Abstract: A combination of the wide bandgap (3.3 eV of GaN to 6.3 eV of AlN) which leads to high breakdown fields. Therefore, output power density has become a very important figure of merit for GaN/AlGaN HFETs. Extensive research has been performed to improve the output power density from 1.1 W/mm in 1996 [1] to the state-of-the-art value of 9.8 W/mm in 2001 [2]. In order to get high power density, the product of ns and electron mobility, ?n, should be maximized. Increasing the Al mole fraction in the AlGaN cap layer will lead to higher , but will drop due to alloy disorder scattering and the crystal quality may degrade as well (e.g., density of impurities is higher.

Keywords: Curvilinear Structure, HFET.