Investigation Of Gate Leakage Current And Forward-Biased Gate Breakdown In HRCL-HEMT

Normally-off high electron mobility transistor(HEMT)with p-GaN gate has become the first generation of commercial GaN power device due to its superior performance and reliability,which can be widely used in consumer electronics,electric vehicles and other fields.The high-resistivity-cap-layer HEMT(HRCL-HEMT)is a p-GaN gate HEMT obtained by H plasma treatment with high breakdown voltage and low current collapse.The gate reliability of p-GaN gate HEMT is in the limelight of the academic circles and the industrial fields.Therefore,this dissertation focuses on HRCL-HEMT,studying its gate leakage current and forward-biased gate breakdown,the main contents are as follows:1.Studies on gate leakage current of HRCL-HEMT.The gate leakage currents of Pd/Au and Ti/Au contact devices have been studied by the temperature-dependent current-voltage(IG-VG)measurement.It is found that the gate leakage current is dominated by surface leakage current when the devices are at the reverse gate bias and low forward gate bias,and the mechanism is two-dimensional variable range hopping(2D-VRH).When the devices are at high forward gate bias,the gate contact has a significant influence on the gate leakage current,the mechanism is found to be thermal field emission(TFE)and Poole-Frenkel emission(PFE)for Pd/Au and Ti/Au contact,respectively.2.Forward-biased gate breakdown in HRCL-HEMT is investigated.The forward-biased gate breakdown characteristics of Pd/Au,Ni/Au and Ti/Au contact devices have been studied by temperature-dependence forward-biased gate breakdown,gate-step stress and time to failure(TTF).When submitted to gate-step stress,the failure of Pd/Au and Ti/Au contact devices occurs through a"current-driven" process and a "field-driven" process,respectively.The gate breakdown voltage of Ni/Au contact device increases with temperature,exhibiting avalanche breakdown characteristic.Besides,the TTF of both Ni/Au and Ti/Au contact devices is found to be Weibull-distributed and there is a negative correlation between the TTF and the initial gate leakage current.3.Preliminary studies on AlBN dielectric.The above studies show that gate leakage current can affect the performance of HRCL-HEMT,so it is necessary to find an appropriate dielectric to improve the gate leakage current.AIN can form a high-quality interface with GaN,but its insulation is poor.Adding B into AIN could improve its insulation.AlBN has been successfully obtained by pulsed laser deposition(PLD),and MIS-HEMT with AlBN dielectric is fabricated.It is found that the performance of A1BN MIS-HEMT is almost the same as that of HEMT through the IG-YG and capacitance-voltage(C-V)measurements.Therefore,a further research about AlBN dielectric is needed.