Preparation And Performance Study Of GaAs Nanowire Photodetectors

Compared with Si and Ge,GaAs nanowires have advantages such as direct band gap（1.42e V）,high opto-electric conversion and high electron mobility,making them ideal for the fabrication of photodetectors,light-emitting diodes and lasers.However,the high surface state density of GaAs nanowires will restrict the transport of charge carriers on the surface of the materials,which leads to the low performance of the prepared devices.Therefore,it is necessary to improve the influence of surface state density on the whole device by other means.The surface state density of GaAs nanowires can be improved by combining Au,Ag and copper nanoparticles with GaAs nanowires.More importantly,the light absorption intensity of GaAs nanowires will be enhanced due to the unique localized surface plasmon resonance（LSPR）properties of noble metal nanoparticles.This is due to the coupling of free electron gas and electromagnetic wave on the surface of noble metal nanoparticles under the excitation of incident electromagnetic wave,thus changing the distribution of light absorption intensity on the surface of GaAs nanowires.In addition,the introduction of Schottky barrier on the surface promotes the separation of carriers inside GaAs nanowires,which further improves the detector performance.In this paper,GaAs nanowire photodetectors modified by Au nanoparticles were prepared and a new method for preparing Au nanoparticles was proposed.The main research contents are as follows:（1）GaAs nanowires were grown on Si（111）substrate by means of MBE growth system using VLS growth mechanism,and the nanowires were tested by SEM and EDX.The GaAs nanowire model and the GaAs nanowire model modified by Au nanoparticles were established by simulation software.The finite difference time domain（FDTD）method is used to simulate the optical field distribution of these models.It can be seen from the simulation results that Au nanoparticles can effectively enhance the light absorption intensity of the nanowires.（2）GaAs nanowire photodetectors were prepared by micro-nano processing technology.At appropriate evaporation rate（0.1（?）/S）and time（10 s）,Au nanoparticles were prepared using thermal evaporation system,and Au nanoparticles were evaporated to the surface of GaAs nanowires in the photodetector channel.The photoelectric characteristics of the devices before and after modification of Au nanoparticles were tested.The test results showed that the dark current,photocurrent and responsivity of the photodetector before modification were 4.6×10^-12A,2.39×10^-10A and 0.569 A/W under the incident light excitation at the wavelength of 532nm and the optical power of 104.86 mw/cm²,respectively,the dark current,photocurrent and responsivity of the photodetector after modification were 1.56×10^-12A、1.26×10^-9A、3.047 A/W.The results surface that the performance of GaAs nanowire photodetectors modified by Au nanoparticles is significantly enhanced.Moreover,the intrinsic mechanism of device performance enhancement is explained by establishing an energy band theory model.The research content of this paper proposes an efficient and simple method to improve the performance of GaAs nanowire photodetectors,which will have great prospects in the application of high-performance detectors.