Research On Structure Design And Simulation Study Of Enhancement-mode AlGaN/GaN HEMT

GaN,as the representative of the third generation of wide bandgap semiconductor materials,with its large band gap width,high electron saturation rate,high temperature resistant,radiation tolerance characteristics is becoming a hot spot of research,especially in high temperature,high power,microwave field has a great application prospect.Because of the characteristic of AlGaN/GaN heterostructure,heterojunction interface can produce high density of the two-dimensional electron gas(2DEG),which forms the conductive channel,so most study of AlGaN/GaN HEMT devices are depletion-mode devices for a long time.In order to achieve the purpose of more applications,we need to realize enhancement-mode device that is normally closed type device.For the purpose of reducing heterojunction 2DEG,thinning barrier layer thickness and fluorine plasma treatment is both feasible to achieve enhancement-mode AlGaN/GaN HEMT devices.According to the corresponding device structure and reasonable physical model,Sentaurus TCAD simulation software is used to study the effect of threshold voltage of two kinds of structure in this thesis,and we propose an optimization of the structure to rise the breakdown voltage of the device on fluorine plasma treatment enhancement-mode devices.The following aspects were studied:2DEG concentration decreases as the barrier layer thinning by explore how barrier layer thickness change threshold voltage.The study found that the threshold voltage of thin barrier layer device rises when the thickness of barrier layer thins.In the barrier layer thickness of 8 nm,the threshold voltage of device is 0.1V.Although it achieves enhancement features,thin barrier layer greatly influences the saturation current.The higher concentration fluorine plasma treatment under the gate causes a bigger loss to 2DEG by explore how the concentration of fluorine plasma influence the threshold voltage.The threshold voltage of device increases with the increased concentration of fluorine plasma treatment,the threshold voltage reached 2.32 V when fluorine plasma concentration is 8.5?1018 cm-3.Considering the high concentration of fluorine plasma treatment can affect the positive feature of devices,the design of symmetric interval fluorine plasma treatment under the gate optimize the output characteristic of the device,saturation current increases by 13%.According to the breakdown mechanism of AlGaN/GaN HEMT,we designed a low density drain HEMT to rise its breakdown voltage(Vbr).we make light dope fluorine plasma treatment in the passivation between the gate and drain to optimize the distribution of electric field in the channel and enhance the Vbr of the device.The breakdown of ordinary fluorine plasma treatment is 297 V,and when the concentration of fluorine plasma treatment is 2.0?1018 cm-3 and area length is 1 ?m,the Vbr of new structure device is 500 V,Vbr increases by 68%.Increasing light dope fluorine plasma treatment and the area length can further raise the Vbr of the device.