EFFECT OF GAAS SURFACE PRETREATMENT ON ELECTRICAL-PROPERTIES OF MBE-ZNSE GAAS SUBSTRATE INTERFACES/

Interface properties of MBE-grown ZnSe/GaAs substrate systems formed o n variously pretreated GaAs surfaces, which include standard chemicall y etched (5H(2)SO(4):1H(2)O:1H(2)O), (NH4)(2)S-x-, NH4I-, and HF-pretr eated 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 stat e density, N-ss, with N-ss,N-min below 4 x 10(11) cm(-2) eV(-1) near E (C) - E(FS) = 1.0 eV. The value is about one order of magnitude smalle r than that of the standard chemically etched interface, and comparabl e to (NH4)(2)S-x- pretreated interface. Nevertheless, C-V characterist ics of ZnSe/n-GaAs samples, which were measured for the first time, in dicate that interface Fermi level, E(FS), is not completely unpinned d ue to the interface states located above the midgap. A consistent resu lt was obtained by DLTS method in determining E(FS) position. The infl uence of N-ss distribution on vertical current conduction is also anal yzed. It is found that U-shaped interface states with N-ss (E) > 1 x 1 0(13) cm(-2) eV(-1) above the midgap may cause an excess voltage drop larger than a few volts at the interface.