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

Abstract

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[1×1] pattern with strong diffuse scattering, while the (111)B[1×1] 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 (IHg/ITe and ICd/ITe ) were larger for the (111)A than for the (111)B surface. The A-face yielded a sharp (2×2) 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.