Design And Optimization Of High Voltage Vertical GaN Power Device With Fluorine-implanted Termination

Gallium nitride?GaN?power devices,as the third-generation semiconductor device,can deliver superior performance for next-generation high-power and high-frequency power electronics systems,because of the high breakdown strength,low on-resistance and high switching speed.However,for emerging vertical GaN power devices,it is usually difficult to reach the ideal parallel-plane BV,due to the electric field crowding around the periphery of the main junction which could lead to premature breakdown.In vertical SiC and Si devices,a variety of termination techniques have been demonstrated to alleviate the electric field crowding at the edge,but these junction-based termination techniques are challenging to realize in vertical GaN devices due to the difficulty in selective p-type doping and activation in GaN.At present,alternative termination techniques have been developed to suppress the premature breakdown in vertical GaN power devices by researchers at home and abroad,primarily including:?1?high-dose(¹0¹⁶ cm^-2)implantation have been used to form edge termination structures by creating deep-level traps in the termination regions;?2?bevel termination with comparable doping concentration(¹0¹⁷ cm^-3)in the p-layer and n-drift layer;?3?nitridation-based termination?NT?has been developed particularly for vertical GaN devices,enabling an enlarged energy barrier height and/or effective barrier thickness at the junction edge.However,these termination techniques are challenging to realize a higher voltage level?>2000 V?in vertical GaN devices,and some of them also cause the forward characteristics degradation of the devices.In view of the above problems and deficiencies,based on the unique feature of the negatively charged fluorine?F?ions in GaN which can favorably modulate the edge electric field,a fluorine-ion-based termination?FIT?technology for vertical GaN power devices has been proposed to suppress the premature breakdown by effectively adjusting the electric field distribution at the main junction edge in this work.In addition,a FIT structure for vertical GaN PiN diode has been also designed and optimized to suppress the electric field crowding at the edge of the pn junction to obtain a higher higher voltage.The key parameters of the FIT,including the F ion dose,the thickness and width of the FIT and the angle of the bevel structure,have been comprehensively investigated by TCAD simulations to reveal their impacts on BV.Moreover,with a tapered dose distribution in the FIT,the device can achieve a higher BV with an enlarged FIT dose window.