Characteristic Of AlGaN/GaN Heterostructures And Of High Electron Mobility Transistors

Microwave power devices with conventional semiconductors have approachedtheir performance limits. Microwave power devices with conventional semiconductorshave approached their performance limits. To meet the future need in wirelesscommunications, research effort has been directed to wide bandgap semiconductors,such as GaN and SiC. AlGaN/GaN High-Electron-Mobility-Transistors (HEMT) areregarded as the ideal microwave power devices in 1-50GHz frequency range. However,the device physics and the fabrication technology of AlGaN/GaN HEMT remainimmature. This dissertation is written in the background. AlGaN/GaNHigh-Electron-Mobility-Transistors (HEMT) are regarded as the ideal microwavepower devices in 1-50GHz frequency range. However, the device physics and thefabrication technology of AlGaN/GaN HEMT remain immature. This dissertation iswritten in the background.Firstly, based on the results of ISE TCAD simulation and a large amounts ofpublished data, analysis of many factors that influence on the density of twodimensional electron gas such as polarity, alloy composition, strain, thickness, anddoping of the AlGaN barrier. Based on the electrostatics analysis, regardless of thedetails to seize the main points, surface states are identified as an important source ofelectrons is obtained. The results of ISE TCAD simulation and a large amount ofpublished data are interpreted by this theory. Then, the conclusions are classified bymethod of the establishment of theoretical physics.Secondly, based on the deep research of AlGaN/GaN heterostructures,an analyticalmodel for the DC characteristics of AlGaN/GaN HEMT is developed.Finally, current collapse of AlGaN/GaN HEMT is researched. The reason causedthe current collapse is briefly introduced, including the model of bias stress and virtualgate and so on. A few methods to decrease current collapse, such as surface treatment,field plate structure, growing capped layer are also described.