Electronic states of ideal Ge-AI interfaces

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The structural complexity normally present at interfaces between metals and semiconductors poses a major obstacle to understanding the electronic structure of such interfaces, particularly the Fermi-level pinning. The difficulty arises from different lattice periodicities and bonding characteristics. One way of avoiding lattice incommensurability is to represent the metal by a jellium model, but this idealization leaves out structural effects and deemphasizes the role of local chemical bonds between metal and semiconductor atoms. We have studied the electronic structure of Ge-Al interfaces using a model which includes these effects and at the same times bypasses the lattice incommensurability problem. In particular, we constructed a lattice-matched interface model using an ideal (001)Ge substrate and a 45° rotated (001)A1 film. We used a repeating slab geometry and considered geometrical configurations which included on-top, interstitial, and Al vacancy models. Using the self-consistent pseudopotential approach, the electronic energy levels, total energies, local densities of states, and work function were calculated in all cases. On the basis of these calculations, it is concluded that Al atoms remove the surface states of pure Ge and replace them by metal-like states. The tails of the metal wave functions in the interfacial region are indeed responsible for pinning the Fermi level as originally proposed by Heine. These results go beyond earlier calculations, enabling us to discuss the effect of the discrete lattice on the electronic structure at the interface. © 1983, American Vacuum Society. All rights reserved.


01 Apr 1983