Impact Of Interface Treatment On The Characteristic Of AlGaN/GaN MIS-HEMTs

Gallium nitride?GaN?-based high electron mobility transistors?HEMTs?has been received broad attention because of its outstanding features as high electron mobility,high current density and high breakdown voltage,etc.It has been an important component of power electronic devices,and has a good application potential in the electric energy conversion.AlGaN/GaN HEMTs suffer from the current collapse and the reliability of device due to the high defect density and the surface states.AlGaN/GaN MIS-HEMTs could reduce the gate leakage current and improve breakdown voltage.In addition,the passivation can improve the interface quality and suppress the current collapse.Therefore,it has great research and application value to develop AlGaN/GaN MIS-HEMTs.In this thesis,the work mainly focuses on the interface improvement of AlGaN/GaN MIS-HEMTs,including of the optimization of ohmic contact,the designing of material structure and the improvement of interface quality.The main contents of this thesis are as follows:1.The influence of different metal thicknesses and annealing condition on Ohmic contact,and the temperature stability of Ohmic contact were investigated.The characteristics of Ohmic contact with different Al and Au thicknesses for different annealing condition was studied.The results showed that Ohmic contact resistance formed by Ti/Al/Ni/Au=20/130/50/50 nm was 0.77?·mm by annealing at 845?.Ohmic contact with 130 nm Al is more stable than that of 100 nm Al and 160 nm Al under testing from 25?to 300?,the difference between Ohmic contact with 50 nm Au and 150 nm Au are not obviously.2.The leakage current and breakdown voltage of AlGaN/GaN/AlGaN High Electron Mobility Transistors on silicon with different GaN channel thicknesses were investigated.The results showed that thin GaN channel was beneficial for obtaining high breakdown voltage,based on the leakage current path and the acceptor traps in the AlGaN back-barrier.The transfer and output characteristics of the devices with AlGaN back barrier are not obviously degraded due to about 1?m GaN channel.The breakdown voltage of the device with 800nm-thick GaN channel was 926V@1mA/mm,and the leakage current increased slowly between 300 V and 800 V.3.The effects of different kinds of interface treatment on the characteristic of AlGaN/GaN MIS-HEMTs were studied in this paper.N₂ and NH₃ plasma pre-treatment were used to improve the interface quality.The results show that N₂ plasma pretreatment could reduce the current collapse of devices.By optimizing the time of N₂plasma pretreatment,it was found that dynamic characteristic of devices with 10 min the pretreatment was improved.It demonstrates that the dynamic characteristic of devices with the annealed AlN interlayer was dramatically improved.The Vth hysteresis were decreased from 411 mV to 111 mV,and the devices current collapse factor were reduced from 42.04 to 4.76 after under OFF-state V_DS stress of 900.