SURFACE-STRUCTURES AND ELECTRONIC STATES OF CLEAN AND (NH4)(2)S-X -TREATED, INAS(111)A AND (111)B

The surface structures, unoccupied and occupied electronic states, and chemical states of surface atoms for clean and (NH4)(2)S-x-treated In As(111)A and (111)B surfaces have been studied using low-energy electr on diffraction (LEED), inverse photoemission spectroscopy (IPES) and ( x-ray and ultraviolet) photoemission spectroscopy (PES). Thermal stabi lity of the treated surfaces upon annealing in an ultrahigh vacuum is also investigated. A diffuse (1 X 1) LEED pattern appears for the trea ted -(111)A and -(111)B surfaces annealed at 230 and 330 degrees C, re spectively, Upon annealing the (111)B sample at 380 degrees C, the (1 X 1) structure remains and the LEED spots become clearer. For the (111 )A annealed at 380 degrees C, the pattern changes to a clear (2 X 2) s tructure which is found for the first time for sulfurized (111) surfac es of III-V compounds. Sulfur is completely desorbed from both the (11 1)A and (111)B surfaces at 440 degrees C, exhibiting the (2 X 2) and ( 1 X 1) structures, respectively. IPES and PES results indicate that un occupied and occupied dangling bonds disappear for the sulfur-adsorbed (111)A-(2 X 2) and (111) B-(1 X 1) surfaces, respectively. S 2p spect ra show that sulfur is bonded to both indium and arsenic on the (111)B surface annealed at less than 340 degrees C and bonded only to indium at 420 degrees C. On the other hand, it is bonded solely to indium on the (111)A surface with and without annealing. Surface core-level shi fts of In 4d and adsorption sites of sulfur are discussed. (C) 1998 Am erican Institute of Physics. [S0021-8979(98)07519-7]