| GaN has great application potential in the field of power electronics because of its excellent performance.Currently,many researches are trying to improve the forward blocking performance of GaN,but devices with reverse blocking capability are also very important in many applications.In RF and power switching applications,the transistor drain will unexpectedly appear negative voltage,so the device must be protected to prevent the device from being damaged by reverse current.In addition,bidirectional switch is an important part of many power converters.Using AlGaN/GaN HEMT with reverse blocking capability to form bidirectional switch can reduce system components,improve switching speed and reduce conduction loss.Based on the above problems,this work proposes an ultra-thin barrier AlGaN/GaN MISHEMT with reverse blocking capability,and optimizes the threshold voltage and reverse breakdown voltage of the proposed device.The main work contents are as follows:1.Structure design and analysis of ultra-thin barrier AlGaN/GaN MISHEMT with reverse blocking capability.The device realizes reverse blocking through MIS-D.During reverse blocking,the depletion region extends from the drain to the gate,and the reverse breakdown first occurs near MIS-D,and the reverse leakage current of the device is still less than 10n A/mm when VDS=-100V.On the other hand,the ultra-thin barrier structure is introduced to avoid etching the barrier layer and realize the depletion of 2DEG under the gate and MIS-D,and the threshold voltage of 0.82V is obtained by designing the barrier layer thickness,Al composition and dielectric thickness.In addition,MIS-D increases the on-resistance of the device and introduces the forward drain turn-on voltage.The simulation results show that the on-resistance of the device increases with the increase of MIS-D length,and the on-resistance of the device is10Ω·mm when the length of MIS-D is 2μm;Reducing the work function of MIS-D metal can reduce the drain turn-on voltage,and the drain turn-on voltage is as low as0.2V when the work function of MIS-D metal is 4.5e V.2.Because the threshold voltage of ultra-thin barrier devices is generally low,this work proposes to replace the original MIS gate with p-GaN,and greatly improve the threshold voltage of devices by using p-GaN and ultra-thin barrier.When the thickness of p-GaN gate is 60nm and the doping concentration is 1×1017cm-3,the threshold voltage of 2.1V is obtained.Furthermore,the threshold voltages of 1.78-3.57V and1.90-3.31V are controlled by changing the thickness and doping concentration of p-GaN.3.The growth process of Si Nx and precursor gas ratio will all affect the recovery of 2DEG by Si Nx passivation layer.In this work,by reducing the positive charge density of the interface between Si Nx and AlGaN near MIS-D,a low-charge region is formed near MIS-D,which is used to simulate the weakening process of the ability of Si Nx passivation layer to recover 2DEG.When the device is in the reverse blocking state,a new electric field peak will be formed at the boundary of the low charge region,which can improve the electric field distribution near MIS-D and increase the reverse breakdown voltage.When the positive charge density at the interface between Si Nx and AlGaN in the low charge region is reduced to 80%of the normal region and the length of the low charge region is 4μm,the reverse breakdown voltage of the device is changed from-265V to-811V,while the on-resistance is only increased by 4.4Ω·mm. |
