Effect of the disordering of thin surface layers on the electronic and optical properties of Si(111)

The degree of disordering and the thickness $d$ of disordered layers and their effect on the band gap $E_g$ of single-crystal Si(111) under Ar$^+$-ion bombardment are studied for the first time. It is shown that the $d$ value at ion energies of $E_0$ = 1 and 2 keV is (100–120) and $\sim$(150–160) $\mathring{\mathrm{A}}$, respectively. In this case, the density of states of electrons in the Si(111) valence band significantly changes, the light transmittance decreases to $K$ = 55–60%, and the $E_g$ value increases by $\sim$10%. Under Ni$^+$-ion bombardment, surface disordering is accompanied by a sharp change in the composition of the surface layers and, as a result, the $K$ value decreases to 5–10%. After heating at $T$ = 900 K, nanocrystals (at doses of $D\le$ 10$^{15}$ cm$^{-2}$) and NiSi$_2$ nanofilms (at $D$ = 6 $\times$ 10$^{16}$ cm$^{-2}$) are formed.