Study Of Novel Structures And Blocking Characteristics In GaN-based HEMTs

Due to many good properties,such as high carrier density,high carrier mobility,high critical electric field strength,low on-resistance,the Ga N-based HEMT has a wide prospect in the field of high-voltage power switching devices.How to improve off-state breakdown voltage without degrading other electrical characteristics as small as possible has been an active research area.The thesis is focused on the research of the blocking characteristics of Ga N-based HEMT with bidirectional blocking capability and the exploration of new methods for higher breakdown voltage based on novel field plate structures and polarization junction.The main factors that restrain the blocking capability of Ga N-based HEMT are also revealed.Main contents and achievements are as follows.1.A novel Ga N-based HEMT with a source-connected T-shaped field-plate is presented and studied for improving blocking voltage and FP efficiency effectively.The mechanism of modulation of the electric potential and the channel electric field distributions with ST-FP is analyszed systematically by simulations.The relationship of the T-shaped field-plate structure and the blocking voltage,FP efficiency is also studied.And the optimization design method of ST-FP is obtained.The off-state breakdown characteristics of Ga N-based HEMT based on super junction structure(SJ HEMT)is investigated by simulations.The mechanism of improving the breakdown voltage with SJ is analyszed.And the relationship between the SJ parameters and breakdown voltage,current as well as on-resistance is studied.Furthermore,the optimization design of SJ is carried out.Simulation results show that the blocking capability of SJ HEMT is better than that of the traditional HEMT and the FP HEMT.2.A novel Al Ga N/Ga N HEMT with a super-juncion field-limiting ring(SJ-FLR HEMT)based on polarization juntion technology is realized,who has a excellent bidirectional blocking capability.The inherent mechanism of improving the bidirectional blocking capability with SJ-FLT is studied by simulations.And the effect of the structure parameters of SJ-FLT on the forward/reverse breakdown voltage,on-state resistance is also investigated.3.Three kinds of Ga N-based bidirectional power switching devices which are based on super junciton(SJ)structure,field-limiting ring(FLR)structure and floating filed plate(FFP),respectively,are proposed.The relation between device structure parameters,on-state characteristics,bidirectional blocking characteristics is analyszed in detail with the aid of numeral simulation.The mechanism of enhancing bidirectional blocking characteristics with the super junciton structure,the field-limiting ring structure and the floating filed plate is revealed.Finally,the valuable research results and regularity are achieved.