Deep Traps in AlGaN/GaN High Electron Mobility Transistors on SiC

Capacitance-voltage (C-V) and current-voltage (I-V) characteristics and deep trap spectra were measured for high-power HEMT structures grown by metallorganic chemical vapor deposition on semi-insulating 4H-SiC substrates and comprised of an AlGaN barrier and GaN(Fe) semi-insulating buffer with the upper (∼100 nm) portion unintentionally doped and lightly n-type. The C-V measurements were performed in the 85–400 K range in the dark and showed a decrease in the threshold voltage for temperatures higher than 200 K. The change was most prominent for temperatures from 290 K to ∼330 K and occured due to deep traps capturing electrons in the AlGaN barrier and near the AlGaN/GaN interface. C-V measurements at low temperature showed that the traps in the AlGaN barrier are located near Ec−2 eV and have a density of ∼1012 cm−2, while the traps at the interface have an optical ionization threshold near 1.7 eV and the density of ∼4 × 1012 cm−2. Capacitance deep level transient spectroscopy (DLTS) and current DLTS (CDLTS) revealed electron traps with levels near Ec−0.56 eV and hole traps with levels near Ev+0.9 eV and Ev+0.5 eV. The Ec−0.56 eV traps are known to be located near the AlGaN/GaN interface in the GaN buffer. The Ev+0.9 eV hole traps are located in the buffer.