A 130nm thin film of β-Ga

2

O

3

is grow on a sapphire（Al

2

O

3

）substrate by atomic layer deposition(ALD)

and X-ray diffraction(XRD)test is conducted on the thin film to verify its quality.Metal-semiconductor-metal(MSM)photoconductive photodetectors with an interdigital structure are prepared on the grown film.The device has an ultra-low dark current of 100fA and an ultra-high photo-to-dark current ratio(PDCR)of 1×10

6

.After rapid annealing of the device

it has an ultra-high photocurrent of 58μA and better device ohmic contacts

but both the light and dark currents increase

the PDCR decrease an

order-of-magnitude

the thin film resistance increases

the electron scattering ability is enhanced

and the device performance becomes weaker compared to that before annealing.Finally

the effect of interdigital spacing and light intensity on device performance after annealing is studued.