| AlGaN/GaN high electron mobility transistors(HEMTs)device has the advantages of high voltage resistance,high temperature resistance and high power due to the excellent characteristics of GaN material.It is a hot spot in the research field of power semiconductor devices.However,due to the polarization effect of AlGaN/GaN heterojunction,there is highdensity natural two-dimensional electron gas(2DEG)in the channel of conventional AlGaN/GaN HEMT,which is a depletion device,which has great limitations in practical engineering application.In addition,although Gan materials have high critical breakdown electric field,the actual withstand voltage value of AlGaN/GaN HEMT devices is far lower than its theoretical value due to the high electric field at the gate edge and the leakage current of GaN buffer layer.Aiming at the two key problems of realizing enhancement mode and high withstand voltage,two device structures are studied and designed to solve these two problems respectively.In order to carry out the research content in depth,the research progress of AlGaN/GaN HEMT devices to realize enhancement mode and improve the withstand voltage value at home and abroad is introduced,the basic mechanism and common methods of realizing enhancement mode are introduced,and the withstand voltage and breakdown mechanism of AlGaN/GaN HEMT devices and common boost withstand voltage technology are analyzed.In order to realize the enhancement mode AlGaN/GaN HEMT device and obtain higher threshold voltage,an enhancement mode AlGaN/GaN HEMT structure with double heterostructures under the gate is designed by using the depletion effect of double heterostructures on channel electrons.The realization principle of the structure is explained by using the charge control model of double heterojunction,the formula of threshold voltage of double heterojunction is deduced,and the feasibility of the structure is demonstrated theoretically.The structure and parameter setting of the device are introduced in detail.The effects of modulation layer thickness,modulation layer length,Al mole fraction and groove depth on the threshold voltage of the device are studied.The study shows that the Al mole fraction of the modulation layer of the device is linearly proportional to the threshold voltage.If the Al mole fraction of the modulation layer is smaller than the barrier layer,the threshold voltage of the device will increase,on the contrary,the threshold voltage will decrease.Increasing the thickness of the modulation layer will make this modulation effect more obvious.When the Al mole fraction of the modulation layer is 0% and the thickness is 112 nm,the threshold voltage of the device can reach 2.13 V,which is 173% higher than that of the ordinary fluted gate structure.In order to solve the avalanche breakdown of conventional AlGaN/GaN HEMT caused by the injection of source electrons into the high electric field region near the gate field plate and improve the withstand voltage value of the device,a new AlGaN/GaN HEMT device structure with intrinsic GaN modulation layer between gate and source is designed.The technical principle of improving the withstand voltage of the intrinsic GaN modulation layer is analyzed.Through the new structure of the modulation layer,the 2DEG in the part regions of the modulation layer corresponding to the channel layer can be completely exhausted,the depletion region of the device can be extended,and the source electrons are difficult to be injected into the high electric field region near the gate field plate.The structure and parameter setting of the device are introduced.The effects of the length and thickness of the modulation layer on the breakdown voltage,specific on-resistance and threshold voltage of the device are studied.The new structure has a modulation layer length of 0.5 μm and thick of 0.25 μm has1086 V breakdown voltage,while the conventional structure is only 862 V.The breakdown voltage of the new structure increases by 26%. |
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