Process for producing doped semiconductor layers

Details Process for producing doped semiconductor layers Process for producing doped semiconductor layers

1991-01-31

1992-11-10

Hearn, Brian E.

Fishing, trapping, and vermin destroying

437 82, 437108, 437139, 437247, 148DIG37, H01L 2120

Patent

active

051622564

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION The present invention relates to a process for
producing doped semiconductor layers having a low concentration of charge carriers.


BACKGROUND OF THE INVENTION

The concentration of n-, respectively, p-charge carriers in semiconductor materials is set by incorporating corresponding doping material elements into the basic crystal lattice. In the conventional processes for fabricating doped semiconductor layers, by way of illustration, VPE, MOCVD, LPE or MBE processes, the concentration of doping material elements in the vicinity of the substrate, on which the layers are produced, is maintained as constant as possible. The doping material element or elements are usually offered in the form of gases, fluids or molecular rays.
In this manner, the constant concentration of doping material elements is set in the solid, i.e. in the produced layer, via the distribution coefficient between the surrounding medium and the solid, thereby setting a constant concentration of charge carriers.
By way of illustration , in order to produce GAInAs layers having a concentration of 10.sup.16 zinc atoms per cm.sup.3, a partial pressure of the zinc compound of approx. 10.sup.-9 bar is needed. On the other hand, setting a doping material concentration of 10.sup.15 cm.sup.-3 requires setting the partial pressure of zinc compounds at a value of less than 10.sup.-10 bar.
As in the conventional processes for producing doped semiconductor layers, the partial pressure of doping material compounds has to be kept constant during the entire production of the layers, producing layers having a low concentration of charge carriers, respectively in the range of 10.sup.15 cm.sup.-3, is technically very elaborate and demanding without any ensurance of actually having set the desired concentration of charge carriers with the necessary precision.
The object of the present invention is to provide a process for producing doped semiconductor layers having a low concentration of charge carriers, which permits producing low concentrations of charge carriers, typically in the range of less than 10.sup.16 cm.sup.-3, with the effort and expense therefor being justifiable.


SUMMARY OF THE INVENTION

The present invention is based on the fundamental concept that setting the desired concentration of charge carriers occurs not by a constant supply of doping material elements during the production of the layers, but rather by a sequence of typically rectangular doping material profiles and establishing an average via the doping material profiles.
For this purpose, the desired layer having a predetermined low concentration of charge carriers is produced by being built up of a multiplicity of substantially thinner layers, which are applied on top of each other and alternately have a relatively high concentration of doping material, and thus a relatively high concentration of charge carriers, and no doping. The thickness and the concentration of charge carriers of the individual layers are calculated in such a manner that averaging "perpendicular to the surface of the layers" over a multiplicity of layers yields the desired low concentration of charge carriers.
The term "no doping" means the areas, which may very well have a very small concentration of doping material elements, by way of illustration, as a result of residues in the reaction vessel due to the production of "the layer lying underneath". Decisive is only that the doping in these areas is small compared with the doping of the intended doped layers and also compared to the desired concentration of charge carriers so that an exact setting of in these areas is not "crucial".
The invented process thus has the advantage that it is not necessary to set the low partial pressures of the doping material carrier compounds required for producing a low concentration of doping material with the necessary precision. Rather all that is needed is to set the partial pressure of the elements "supplied" for the doping exactly in a relatively high pressure range in the thin layers having a com

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patent: 4571275 (1986-02-01), Moitsvold
patent: 4859627 (1989-08-01), Sunakawa
patent: 4960728 (1990-10-01), Schaake et al.
E. F. Schubert et al. "Diffusion of Atomic Silicon in Gallrium Arsenide", Applied Physics Letters, vol. 53 No. 4 Jul. 25, 1988 American Institute of Physics New York, N.Y. pp. 293-295.

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