AlGaN/GaN High Electron Mobility Transistor with Thin Buffer Layers

An AlGaN/GaN high electron mobility transistor (HEMT) on a high-temperature-grown GaN buffer layer as thin as 0.35 µm has been demonstrated for the first time. The investigation of device characteristics is carried out using fat field-effect transistor (FATFET), ring-type FET and Hall measurements. The field-effect mobility obtained from the FATFET is about 1200 cm 2 /Vs, whereas the mobility in the buffer layers is around 200 cm 2 /Vs. A leakage current is found to be due to the non-semi-insulating underlying buffer layers. A two-layer model was adopted to separate the surface channel and buffer channel from Hall measurement data. The surface mobility enhancement can be attributed to the screening effect of ionized impurity and defects by the accumulated electrons.