Study Of A High Linearity Al_x Ga_1-xn/al_yga (1-y)n/gan Hemt

In recent years, Global wireless communication industry has developed rapidly. The higher and higher perpormances of radio frequency devices are required in the application to either military or civil. The first generation semiconductor material Silicon has played an important role for a long time. However, with the higher and higher perpormances of devices required, the performances of Si device can not meet the requirement. And then, the second generation semiconductor material GaAs is found and has become main material of microwave devices. With the advanced research and development of science, the potential of GaAs device has reached its limite in the frequency and power density. In recent years, a wide bandgap semiconductor has become the research hotspot. At present, the third generation wide bandgap semiconductor material GaN has the capability of wide bandgap, comparing with BJT, MOS, and GaAs device, GaN HEMT shows the performance of high power density . At the same time the research indicates that GaN HEMT has also the performances of high frequency, low noise, high efficiency, and high linearity. This thesis focuses on the research of device structure of AlGaN/GaN HEMT for improving linearity.Firstly, it introduces the basic theory and operation principle, and a new composite-channel Al_xGa_1-xN/Al_yGa(1-y)N/ GaN HEMT (CC-HEMT). It also presents the character and performance, especially linearity of above device. The linearity of CC-HEMT is much better than conventional AlGaN/GaN HEMT.Secondly, poisson and schrodinger equations are adopted to numerically calculates performance parameters, such as the electron concentration of two-dimensional electron gas,, transverse electric field, electrion density per unit and so on, which base on different barrier layer thickness, Al composition, doping concentration, isolation layer thickness, composite-channel layer thickness and its Al compostion. The influence of the change of two-dimensional electron gas, transverse electric field, electron density on calculation results is analyzed basing on theory of semiconductor energy band and quantum well.Then, the DC and AC performances of CC-HEMTs with different structure are simulated by using Silvaco TCAD software. And simulated results are given. The optimized epi-layer structure is obtained definitely after combining with theoretical calculation. follow on, fabrication process and measurement results of CC-HEMT with 1um gate length and the sapphire substrate..Finally, the CC-HEMT with isolation layer of AlN is proposed according to the international research and development near years. The structure of a novel high linearity CC-HEMT is achieved after design and simulation are finished. It has become the theory foundation of fabrication of device.