Effect of C-doped GaN film thickness on the structural and electrical properties of AlGaN/GaN-based high electron mobility transistors

High-resistivity carbon doped GaN (C-GaN) is highly desirable for high electron mobility transistors (HEMTs) application to reduce the leakage current at high electric fields. Herein, we investigate the structural and electrical properties of AlGaN/GaN-based HEMTs with different thicknesses of the underlying C-GaN layer. Reciprocal space mapping analysis indicates more lattice defects within GaN layer of the AlGaN/GaN heterostructure with thicker underlying C-GaN layer. Finite element method simulations reveal that the stress distribution over the AlGaN/GaN heterostructure thickness can be tuned by increasing the underlying C-GaN layer thickness from 2 to 7 μm. Consequently, a significant decrease of two-dimensional electrons gas mobility from 1188 to 653 cm2 V−1 s−1 measured by Hall effect method is observed at a higher underlying C-GaN layer thickness (7 μm). The change of electrical properties for HEMT structures with different underlying C-GaN thicknesses is not only affected by structural quality of the epilayers but also by thermal stress over HEMT structure thickness. Our results pave the avenue for improving the electrical properties of HEMT with a suitable thickness of underlying C-GaN layer.