Study On The MOCVD Growth Of Nanostructured β-Ga₂O₃ Films And Ultraviolet Detectors

β-Ga₂O₃ is a new type of ultra-wide bandgap semiconductor with a bandgap width in the range of 4.2～5.0 e V.This material shows the advantages of high critical breakdown electric field,low light absorption in the long-wave band,and high surface activity to gas molecules;therefore,it is prospective in many application fields such as power electronic devices,transparent conductive electrodes,solar-blind ultraviolet photodetectors,gas sensing,and photocatalysis.In recent years,great progress has been made in film growth and device preparation,and many results have been reported,but there is still room for further research in both the structural morphology ofβ-Ga₂O₃ films and device applications.In terms of the structural morphology ofβ-Ga₂O₃ films,nanostructured films have many unique properties,such as optical resonance in the wavelength domain,surface activity enhancement,and quantum confinement effect.By designing the nanostructured morphology ofβ-Ga₂O₃ films,the application range ofβ-Ga₂O₃ can be effectively extended and the device performance can be enhanced,which has great potential for application in solar-blind ultraviolet detection.However,the preparation technology ofβ-Ga₂O₃ nanostructured films is still focused on chemical synthesis such as powder heating,and there are few reports on the application of the modern epitaxy process.In terms of device applications,β-Ga₂O₃ also has significant advantages in photonic device applications by its excellent optical properties,but no relevant reports have been made so far.In this paper,we address the above difficult and hot issues in the preparation ofβ-Ga₂O₃nanostructured films and their devices,and the study ofβ-Ga₂O₃ photonic devices in the following aspects:1.β-Ga₂O₃ nanowire films with a high specific surface area were prepared on p-type Ga As substrates by the thermal oxidation method.The crystal properties,surface morphology,optical properties,the growth mechanism ofβ-Ga₂O₃ nanowire films,and the junction properties of heterojunctions were investigated in a detail.In addition,the MOCVD process and the thermal oxidation method have been combined for the heterogeneous growth ofβ-Ga₂O₃ nanostructured（nanowire）films.The effects of gas phase VI/III ratio and growth temperature on the properties of nanowire films during the MOCVD process were systematically investigated.It is found thatβ-Ga₂O₃nanowires are grown under the induction of the high-energy surface of the nanostructured seed layer;moreover,there is a high correlation between the crystal quality,luminescence properties,and nanostructure morphology.The optical properties of the nanostructured films were simulated by the finite element method,and the strong light-trapping effect of theβ-Ga₂O₃ nanowire films was verified.2.Based on a method to prepare periodic nano-hole array templates,a selected area growth method forβ-Ga₂O₃ nanowire films based on a high-temperature MOCVD process was proposed.Using this method,we have performed heterogeneous growth ofβ-Ga₂O₃ nanowire films on p-type Si substrates and c-plane sapphire substrates,respectively.Experiments on different gas phase VI/III ratios,growth pressures,and temperatures were performed,and the effects of each growth parameter on the morphology and properties ofβ-Ga₂O₃ nanowire films were systematically explored.It was found that the periodic circular hole array template induced the formation of a selective regional nucleation mode,the nanowire growth was achieved by the transfer of the guiding crystal steps at the top of the nanowires.Two solar-blind ultraviolet photodetectors of photovoltaic and photoconductive were prepared,and their response to 254 nm light is 261 A/W and 113 A/W,respectively.3.β-Ga₂O₃ planar films were grown on a c-plane sapphire substrate by high-temperature MOCVD,and aβ-Ga₂O₃ optical waveguide device based on a multi-mode interferometer structure was fabricated.We investigated the changes in the thickness and surface roughness of the films prepared at different growth times and analyzed the optical properties ofβ-Ga₂O₃ films.The geometric structure of theβ-Ga₂O₃ optical waveguide device was optimized by simulation.The device was prepared by combining the film preparation with the photolithography and the dry etching process.We measured the optical transmission loss and output spectrum of the device.The results show that the optical transmission loss of theβ-Ga₂O₃ optical waveguide is 9 d B/cm,and theβ-Ga₂O₃ optical waveguide device shows the all-optical solar-blind ultraviolet detection function under the passive condition.Under solar-blind ultraviolet irradiation,the output spectrum shows a shift of 0.1 d B.Based on the experimental phenomena,the all-optical detection theory of theβ-Ga₂O₃optical waveguide device was illustrated.This passive all-optical detection form is mainly based on the photo-induced refractive index change effect caused by free carrier absorption inβ-Ga₂O₃.