Deep traps and instabilities in AlGaN/GaN high electron mobility transistors on Si substrates

Abstract

Deep traps were studied in multiple-finger AlGaN/GaN transistors with broad periphery by means of current–voltage and capacitance–voltage characteristics, reverse deep level transient spectroscopy, deep level transient spectroscopy with electrical (DLTS) and optical DLTS injection, and current DLTS (CDLTS) with gate voltage and drain voltage pulsing. Deep electron traps with activation energies of 0.25, 0.36, 0.56, and 0.8–0.9 eV are found to be responsible for variations in threshold current with applied gate bias. These traps also give rise to current transients observed at different temperatures in CDLTS. The 0.25 and 0.56 eV centers are most likely located at the AlGaN/GaN interface. The 0.25 eV state is believed to be nitrogen vacancy-related, the 0.36 eV level is of unknown origin, the 0.56 eV level is likely due to point defects enhanced in the presence of dislocations, and responsible for low luminescence efficiency of nonpolar n-GaN and for degradation of GaN transistors and light-emitting diodes and light-emitting diodes, while the 0.8 eV-level has been attributed to either interstitial Ga or N. Hole-trap-like relaxations in CDLTS were observed at temperatures higher than ∼300 K and attributed to hole traps near Ev + 0.9 eV located in the buffer layer. These have previously been assigned to either gallium vacancy-oxygen acceptor complexes (VGa-O)2− or carbon on nitrogen site acceptor (CN−) complexes. These results show that the stability of GaN-based high electron mobility transistors on Si is still dominated by the high concentration of point defects present in the material.