Chemical cleaning of InP surfaces: Oxide composition and electrical properties

Abstract

Unintentionally doped (100) InP wafers were ‘‘cleaned’’ with 12 different etching procedures, either found in the current literature or adapted from Si technology. We present the results of x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering experiments together with electrical properties of Au/InP contacts realized on the same samples. We can distinguish: first, the solutions which result in a rather clean InP surface and give metal-semiconductor Au/InP diodes from those which lead to an approximately 20-Å-thick oxide layer and give metal-insulating-semiconductor structures, and second, the solutions which give electrically stable structures from those which lead to very unstable ones. Detailed electrical measurements [J-V; J(V,T); C(V,T)] have been performed on two kind of stable surfaces: on ‘‘clean’’ etched ones and on one oxidized with NH4OH-H2O2-H2O (5:1:100) solution. For the first ones, a quasi-ideal metal-semiconductor diode is found. For the oxidized surfaces, current flow is controlled by pure tunneling through the oxide layer. A correlation between surface composition evaluated with XPS and surface electrical properties has been clearly established: the electrical properties of the relatively P-rich oxides are quite unstable while the others, In rich, remain stable over several months. The composition and the nature of the various oxides are discussed.