Abstract
Interface properties of MBE-grown ZnSe/GaAs substrate systems formed on variously pretreated GaAs surfaces, which include standard chemically etched (5H2SO4:1H2O2: 1H2O), (NH4)2Sx-, NH4I-, and HF-pretreated surfaces, are investigated by capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. A HF-pretreated and annealed ZnSe/p-GaAs sample showed marked reduction of interface state density, Nss, with Nss,min below 4 x 1011cm-2 eV-1 near Ec- EFS= 1.0 eV. The value is about one order of magnitude smaller than that of the standard chemically etched interface, and comparable to (NH4)2Sx- pretreated interface. Nevertheless, C-V characteristics of ZnSe/nGaAs samples, which were measured for the first time, indicate that interface Fermi level, EFS, is not completely unpinned due to the interface states located above the midgap. A consistent result was obtained by DLTS method in determining EFS position. The influence of Nss distribution on vertical current conduction is also analyzed. It is found that U-shaped interface states with Nss(E) > 1 x 1013 cm-2 eV-1 above the midgap may cause an excess voltage drop larger than a few volts at the interface.
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