Electrical and optical characterisation in AlGaN/GaN/Si HEMTs

Abstract

AlGaN/GaN/Si high electron mobility transistors (HEMTs) grown by molecular beam epitaxy were investigated using complementary electrical (I–V–T), optical (photoluminescence), and spectroscopic (DLTS) techniques in order to elucidate the role of defects in carrier transport and recombination mechanisms. The temperature-dependent I–V characteristics reveal pronounced Schottky barrier inhomogeneity and a strong contribution of defect-assisted transport, particularly under reverse bias conditions. DLTS measurements identify a dominant trap level (H1) located at 0.28 eV with a capture cross section of 2.32 × 10−¹⁶ cm² and a high concentration of 2.8 × 10¹⁵ cm−³, indicating a significant density of electrically active defects at the AlGaN/GaN heterointerface. These defects act as intermediate states enhancing trap-assisted tunnelling and generation–recombination processes, thereby contributing directly to the leakage current. Photoluminescence results further support this interpretation, showing temperature-dependent quenching and linewidth broadening consistent with non-radiative recombination involving the same defect states. By combining these experimental observations, a unified physical picture is established linking barrier inhomogeneity, 2DEG-related recombination, and interface trap states. These findings highlight the critical impact of interface-related defects on the electrical and optical performance of AlGaN/GaN HEMTs and provide valuable insights for device optimisation.