Numerical Simulation And Modeling Of Direct Current For N-face GaN Based HEMTs

Due to its wide bandgap, the resistance to high temperature and high pressure, and the wide detective ability for the wavelength range from ultraviolet to infrared, the semiconductor GaN material has excellent performance at high power, microwave and radiation electronics, as well as photo-detectors and illuminating devices. Although the application of GaN has been greatly developed in the past few years, researches were mainly focused on Ga-face devices, and N-face device structures received little attention due to several growth-related defects, such as the high requirement of growth condition and the bad material quality. Furthermore, the different direction epitaxial growth of wurtzite GaN semiconductor, show a significant difference in performance because of its strong polarization characteristic. N-face GaN based devices exhibit more superiority than the Ga-face ones in various aspects. Compared with Ga-face GaN-based hetero-junction devices, the N-face ones show several advantages include lower contact resistance, better electron confinement and low gate leakage current etc. Due to the excellent performance, the N-face GaN materials have been widely applied in areas like microwave and high frequency device, terahertz photo detectors, the solar cell, light emitting diode, as well as gas detection. As the material growth ability of N-face GaN materials and structures has been greatly improved, the advantages of N-face GaN materials and GaN-based devices will be further presented.In this thesis, we investigate the influence on the density of 2-dimensional electron gas caused by the polarization effect at the interface of AlGaN/GaN hetero-junction by comparing different Al molar composition and AlGaN barrier layer thickness. Numerical simulation methods based on solving poisson equation, carrier transport equation, temperature equation etc. have been employed to investigate the direct current (dc) output characteristics of N-face polarization GaN/AlGaN high electron mobility transistor. Firstly, physical models based on Sentaurus Device simulation platform was introduced briefly; then, a structure of N-face GaN/AlGaN HEMT device was built, which has been combined with the experimental data; the physical model was further modified according to the corresponding experimental results, before simulating. Finally, the dc output characteristic curve of N-face GaN/AlGaN HEMT devices was analyzed in terms of the thickness of the AlGaN barrier layer, Al molar composition and gate length. Results show that the larger the Al molar composition, the greater the potential of AlGaN barrier layer, and the shorter the gate length, the dc output performance of the device will be better, to some extent. And when the concentration of Si-doping in the background reaches 1018cm*3 or more, it has a significant effect on the channel electron gas concentration which determines the performance of the device. The analysis results have some significance on the manufacturing of N-face GaN/AlGaN heterostructure devices as well as the improvements of its performance.