Design And Optimization Of Diamond Based Schottky Diodes

Diamond,as a candidate for a new generation of wide-bandgap semiconductors,possesses several unique properties such as high critical breakdown electric field,high carrier mobility,high thermal conductivity,and low dielectric constant.These characteristics enable diamond devices to operate in extreme environments such as high temperature,high pressure,and high frequency.Currently,diamond-based Schottky diodes have achieved a blocking voltage of 10 k V,but there is still a large gap from ideal performance.E-field concentration at the edge of Schottky junction is one of the important reasons affecting their reverse characteristics.In addition,because of the high critical breakdown electric field of diamond,the device will face the risk of dielectric breakdown.In view of the above problems,this thesis focuses on the breakdown mechanism and electric field optimization by using TCAD simulation.The main research contents are as follows:1.Junction termination technology is one of the methods to alleviate the electric field concentration effect at the electrode edge.(1)The breakdown point of the device with metal field plate terminals is located in the dielectric layer at the end of the field plate,making it difficult for the metal field plate to play its intended role.By optimizing the length of the field plate and the thickness of the field oxygen,the breakdown voltage can be increased from 1331 V to 1997 V.Then the dielectric materials are studied.The dielectric materials with high dielectric constant or high critical breakdown electric field are the most suitable.On this basis,the slope field plate and the multi-level field plate are proposed,and the breakdown voltage is increased to 2489 V and 2623 V respectively.But the breakdown point is still in the dielectric layer.(2)The trench terminal essentially transfers the electric field into the dielectric layer,so the breakdown voltage of devices with trench terminal is generally lower than that of devices without junction terminal.For this reason,a longitudinal field plate is proposed,and a transverse electric field is introduced to improve the withstand voltage.Finally,a breakdown voltage of 1724 V is achieved.(3)The floating metal ring does not need dielectric withstand voltage,so there is no risk of dielectric breakdown.A single FMR has a very limited effect on the reverse characteristics,but multiple FMRs can achieve good results.Finally,with three FMRs and optimized ring spacing,a breakdown voltage of 2607 V is achieved.2.Based on the research of traditional junction terminals,a field plate junction terminal with mesa structure is proposed.This structure is to reduce the electric field of the dielectric layer by introducing a trench structure at the end of the stepped field plate.In order to completely avoid the problem of dielectric breakdown,two schemes are proposed to transfer the breakdown point to diamond:(1)The first step field plate is close to the diamond,thus introducing a stronger electric field spike on the diamond surface.In this scheme,the on-state resistance of the device is 28.34 mΩ·cm~2and the breakdown voltage is 3472 V and BFOM value is 425.362 MW/cm~2.And the junction terminal efficiency is 65.97%.(2)The trench structure penetrates the dielectric layer,and then grows diamond on the drift layer to realize the transfer of the breakdown point.In this scheme,the on-state resistance of the device is 27.56 mΩ·cm~2,the breakdown voltage is 3314 V and the BFOM value 398.4 MW/cm~2.And the junction terminal efficiency is 80.27%.Finally,a vertical hydrogen-terminated diamond Schottky diode is proposed to reduce the on-state resistance and reverse leakage current.The current density of this device is 170.20 A/cm~2with the forward bias of 10 V,the on-state resistance is 25.32 mΩ·cm~2,and the reverse leakage current is three orders of magnitude lower than that of the non-terminal device.