Research On The Effects Of Strain On The Characteristics Of AlGaN/GaN HEMT

In this thesis,the strain mechanism of AlGaN/GaN HEMT and the effect of strain variation on the device characteristics were studied.GaN is a typical representative of the third generation of semiconductor materials,with excellent characteristics such as wide band gap,high electron mobility and high electron saturation rate,which is suitable for harsh environment,such as high frequency,high temperature and high pressure.Moreover,the two-dimensional electron gas(2DEG)with high electron mobility and high electron density can be formed in the interface of AlGaN/GaN heterostructures due to the polarization effect of Ga N material.Meanwhile,there is strain in AlGaN/GaN heterostructures,and 2DEG is very sensitive to the variations of strain.In this thesis,the effects of strain variations on the characteristics of AlGaN/GaN HEMT devices were studied using Sentaurus TCAD simulation software based on the principle and strain model of AlGaN/GaN HEMT device,and the relationship between strain and electrical properties is established,meanwhile the effect of strained lattice constant or strain relaxation on transfer characteristic,output characteristic and breakdown characteristic of the device is illustrated.The results show that the strain values of the heterostructures of AlGaN/GaN HEMT is approximately proportional to the threshold voltage and saturated drain current,and the breakdown voltage is also improved due to the adjustment of strain.When the strained lattice constant(a)in the AlGaN/GaN HEMT increases by 0.001 ?,the threshold voltage is decreased by 0.085 V and the saturated drain current is increased by 0.028 A;meanwhile the strain relaxation degree(R)in the AlGaN/GaN HEMT increases by 0.05,then the threshold voltage is increased by 0.095 V and saturated drain current is decreased by 0.028 A.Furthermore,to optimize the breakdown voltage of the AlGaN/GaN HEMT,the local step-strain is added near the gate edge in the AlGaN layer.When the strained lattice constant near gate edge decreases,the distribution area of electric field near the gate edge will expand and the peak of the electric field will decrease,meanwhile the breakdown voltage of the device will increase.The results of the study on the strain and electrical transport are beneficial to regulate the electrical properties in the AlGaN/GaN HEMT.Aiming at electrical degradation in the AlGaN/GaN HEMT,the relationship between electric field,strain and electrical properties of the device based on strain model was explained in this thesis,and the strain mechanism of the electrical degradation in the AlGa N/GaN HEMT was also elaborated.Based on the theoretical relationship between strain and electrical degradation,the effects of different regional strain on the electrical degradation of AlGaN/GaN HEMT were studied by simulation.The results show that: firstly,the variations of strain in the barrier layer underneath the gate have significant influence on electrical degradation of the device compared to other two regions;secondly,the impact of strain variations in the barrier layer between gate and source on the transfer characteristics and output characteristics is more obvious than that between gate and drain,while the effect of strain variations in the barrier layer between gate and drain on breakdown characteristics of the device is greater than that between gate and source.