GROWTH AND OPTIMIZATION OF ALGAN/GAN HETEROSTRUCTURES
The AlGaN/GaN heterostructure is the mainstream structure of GaN HEMTs. Based on a type I heterojunction band structure similar to that of AlGaAs/GaAs heterostructure, the AlGaN/GaN heterostructure has a two-dimensional electron gas (2DEG) at the GaN side. Whereas AlGaN/GaN heterostructure as a whole has a rather wide band gap and a high breakdown voltage; the large conduction band offset at the AlGaN/GaN interface, together with its strong piezoelectric and spontaneous polarization, is favorable for the formation of deep and narrow quantum wells and the accumulation of high density 2DEGs. The 2DEG possesses, owing to its distribution and transport characteristics, remarkably higher mobility and saturation velocity. Therefore the AlGaN/GaN heterostructure is an ideal candidate for microwave power devices (Figure 5.1).