InGaN layer effects in DH-HEMT transistors based on the AlGaN/GaN

The AlGaN/GaN high-electron mobility transistors (HEMTs) have shown outstanding performance in the last years. With tremendous progresses made during the last decade in material quality and device processing, AlGaN/GaN HEMTs have been improved significantly in both dc and Rf performances [1-2]. Meanwhile, more advanced device structures are being explored for further performance improvement. For example, double-channel HEMTs [3] and composite-channel HEMTs have been studied for higher carrier density and improved linearity. To improve carrier confinement which could result in an improved pinch-off behavior, double-heterostructure HEMTs are also being investigated. Using AlGaN buffer layer with Al composition of 4%, Micovic et al. demonstrated a GaN double heterojunction HEMT with improved buffer isolation. However, a high Al composition in the AlGaN buffer layer is still difficult to achieve. Simin et al. has implemented AlGaN/InGaN/GaN HEMTs and MOSHFETs [4] in which InGaN has been used as the channel material which is confined from both sides by AlGaN and GaN. In this paper, we study the use of ultrathin layers of InGaN to raise the conduction band of the GaN buffer with respect to the GaN channel in order to increase the confinement.On the other hand, owing to the opposite piezoelectric polarization field in the InGaN layer [5] ,an additional potential barrier is created between the channel and the buffer layer.This additional barrier leads to better carrier confinement and better buffer isolation,which in turn, enables improved device performance,i.e.,higher transconductance and lower leakage current .The effects of In composition on the device characteristics are studied in samples with In composition of 5% and 10%.