| Ultraviolet(UV)detectors have very broad prospects in the military and civilian fields,such as missile warning,flame detection and optical communication.The performance of the UV detector is highly dependent on the property of the material.Indium oxide(In2O3)is an n-type wide bandgap semiconductor with an optical band gap of approximately 3.7 eV and high mobility,which make it suitable for UV detectors.However,due to the presence of oxygen vacancies in In2O3,the carrier concentration is too high and the presence of two-dimensional electron gas on the surface affects its application in UV detectors.In this paper,we use Mg doping to improve the MSM structure and NiO/In2O3 heterojunction structure UV detectors.We also investigated the effect of Mg-doped In2O3 on its electronic structure and the electronic structure of the NiO/In2O3 heterojunction by photoelectron spectroscopy.The main contents are as follows:(1)We prepared In2O3 thin film,MSM structure UV detector and NiO/In2O3 heterojunction UV detector by sol-gel method.When the Mg doping concentration reaches 5%,the optical band gap of In2O3 increases from 3.70 eV to 3.72 eV,the carrier concentration decreases from 1019 cm-3 to 1015 cm-3.and the mobility decreases from 5.5 cm2 v-1 s-1 to 0.5 cm2 v-1 s-1.The response peak of In2O3 MSM structure UV detector is located in deep ultraviolet region with a wavelength of 250 nm.When the Mg doping concentration reaches 5%,the responsivity is reduced from 45 A/W to 0.58 A/W,but the interference is enhanced,the response speed is increased,the decay time of photocurrent is shorted from 152 s to 12 s.The dark current of the NiO/In2O3 heterojunction UV detector decreases from 120 μA to 0.69 μA,the rectification rate under ±3 V bias increases from 42 to 7200.The NiO/In2O3 heterojunction UV detector has self-power characteristics.The photocurrent rise and decay time are 0.19 s and 0.4 s without external bias.(2)We found an occupied state below the Fermi level of In2O3 thin films by low-energy photoelectron spectroscopy,which confirmed that the existent of two-dimensional electron gas and downward band bending at In2O3 surface.It was confirmed by high-energy synchrotron radiation photoelectron spectroscopy that the built-in electric field is 1.0 eV,the conduction band offsset(ΔEc)is 2.15 eV,and the valance band offset(AEv)is 1.35 eV the band offset results indicate that the formation of type-Ⅱ staggered band alignment at the NiO/In2O3 heterojunction interface.When the Mg doping concentration reaches 5%,the built-in electric field is reduced to 0.65 eV From the analysis of photoelectron spectroscopy data,Mg doping reduces the carrier concentration of In2O3 and reduces the dark current of the UV detector,thus improving the performance of the devices. |
