ORDERED HG0.8CD0.2TE (111)A AND (111)B SURFACES - PREPARATION BY ANNEALING IN HG VAPOR AND CHARACTERIZATION BY LOW-ENERGY ELECTRON-DIFFRACTION, AUGER-ELECTRON SPECTROSCOPY, AND ELECTRON ENERGY-LOSS SPECTROSCOPY

Reported here are studies in which an oriented single-crystal, Hg0.8Cd0.2Te (111), was etched with methanolic bromine solution, ion bombarded with Ar+, and annealed in Hg vapor. Both parallel faces of the crystal, the metal-terminated (111)A surface and the Te-terminated (111)B surface, were characterized after each of the above stages of preparation by Auger electron spectroscopy (AES), electron energy-loss spectroscopy (EELS) and low-energy electron diffraction (LEED). After polishing in air the (111)A and (111)B surfaces were found to be contaminated with C and S-containing substances, and deficient in Cd; the LEED patterns were diffuse. EELS spectra showed a broad C-H stretching band near 2980 cm-1 and another broad band centered at 1300 cm-1 due to C-H bending and C-C stretching of surface hydrocarbons. Etching with bromine solution in air removed S-containing surface contaminants, without significantly changing the LEED and EELS results. Argon ion-bombardment removed the C contamination and increased the Cd content to expected levels, while decreasing the Hg content substantially. LEED showed a (111)A [1 X 1] pattern with strong diffuse scattering, while the (111)B [1 X 1] pattern was comparatively weak, indicating that detectable long-range order existed somewhere within the outermost few atomic layers. EELS of both faces displayed a peak at about 140 cm-1 attributable to the excitation of surface phonons. When the ion-bombarded crystal was annealed in Hg vapor, the Hg surface concentration increased. The ratios of metal to Te Auger intensity (I(Hg)/I(Te) and I(Cd)/I(Te)) were larger for the (111)A than for the (111)B surface. The A-face yielded a sharp (2 X 2) LEED pattern, while the B-face displayed a reproducible, complex, three-fold symmetric pattern indicative of a faceted surface. The annealed surfaces exhibited virtually the same EELS spectra as bombarded surfaces. The annealed surfaces are stable in vacuum, as judged by AES, LEED, and EELS.