Investigation of Electrical Characteristics of Multi Gate AlGaN/ GaN HEMT
Gallium Nitride (GaN) has recently attracted widespread attention for promising applications in the RF domain. Due to wider bandgap, GaN based devices show exceptional performance at higher temperatures. Additionally, they permit device operation at higher voltages and enable high frequency operation because of higher bandgap energy (i.e. 3.4 eV). Higher sheet carrier densities, higher thermal conductivity, higher electron mobility, and higher breakdown field are the major factors which provide better performance in case of GaN based heterostructures. Additionally, GaN based heterostructures have unintentionally doped two-dimensional electron gas (2DEG). Owing to their high sheet carrier density in 2-D Electron Gas (2DEG), GaN based High Electron Mobility Transistors (HEMTs) have been observed to provide excellent performance in high–power switching applications and large breakdown field strength.
The power–switching performance is however limited by the conduction losses in the ON–state resistance RON and the OFF–state breakdown voltage VBR. It is therefore a necessity to enhance the OFF-state breakdown while keeping RON as low as possible. Various device configurations have been studied in order to improve the device performance characteristics such as the cut–off frequency ( ), power density, power added efficiency, breakdown voltage, etc. The modifications that have been extensively studied are the field plate length, different substrate material along with different crystal orientations, buffer layer thickness, choosing different material for passivation layers such as Si3N4 or SiO2, insulation material for gate, GaN cap layer, field plate (FP) structures along with additional floating gates. Recently, multi-gate structures have intrigued researchers because of the potential to sustain even at higher temperatures and operating voltages owing to the greater field confinement and switching behaviour. Source connected field plate structures have also been studied with the prospective of achieving higher OFF–state breakdown voltage and enhancing the power gain of GaN–based HEMT devices.
This work involves exhaustive simulations of the Field Plate HEMT architecture where the effect of GaN cap layer on the electrical characteristics of AlGaN/ GaN HEMT have been investigated using Silvaco device simulator tool. Thermal simulations have also been performed to investigate the effect on the device performance parameters.
Chapter 1 provides a brief introduction on the High Electron Mobility Transistor (HEMT).
Chapter 2 describes the simulation results of the Field Plate HEMT model analyzed in this project work. Effect of field plate misalignment on the electrical characteristics of the device has also been investigated.
Chapter 3 discusses the thermal simulation results of the device analyzed in Chapter 2.
Keywords: Field Plate; HEMT; Transconductance; 2-D Electron Gas; Breakdown Voltage; Cut – Off Frequency; Stern Stability Factor