Electronic properties of the Cs covered GaAs(100) Ga-rich surface

Room temperature adsorption of Cs on the GaAs(100) Ga-rich surface has been studied in ultrahigh vacuum with threshold photoemission spectroscopy. The surface band structure has been investigated in a wide range of Cs coverages. Two Cs-induced bands A1 and A2 below the EF are revealed at low coverages. The evolution of the bands completes at coverage Θ∼0.7 ML corresponding to the saturation of Ga dangling bonds. At Θ>0.7 ML, the broad features P and C are found in the spectra. The modification of the spectra provides evidence of two adsorption phases with a strong and a weak Cs bonding. The results specify the A1 and A2 bands to be originated from local interaction of Cs-atoms with Ga dimers. The P and C features can be attributed to Cs surface plasmon and to plasmons excited in Cs quasi-2D or 3D clusters. The Cs/GaAs(100) Ga-rich interface is found to be semiconducting up to 0.9 ML.