Research On E-mode Ultra-thin Barrier AlGaN/GaN HEMT

Compared with conventional Si-based power MOSFET,AlGaN/GaN HEMT has lower conduction losses,smaller parasitic capacitance(CISS and COSS),and there is no parasitic body diode.It has a very broad application prospect in high-frequency and high-speed fields,and can satisfy the development trend of power system pursuing higher power density and lower power consumption.However,due to the high concentration of 2DEG at the interface of AlGaN/GaN heterojunction caused by polarization effect,Al-GaN/GaN HEMTs are intrinsic D-mode devices.E-mode power switches are more suit-able for power systems because they have fail-safe function and only need single power supply.Therefore,in order to apply GaN HEMT to power field,improve power system conversion efficiency and reduce system loss,this paper focuses on the research of the E-mode ultra-thin barrier AlGaN/GaN HEMT.From device design,device fabrication to device performance characterization and analysis,a complete device research has been carried out in this paper.Besides,in order to solve the problems that the threshold voltage of ultra-thin barrier AlGaN/GaN HEMT is too low and the threshold voltage modulation range of conventional p-GaN HEMT is too small,an E-mode ultra-thin barrier Al-GaN/GaN HEMT with hybrid gate structure is proposed to achieve a larger threshold voltage(2.04 V)and a wide range of threshold control(1.63 V?3.84 V).The main re-search contents of this paper are as follows:(1)Based on the principle of polarization modulation,the key structural parameters of the device were designed by simulation.Base on the mechanism of LPCVD-SiNx passivation layer recovering 2DEG con-centration,By regulating the interface charge at the Si3N4/AlGaN interface,the recovery effect of LPCVD-SiNx passivation layer on 2DEG in the non-gate region was simulated,and the recovered 2DEG concentration was in good agreement with the experimental re-sults reported in the paper.On this basis,the key structural parameters(AlGaN barrier layer thickness,Al composition,etc.)of the device were simulated and designed based on the principle of polarization modulation,so as to obtain the E-mode performance and guide the device fabrication.(2)Fabrication and test of E-mode ultra-thin barrier AlGaN/GaN HEMT.After designing the key structural parameters of the device in the Sentaurus-TCAD simulator,an E-mode ultra-thin barrier AlGaN/GaN HEMT was fabricated based on a 6-inch Si-based GaN epitaxial.The threshold voltage of device is 0.8 V,the saturated current and the on-resistance are 500 mA/mm and 12.3 ?·mm,respectively.And the gate leakage as low as nA/mm level.By analyzing the device fabrication process,the mecha-nisms of the two phenomena are respectively proposed:the GaN Buffer layer has a lon-gitudinal leakage pathway,and there is an interfacial trap capture effect and a substrate heat electron injection effect in the high electric field.It provides theoretical support for further optimization device fabrication process.(3)An ultra-thin barrier AlGaN/GaN HEMT based on hybrid gate structure is pro-posed.The ultra-thin barrier AlGaN/GaN HEMT also has a problem of low threshold volt-age.In addition,due to the very low ionization and activation rates of p-type doping in GaN materials,it is difficult to grow p-GaN layer with high hole concentration(>3 x 1017 cm-3)in conventional p-GaN HEMT,which is not convenient to achieve a wide range of threshold voltage modulation,and can not satisfy different application scenarios.There-fore,from the perspective of structural optimization,a novel enhanced ultrathin barrier AlGaN/GaN HEMT with(p-GaN/MIS/Gate Field Plate)hybrid gate structure is proposed in this paper.This device combines the thin barrier and p-Gate technology,and has a stronger ability to regulate the energy band of AlGaN/GaN heterojunction under the gate.Based on light-doped p-GaN,a larger threshold voltage(2.04 V)and a larger range of threshold voltage modulation(1.63 V?3.84 V)are realized.