The Fabrication And Properties Of GaN/Ga₂O₃ Pn Junction Based Self-powered Ultraviolet Photodetectors

With the development of the photoelectronic detecting technique,ultraviolet?UV?photodetectors?PDs?have huge applications in flame detection,ozone hole monitoring,ultraviolet communication and national defense pre-warning and tracking,etc.At present,the UV detectors on the market are mainly vacuum UV multiplier tubes and Si-based UV detectors.The vacuum UV multiplier tubes have the disadvantages of bulky,fragile and high power consumption.However,the Si-based UV detector requires an expensive filters to achieve the detection of ultraviolet light.The wide bandgap semiconductor materials with a greater bandgap than 3.0 eV are only sensitive to UV light and allows direct detection of UV light without the need for additional filters.GaN has a wide bandgap of 3.4 eV and is an ideal UV detector raw material.Currently,most GaN-based UV detectors are based on photoconductive metal-semiconductor-metal?MSM?structures.UV detectors based on this structure tend to have persistent photoconductivity and slow response time,and the structure requires external bias to work,which increases the power consumption of the device,limiting the application of the device.In contrast,self-powered UV detectors based on pn junctions or heterojunction structures show great advantages without bias applied.In this paper,a built-in electric field is formed through the formation of pn junction,and the photogenerated carriers are rapidly separated at the interface and transported to the corresponding electrodes,so that the detection of the ultraviolet signal can be realized without the need of external power supply.In this work,GaN with a bandgap of 3.4 eV is used as the p-type material and Ga₂O₃ with a bandgap of 4.9 eV as the n-type material?which also serves as a window layer material?,Ga₂O₃ thin films were grown on GaN thick films by pulsed laser deposition?PLD?,a self-powered UV detector with GaN/Ga₂O₃ pn junction was prepared,and a larger built-in electric field was obtained by doping Ga₂O₃ films with Sn which improved the performances.The main contents and achievements are as follows:1.GaN/Ga₂O₃ pn junction based self-powered ultraviolet photodetectors.Ga₂O₃ film was deposited on the p-GaN film to construct pn junction by pulse laser deposition?PLD?technology with 750?of the sapphire temperature and under vacuum situation(2.0×10^-5Pa).The results of the crystallinity show that Ga₂O₃ film is grown along with the orientation of?-201?direction,and the thickness is about 375nm.The photoelectric properties exhibit a typical rectifying characteristic and self-powered characteristic,and the IV curve without passing zero,shows the photovoltaic characteristics,andexhibits self-powered characteristics under 254nm and 365nm light.It also exhibits higher I_photo/I_dark?152?,quicker responsetime?0.08s?,extremly higher responsivity?54.43mA/W?and high detectivity(1.23×10¹¹cm·Hz^1/2·W^-1)under 365nm light with the light intensity of 1.7mW/cm².2.GaN/Sn:Ga₂O₃ pn junction based self-powered ultraviolet photodetectors.Sn-doped Ga₂O₃ films can increase the Fermi level close to the conduction band and form a larger built-in electric field with the p-type GaN to increase the separation of photogenerated carriers.The PLD method was used to grow a Sn-doped Ga₂O₃ thin film?2%doping concentration?on a p-GaN thick film substrate at different oxygen pressures and different substrate temperatures to form a GaN/Sn:Ga₂O₃ pn junction.With the increase of the growth temperature and the decrease of the oxygen pressure,the crystallinity,surface flatness and photocurrent of the Sn:Ga₂O₃ thin film both increase.The samples prepared under vacuum(8.0×10^-4Pa)and 750?exhibited the highest UV performance.The detectors based on GaN/Sn:Ga₂O₃ pn junctions had obvious photoelectric response only to light with wavelengths less than 385 nm.Under the condition of 254 nm illumination and 0 V bias,with the increase of light intensity from 50?W/cm² to 1800?W/cm²,the photocurrent showed a linear increase,while the photoresponsiveness showed a downward trend with the maximum responsivity reaching 3.05A/W and reaching the highest detectivity(1.69×10¹³Jones).Under the light intensity of 500?W/cm²at 254nm,the heterojunction has a dark current of about 10^-11A,a photocurrent level of about 10^-6A,a I_light/I_darkark ratio?10⁵?,a faster response time?rise time of 23.6 ms,fall time of 31.5ms?.