Study On The Characteristics Of Recessed AlGaN/GaN MOS-HEMT

The current-voltage characteristics and the capacitance-voltage characteristics of recessed Al Ga N/Ga N MOS HEMT are studied in this paper, and its interface state is also analyzed.Firstly, the structure of recessed MOS HEMT is designed with the simulation tool of Silvaco TCAD. After gradual analog, detailed structure parameters and trap doping are determined. Then the enhancement-mode device is achieved and compared with traditional devices.Secondly, fundamental characteristics of the recessed MOS HEMTs and the conventional ones have been tested and analyzed with precise semiconductor analysis meter Keithley4200 scs. On one hand, it is found that the output current of recessed MOS HEMTs is larger than that of HEMTs. Etching of the barrier layer would increase the threshold voltage of recessed MOS HEMTs. In the paper, MOS HEMTs are proved to have a stronger ability to reduce its gate leakage current and smaller transconductance because of the metal-oxide-semiconductor structure. On the other hand, it is also discovered that subthreshold characteristics and output characteristics are improved along with the etching depth increasing. And densities of the traps in the interface between Al2O3 and Al Ga N are estimated.Thirdly, channel hot electron injection and gate electron injection have been tested. It is determined that the gate electrons may enter into channel under high electric field on the condition of gate electron injection stress, which would influence the 2DEG density. The degradation mechanism is proposed that the interface traps between dielectric and barrier trapping the channel hot electrons or the gate electrons would form a layer of negative charges. The mechanism is used to analyze on-state and off-state degradation.Fourthly, the interface states of Al Ga N/Ga N heterojunction are tested with the method of conductivity. It is found that there is more than one type of traps in recessed MOS HEMT. And the density of the interface states increases with etching depth. But there is no obvious change of trap energy level.Finally, the effect of direct-current gate voltage stress on the interface states of MOS HEMTs is introduced. The density decreases after positive gate stress because of the trap energy level dropping. And it decreases after negative gate stress because of energy level up. But all of the trap time constants are the microsecond.