Simultaneous analysis of current–voltage and capacitance–voltage characteristics of metal–insulator–semiconductor diodes with a high mid-gap trap density

Abstract

We present an improved method to analyze simultaneously the current–voltage and capacitance–voltage characteristics of metal–insulator–semiconductor (MIS) diodes. We use the method to study the effect of Zn doping concentration on the current transport in Au MIS contacts fabricated on In0.21Ga0.79As layers grown by metalorganic vapor phase epitaxy on highly doped GaAs substrates. At room temperature and for low reverse bias voltage, the generation/recombination process via mid-gap traps is the only dominant mechanism in these MIS diodes. For high reverse bias, both this mechanism and thermionic-field emission control current transport. The generation/recombination current observed is due to donor type mid-gap traps whose density shows an almost linear dependence with Zn concentration. The value of the barrier height at zero bias and at room temperature (φb0=0.73 V±12%) is independent of the Zn concentration. For the procedure used to prepare the In0.21Ga0.79As:Zn surfaces, the thickness of the oxide layer and the transmission coefficient of holes across this layer depend on the Zn doping concentration in the range 7×1014⩽NA⩽5×1018 cm−3. Zn doping seems to inhibit the formation of the unintentional native oxide on the surface of In0.21Ga0.79As epilayers.