الفهرس 
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Abstract
The aim of this thesis is to develop an accurate and complete model for High Electron Mobility Transistors (HEMTs). The model is based on a first principle theory in which Schrodinger’s wave equation and Poisson’s equation are solved numerically and self - consistently, in order to derive all the electronic properties of the Two-Dimensional Electron Gas (2DEG) system. The obtained results for 2DEG charge control are compared with the widely-used triangular approximation results. It is found that, from device modeling point of view, the triangular approximation can estimate the charge density with reasonable accuracy, while the exact analysis can describe accurately a number of device phenomena that could not be analyzed using approximate models. An analytical function is proposed to fit the numerical charge control data for the 2DEG and AlGaAs channels, which unifies the treatment for both conduction mechanisms in the two channels. A single analytical expression for the total drain current in the device including both 2DEG and AlGaAs components is derived. The effects of mobility degradation, channel length modulation in the saturation region, and parasitic drain and source resistances have been considered, as well as the dependence of saturation voltage on drain voltage. Using this current voltage model, the conduction mechanism in both channels has been explained for different gate and drain voltages. Analytical expressions for the most important small signal parameters at non- thermal equilibrium has been developed. The contribution of the charge components defining the gate capacitance have been extensively studied at different bias conditions. The model results in accurate description of the small signal parameters in the linear and saturation regions. Furthermore, the model has been also used to perform a so called “computer experiment”, in order to compare the performance of AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs HEMTs with identical structure. The results have shown that pseudomorphic HEMT outperforms conventional HEMT in terms of output drain current, transconductance, and unity current-gain cut-off frequency. In order to check the validity of the model, the obtained results are compared with available experimental data, and are found to be in good agreement over a wide range of bias levels.Finally,as a practical example ofHEMTs in analog applications, a low noise, high gain, microwl amplifier operating at a frequency of 7 GHz, has been designed, implemented ~ analyzed. The amplifier design of has been accomplished using the micros! technology and an AIGaAslInGaAs on GaAs pseudomorphic HEMT as an act element.