Research On Reverse Electrical Characteristics Of Lattice Matched InAlN/GaN High Electron Mobility Transistors

As the gallium nitride(GaN)material has excellent properties such as wide band gap,high breakdown electric field,high electron mobility,radiation resistance and heat resistance,Ga N-based power electronic devices have good high temperature resistance,fast switching characteristics,low On-resistance,high breakdown voltage and other properties.Therefore,it is being widely used in high-temperature,high-stress,highfrequency and high-power applications,such as LED lighting,solar cells,and photodetectors.It can also be used in fields such as sensors and material strain adjustment.Although due to the advancement of technology,Ga N-based electronic power devices such as Al Ga N/Ga N high electron mobility transistors(HEMTs),latticematched InAlN/GaN HEMTs,etc.have been well developed in the fields of biology and optoelectronics.But due to Ga N-based materials have quite a lot internal defects,so there are still many electrical reliability problems that need to be solved urgently.In this paper,through electrical testing,optical testing,and microstructure characterization under electron microscopy,we have thoroughly studied the reliability problems of the reverse transport mechanism,reverse current degradation,and premature breakdown of lattice-matched InAlN/GaN heterostructure devices.Based on the research results,some measures to improve the reliability of the device are proposed.The research contents of the thesis are summarized as follows:(1)Based on data fitting results of variable temperature current-voltage(I-T-V)and capacitance-voltage(C-V)tests on lattice-matched InAlN/GaN Schottky diodes,through the obtained results,a precise conductive dislocations physical model of Ga Nbased Schottky diodes in the reverse transport process is proposed,which clearly reveals its specific role in the reverse leakage of Ga N-based Schottky diodes.The results show that the reverse leakage current of the lattice-matched InAlN/GaN Schottky diode has a strong bias and temperature dependence characteristics.In the low-bias region,the current is dominated by the dislocation-related Frenkel-Poole(FP)emission mechanism.In the high-bias region,the current is dominated by the dislocation-related Fowler-Nordheim(FN)tunneling mechanism.The donor state of dislocation boundary ionization effectively reduced the position of the conduction band,thereby significantly reducing the Schottky barrier there and becoming an effective local conduction channel.The effective current barrier height is about 0.6 e V.(2)Firstly,based on the current-voltage(I-V)and capacitance-voltage(C-V)tests during the current degradation process of the lattice-matched InAlN/GaN Schottky diode,it is concluded that the degradation does not change the reverse current of the device.In the low-bias region,the FP emission mechanism is the dominant mechanism.In the high-bias region,the Fowler-Nordheim tunneling mechanism should be mainly responsible for the leakage current.This conclusion is of instructive significance for the analysis of the physical mechanism in the degradation process of Ga N-based HEMTs;Secondly,the changes in the leakage current and the "hot spot" map when the diode is degraded under the reverse voltage of-15 V and-2V are compared,indicating that only under the reverse bias voltage exceeding the threshold voltage,the device will suffer current degradation,and it is considered that FN tunneling should be the cause of permanent current degradation;Finally by applying a continuous reverse voltage stress of-14 V to the device,the reverse leakage current(I)change curve with the degradation time is recorded.then by counting the number of "hot spots"(n)(ie independent failure points)recorded by the emission microscope(EMMI)technology,the author establishes the functional relationship between I and n,which obey the Weibull distribution function.The function curve obtains two linear regions with different slopes through fitting,which correspond to the "bathtub curve" respectively.Two linear regions corresponding to early failure phase and loss failure phase.The significance of this method is to obtain the failure rule of this type of device through the analysis of a small sample.(3)Firstly,based on the breakdown behavior test of lattice-matched InAlN/GaN HEMTs,it is proposed that during the breakdown of the device,the increase in the defect density caused by the increase of the voltage between gate and drain leads to the breakdown to reach the critical value.Then the device reaches a permanent failure state.Secondly,Sentaurus TCAD simulation software was used to simulate the electrical characteristics of Schottky drain and grid-matched InAlN/GaN HEMTs with gate and drain field plates.Through simulation data analysis,it was concluded :1)when ohmic drain was replaced with Schottky drain,the leakage current of the device was reduced;2)The addition of a gate field plate can effectively share the electric field on the side near the drain under the gate,which increases the breakdown voltage of the device.What's more,the breakdown voltage continues with the increase of the length of gate field plate increase.3)When the drain field plate is added,as the length of the drain field plate increases,the peak electric field at the edge of the field plate gradually approaches the gate,and the potential distribution line will also move towards the gate which lead to denser electric field lines between the electrode of gate and drain.In the other words,breakdown voltage of the device decreases when the length of the drain field plate increases.The study strongly revealed that the fundamental means to improve the breakdown characteristics of HEMTs is to reduce the electric field on the side of the gate close to the drain.The simulation results provide a good theoretical basis for the improvement of the process plan.