Defect levels in n-type gallium arsenide and gallium aluminum arsenide layers

Capacitance-voltage/time measurements have been made on Au-Schottky barrier diodes to LPE, VPE, bulk, OMVPE-GaAs, GaA1As and MBE-GaAs/GaA1As quantum w ells 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 obse rve the emission of carriers from deep levels up to a pressure of 50 x 10(8 ) Pa. The effect of annealing on traps in VPE-GaAs has also been investigat ed. It has been shown that emission from the 0.83 eV (EL-2) level in GaAs i s not dependent on electric field in the range of about 60-125 kV/cm. The e nergy pressure coefficient of this level in GaAs has been measured as 4.0 x 10(8) meV/Pa by extending measurements, for the first time, to 15 x 10(8) Pa. From emission studies at 50 x 10(8) Pa, it has been shown that the leve l EL-2 is coupled to the L minima and the T-L energy separation of 0.282 eV accounts for most of the experimental data. The 0.83 eV level has also bee n 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 i n 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 sim ilar level found in GaAs/GaA1As MBE quantum wells, the energy pressure coef ficient has been measured to be as high as (13.8 +/- 0.8) x 108 meV/Pa. In some samples, 0.83 and 0.76 eV electron levels exist together, clearly show ing that these are two different levels. The 0.64 eV hole trap level has no t only been found in LPE-GaAs, GaA1As, heat treated VPE but also in 'as-gro wn' VPE-GaAs. The present results have discounted the pure Ga and As vacanc y 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.