Research On The Growth Of Inas Nanowires And Their Applications In Photoelectric Devices

In recent years,Semiconductor nano wires(NWs)have been widely researched due to their unique structural characteristics and novel physical properties.Considering the direct narrow band gap and high electron mobility,InAs nanowires have broad prospects for the high-speed optoelectronic devices.The present thesis mainly focuses on the controllable growth of pure crystalline InAs NW and the fabrication and application of nanowire optoelectronic devices.The main contributions are as follows:(1)Pure WZ InAs NWs over a wide diameter range are grown on an InP substrate by Au-catalyzed MOCVD.It is observed that the crystal structure of NWs strongly depends on the growth temperature and ?/?ratio.Under the optimum growth temperature of 450 ? and the optimum?/? ratio of 70,pure WZ phase is obtained over the full length of the NW,covering a broad diameter range of several hundred nanometers.The diameter is far beyond the maximum diameter of WZ InAs NWs reported previously(typically less than 100 nm).In addition to the optimization of growth conditions,the broad diameter range of WZ phase is attributed to a high actual ?/? ratio due to the adsorption of In by the InP substrate(2)The self-catalyzed growth of InAs NWs on InP substrate are systematic investigated by MOCVD.The NW growth rate decreases with the increasing temperature,which is contrary to the traditional vapor-liquid-solid(VLS)mechanism.The reason for this phenomenon is that the competition of the supply of In adsorption atoms diffused from the substrate is exacerbated at higher temperatures.Twin faults are observed in the self-catalyzed InAs nanowires due to the unstable In droplets caused by the surface diffusion effect.The NWs exhibit kinking at a certain V/III ratio.The twin faults are dramatically suppressed and even completely eliminated in the NW branch after kinking.(3)Top-gate/back-gate field effect transistors based on single InAs NW are fabricated through our experiments.The highest mobility of InAs NW-FETs is calculated to be 5790 cm2/V·s.The electron mobilities in the InAs NWs depend on their crystal quality,and the pure crystalline NWs exhibit much higher electron mobility than those with dense SFs.A native indium oxide layer outside of the InAs NW acts as photogating layer.Under illumination of 532 nm laser,the device exhibits negative/positive photoconductivity at low/high incident light intensities respectively,which is caused by the difference of electron mobilities in nanowire core and shell due to the photogating effect.Pure positive/negative photoresponse is obtained by applying a relatively high negative/positive gate voltage respectively,which is attributed to a gatevoltage-induced barrier height modulation between the trap state energy level in the photogating layer and the conduction band.(4)A photonic neuromorphic device based on InAs NW is fabricated by mimicking the synaptic behavior.Due to the photogating effect,the device exhibits negative photoresponse and persist photoconductive under the illumination of 532 nm laser.The neuromorphic behavior is mimicked in the negative photoresponse range and the mimicking is mainly in synaptic plasticity of short-term potential(STP)and long-term potential(LTP).The transition from STP to LTP is observed as the stimulus intensity increases,which is in accord with the feature of cooperativity.Moreover,by mimicking the role of ions in a biological pre-synapse,the trapped hot electrons mimicked PPF behavior and the PPF index decreases with the increased interval time,which is analogous to the behavior in a biological synapse.These results demonstrate the feasibility of NW-based artificial synapses for emerging photonic neuromorphic networks.