The Preparation And Characteristic Research Of CuGa_xO_y/β-Ga₂O₃ Heterojunction And(Al_xGa_1-x)₂O₃ Film

The third-generation semiconductor materials have great developmental prospects and play a key role research significance in ultraviolet detection and power electronics due to their large band gap and high breakdown field strength.Especially,the β-Ga2O3 has a bandgap of up to 4.9 eV and a breakdown field strength of 8 MV/cm,making it an ideal material for preparing ultraviolet detectors and electronic power devices.However,at present,the β-Ga2O3 based UV detectors of metal-semiconductor-metal type and Schottky type still confront the problems of high dark current and low detection efficiency.At the same time,β-Ga2O3 based Schottky barrier diodes also are facing the issues of large reverse leakage current and low breakdown voltage.The hetero-junction prepared based on the semiconductor energy band engineering can assist in regulating the carrier transmission and recombination at interface,so it can effectively reduce the leakage current and increase the breakdown voltage of the hetero-junctions,improving the semiconductor device performance.In this thesis,the principles of reactive deposition epitaxial growth of materials,material characteristics,and the preparation and characterization of β-Ga2O3-based heterojunction UV detectors and barrier diode devices were studied.This thesis is mainly divided into the following aspects:(1)According to energy band theory,the ohmic contact formation is proposed on wide bandgap n-type semiconductor materials using metals with lower work functions.This ohmic contact was prepared on a low-doped β-Ga2O3 single crystal substrate using metal Mg-Au.Later,the effects of different annealing temperatures on the ohmic contact and stability were studied.The study found that after annealing at 300℃,400 ℃,and 500℃,the Mg and β-Ga2O3 formed a good ohmic contact.As the annealing temperature increases,the total resistance increases due to an increase in the electrode resistance during annealing.In addition,the electrode film annealed at 300℃ and 500℃ were cracked and formed a metastable Mg-Au alloy phase,so after 37 days the electrode was oxidized and the ohmic contact characteristics deteriorated.While the electrode after 400℃ annealing formed continuous and stable Mg2Au alloy film,so there was no obvious degradation of ohmic contact characteristics.In addition,the carrier flow mechanism of the Au/Mg/β-Ga2O3 ohmic contact(sample annealed at 400℃)interface is dominated by the thermal electron emission model,and the effective barrier height is 0.1 eV.(2)Using the reactive deposition epitaxy method combined with chemical mechanical polishing technology,CuGaO2/β-Ga2O3 and CuGa2O4/β-Ga2O3 hetero-junctions with clear interfaces were obtained by changing the oxygen partial pressure to control the growth process of the CuGaxOy thin film.The XRD results of the CuGaxOy film before and after chemical mechanical polishing and the EDS of the elements at the interface show that,under the action of high temperature,the Cu evaporated and diffused to the surface of the oxidant substrate reacts with oxygen in the atmosphere to form copper oxide.The Cu of the copper oxide diffuses toward the substrate and the Ga in the substrate diffuses in the epitaxial direction.At the same time,the Cu,Ga,and O crystallizes to form CuGaxOy film.AFM test results show that CuGaO2 film has grain boundaries due to Cu agglomeration effect at low oxygen partial pressure;Cu agglomeration effect is suppressed under high oxygen partial pressure,so there is no obvious grain boundary in CuGa2O4 film.An ultraviolet(UV)detector was prepared based on CuGaO2/β-Ga2O3 hetero-junction.The results show that this hetero-junction ultraviolet detector has an obvious response to 254 nm ultraviolet light,and this response is relatively fast.Moreover,this hetero-junction UV detector has a self-power UV response characteristic.(3)CuGa2O4/β-Ga2O3 hetero-junction was prepared by annealing Cu/β-Ga2O3 samples in air.The in-plane epitaxy relationship between CuGa2O4 and β-Ga2O3 substrate was studied via HRXRD-Phi scanning.The forward turn-on characteristics and reverse breakdown characteristics of CuGa2O4/β-Ga2O3 heterojunction barrier diodes were prepared and studied.The ideal factor is 2.74,the forward turn-on voltage is 0.86 V,and the reverse breakdown voltage is 174 V.(4)A β-(AlxGa1-x)2O3 alloy film with high Al composition was prepared on a sapphire substrate based on the sublimation characteristics of β-Ga2O3 and the theory of reactive epitaxy deposition.The XPS,SEM and 3D AFM test results show that the Ga composition is 0.476 and the surface of β-(AlxGa1-x)2O3 film is mound-like three-dimensional when the growth temperature is 1400℃;while the Ga composition is 0.511 and the surface of the β-(AlxGa1-x)2O3 film is mainly expressed as step profile when the growth temperature is 1450 ℃.This indicates the surface is induced by different Ga components.The effects of different growth temperatures on the crystal quality and optical properties of β-(AlxGa1-x)2O3 alloy films were also studied.