Research Of Novel Enhancement AlGaN/GaN HEMT And SBD

Gallium Nitride(GaN) material has the merits of wide band gap, high critical electric field and high electron saturation velocity etc. Especially, the strong polarization effects of AlGaN/GaN heterojunction make the formation of two Dimensional Electron Gas(2DEG), which enables AlGaN/GaN HEMT(High Electron Mobility Transistor) to keep low conduction loss, fast switching speed etc. However, 2DEG hinders the realization of enhancement-mode(E-mode) HEMT. Fluorine ion implantation technology is an effective approach in fabricating high-performance E-mode AlGaN/GaN HEMTs. Owning to F ions’ strong electronegativity, the conduction band of the AlGaN/GaN heterojunction is raised, realizing in a normally-off AlGaN/GaN HEMT. However, the high concentration F- reduces 2DEG concentration and decreases the electron mobility of the channel, degrading the device forward conduction ability. Meanwhile Buck and Boost circuits are commonly used in power management, in which power rectifier is a key device. An excellent power rectifier should keep low forward voltage drop and high reverse breakdown voltage.This work is focused on two important issues: one is proposing Hybrid-Channel E-mode AlGa N/GaN HEMT to improve the performance of conventional F--based HEMT, and the other one is investigating the characteristics of AlGaN/GaN SBD(Schottky Barrier Diode). The main research contents include:(1) A novel Hybrid-Channel E-mode Al GaN/GaN HEMT(HCE-HEMT) is proposed. The hybrid channel comprises both high concentration F- and low concentration F-, while the high concentration F- is located at both sides of the gate-controlled channel to modulate the threshold voltage of the device that results in a normally-off AlGaN/Ga N HEMT. Meanwhile, the low concentration F- is seated in the middle of gate-controlled channel to suppress the gate forward leakage current, thus the gate voltage swing can be improved. Due to the low concentration of F-, the 2DEG under this region is weakly depleted. Moreover, the length of the high concentration F- region is optimized to be only 40% of gate length, alleviating influences of high concentration F- on channel. The simulation results show that maximum drain current density is improved by 40.3% with corresponding reduction of specific on-resistance by 23.3% in the proposed device compared with conventional F- implanted E-mode AlGaN/GaN HEMT. Furthermore, the breakdown voltage is only decreased by 5.3%.(2) To further improve the breakdown characteristic of HCE-HEMT, a Hybrid-Channel E-mode AlGaN/GaN RESURF HEMT(HCER-HEMT) is proposed. The only difference is that an extra low concentration F- is seated in drift region, which is simultaneously implementated with low concentration F- in the middle of gate-controlled channel. HCER-HEMT uniforms the surface electric field and improves the breakdown voltage of HCE-HEMT from 232 V to 347 V.(3) AlGaN/GaN SBD key production technology and process flow are investigated. Then the forward conduction characteristic and reverse breakdown characteristic are tested and analysised.Finally solutions for existing problems in the device is proposed.