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 fabricated on Zn-doped InP layers grown by metal-organic vapor phase epitaxy. A recently developed method was used for the simultaneous analysis of the current-voltage (I-V) and capacitance-voltage (C-V) characteristics in an epitaxial MIS diode which brings out the contributions of different current transport mechanisms to the total current. I-V and high-frequency C-V measurements were performed on two MIS diodes at different 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 independent both of the Zn-doping density and of the surface preparation. The interface state density distribution N-ss as well as the thickness of the oxide layer (2.2 +/- 15% nm) unintentionally grown before Au deposition 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 much lower for the highly-doped sample. Our results indicate that at high temperatures, independent of the Zn-doping concentration, the interfacial layer-thermionic (ITE) and interfacial layer-diffusion (ID) mechanisms compete with each other to control the current transport. Ar intermediate temperatures, however, ITE and ID will no longer be the only dominant mechanisms in the MIS diode fabricated on the highly-doped sample. In this case, the assumption of a generation-recombination current permits a better fit to the experimental data. Analysis of the data suggests that the generation-recombination current, observed only in the highly-doped sample, is associated with an increase in the Zn-doping 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 reserved.