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Abstract
AIGaN/GaN high electron-mobility transistors (HEMTs) have demonstrated device characteristics, which make them excellent candidates for high-power, high-&equency, and high-temperature applications because of their unique material properties. With the combined merits of high power and high speed, the GaN-based HEMTs is the subject of this thesis.
The electron concentration in the two dimensional electron gas (2DEG) is numerically calculated &om the simultaneous solution of SchrOdinger’s and Poisson’s equations. This quantity is then fitted to a new closed form expression. An improved AIGaN/GaN HEMT model is presented taking into account the self-heating effect to obtain the current-voltage characteristics, transconductance, output conductance, and gate capacitance for devices fabricated on SiC substrate. The theoretical predictions of the model are compared with the experimental data and shown to be in good agreement over a wide range of bias conditions. Moreover, study of several parameters (such as substrate, gate length, and mole &action) on the DC, and microwave performances are presented.
Investigations on microwave noise performances of GaN-based devices are carried out, because of their unique performance features (no protection circuits, high breakdown voltages). The present study includes microwave noise performance of AIGaN/GaN, its dependence on mole &action, substrate, biasing, temperature, and gate length.
An analysis of the second- and third-order 1M (Intermodulation) products resulting from nonlinear drain-source current characteristic for AIGaN/GaN HEMT amplifiers, using the Taylor series is presented. The second and third-order intercept points are also determined and their effects on device performance are analyzed.
The physical significance of the well known equivalent circuit models of microwave device is presents. A technique to extract the equivalent circuit parameters
from S-parameters data is introduced. The study proposes a new model for the intrim equivalent circuit adding two impedances: one, to represent the charge transfer transie time effect and the other represents, the substrates effect. A simple analysis, based on tI intrinsic and extrinsic elements of the S-parameters measurement data to investigate tI output power; gain; and Power Add Efficiency (P AE) as a function of input power j different substrate, mole fraction, and the effect of a very thin aluminum nitride (AU layer between the AIGaN and GaN are presented. A power characteristics dependence temperature with different gate length is also discussed.