Research On High-responsivity ?-Ga2O3 Based Solar-Blind Ultraviolet Photodetectors

In recent years,with the demand of missile launch warning and ozone-hole monitoring,the development of solar-blind UV photodetector has become more and more important.The commonly used silicon-based photodetectors are difficult to meet the requirements of solar blind UV photodetection due to the limitations of silicon materials.The solar-blind photodetectors based on wide band gap semiconductor materials have become a new research hotspot owing to their excellent performance.?-Ga₂O₃ is suitable for solar-blind photodetection as a result of its direct band-gap of 4.9 eV without additional alloying process required for other wild band-gap semiconductors,such as AlGaN and MgZnO.High-quality,single-crystal,large size?-Ga₂O₃ can be easily fabricated by melt method.Besides,?-Ga₂O₃ has a high transmittance in visible and UV light,high mobility and breakdown electric field,and high thermal stability and chemical stability.Therefore,?-Ga₂O₃ has been studied extensively in recent years,it is not only an important candidate material for the development of power semiconductor devices,but also has an important application prospect in the field of solar blind ultraviolet detection.In this paper,high crystalline quality?-Ga₂O₃ thin films were prepared by molecular beam epitaxy,and a solar-blind UV detector was developed to improve the photoelectric response characteristics of the device through the adoption of two approaches.First,Sn nanoparticles array with different sizes and distribution were prepared on?-Ga₂O₃ thin film by nanosphere photolithography,inducing localized surface plasmon resonance enhancement,which effectively improves the responsivity.Second,ultra-thin Al₂O₃ films were deposited by atomic layer deposition on?-Ga₂O₃ thin film which effectively suppresses the dark current and improves the sensivity.The main research work is as follows:?1?The effect of the size and distribution of Sn nanoparticles on?-Ga₂O₃-based MSM photodetectors was investigated.This paper optimizes the manufacturing process to achieve effective regulation of the size and distribution of Sn nanoparticles.The results show that the absorbance is enhanced with the increase of particle diameter and distribution density.Among all samples,the Sn nanoparticles array with a diameter of 50nm showed the greatest performance improvement.The photo-current and responsivity were increased by 2 times.Although dark-current slightly increased due to the existence of Sn nanaoparticles between the electrode and the semiconductor,the specific detectivity was still increased by 1.9 times.Sn nanoparticls were excited into plasmons,inducing locialized surface plasmon resonance and forming a strong localized electromagnetic field;hence more photons were collected,the absorbance and performance of photodetectors were improved.?2?The effect of Al₂O₃ surface insulator film on?-Ga₂O₃-based photodetector was investigated.In this paper,an ultrathin Al₂O₃ film was deposited on the surface of?-Ga₂O₃ film by atomic layer deposition technique,and a metal-insulator-semiconductor-insulator-metal?MISIM?structure UV photodetector was developed.The results indicate:the 3-nm-thick Al₂O₃ insulator film showed the greatest performance improvement.The dark-current was reduced by 38%without photo-current decreasing,the light-dark current ratio was increased by 3 times,and the specific detectivity was increased to 2 times.The Al₂O₃ insulator film can generate a barrier that blocks the carrier transport between the metal and semiconductor,which can effectively reduce the dark-current of the?-Ga₂O₃-based MSM solar-blind photodetector.The defects located at the interface between the Al₂O₃ and?-Ga₂O₃ can generate an interface-trap-controlled charge injection under UV illumination,thereby increasing the carrier concentration and promoting the photocurrent.Defects can also act as recombine center,which can effectively reduce the life time of non-equilibrium carrier,leading to the improvement of transient response.