Study On The Surface Potential Based Model Of GaN HEMT

Gallium Nitride High Electron Mobility Transistor (GaN HEMT) models are basics of the GaN Microwave Monolithic Integrated Circuit (MMIC) CAD. But the existed GaN HEMT physical models not only can’t solve the numerical computation problems which come from self consistently solving carrier transport equation and physcial problems which deal with the quantum effect and the polarization charge on the hetero-junction interface, but also can’t describe the variety of device structure and the complexity of the physical effects. By contrast, the surface potential based model is more accurately characterize the transistor physical essence which can add new physical effects to model and surface potential equation. Now the study on the surface potential model was still in the initial stage, this paper made an intensive study of GaN heterogeneous structure and relativity between physical characteristics, mainly focused on the the modeling method and technology based on the surface potential for GaN HEMT device. It can be summarized as follow:1) Based on the semiconductor theory and quantum theory, this paper analyze the device epitaxial layer structure. In this work, the effects of the polarization, the Fermi level and the doping in barrier are incorporated into the surface potential equation, and the surface potential equation for GaN HEMT was built; Numerical self consistent solutions of the equation were got by using the newton iteration method. The precise numerical solution of the surface potential verified the feasibility of the surface potential equation.2) The difficulties have been broken through, such as the building of the surface potential equation for GaN HEMT, the analytical solution of the transcendental equation, the exploitation of the continuous function and smoothing factor. This paper deduced the equation of the body charge density in new three regions which can avoid the hardly continuum of the PSP charge model, and got the continuous I-Vand C-v characteristic equations in all the work area; The new mobility model is built according to the scattering mechanisms of GaN HEMT device; The developed surface potential based compact core model achieved the fitting of the current and charge characteristics, first-order derivative (conductance, capacitance, trans-conductance) and higher-order derivative. The TCAD tools simulated the direct-current characteristic of GaN HEMT (AlGaN/GaN HEMT and AlGaN/AlN/GaN HEMT. Good agreement with TCAD simulations verified the accuracy of model.3) Based on GaN HEMT compact core model, this paper proposed the topology structure of the model which can accurately characterize high order behaviors and the high frequency parasitic effects, and the model parameters and the flow of the parameter extraction are presented. In he end, this paper developed a surface potential based compact model for GaN HEMT. The measured and modeled results have good fitting.The paper presented the surface potential compact model and modeling methods based on the physical mechanism and the structural.parameter information. It has made great progress in the surface potential modeling and the research of current and charge/capacitance characteristics. This work provided the credible forms of the equation and the theoretical basis to the modeling, and the base of GaN HEMT model which can be used for the digital signal, the digital and analog mixed signal simulation. To accurately describe the device practical behavior and enrich the representation ability, this model not only need be practical developed and empirical/semi empirical processed but also expanded the current equation and charge equation.