Passivation versus Etching: Adsorption ofI2on InAs(001)

Halogen adsorption on certain III-V semiconductor surfaces forms ordered overlayers, while other surfaces etch. The microscopic mechanism underlying this behavior is investigated by comparing the adsorption of ${\mathrm{I}}_2$ on In- and As-terminated InAs(001) surfaces. On the In-terminated surface, a well-ordered $(1\times 1)$ structure forms and all of the iodine attaches to In. The As-terminated surface becomes disordered, however, and iodine attaches to both In and As. These observations can be explained by assuming that iodine initially bonds to In atoms, whether they are in the first or the second layer.