Influence of Ba atom adsorption and implantation of Ba$^+$ ions on the electronic structure of single crystalline Ge

The effect of the adsorption of Ba atoms with a thickness of $\theta\le$ 3–4 monolayers and the implantation of Ba$^+$ ions with an energy of $E_0$ = 0.5–2 keV on the density of states of electrons in the valence band, the parameters of the energy bands, and the emission and optical properties of Ge(111) has been studied for the first time. It is shown that during the adsorption of Ba atoms with $\theta$ = 1 monolayer, the value of the thermoelectric work function $\varphi$ decreases by $\sim$1.9 eV, and the value of the secondary electron emission coefficient and the quantum yield of photoelectrons $Y$ increases by 1.5–2 times. In the case of implantation of Ba$^+$ ions with $E_0$ = 0.5 keV at an irradiation dose $D$ = 6$\cdot$10$^{16}$ cm$^{-2}$, the density of state of valence electrons and the parameters of the energy bands change sharply; the quantum yield of photoelectrons increases by a factor of 2 or more. The observed changes are explained by the formation on the surface of a thin ($\sim$25–30 $\mathring{\mathrm{A}}$) amorphous doped layer consisting of nanoscale phases of the Ba–Ge type ($\sim$60–65 at.%). And excess (unbound) Ba and Ge atoms. In this case, the band gap $E_g$ decreases by $\sim$0.3 eV.