Abstract
Cooperative phenomena on the surface of a semiconductor caused by chemisorbed atoms behaving as surface donors are investigated. The polarisability alpha along the crystal surface rises sharply with the degree of covering n. At some critical value of nc, alpha diverges, which gives evidence of a transition of the adatom system for the insulating state to the metallic one. The Kubo formula is used to calculate alpha at small n when alpha is determined by the Van der Waals interaction between adatoms. Then an approximate analytical continuation of the expression for alpha is carried out to n=nc. The metallisation conditions for a surface donor system may be even more favourable than that for donors in the bulk of the semiconductor. Metallisation of adatoms makes them acquire new physical properties. So the decrease in the heat of adsorption Q with rising n may be explained by the increase in the electron Fermi energy of the surface metal with the degree of covering, the dependence of Q on n being close to linear.