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Posted: October 20, 2006
A generalized model for determining metal-induced reconstruction of compound semiconductor surfaces
(Nanowerk News) Chinese Academy of Sciences (CAS) physicists have proposed a generalized electron-counting model to serve as the guiding principle in understanding metal-induced surface reconstruction of compound semiconductors. The work was reported in Sept. 22 issue of Phys. Rev. Lett.
On a typical semiconductor surface, atoms in the top layers often rearrange themselves to form a reconstructed surface. For compound semiconductors such as GaAs and ZnSe, a simple electron-counting (EC) model has proven to be exceptionally instrumental in identifying the various forms of surface reconstruction. Since its proposal, the EC model has been applied successfully to many homogeneous semiconductor systems. It has also been extensively invoked in determining the structures of surface defects, such as vacancies, steps, and islands formed during homoepitaxial growth.
Metal growth on semiconductors is indispensable for many important technological applications. At the earliest stages of growth, adsorption of a submonolayer of metal often leads to the appearance of much richer surface reconstruction patterns than that in the corresponding homogeneous case. Because the reconstruction influences many important properties of the metal/semiconductor contacts such as the Schottky-barrier heights, it is vital to understand the precise form of reconstruction for a given system. More recently, such reconstructions have also been shown to play an important role in influencing the growth of diluted magnetic semiconductors at the growth front. To date, determination of metal-induced reconstruction of compound semiconductor surfaces has been primarily relying on a trial-and-error approach, typically with structural characterization using scanning tunneling microscopy (STM) or other techniques and results from extensive first-principles calculations as inputs on a case-by-case basis.
Based on theoretical analysis, first-principles calculations, and experimental observations, ZHANG Lixin, a doctoral student at the CAS Institute of Physics (IOP), establish a generic guiding principle, embodied in generalized electron counting (GEC), that governs the surface reconstruction of compound semiconductors induced by different metal adsorbates. The work has been completed under the guidance of Zhang's tutor ANG En'ge and in cooperation with physicists in and outside IOP. Within the GEC model, the adsorbates serve as an electron bath, donating or accepting the right number of electrons as the host surface chooses a specific reconstruction that obeys the classic electron-counting model. The predictive power of the GEC model is illustrated for a wide range of metal adsorbates.