| Silicon carbide has been recognized as one of the wide bandgap semiconductor materials which can replace silicon for certain power device applications.4H-SiChave wide bandgap,high critical breakdown electric field and carrier saturation velocity and the characteristics of high thermal conductivity,especially suitable for used in radiation resistance,high temperature,high frequency,high power and high density integrated electronic devices.Now existing planar 4H-SiC PiN diode,4H-SiC Schottky diode and the trench structure of JBS diode,DMT diode all have good electrical performance.In particular,the trench structure of the 4H-SiC device,which has the advantage of the 4H-SiC and the trench structure,has realized thecompromise betweenthe forward voltage drop and reverse leakage current,is the popular development direction of modern devices.Along with the ultra-thin epitaxy technology such as molecular beam epitaxy,chemical vapor deposition development,the preparation of polysilicon/4H-SiC heterojunction has no problem.The polysilicon/4H-SiC heterojunction diode and the 4H-SiC Schottky diode are all unipolar device,but the Schottky junction greatly influenced by image force effect and tunneling effect which the reverse leakage current is larger,So the polysilicon/4H-SiC heterojunction have more advantages for power devices application.Based on the properties of silicon carbide and the physical properties of polysilicon/4H-SiC heterojunctions,and the working principle of 4H-SiC diodes and the band structure of polysilicon/4H-SiC,the paper designthree kinds structure of new type semiconductor diode and then Verify the feasibility of these devices and study the electrical characteristics by the simulation software Silvaco-TCAD.The first structure is DualPolysilicon/4H-SiC Heterojunction diode(DHT diode),which use the polysilicon/4H-SiC heterojunctions with different barriers height instead of the Schottky junction of the DMT diode.The DHT diode,which realized the compromise of the forward voltage drop and reverse block voltage,use the polysilicon/4H-SiC heterojunction to achieve further less leakage current.Based on the contrast the forward and reverse characteristics of DHT and DMT diode,at the same time,further studied about the effect on electrical characteristics of the device structure parameters,the interface charge,temperature.The second structure is Junction Barriers Schottky-Heterojunction Diode(JBSH diode).In JBS diode,the forward current flows main through the Schottkyregion,this can result the resistance of the drift region under the P~+region being very high.In order to solve this problem,p~+polysilicon regions are added in P~+region,thus forming a new JBSH diode which increases the current flows area and effectively reduce the resistance of drift region but also leads to the decrease of the breakdown voltage.So the author optimized the parameters of structure and analysis the I-V characteristics of JBSH diode,in order to realize the compromise of the resistance of the drift region and the breakdown voltage.The third structure is Merged PiN and Heterojunction diode(MPH diode)which can be thought of as the combination of PiN diode and polysilicon/4H-SiCheterojunction diode.This chapter analysis the forward and reverse characteristics of the MPH and MPS diode,the result shows that the MPH diode in security as MPS diode forward voltage drop and low resistance of drift region,at the same time,significantly reduce the reverse leakage current.Also studied the influence of temperature on the I-V device characteristics and analyses the factors influencing the device of power loss. |
