Peculiarities of photoelectron spectra of Ge implanted with Na$^+$ ions

Using the methods of Auger electron and photoelectron spectroscopy and light absorption spectroscopy, the composition, densities of state of electrons in the valence band, and parameters of the energy bands of Ge (111) implanted with Na$^+$ ions with an energy of $E_0$ = 0.5 keV at a dose of $D_{sat}$ = 6 $\cdot$ 10$^{16}$ cm$^{-2}$ and a thin layer of NaGe$_2$ obtained by annealing ion-implanted Ge. It is shown that a narrow $n$-type band ($\sim$ 0.2 eV) appears in the Ge valence electron spectrum after ion implantation near the bottom of the conduction band, which is explained by the presence of a large number of unbound Na atoms in the ion-implanted layer. NaGe$_2$ nanofilms with a band gap of $\sim$0.45 eV was obtained for the first time by annealing ion-implanted Ge.