Research On Novel Structure And Characteristic Of AlGaN/GaN HEMT Device

Power semiconductor devices have been widely used in power electronics,microwave communication and other fields.In recent years,the market has made new demands on the performance of working frequency and voltage tolerance.As the silicon device has gradually approached its theoretical limit,GaN materials with the advantages of wide bandgap,high puncture electric field,high temperature resistance and radiation resistance have considerable potential market value.The 2DEG with high density and high mobility existing in AlGaN/GaN heterojunction can achieve high voltage tolerance and high frequency performance of HEMT devices.In this paper,the performance and process of enhanced AlGaN/GaN MISHEMT were studied by simulation and experiment,and a development of new structure of the gate-sinking AlGaN/GaN HEMT was carried out.The main contents include:?1?Through silvaco atlas simulation,the influence of gate groove etching and gate dielectric on HEMT performance was studied.With the increase of etching depth,the threshold voltage(V_TH)and the gate leakage current?I_G?of HEMT increase.The recessed-gate MISHEMT can be achieved by gate dielectric deposition,the I_G,the maximum transconductance(G_M-max)and the saturation current(I_DS-max)of the device are decreased with the increase of the thickness of the gate dielectric.The breakdown voltage(BV_DS)of the conventional HEMT and the recessed-gate MISHEMT increases with the increase of the gate-drain distance(L_GD),but the recessed-gate MISHEMT has greater BV_DS when the L_GD is equal to the same.?2?The recessed-gate MISHEMT was fabricated by etching about 20 nm AlGaN layer in the way of multiple low-speed etching,a V_TH of 1.4 V enhanced device was successful achieved.With a gate voltage bias(V_GS)of 5V,the I_DS-max and the on resistance(R_on)of the device are 390 mA/mm and 15.31?mm,respectively.The I_G of the recessed-gate MISHEMT is maintained at 10^-10 mA level,6 orders of magnitude smaller than the conventional Schottky-gate HEMT.A method of etching interface repairing by the thermal oxidation and wet etching after ICP dry etching gate groove was proposed.The R_on of the device is reduced to12.43?mm,the I_DS-max is elevated to500mA/mm at V_GS=5 V,the G_M-max is 170mS/mm,and an on-off current ratio of 10⁶ is achieved.?3?A new structure of AlGaN/GaN HEMT was designed and fabricated based on Ta-metal gate-sinking,the time and the temperature of annealing process are found to be the control factors of gate-sinking effect by comparative study.The V_TH of the device shifts from-6 V to-3 V after 200s annealing at 450?.The V_TH and the I_G of the device will rise with the increase of the annealing time and temperature,and the deposition of TaNx gate with upgrade schottky barrier can further enhance the threshold voltage and inhibit the gate leakage current.The thermal oxidation gate-sinking AlGaN/GaN MISHEMT was achieved by annealing in oxygen environment.After 550?annealing for an hour,the V_TH of the device is elevated to-2.3 V and the I_G keeps at 10^-5 mA level.When the gate-singking happens in thermal oxidation process,the surface layer of Ta-metal is oxidated to be Ta₂O₅ as high-k dielectric,which can suppress the I_G.