ABSTRACT
This chapter demonstrates the original mechanism of enhancement-mode and depletion-mode HFETs. It also demonstrates the charge control model, which is used to demonstrate main mechanism of 2DEG depletion for enhancing threshold voltage. The hole in the P-type region of GIT can inject into the 2DEG region to generate conductivity modulation as a mechanism observed in an insulated gate bipolar transistor. Another E-mode HFET with a double-barrier layer by way of selective-area molecular beam epitaxy regrowth was proposed by Hughes Research Laboratories on the basis of support of the Next Generation of Nitrides Electronics Project from the US Defense Advanced Research Projects Agency. In 2005, an E-mode AlGaN/GaN HFET using the fluoride-based plasma-treatment technique, was proposed, for the first time by Chen's team from the Hong Kong University of Science. In a GaN-based HFET with a single barrier, if there is no Schottky contact at the surface of the AlGaN barrier, the 2DEG is mainly from the ionized donor surface states.
