Breakdown Mechanism And New Structure Of Vertical GaN Based Device

GaN is a typical representative of the third-generation wide bandgap semiconductor materials with features such as large band gap,high saturation electron drift velocity,high critical breakdown field,and good thermal conductivity.Experiments and theories show that GaN materials are very suitable for fabricating high-power devices.GaN-based vertical structure devices with large current and high breakdown voltage are being studied extensively.In this paper,the basic properties of GaN materials are briefly described.A detailed comparision of GaN-based lateral rectifier diodes and vertical rectifier diodes is made.The advantages of vertical rectifier diodes and the disadvantages of lateral rectifier diodes are pointed out.And the principle of vertical rectifier diodes which include PN junction,schottky barrier diode and junction barrier schottky diode are analyzed.The structural parameters that affect the optimal value and breakdown voltage of JBS are discussed emphatically.Two new structure to improve breakdown voltage of JBS are proposed innovatively:the new charge compensation structure and the high-K/low-K compound dielectric structure.The simulation results of Silvaco TCAD tools show that the both structures can improve the breakdown voltage effectively and a higher figure of merit of devices can be achieved.In order to solve the problem of the electric field line concentration near the pn junction and non-uniform electric field distribution in the drift region of JBS devices,a GaN-based JBS device with charge compensation layer structure was proposed in this paper.The fixed negative charge between the interface of Al₂O₃ dielectric layer and GaN material to invert the N-type GaN in the drift region,and the high concentration hole charge column which is induced by the fixed negative charge can further extend the depletion region and make the electric field in the drift region distribute more uniform.and thus greatly enhance the breakdown voltage.It can be seen that when the fixed negative charge density is 5×10¹² cm^-2 and the doping concentration in the drift region is 1.5×10¹⁶ cm^-3 throuth simulation and optimization,the breakdown voltage of the device can reach 3691 V with 3.7 mΩ?cm² of on-resistance.A GaN-based JBS with superior performance is realized in theory.In order to further improve the performance of GaN-based JBS and the feasibility of the process implementation,a novel GaN-based JBS with high-K/low-K compound dielectric structure was proposed in this paper.There is discontinuity of electric field between interfaces of high-K and low-K compound dielectric layers with different dielectric constants.And a new electric field is introduced through the discontinuity of this electric field.The electric field line concentration effect at the junction edge can be suppressed to a certain extent due to the high-K compound dielectric layer is adjacent to the P⁺region.Therefore the peak electric field near the junction surface is suppressed,and the electric field far from the junction surface is improved,so that the electric field distribution in the drift region become more uniform and an enhancement of breakdown voltage can be achieved.The simulation results show that when the doping concentration in the drift region is 1.5×10¹⁶ cm^-3 and the thickness is 16μm,two electric field peaks in the drift region can be achieved with a high-K layer and two low-K layer,so that a breakdown voltage of 3491 V is achieved,which is increased by91%compared with the conventional structure.The on-resistance is 10.9 mΩ?cm² and turn-on voltage is 0.6V,resulting in a figure-of-merit of 1.1 GW/cm².