Fabrication And Transport Properties Of Inas Nanowire Based Electronic Devices

Semiconductor nanowires(NWs)exhibit excellent electrical transport properties owing to their quasi one-dimensional confined channel.The semiconductor nanowire device is expected to become one of the most promising devices in nanoelectronics and nanophotonics in the future due to the bottom-up controllable growth and better compatibility with CMOS technology.Among many semiconductor nanowires,InAs nanowires have many advantages such as narrow band gap,extremely high electron mobility,extremely small electron effective mass,large Lande g factor,strong spin-orbit coupling and become the ideal materials for novel electronic devices such as high-performance field-effect transistors(FET)etc.This thesis focuses on the research of the fabrication and transport properties of InAs nanowire based electronic devices.Firstly,the InAs nanowires are grown on Si substrate using molecular beam epitaxy.Three types of devices are then prepared and studied:InAs nanowires spin injection devices,InAs nanowire resistive switching devices and InAs nanowire FET with self-aligned top-gate.The main results are as follows:(1)The InAs NWs were grown in a catalyst-free manner on n-type Si(111)substrates by molecular-beam epitaxy.The NW has a mixture of wurtzite and zinc-blende crystal structure with a large number of stacking faults.Large spin signal was achieved in the two-terminal device by local measurement.Meanwhile,the spin diffusion length(lsf)of the InAs NW was calculated to be 1.9 ?m.It is found that the observation of large spin signal requires not only very large lsf but also a high contact resistance.Then we invesgated the effects of barrier layer thickness on the differential resistance and spin injection in the four-terminal devices by non-local measurement.It is found that the spin signal is very sensitive to the barrier layer thickness.When the thickness of Al2O3 tunneling barrier increases to 3 nm,a magnetoresistance of 4.2%was obtained.The spin diffusion length was calculated to be 1.84 ?m which matches well with the result in local measurement.Based on the electrochemical bubble method transfer of single crystal graphene,we invesgated a novel InAs nanowire device using single crystal graphene as tunneling barrier.Compared with devices using MgO and Al2O3 as the barrier material,though the new device has a small magnetoresistance of about 12.8%,the spin signal is larger.The calculated spin diffusion length of InAs nano wire is 2.18 ?m which is the highest value in our experiment.(2)In the InAs nanowire device with Pt electrodes,a significant resistance switching behavior was found.We tested both the switching reproducibility and retention performance of the device and the results indicate that the resistance switching has good stability.The resistance values of low resistance state(LRS)and high resistance state(HRS)are distributed in a narrow range while Vset is in the millivolt range and the distribution range is narrow as well.We then fitted the?-? curve of the positive voltage region with several conduction mechanisms.The results show that the HRS state was dominated by Schottky conduction while the LRS state in the high-field and low-field region were dominated by SCLC conduction and Ohmic conduction respectively.We then proposed the resistance switching mechanism of the InAs nanowire device.Due to the presence of a thin oxide layer between the Pt electrode and the InAs nano wire,a larger Schottky barrier exists at the interface of Pt contact which dominates the conduction leading to the HRS state of the device.When the voltage increases to Vset,the oxygen vacancies in the oxide layer migrate to the interface of Pt contact,which greatly reduces the barrier hight and the device transits to LRS state.With the decrease of the voltage,the current is further reduced.Ohmic conduction mechanism dominants at this region owing to the amount of thermal excitated electrons in the oxide layer are sufficient to meet the requirements of ohmic conduction.(3)Self-aligned top-gate devices based on single InAs nanowire were fabricated and their DC characteristics were invesgated.By comparing back-gate devices and common top-gate devices,it was found that the characteristics of self-aligned top-gate devices are greatly improved.The normalized output current is as high as 70 ?A/?m,the field-effect mobility of InAs nano wires reaches 1000 cm2/Vs,the peak transconductance reaches 4.3 ?S,device on/off ratio is up to 104 and the subthreshold swing decreases to 660 mV/dec.