Effect of different cation-anion bond strengths on metal-ternary-semiconductor interface formation: Cu/Hg0.75Cd0.25Te and Cu/CdTe.

Abstract

The effect of the very different Hg---Te and Cd---Te bond strengths in ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te (MCT) upon interface formation with a noble metal is investigated via a comparative study of the Cu/n-type CdTe and Cu/p-type MCT (x=0.25) interfaces formed in ultrahigh vacuum at room temperature. The interfaces were studied using x-ray and ultraviolet photoelectron spectroscopy and low-energy electron diffraction. For Cu/CdTe there is a limited movement of Cd and Te into the Cu and no detectable migration of Cu into the semiconductor. For Cu/MCT, Hg is lost and there is movement of Cu into MCT as well as a pronounced movement of Cd and Te into the Cu for both the low- and high-coverage regimes. At a coverage of 2.5 monolayers (ML) the Cu intermixes into the top \ensuremath{\sim}20 A\r{} of the semiconductor as \ensuremath{\sim}20% of the Hg is depleted from this region, while at high coverages (>100 ML) the near-surface region of the Cu overlayer contains roughly 5% Cd and 35% Te, an order of magnitude more Cd and Te than for Cu/CdTe. The differences in the CdTe and MCT behavior are attributed to the weakness of the Hg---Te bond. For MCT, on deposition of 0.1 ML Cu the bands bend 0.1 eV upwards from the initial pinning position of the surface conduction-band minimum (CBM) at the Fermi level ${E}_{F}$ (within 0.1 eV). For Cu/CdTe, deposition of 0.1 ML Cu causes the bands to bend 0.2 eV up from their initial pinning position of ${E}_{F}$ 0.3 eV below the CBM.