Study On Leakage Mechanism Of GaN Buffer Layer In GaN-based Heterostructures

Despite the great progress that have been made in high-power and microwave characteristics of AlGaN/GaN HEMT, GaN-based HEMT devices have many questions. The reduction of buffer leakage current through GaN buffer layer when it is used for high-power operation is one of the most important problems. So it is necessary for GaN buffer layer to have high resistivity to suppress the buffer leakage current.In this paper, the source of the background carrier in GaN buffer layer, the mechanism of C-V measurement, correlation between the buffer leakage current and different nucleation layer of AlGaN/GaN heterostructure and inhibition carrier of the GaN buffer background by high-temperature AlN interlayer are studied. The major research work and results are as follows:Ⅰ. Firstly, correlation between buffer leakage current and different nucleation layers of AlGaN/GaN heterostructure have been analyzed by comparing depletion capacitance of C-V characteristics in GaN-based heterostructures. The results show that, there is an n-type GaN conductive layer with high background carrier concentration near the GaN/substrate interface in buffer layer based on the thinner nucleation layers. Contrarily, high resistivity GaN buffer layer are formed based on a thicker nucleation layer.Ⅱ. By SIMS analysis of GaN-based heterostructures, we found that Al and O elements were located at the region of vertical dislocation line which across whole the GaN-based layer. There is an obvious difference between Al and O element distribution. The O atom is mainly from decomposition of the Al2O3 substrate at high growth temperature. While the Al atom comes from diffusion of the surface dissociative Al atoms directly by TMAl decomposition during the growth of the AlGaN barrier layer. So the concentration of the Al atoms become higher when it is more near the surface, and O atom concentration become larger near the GaN/substrate interface. The high background carrier concentration of GaN buffer layer is mainly comes from these O atoms.Ⅲ. We adopt an AlN inserting layer at high temperature to hold back O atom diffusion and the buffer layer reveals a high resistivity.