CHANGES IN TRANSITION-TEMPERATURE OF THE SI(111)1X1-7X7 PHASE-TRANSITION OBSERVED UNDER VARIOUS OXYGEN ENVIRONMENTS

In order to investigate the role of oxygen atoms in the Si(111)1 X 1-7 X 7 phase transition, the transition was examined accurately under ex tremely high vacuum conditions (<4 X 10(-10) Pa). Transition temperatu re was measured for the modified-FZ crystal (resistivity; 4 x 10(4) Oh m cm) in which the oxygen concentration was 7.0 X 10(15) atoms/cm(3), and for a CZ crystal (resistivity: 5 Ohm cm) which contained 6.4 X 10( 17) oxygen/cm(3). The transition point was decided to be 1049 K for th e modified-FZ crystal, and was lower than that for the CZ crystal by 4 0 K. By taking advantage of the modified-FZ in which the contribution of outdiffusion to the surface equilibrium oxygen concentration is exp ected to;be quite low, the oxygen concentration in the surface region was controlled by quenching right after high temperature flashing and/ or oxygen exposure. The transition temperature was changed depending o n the oxygen concentration. These experimental facts indicate that the difference in the transition temperatures can be ascribed to the infl uence of oxygen concentration on the stability of the 7 X 7 structure.