DE19522054C1 - Development of germanium quantum wires on silicon@ substrates - Google Patents

Abstract

To produce Ge quantum wires on Si substrates for semiconductor components, through a spontaneous organised epitactic growth of Ge nanostructures, an atomically clean Si surface is prepared in ultra-high vacuum, at a pressure of about 10-10 mbar. This is followed by an in-situ deposition of a Si buffer layer. Anisotropic Ge islands are formed on the buffer layer, by vapour deposition, with a substrate temp. of 400-500 deg C. The remaining Si surfaces, free of Ge, are nitrated by NH3 adsorption at 600 deg C. Further Ge vapour deposition gives a selective epitactic growth of the Ge islands until the Ge quantum wires are formed. The Ge quantum wire structures are covered by a further vapour deposition of a Si layer.

Description

The invention relates to a method for producing Quantum wires on Si substrates for semiconductor devices self-organized epitaxial growth of Ge nanostructures.

On the way to maximum integration are getting smaller and smaller Semiconductor structures sought, so that the manufacture and the Investigation of dimensionally reduced semiconductor structures two have become essential components of modern solid state physics are.

Widely used to produce quasi-two-dimensional hetero structures on the nanometer scale are currently lithographic Techniques. However, the minimum achieved with this is lateral dimensions much larger than the vertical ones, too leads to relatively small distances between the subband energies. These narrow subband gaps are created by the Energy level broadening due to fluctuations in Wire width and of defects during structuring process arise, additionally obscured. To in particular Different methods of reducing the defect density Direct production of quantum wire structures based on the based on epitaxial growth. That includes that Growth of tilted superlattices on vicinal surfaces, the growth grid-inserted heterostructures and the stress-induced Confinement. With these structures, lateral dimensions can be achieved, which are comparable to the vertical. she in principle allow large subband spacings, as they are for optical and electrical device developments are required. The most  The most frequently used method concerns the growth of tilted Superlattice by evaporating fractions of monolayers themselves alternating composition on stepped surfaces by creates a slight misorientation of special surfaces will. Your successful application so far is because of poor control of local misorientation, the Cracking and because of the stability of the growth rate very much limited. The wires produced therefore suffer Inconsistency in shape, size and direction and until today no clear indication of a one-dimensional confinement effect observed.

From surf. Sci., Vol. 265, 1992, pp. 156-167 and from Ultramicroscopy, 42-44, 1992, pp. 832-837 and pp. 902-909 it is known that both on the Si (001) and on the Si (113) surface anisotropic determined by the structure of the substrate surfaces Growth of Ge takes place in the initial phase.

In J. Vac. Sci. Technol. B, vol. 12, 1994, pp. 2699-2704 detected by means of X-ray photoelectron spectroscopy be that by NH₃ adsorption on Si (001) initially a quick Nitration takes place at high exposures in one Saturation state passes because the reacting Si is slow can diffuse through the nitride layer formed. In contrast the Ge (001) surface is opposite to a thermal one Nitriding completely inactive by NH₃. That also applies Ge / Si heterostructures on which only Si are nitrided could.

The invention has for its object Ge quantum wire structures by evaporating Ge onto suitable Si surfaces to generate directly.

This object is achieved through the characteristic features of the patent claim 1 solved. An advantageous further development is in claim 2 specified.

The structural architecture of suitable Si surfaces (e.g. Si (001) and Si (113)) and the possibility of passivation of the Si atoms  by thermal nitriding allow the direct synthesis of Quantum wire structures by vapor deposition of Ge zu. These Structures have electrical transport properties that between those infinitely extended three-dimensional solids and those of molecular clusters.

The invention is described below with the aid of an embodiment game are explained in more detail:

Since both on the Si (001) and on the Si (113) surface one determined by the structure of the substrate surfaces anisotropic epitaxial growth of Ge in the initial phase is observed that z. B. on Si (001) to 2 × n structures with n 8th leads, is used in the invention, these elongated Ge islands by selective Ge deposition to quantum wires reinforce. This is the strict thermal Nitration selectivity between Si and Ge exploited. So it was as is known by means of X-ray photoelectron spectroscopy (XPS) demonstrated that by NH₃ adsorption at 600 ° C on Si (001) initially a rapid nitriding of the Si atoms takes place. she changes to a saturated state at high exposures because the reacting Si atoms only slowly through the formed Diffuse nitride layer.

In contrast, the Ge (001) surface is opposite one thermal nitration by NH₃ completely inert. That is true also towards Ge / Si heterostructures on which only Si nitrides could be.

It follows that the Si atoms of a Ge / Si heterostructure to passivate thermal nitriding during the subsequent Ge-evaporation is a selective epitaxial growth of anisotropic Ge islands up to the formation of Ge quantum wires to reach.

Claims (2)

1. Process for the production of Ge quantum wires on Si substrates for semiconductor components by self-organized epitaxial growth of Ge nanostructures, characterized in that an atomically clean Si surface is prepared in an ultra-high vacuum,
that a Si buffer layer is then deposited in situ,
that Ge is evaporated onto the buffer layer at a substrate temperature between 400 and 500 ° C to form anisotropic Ge island,
that the remaining Ge-free Si surface is nitrided at temperatures up to 600 ° C by NH₃ adsorption,
that a selective epitaxial growth of the Ge islands until the formation of quantum wires is then generated by renewed Ge vapor deposition and
that the Ge quantum wire structures are then covered by vapor deposition of a Si cover layer. 2. The method according to claim 1, characterized in that is prepared at a pressure of about 10 ^-10 mbar.