Research On Fabrication Of Ga₂O₃ Thin Films By PLD And Its UV Response Characteristics

In the past 50 years,photoelectric detectors based on the semiconductor thin-film have become a mainstream research hotspot because of their advantages such as small size,low cost,and low power consumption.Compared with other wide bandgap semiconductor materials,such as MgZnO,AlGaN and diamond,Ga₂O₃ is more sensitive to ultraviolet?UV?light,and the response of Ga₂O₃ detectors in solar-blind UV light region?220-280 nm?is much higher,is one of the ideal materials for fabricating high-performance solar-blind UV detectors.However,there are just some problem in Ga₂O₃ solar-blind UV detector,such as high dark current,low signal-to-noise ratio,slow response and recovery time,etc.which limits its application in commercial and other fields.Therefore,the reduction of the dark current and the improvement of the signal-to-noise ratio of the Ga₂O₃ ultraviolet detectors were the focus of this thesis.The main content of this paper is finding an effective method to reduce the dark current,and improve the signal-to-noise ratio and response-recovery speed of the Ga₂O₃ UV detectors,which is conducted through decreasing the growth temperature of the Ga₂O₃ thin film,growing?400??-Ga₂O₃ or introducing?-phase Ga₂O₃ into the?-Ga₂O₃ thin film during its deposition process,and the relatively reasonable explanations are proposed.The main result in this thesis are listed as follows:?1?The Ga₂O₃ films were fabricated on the c-plane sapphire substrates by the PLD method.The effects of changing growth temperatures on the crystal quality of Ga₂O₃ films and the ultraviolet response characteristics of Ga₂O₃ ultraviolet detectors were studied.When the growth temperature decreased,the Ga₂O₃ thin film changes from crystalline state to amorphous state,and the UV absorption edge moves toward the long wavelength side.With the decrease of growth temperature,the dark current of the Ga₂O₃ ultraviolet detector is reduced from 5.6×10^-77 A to 3.2×10^-1111 A,and the signal-to-noise ratio of the device increased from 230 to 14,000.For the UV detector fabricated on the amorphous Ga₂O₃ thin films grown at 450?,the response of the device is as high as 318 A/W at 240 nm UV light under 25 V bias voltage,which is attributed to the introduction of high gain due to the multiple tunneling of photogenerated carriers under ultraviolet light irradiation.?2?The Ga₂O₃ films were fabricated on the c-plane sapphire substrates by the PLD method.The effects of changing growth oxygen pressures on the growth orientation of Ga₂O₃films and the ultraviolet response characteristics of Ga₂O₃ ultraviolet detectors were studied.As the oxygen pressure increased from 0.5 Pa to 2 Pa,more?-Ga₂O₃ with?400?orientation appear in the?-Ga₂O₃ thin films because the atomic migration energy decreases.When the oxygen pressure is over 2 Pa,the fabricated?-Ga₂O₃ films show multi orientation growth.The band gap of the?-Ga₂O₃ films increases with the increase of oxygen pressure,and a blue-shift of the UV absorption edge is observed.When other orientation?-Ga₂O₃ were mixed into the?^<sub>2^<sub>01??-Ga₂O₃ thin film at higher oxygen pressure,the responsivity of Ga₂O₃ultraviolet detectors decreased from 17.7 A/W to 0.03 A/W,and the dark current of the device decreased from 3.63 mA to 0.9 nA.The I_?250nm?/I_dark ratio of the Ga₂O₃ ultraviolet detector composed of both?400?and?^<sub>2^<sub>01??-Ga₂O₃ is up to 2.3×10³ when deposited at 2 Pa.Meanwhile,the response time of the device composed of both?400?and?^<sub>2^<sub>01??-Ga₂O₃ is just0.29?s with the UV on,and the recovery time of the device is just 0.07 ms and 0.21 ms with the UV off.?3?The Ga₂O₃ films were fabricated on the a-plane sapphire substrates by PLD method.The effects of changing oxygen pressures on the crystal structure of Ga₂O₃ films and the ultraviolet response characteristics of Ga₂O₃ ultraviolet detectors were studied.At higher oxygen pressure?>2 Pa?,the Ga₂O₃ thin films show a single?-phase structure.In addition to?phase,?-phase structure was found in Ga₂O₃ films prepared under lower oxygen pressure.As the deposition oxygen pressure decreased,more?-Ga₂O₃ was introduced into the?-Ga₂O₃thin films.When slightly numbers of?-Ga₂O₃ was introduced into the?-Ga₂O₃,the UV response of the detectors prepared from Ga₂O₃ thin films with mixed-structure is obviously higher than that of single-phase?-Ga₂O₃ devices.The responsivity of the Ga₂O₃ UV detector prepared from Ga₂O₃ thin films at 1 Pa reached 12 A/W at 260 nm UV light under 25 V bias voltage.