Characterization of traps in GaAs/W Schottky diodes by optical and electrical deep-level transient spectroscopy methods

Abstract

Both the electrical and optical deep-level transient spectroscopy (DLTS) measurement methods were used to investigate the deep traps in GaAs that originate from the impurities included in the Schottky metal on GaAs/W Schottky diodes. Two distinct electron traps (E1 and E2, whose activation energies EA were, respectively, 0.65 and 0.58 eV) were detected by electrical DLTS in samples annealed at 650 °C. The variation of EA and trap density with changes in the Schottky barrier height indicates that the trap E1 can be identified with the EL2 usually observed in the GaAs grown by metalorganic chemical-vapor deposition. In addition, the trap E2 is found to be due to impurities that diffused from the W film into the GaAs layer during annealing. Four hole traps with activation energies of 0.76, 0.55, 0.43, and 0.30 eV were detected by optical DLTS in samples annealed at 650 °C. Comparison of the EA for each hole trap with data previously reported indicates that the first three traps are due to the transition metals Cr, Fe, and Cu, and that the last one is due to a native defect. These metals are confirmed from secondary-ion-mass spectroscopy analysis to be included in the as-deposited W film. Furthermore, these traps are also observed in GaAs permeable base transistors with the buried W gate.