Breakdown Mechanism And New Structure Of Vertical GaN Based Device

At present,the global semiconductor industry develops rapidly,espesically in restent years,the earth is facing an issue of energy shortages,environment degradation and other tests.GaN based vertical architectures are best choice for achieving high breakdown voltages and high amperage devices,do not suffer from thermal management issues associated with thin films surfaces,and provide increased number of die on a wafer.The vertical GaN based device can meet the needs of high power and low cost field.In this paper,the basic properties of GaN materials are briefly described,and the mechanism of GaN vertical power diode are analyzed.The structural parameters that affect the optimal value of vertical device are discussed emphatically.And make a detailed comparison between lateral diodes and vertical diodes,pointing out the advantages of vertical diodes and the lacks of lateral diodes,then two new vertical structures are proposed: the new charge compensation structure and the high-K/low-K compound dielectric structure.The simulation results show that the novel structures can significantly improve breakdown voltages and low on-resistance of vertical device.To solve the problem of the electricfield line concentration near the pn junction and the uneven distribution of electric field in n-type GaN,a new vertical GaN pn diode has been carried out,the vertical diode has a charge compensation structure which can introduce a high-density hole at the interface,because the n-type GaN could be inverted by utilizing the negative fixed charge,which can extend the width of the depleted region in n-type layer,and thus greatly enhance the breakdown voltage.After verified by simulation and optimization when Tn is 17.5μm and Nn is 1×1016cm-3,it realizes a breakdown voltage of 5965 V with 1.52mΩ·cm~2,enabled the diodes that approached the theoretical limits for GaN.The feasibility of fabrication process for novel structure still needs time to verify.However,it provides a new idea for design GaN based vertical diodes.In order to further enhance the performance of pn diodes,a vertical GaN p-n junction diode with high-K/low-K compound dielectric structure is proposed based on the existing process conditons.The high-K/low-K compound dielectric structure consists of a layer of high dielectric constant and multilayer dielectric layers which have a lower dielectric constant.These compound dielectric layers formed electric field will be suppressed due to the effects of high-K passivation,and a new electric field peak will be introduced into the p-n diode,because of a discontinuity of electrical field at the interface of high-K and low-K layer.Therefore the distribution of electric field in p-n diode will become more uniform and an enhancement of breakdown voltage can be achieved.Numerical simulation demonstrate that GaN CD-VGD with a BV of 10650 V and a Ron of 5.83mΩ·cm~2,the average breakdown electric field is 3.1 MV/cm,resulting in a figure-of-merit of 19GW/cm~2,its FOM value is very close to the GaN-limit.