A study of the chemical and electrical disruption to mercury cadmium telluride upon interface formation and surface processing.

摘要

The chemical and electrical disruption induced to the HgCdTe lattice during such processes as metal contact formation, surface passivation, and surface etching often causes a degradation in performance of solid state HgCdTe devices. The aim of this work was to achieve a better understanding of the effects of chemical and electrical disruption that are induced in the HgCdTe lattice under conditions encountered during surface processing. To study the effects on the lattice during the initial stages of overlayer growth, atomically clean (110) HgCdTe surfaces were prepared by cleaving in situ in ultrahigh-vacuum, and photoemission electron spectroscopy and low energy electron diffraction were employed to monitor the surface chemistry, morphology, and band bending subsequent to each overlayer deposition. The depositions ranged from sub-monolayer at lower coverages to several monolayers (ML) at higher coverages. Ag, Pd, Al, and Si overlayers were investigated, and simplification the metal interfaces by reducing the Hg loss and consequent disruption of the HgCdTe lattice was achieved by lowering the substrate temperature from room temperature (RT) to lower temperature (170 K and 100 K) during the metal interface formation. For the Ag, Al, and Pd 100 K growths, more abrupt interfaces were indeed formed with less disruption and intermixing of metal and substrate components. For all three metals at low temperature the surfaces became degenerate n-type (0.6 eV above the valence band maximum) at these more abrupt interfaces, behavior not observed for the Pd and Ag RT cases. With increased metal coverage ({dollar}>{dollar}1 ML) for the Al and Pd case and upon warming to RT for the Ag case, the interfaces became disrupted and the Fermi level moved from this position toward the position seen for the corresponding RT metal growth. This Fermi level movement is consistent with the overlayer metal moving into the lattice, thus doping the semiconductor. To probe the surface in which actual device processing occurs, etching studies were conducted on the technologically important (111) surface. The etchants investigated caused a change in the surface stoichiometry primarily in the form of Cd loss, and a pinning of the Fermi level 0.15 {dollar}pm{dollar} 0.05 eV above the conduction band minimum. The nature of the bonding in Hg{dollar}sb{lcub}1-x{rcub}{dollar}Cd{dollar}sb{lcub}x{rcub}{dollar}Te was also probed by investigating the resultant defect structure of a Hg{dollar}sb{lcub}0.70{rcub}{dollar}Cd{dollar}sb{lcub}0.30{rcub}{dollar}Te/CdTe heterojunction damaged by ion bombardment. Analysis by transmission electron microscopy reveals that the bonding in HgCdTe has a more metallic nature than in CdTe.