Influence of the Al content of the AlGaN buffer layer in AlGaN/GaN high-electron-mobility transistor structures on a Si substrate (original) (raw)

We investigated the effect of the Al content in the AlGaN buffer layer on the initial AlN nucleation layer, for AlGaN/ GaN high-electron-mobility transistors (HEMT), on a Si substrate. Reducing the Al content in the AlGaN layer decreased the surface pit density of the AlGaN layer, and increased the leakage current of the AlGaN/AlN/Si structures, but the crystal quality of the AlGaN layer was not changed by the Al content. The dislocation density of the GaN layer and the two-dimensional electron gas characteristics of the HEMT structures, were almost the same for the AlGaN buffer layer with differing Al content. However, the vertical-direction breakdown voltage (VDBV) was decreased at an Al content of 0.760 compared with other HEMT structures. In addition, the fluctuations of SLS layer were observed at an Al content of 0.760. The warpage and cracking of the HEMT structures were minimized at an Al content of 0.558. Based on these results, the VDBV of HEMT structures are not correlated with the VDBV of the AlGaN buffer layer. However, the VDBV of HEMT structures is affected by the surface pit density of the AlGaN buffer layer. In addition, the warpage of HEMTs on a Si substrate, can be controlled by the Al content of the AlGaN buffer layer.