We investigated the influence of highly doped As on the step structure
s of Si(001) by using a Scanning Tunneling Microscope (STM). Line shap
ed protrusions on the terraces and regularly aligned triangular-shaped
step structures were observed. To clarify the formation mechanism of
the peculiar structures, an Atom Probe combined with an STM system was
used to know the chemical species on the surface. The AP mass spectru
m showed that As as well as Si atoms were clearly detected. Further As
concentration was much higher than the bulk concentration. The surfac
e structures may be formed by the outdiffusion of As atom to the surfa
ce. (C) 1998 Elsevier Science B.V. All rights reserved.