3on sapphire might have more oxygen vacancies than the bulk material.