M.Sc Thesis

M.Sc StudentNasser Karam
SubjectIntegration of Device and Circuit Simulation Programs of
GaN Transistors
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Dan Ritter
Full Thesis textFull thesis text - English Version


The gallium nitride semiconductor technology has already transformed the lightning industry, and is currently developed also for power electronics applications. The great promise of this semiconductor for power applications is related to its wide band gap allowing for high breakdown field, high electron saturation velocity, and low thermal resistance. More than tenfold improvement of performance is expected for power devices compared to silicon transistors. The applications of GaN transistor are classified into two categories: power handling (switching) and power radio frequency (RF) devices.

The GaN power transistor technology has not yet fulfilled its potential, and further device optimization is still required. In well-developed technologies such as the silicon technology, technology computer aided design (TCAD) software is the prevailing tool for device optimization. The main setback of GaN TCAD is the lack of appropriate models, primarily electron trapping effects. Traps are routinely introduced into the material to enhance its resistivity, yet their effect on device performance is not fully understood.

The key parameter that requires optimization in GaN RF transistors is the power efficiency. In this work, we have established a clear procedure that allows for an accurate prediction of the device's large signal performance by TCAD software. For that, we have developed a complete calibration procedure suitable for TCAD. The tuned parameters were chosen to allow for the introduction of minimal ambiguity into the simulation, and easy extraction from available measurement data. The calibration procedure relies on simulation configurations specially developed to correspond with the different experimental setups, such as pulsed I-V, small signal parameter extraction, high frequency large signal sweeps and load-pull.

Finally, we have implemented and validated the developed calibration procedure and simulation setups by simulating a real AlGaN/GaN high electron mobility transistor intended for RF applications, fabricated in the X-band GaN lineup of the Ferdinand - Braun institute. Over all, we report very good agreement found between the simulation and measurement, comparable to the results achieved by state-of-the- art compact model.