High signal/noise ratio and high-speed deep UV detector on β-Ga2O3 thin film composed of both (400) and [formula omitted] orientation β-Ga2O3 deposited by the PLD method

Abstract

The effect of oxygen pressure on deposition orientation and the UV response characteristics of the β-Ga2O3 thin film by the Pulse Laser Deposition (PLD) method were studied. The β-Ga2O3 thin film deposited mainly along (2¯01) orientation at 0.5 Pa oxygen pressure, however it deposited more along (400) orientation when the oxygen pressure increased from 0.5 Pa to 2 Pa. The decrease in the migration energy of reactive Ga and O atoms from Ga2O3 target at higher oxygen pressure is the main reason for the change in the orientation of the β-Ga2O3 thin film. The β-Ga2O3 thin film that was constituted mainly by (2¯01) and (400) orientations β-Ga2O3 was made at 2 Pa, where the band gap of the β-Ga2O3 thin film is wider than the (2¯01) orientation ones deposited at smaller oxygen pressure, and the maximum response of the β-Ga2O3 thin film shifted considerably from 255 nm to 240 nm compared with (2¯01) orientation β-Ga2O3 thin film. Because the Idark of the UV detector based on the mix-orientation β-Ga2O3 thin film is just 2.53 nA under 25 V bias voltage, which is much smaller than that of the (2¯01) β-Ga2O3 based detector, the Iuv/Idark of the mix-orientation β-Ga2O3–based detector reached 2500 at 25 V bias voltage. This value is much higher than the (2¯01) β-Ga2O3–based detector both in our experiments and in reported results. Wider band gap (400) β-Ga2O3 and relative higher density of boundaries at the interfaces between (400) and (2¯01) β-Ga2O3 are the main reasons for the smaller Idark and the higher Iuv/Idark of the β-Ga2O3 UV detector deposited at 2 Pa. The β-Ga2O3 thin film deposited along multiple orientations at oxygen pressure over 2Pa, the UV response, and Iuv of the β-Ga2O3 thin films deposited at higher oxygen pressure was much smaller than the one deposited at 2 Pa, and the Iuv/Idark was also much smaller. In addition, the UV β-Ga2O3 detector that composed of both (400) and (2¯01) β-Ga2O3 showed similar response time (0.8 us) and much smaller decay time (80 us) compared with the (2¯01) β-Ga2O3–based detector, which was also much faster than the reported results. Therefore, when appropriate numbers of (400) β-Ga2O3 were mixed into the (2¯01) β-Ga2O3 thin film, the mix-orientation β-Ga2O3–based UV detector showed a much lower noise level, much higher signal/noise ratio, and much faster decay speed at shorter wavelength UV light compared with a single (2¯01) β-Ga2O3–based based UV detector.