Growth and characterization of InGaN back barrier HEMTs structure with a compositionally step-graded AlGaN layer

A novel InGaN back barrier high electron mobility transistors structure with a compositionally step-graded AlGaN barrier layer was grown by metal organic chemical vapor deposition on sapphire substrate. The structural and electrical properties of two samples were investigated and compared: the first sample is the step-graded structure and the second one is the high Al structure as a comparison. By calculating full width at half maximum of XRD measurements, the densities of screw-type threading dislocations are 8.34 x 10(8) cm(2) and 11.44 x 10(8) cm(2) for step-graded structure and high Al structure, respectively, which are consistent with the results of atomic force microscopy. By Hall measurements, the measured two-dimensional electron gas mobility was 1820 cm(2)/(V.s) for step-graded structure, and 1300 cm(2)/(V.s) for high Al structure, respectively. The step-graded structure improves the crystal quality of AlGaN layer due to the released lattice strain. The device was fabricated and leakage current is only 28 mu A when the drain voltage is 10 V; it was found that the InGaN back barrier could effectively reduce the buffer leakage current.