Ge(111)-Ga at low coverages: the stabilization of the moderate-temperature phase of Ge(111)

Abstract We have studied the Ge(111) Ga phase of lowest adsorbate coverage. Its low-energy electron-diffraction pattern shows split spots at the half-order reflections exactly like those observed for the moderate temperature phase (between 300°C and 775°C) of clean Ge(111). Scanning tunneling microscopy (STM) topographs exhibit an irregular structure formed by domains in which adatoms build a (2 × 2) mesh. This structure has some similarity with the I(2 × 2) reconstruction which was proposed [R.J. Phaneuf and M.B. Webb, Surf. Sci. 164 (1985) 167] as a structural model for the moderate temperature phase of Ge(111). STM images which we obtained for the same section of the surface at both positive and negative bias provide some clue for the understanding of the role played by Ga in this phase. Throughout a wide range of Ga coverages (0.05–0.5 ML) this non-periodic reconstruction is stable and some localized defects indicate a timid tendency to the formation of (√3 × √3) reconstructed areas. In contrast to Si(111) Ga , no (√3 × √3) phase is observed for 1 3 ML Ga coverage on Ge(111).