Research And Fabrication Of Recessed-Gate GaN HEMT Devices

Power devices are important components of power conversion,and their performance is a key factor affecting power conversion efficiency.Silicon-based power devices have been developed for nearly 60 years and can not meet the increasing performance requirements of people.Therefore,it is urgent to find a new semiconductor material to replace silicon.Gallium nitride?GaN?is regarded as the best successor because of its excellent performances such as wide bandgap,high electron saturation speed and high critical breakdown electric field.GaN-based high electron mobility transistor?HEMT?is a heterojunction field effect transistor,which can work in harsher environments such as high voltage,high frequency and high temperature.It is favored by automotive electronics,power supply,rail transit,aerospace,weapons and other important fields.Due to the existence of polarization effect,conventional AlGaN/GaN HEMT is a normally-on device.Considering the complexity of driving circuit and the reliability of system,it is necessary to develop the enhancement-mode?E-mode?GaN HEMT devices.In this experiment,the E-mode Al₂O₃/AlGaN/GaN MIS-HEMTs are realized by recessed-gate technique.This technique is a simple and efficient way to adjust the threshold voltage by controlling the etching depth of the recessed-gate.However,the damage and the interface state caused by gate recesse etching process will seriously affect the performance of devices.Therefore,how to develop a high efficient and quality gate recesse etching technique has become the focus of research.Firstly,this paper further optimizes the ohmic contact in GaN HEMT devices through experiments based on the previous work.The ohmic contact resistance of 0.60?·mm is obtained when the annealing condition is 850?/35 s and the etching depth of the barrier layer is 8 nm.Secondly,the principle and characteristics of inductively coupled plasma?ICP?dry etching technique and high temperature thermal oxidation wet etching technique are studied in the most critical gate recesse etching process.ICP dry etching technique has high efficiency and low cost,and high temperature thermal oxidation wet etching technique has high quality and low damage.Therefore,this experiment fully exploits the advantages of both.The E-mode AlGaN/GaN HEMTs were fabricated by two-step etching technique,combining ICP dry etching technique with high temperature thermal oxidation wet etching technique.The two-step etching is a high efficiency,high quality,low damage and low cost etching technique,which can be self-terminated at the AlGaN/GaN interface.Finally,two kinds of E-mode Al₂O₃/AlGaN/GaN MIS-HEMT devices with threshold voltage exceeding+3 V were successfully fabricated by ICP dry etching technique and two-step etching technique respectively.The test results show that the devices fabricated by two-step etching technique exhibit many advantages in performance,such as large saturated output current,high I_on/I_off,low threshold voltage hysteresis,large gate voltage swing,small off-state leakage current and high breakdown voltage.Therefore,two-step etching technique can be used to fabricate high-performance Recessed-gate E-mode GaN HEMT devices...