Surface Science 454–456 (2000) 539–542 www.elsevier.nl/locate/susc Metal-induced gap states at InAs(110) surface M.G. Betti *, G. Bertoni, V. Corradini, V. De Renzi, C. Mariani INFM, Dipartimento di Fisica, Universita ` di Modena e Reggio Emilia, via G. Campi 213/A, I-41100 Modena, Italy Abstract High-luminosity and high-energy-resolution photoemission spectroscopy can provide direct observation of the spectral density of metal-induced states throughout the whole band gap, even at extremely low metal deposition. We present a study of the density of states of a two-dimensional electron gas induced in the InAs(110) conduction band by deposition of caesium, antimony and silver adatoms. We follow the density of states redistribution between the two-dimensional electron-gas channel and the appearance of metal-induced gap states. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Indium arsenide; Metal–semiconductor interfaces; Photoemission (total yield ); Schottky barrier 1. Introduction adatom concentrations [2,3]. In the MIGS model a strong correlation exists between the onset of The study of metal–semiconductor interfaces is overlayer metallicity and final SB height, and it is a fundamental subject in surface and interface better suited for the high-coverage regime, while physics owing to its attractive technological the defect model can be applied to the interfaces aspects. Much effort is being devoted to the rela- at the low-coverage stage. The SB models still raise tionship connecting macroscopic effects and micro- much controversy. The complexity of the interface scopic properties. An intriguing question is the morphology and the atomic geometry of the ada- relationship between Schottky barrier (SB) forma- toms can induce misleading interpretations of the tion and the evolution of the electronic states in experimental data [4,5]. the energy-gap region. A good tool to investigate the correlation Schottky barrier models can be classified into between macroscopic and microscopic aspects of two main groups: (1) the metal-induced gap states the SB formation is to study different adatom (MIGS) model, where the barrier height is deter- interactions with a semiconductor substrate free mined by the consistently induced electronic charge from surface intrinsic states in the bulk gap. A accumulated at the metal–semiconductor interface model system is the formation of an accumulation [1]; and (2) the unified defect model, where the layer at the surface of a narrow-gap n-type doped Fermi energy is assumed to be pinned by the semiconductor. When a metal is deposited on defects created at the surfaces even at very low n-type doped InAs(110) or InSb(110), the Fermi energy might move well inside the semiconductor * Corresponding author. Present address: Dipartimento di conduction band. In particular, by depositing tiny Fisica, Universita ` di Roma ‘La Sapienza’, p.zale A. Moro 2, amounts of caesium and silver on the InAs(110) I-00185, Rome, Italy. Fax: +39-06-4957697. E-mail address: betti@roma1.infm.it ( M.G. Betti) surface a giant accumulation layer is produced [6– 0039-6028/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S0039-6028(00)00065-0