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ZnSe AND GaAs EPITAXY ON Si(100) SURFACES

IP.com Disclosure Number: IPCOM000026327D
Original Publication Date: 1991-Apr-30
Included in the Prior Art Database: 2004-Apr-05
Document File: 4 page(s) / 189K

Publishing Venue

Xerox Disclosure Journal

Abstract

The problem of charge mismatch in the epitaxy of GaAs and ZnSe on Si (100) surfaces is completely eliminated by insertion of a suitable monolayer of atoms at the materials' interface. For most crystallographic orientations, and in particular for the (100) surface, perfect epitaxy leads to an interface charge density or dipole which causes atomic rearrangements and mixing at the interface preventing, in many cases, defect free growth.

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XEROX DISCLOSURE JOURNAL

ZnSe AND GaAs EPITAXY ON

Si(100) SURFACES James D. Chadi

Proposed Classification

U.S. C1.437/976 Int. C1. HOll21/461

Zn Se As Si Ga

Fig. 1

Fig. 2

XEROX DISCLOSURE JOURNAL - Vol. 16, No. 2 MarchlApril1991 145

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ZnSe AND GaAs EPITAXY ON Si( 100) SURFACES(Cont'd)

The problem of charge mismatch in the epitaxy of GaAs and ZnSe on Si (100)
surfaces is completely eliminated by insertion of a suitable monolayer of atoms at the materials' interface. For most crystallographic orientations, and in particular for the (100) surface, perfect epitaxy leads to an interface charge density or dipole which causes atomic rearrangements and mixing at the interface preventing, in many cases, defect free growth.

The simplest recipe is obtained for ZnSe epitaxy on Si where a monolayer of As (or other Group V) atoms is shown to totally remove the charge mismatch properties of the interface. For GaAs epitaxy on Si, a monolayer consisting of two kinds of atoms is necessary to accomplish the same goal. The theoretical tool used in deriving these results is very simple, and depends only on "electron counting," The primary criteria are that all atoms should be able to satisfy all their bonding requirements without becoming charged. and that the orbital occupancies of the epitaxial atoms near (and away from) the interface should be the same as those in the corresponding bulk materials. Fractional electronic occupations in Ga and As orbitals is employed to calculate the number of electrons in dangling-bond orbitals.

The fractional charges in each atomic bond orbital can be obtained by noting that in bulk GaAs, each Ga (As) atom makes four bonds with its As (Gal nearest neighbors. Since Ga has three valence electrons, it contributes, on average, 3/4 electron (.75 e) to each bond. Similarly As with five valence electrons contributes, on average, 514 electrons (1.25 e) to each of its orbitals. Application of the same scheme to ZnSe leads to 0.5 e in each Zn orbital and 1.5 e in each Se orbital. For Si, each dangling bond at the surface contains one electron.

In the epitaxy of ZnSe on the Si (100) surface, starting with a monolayer of Se, each Se atom uses two of its valence electrons to form two back bonds with the Si substrate atoms, leaving four electrons in the two remaining nonbonded orbitals. These orbitals are completely full, thereby making the surface unreactive to further chemical reactions if the overlayer forms an ideal 1x1 lattice. Similarly, if Zn instead of Se is used as the first monolayer, its two valence electrons make two bonds to the Si substrate leaving no electrons for further bonding.

If As or other group V element is the first layer over the Si substrate, as shown in Fig. 1, two valence electrons are used to make the necessary bonds to the Si substrate, leaving three electrons in the remaining two dangling bonds. The occupation of each dangling bonds is...