Defect Levels in n-Type Gallium Arsenide and Gallium Aluminum Arsenide Layers

Abstract

Capacitance-voltage/time measurements have been made on Au-Schottky barrier diodes to LPE, VPE, bulk, OMVPE-GaAs, GaAlAs and MBE-GaAs/GaAlAs quantum wells to detect and characterize deep levels. LPE-GaAs was-grown by varying the degree of melt under-and super-saturation to study the effect on traps. Cylinder-piston assembly and Bridgman anvil systems were employed to observe the emission of carriers from deep levels up to a pressure of 50 Â 10 8 Pa. The effect of annealing on traps in VPE-GaAs has also been investigated. It has been shown that emission from the 0.83 eV (EL-2) level in GaAs is not dependent on electric field in the range of about 60-125 kV/cm. The energy pressure coefficient of this level in GaAs has been measured as 4.0 Â 10 8 meV/Pa by extending measurements, for the first time, to 15 Â 10 8 Pa. From emission studies at 50 Â 10 8 Pa, it has been shown that the level EL-2 is coupled to the L minima and the G-L energy separation of 0.282 eV accounts for most of the experimental data. The 0.83 eV level has also been found to exist in LPE-GaAs and it has been concluded that Ga vacancy and As Ga antisite defect complex are responsible as the most likely source of its origin. It has been concluded that the absolute position of the level in the band gap remains almost invariant with pressure and that there is no need to assume a pressure dependent Franck-Condon shift. However, for a similar level found in GaAs/GaAlAs MBE quantum wells, the energy pressure coefficient has been measured to be as high as (13.8 AE 0.8) Â 10 8 meV/Pa. In some samples, 0.83 and 0.76 eV electron levels exist together, clearly showing that these are two different levels. The 0.64 eV hole trap level has not only been found in LPE-GaAs, GaAlAs, heat treated VPE but also in 'as-grown' VPE-GaAs. The present results have discounted the pure Ga and As vacancy model for the 0.83 and 0.64 eV levels in VPE and LPE-GaAs, respectively. We attribute the 0.64 eV hole level to a Ga vacancy-Cr complex.