Channel Carrier Transport Characteristic Of AlGaN/GaN MIS-HEMT Devices

GaN-based MIS-HEMT devices have the advantages of low off-state leakage current and high breakdown voltage,which is an ideal choice for studying high-efficiency GaN-based microwave power devices.However,channel carrier transport properties are easily influenced by gate insulation layer,interface state and temperature,which has a certain impact on the performance and reliability of devices.Therefore,it is of great significance to study the carrier transport properties of MIS-HEMT devices.In this paper,the characteristics of AlGaN/GaN MIS-HEMT device and channel carrier transport are studied by combining simulation with experiment.The main works are as follows:?1?Silvaco simulation software has been used to study the effects of interface state density,gate dielectric layer thickness and recess-etching depth on the DC characteristics of AlGaN/GaN MIS-HEMT devices,which provides a reference for device structure design.The results show that the existence of interface states has a great influence on device characteristics,and measures should be taken to reduce the density of interface states in the process of device manufacturing.The selection of gate dielectric layer thickness and recess-etching depth should be appropriate,otherwise the device characteristics will be affected.Subsequently,we designed the MIS-HEMT device with Al₂O₃/AlN stacked gate dielectric structure for this experiment,and briefly introduced the fabrication process of the device.Then,the DC characteristics of the device were preliminarily tested.?2?The influence of temperature on the characteristics of MIS-HEMT devices has been studied by combining Silvaco simulation with temperature-varying DC measurement.The simulation results show that the carrier diffusion to GaN buffer layer is caused by the increase of temperature,which is the main reason for the degradation of device characteristics at high temperature.Subsequently,the influence of temperature and recess-etching on the characteristics of MIS-HEMT devices is summarized by means of low temperature DC testing and previous research results on the high temperature reliability of MIS-HEMT devices.At low temperature,the threshold voltage of the devices is slightly negative drift,the transconductance peak value is increased,the output current is increased,and the on-state leakage is slightly increased.At high temperature,the threshold is slightly positive drift,the transconductance peak value decreases,the output current decreases,and the off-state leakage increases.Recess-etching can cause positive drift of threshold voltage,increase of transconductance peak and increase of off-state leakage of MIS-HEMT devices.?3?The effects of temperature and recess-etching on carrier transport characteristics of MIS-HEMT devices were studied by combining temperature-varying C-V test with MATLAB simulation,and the transport mechanism was also studied.According to the results of low temperature C-V test and the previous research results on the transport characteristics of MIS-HEMT devices at high temperature,we can get the influence of temperature and recess-etching on the carrier transport characteristics of MIS-HEMT devices:at low temperature,the channel 2DEG concentration of MIS-HEMT devices increases,the corresponding depth of concentration peak increases,the carrier field effect mobility increases,and recess-etching at low temperature.After etching,the field effect mobility of Schottky gate HEMT devices increases,while that of MIS-HEMT devices decreases.At high temperature,the 2DEG concentration of MIS-HEMT device decreases,the depth corresponding to the peak concentration becomes shallow,and the field effect mobility decreases.According to the simulation results of MATLAB,at temperatures below 180K,acoustic deformation potential scattering and piezoelectric scattering are the main scattering mechanisms affecting carrier mobility;when the temperature is higher than180K,polar optical phonon scattering is the main mechanism affecting carrier mobility.