EFFECT OF DOPING ON THE FORWARD CURRENT-TRANSPORT MECHANISMS IN A METAL-INSULATOR-SEMICONDUCTOR CONTACT TO INP-ZN GROWN BY METAL-ORGANIC VAPOR-PHASE EPITAXY

A detailed study of the effect of doping density on current transport was undertaken in Au metal-insulator-semiconductor (MIS) contacts fabr icated on Zn-doped InP layers grown by metal-organic vapor phase epita xy. A recently developed method was used for the simultaneous analysis of the current-voltage (I-V) and capacitance-voltage (C-V) characteri stics in an epitaxial MIS diode which brings out the contributions of different current transport mechanisms to the total current. I-V and h igh-frequency C-V measurements were performed on two MIS diodes at dif ferent temperatures in the range 220-395 K. The barrier height at zero bias of Au/InP:Zn MIS diodes, phi(o) (1.06 V +/- 10%), was independen t both of the Zn-doping density and of the surface preparation. The in terface state density distribution N-ss as well as the thickness of th e oxide layer (2.2 +/- 15% nm) unintentionally grown before Au deposit ion were independent of the Zn-doping concentration in the range 10(16 ) < N-A < 10(17) cm(-3); not so the effective potential barrier chi of the insulator layer and the density of the mid-gap traps. chi was muc h lower for the highly-doped sample. Our results indicate that at high temperatures, independent of the Zn-doping concentration, the interfa cial layer-thermionic (ITE) and interfacial layer-diffusion (ID) mecha nisms compete with each other to control the current transport. Ar int ermediate temperatures, however, ITE and ID will no longer be the only dominant mechanisms in the MIS diode fabricated on the highly-doped s ample. In this case, the assumption of a generation-recombination curr ent permits a better fit to the experimental data. Analysis of the dat a suggests that the generation-recombination current, observed only in the highly-doped sample, is associated with an increase in the Zn-dop ing density. From the forward I-V data for this diode we obtained the energy level (0.60 eV from the conduction band) for the most effective recombination centers. (C) 1998 Elsevier Science Ltd. All rights rese rved.