Deep levels investigation of AlGaN/GaN heterostructure transistors

Abstract

Abstract In this work we investigate AlGaN/GaN HEMTs structures grown by metalorganic chemical-vapor deposition on SiC substrates. They consist of a 22 nm thick undoped AlGaN barrier with Al mole fraction x=0.24 on top of a 1.7 μm unintentionally doped GaN buffer layer. Structures with large gate are analyzed by Fourier transform deep level transient spectroscopy (FT-DLTS) between 100 and 450 K. The dominant traps are found to be electron traps with activation energies of 0.12, 0.15, 0.21, 0.40, 0.49 and 0.94 eV. The detailed analysis of DLTS spectra shows a strong dependence on the electric-field in the space charge region of the Schottky contact. Poole–Frenkel mechanism is observed and confirmed by the reverse current characteristic analysis. The nature of the deep traps is also discussed.