Method For Depositing A Crystal Layer At Low Temperatures, In Particular A Photoluminescent IV-IV Layer On An IV Substrate, And An Optoelectronic Component Having Such A Layer

Abstract

A method for depositing a monocrystalline semiconductor layer consisting of a first element and a second element, wherein the first elements is fed as part of a hydride, and the second element is fed as part of a halide, together with a carrier gas, into a process chamber of a reactor, wherein radicals are produced from the hydride at a distance away from a surface of a semiconductor substrate, wherein at a temperature below a decomposition temperature of the radicals, at a total pressure of the gas in the process chamber sufficiently low to avoid a reverse reaction of the radicals in the gas phase the radicals and the halide are brought to the surface of the semiconductor substrate which is heated to a substrate temperature lower than the decomposition temperature, wherein heat released during a first exothermic chemical reaction drives a second endothermic chemical reaction.

Claims

1. A method for depositing a monocrystalline semiconductor layer consisting of a first element and a second element, wherein the first element is fed as part of a hydride, and the second element is fed as part of a halide, together with a carrier gas formed by an inert gas, into a process chamber of a CVD reactor; wherein gaseous radicals are produced from the hydride at a distance away from a surface of a semiconductor substrate, wherein the radicals have the property to decompose at a temperature higher but not lower than a decomposition temperature; wherein at a temperature below said decomposition temperature, at a total pressure of the gas in the process chamber sufficiently low to avoid a reverse reaction of the radicals in the gas phase the radicals and the halide are brought to the surface of the semiconductor substrate which is heated to a substrate temperature lower than said decomposition temperature; wherein the method comprising a first chemical surface reaction in which the radicals react exothermically with the halide at the surface of the semiconductor substrate, wherein products of the first reaction comprising atoms of the first element and atoms of the second element and heat released during the first reaction remaining at the surface of the semiconductor substrate; wherein the method comprising a second chemical surface reaction in which the radicals decompose endothermically into atoms of the first element remaining at the surface of the semiconductor substrate; wherein said heat being released during the first reaction drives the second chemical surface reaction and locally heats the surface of the substrate to a temperature sufficiently high for the atoms of the first element and of the second element to be integrated into the surface in crystalline order.

2. The method according to claim 1, wherein the formation of the radicals takes place at a minimal or no presents of H.sub.2.

3. The method according to claim 1, wherein the decomposition temperature of the radical is defined as the temperature at which only an extremely small growth of 1 nm/h and less of the first element on the substrate would take place without the admixture of said halide.

4. The method according to claim 1, wherein the first element is an element of the V main group, for example arsenic, phosphorus, antimony or nitrogen, the second element is an element of the III main group, for example aluminium, gallium or indium,

5. The method according to claim 1, wherein the first element is an element of the IV main group, for example carbon, silicon or germanium, and the second element is an element of the IV main group, for example carbon, silicon, germanium or tin.

6. The method according to claim 1, wherein the first element is an element of the VI main group and the second element is an element of the II main group.

7. The method according to claim 1, wherein the radicals are produced by pneumatic expansion of the first gaseous starting material when feeding into the process chamber from a pressure greater than 1,000 mbar to a process chamber pressure of less than 300 mbar.

8. The method according to claim 5, wherein the hydride is Ge.sub.2H.sub.6 and/or Si.sub.2H.sub.6 and is fed with a partial pressure of from 60 Pa to 120 Pa into the process chamber.

9. The method according to claim 8, wherein the halide is SnCl.sub.4 and is fed with a partial pressure of from 0.1% to 5% of the partial pressure of the hydride, in particular with a partial pressure of from 0.03 Pa to 1.25 Pa into the process chamber.

10. The method according to claim 9, wherein the layer or the layer sequence is deposited on a Ge buffer layer applied to a Si substrate.

11. The method according to claim 10, wherein the substrate temperature lies in a range between 350 C. and 390 C.

12. The method according to claim 8, wherein the layer or layer sequence is deposited with a growth rate in the range between 15 nm/min and 50 nm/min.

13. The method according to claim 5, wherein the layer is a GeSn layer or an SiGeSn layer and the Sn proportion lies in the range between 8% and 20%, preferably is greater than 10%, and preferably lies in the range between 10% and 14%.

14. The method according to claim 5, wherein the layer sequence is a GeSn layer which is arranged between two SiGeSn layers.

15. The method according to claim 4, wherein the hydride is NH.sub.3 or NH.sub.2R, wherein R is an organic group, and the halide is GaCl.sub.3.

16. The method according to claim 15, wherein the substrate temperature lies in a range between 600 K and 950 K, wherein the total pressure lies in a range between 20 hPa and 200 hPa, wherein the lateral flow velocity in a process chamber of a CVD reactor lies between 0.1 ms and 10 ms, wherein the partial pressure of GaCl.sub.3, NH.sub.3 or NH.sub.2R lies in a range between 1 and 3000 Pa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Details of the invention will be explained hereinafter on the basis of the accompanying drawings, in which:

[0020] FIG. 1 shows the cross-section through a CVD reactor as can be used to deposit the layers;

[0021] FIG. 2a shows the electrical band structure of a GeSn semiconductor with an Sn proportion of 8%;

[0022] FIG. 2b shows the electrical band structure of a GeSn semiconductor with an Sn proportion of 13%;

[0023] FIG. 3a shows the photoluminescence spectrum of a GeSn semiconductor layer with an Sn proportion of 8%;

[0024] FIG. 3b shows the photoluminescence spectrum of a GeSn semiconductor layer with an Sn proportion of 9.6%;

[0025] FIG. 3c shows the photoluminescence spectrum of a GeSn semiconductor layer with an Sn proportion of 11%;

[0026] FIG. 3d shows the photoluminescence spectrum of a GeSn semiconductor layer with an Sn proportion of 12.6%;

[0027] FIG. 4 shows the example of a layer sequence according to the invention;

[0028] FIG. 5 shows an illustration according to FIG. 1 relating to the deposition of GaN.

DETAILED DESCRIPTION

[0029] FIG. 1 shows, largely schematically, the cross-section through a CVD reactor as is used to carry out the method or to deposit the layers of the components according to the invention. What is not illustrated is an external gas supply for providing the process gases, specifically Si.sub.2H.sub.6 and Ge.sub.2H.sub.6 and also SnCl.sub.4 and, as inert gas, N.sub.2. The reactor has a housing which is closed in a gastight manner outwardly and of which the interior can be evacuated by means of a vacuum arrangement or can be regulated to a total pressure in the range from 0 mbar to 1,000 mbar. A gas inlet member 1 in the form of a showerhead is disposed inside the reactor housing. Here, the interior is a gas distribution chamber, to which the process gases and the inert gas are fed. FIG. 1 shows a gas inlet member 1 having just one gas distribution volume. However, provision is also made so that the three process gases are introduced separately from one another into a process chamber 3 arranged below the gas inlet member 1, in each case through a gas distribution chamber. This occurs through gas outlet openings 2 in a gas outlet surface of the gas inlet member 1.

[0030] The base of the process chamber 3 is formed by a graphite susceptor 5, which is distanced from the gas outlet surface by approximately 1 cm to 2 cm. One or more Si substrates 4 are disposed on the susceptor 5.

[0031] A heater 6 is disposed below the susceptor 5, for example a lamp heater, in order to heat the susceptor 5 to a process temperature of, for example, 300 C. to 400 C.

[0032] Four experiments will be explained by way of example in order to explain the essence of the invention. The growth temperature of the four layers A, B, C, D can be inferred from the table below.

TABLE-US-00001 SnCl.sub.4 Steam Total Reactor Ge.sub.2H.sub.6 SnCl.sub.4 bubbler Growth pressure x_Sn flow pressure Temperature flow flow temperature time SnCl.sub.4 (at. %) (sccm) (mbar) ( C.) (sccm) (sccm) ( C.) (min) (mbar) A 8 2000 60 390 400 25 20 3.75 25 B 9.6 2000 60 375 400 25 20 4.83 25 C 11.1 2000 60 375 400 25 20 6 25 D 12.6 2000 60 350 400 12 20 13.33 25

[0033] N.sub.2 was used as carrier gas. The SnCl.sub.4 bubbler, however, was operated with H.sub.2 as carrier gas so as to conduct gaseous SnCl.sub.4 into the reactor. The layers A and C were seemingly produced with the same growth parameters. However, it should be taken into consideration here that on account of a drift in the CVD system, in particular in the SnCl.sub.4 source, the actual SnCl.sub.4 flows were different. The dilution ratio of SnCl.sub.4 in the H.sub.2 carrier gas flow through the bubbler was approximately 10% and was subject to a drift, which in particular was dependent on the fill level of the liquid starting material in the source container.

[0034] A Ge buffer layer was first deposited on an Si(001) substrate. The Ge buffer layer had a high-quality surface. It was a Ge buffer layer having few defects and having a surface roughness in the region of 0.25 nm. The Ge buffer layer was deposited by introducing Ge.sub.2H.sub.6 into the process chamber.

[0035] With a Ge.sub.2H.sub.6 flow of 400 sccm and a total flow of 2,000 sccm at a total pressure of 60 mbar, layers of Ge.sub.1-31 xSn.sub.x were deposited onto the Ge buffer layer in four different experiments, wherein the Sn proportion was 8%, 9.6%, 11.1% and 12.6%. The deposition was performed at different temperatures, wherein the growth temperature had an influence on the Sn integration. The growth rates varied between 17 nm/min and 49 nm/min. Layers were deposited in a thickness of approximately 200 nm.

[0036] FIGS. 2a and 2b show the band structure of a Ge.sub.1xSn.sub.x crystal, wherein FIG. 2a shows the band structure of a crystal with an Sn proportion of 8% and FIG. 2b shows the band structure with an Sn proportion of 13%. FIG. 2a shows that the direct band gap ( valley) has a greater energy than the indirect band gap ( valley). With increasing rise of the Sn proportion, both the indirect band gap ( valley) and the direct band gap ( valley) are displaced, wherein the energy of the band gap of the direct band transfer decreases more significantly, such that the band transfer changes from indirect to direct in a region between 8% Sn proportion and 13% Sn proportion. Since the band structure is not only dependent on the Sn proportion, but also on the lattice strains, a critical Sn proportion cannot be specified.

[0037] FIGS. 3a to 3d show the photoluminescence spectrum of layers having different Sn proportions. It can be seen that the layer A with an Sn proportion of 8% has only a low photoluminescence, the layer B with an Sn proportion of 9.6% already has an identifiable photoluminescence, the layer C with an Sn proportion of 11.1% has significant photoluminescence, and the layer D with an Sn proportion of 12.6% has a strong photoluminescence, in each case at 20 K.

[0038] FIG. 4 shows the example of a light-emitting layer structure consisting of a layer sequence 13, 14, 15 with a layer thickness of at least 200 nm. From the layer sequence illustrated in FIG. 4, it is possible for example to produce a laser component which can be integrated monolithically into a circuit which has been applied monolithically to a silicon substrate 11. A Ge buffer layer 12 is first deposited on a silicon substrate 11. The first layer SiGeSn 13 of the layer sequence, which is p-doped, is then deposited on the Ge buffer layer 12. An active GeSn layer 14 is deposited thereon. An n-doped SiGeSn layer 15 is lastly deposited on the active layer 14. The Sn proportion (x value) lies in the range between 0.1 and 0.14. The Si proportion (y value) lies in the range between 0 and 0.2.

[0039] In the method, Ge.sub.2H.sub.6 is fed from a storage container at a pressure of more than 1,000 mbar together with N.sub.2 into the gas inlet member 1. Ge.sub.2H.sub.6 and Ge H.sub.3* are in thermodynamic equilibrium in accordance with the following equilibrium reaction.

Ge.sub.2H.sub.6.fwdarw.2GeH.sub.3*

[0040] Whereas, in the storage container, the left side of the equilibrium reaction dominates, the method is carried out so that the right side of the equilibrium reaction dominates in the process chamber. The decomposition of G.sub.2H.sub.6 into GeH.sub.3* is achieved on account of a pneumatic expansion of the gas from a pressure above atmospheric pressure to a sub-atmospheric pressure. In the exemplary embodiment the expansion occurs after 60 mbar.

[0041] Furthermore, SnCl.sub.4 is introduced into the process chamber, With N.sub.2 as carrier gas, SnCl.sub.4 and GeH.sub.3* are conveyed to the surface of the substrate 4, which lies on the heated susceptor 5 and has a surface temperature between 350 C. and 390 C. SnCl.sub.4 and GeH.sub.3* are adsorbed at the surface and react there exothermically with one another,

4GeH.sub.3*+3SnCl.sub.4.fwdarw.4Ge+3Sn+12HCl+energy

[0042] The HCl arising during this reaction is conveyed from the process chamber 3 by the carrier gas. The energy released leads to a local heating of the surface. The Ge atoms and Sn atoms remain adsorbed at the surface.

[0043] As a result of the local increase in the temperature of the surface, the following endothermic decomposition reactions take place.

2GeH.sub.3*+energy.fwdarw.2Ge+3H.sub.2

[0044] In parallel, the following decomposition reaction of undissociated Ge.sub.2H.sub.6 can also take place.

Ge.sub.2H.sub.6+energy.fwdarw.2Ge+3H.sub.2

[0045] The hydrogen arising as a result is transported away by the carrier gas. The surface is heated locally to such a temperature that the Ge atoms and Sn atoms have a sufficient surface mobility to form a crystal in a monocrystalline manner. At the process temperature (350 C. to 390 C.), the crystal thus deposited has a crystal structure which lies far beyond the thermodynamic equilibrium (instead of an Sn proportion of at most 1%, the Sn proportion can be up to 20%).

[0046] If an Si component is additionally also introduced into the process chamber, this occurs with use of Si.sub.2H.sub.6 as starting material, which is decomposed into adsorbed Si atoms similarly to the above-described mechanism.

[0047] Layers having the following composition are deposited

Si.sub.yGe.sub.1xySn.sub.x

0.008x0.14

0y0.2

[0048] The layer 14 or layer sequence 13, 14, 15 should have a minimum thickness d of at least 200 nm, preferably at least 300 nm in accordance with the invention. With a layer thickness of this type, which is deposited with growth rates of from 15 nm/min to 50 nm/min, the dislocation density in the layer volume, i.e. above a boundary region to the buffer layer 12 having a thickness of from 10 nm to 20 nm, is at most 10.sup.5cm.sup.2to 10.sup.6cm.sup.2. In the boundary region, i.e. in the first 10 nm to 20 nm of the layer or layer sequence, the dislocation density can assume much higher values. However, screw-like or thread-like dislocations there have a maximum density of 510.sup.6cm.sup.2.

[0049] In a variant of the invention an element semiconductor, for example a diamond layer, a silicon layer, or a germanium layer is deposited by low-temperature epitaxy. In order to deposit a diamond layer, CH.sub.3* reacts with CCl.sub.4 to form diamond. In order to deposit a silicon layer, SiH.sub.3* reacts with SiCl.sub.4 to form silicon, and in order to deposit a germanium layer GeH.sub.3* reacts with GeCl.sub.4 to form germanium.

[0050] With reference to FIG. 5, a further exemplary embodiment will be described hereinafter, in which NH.sub.3 is fed from a storage container at a pressure of more than 1,000 mbar together with NH.sub.2 into a gas inlet member 1. Radicals NH.sub.2* are produced thermally, but also with other suitable means, for example a plasma generator or other type of energy feed, in accordance with the following reaction

NH.sub.3.fwdarw.NH.sub.2*+H

[0051] In addition, GaCl.sub.3 is fed into the process chamber through the gas inlet member 1.

[0052] In a variant of the method, NH.sub.2R is fed into the process chamber instead of NH.sub.3, since this process gas can be brought into the form of the radical NH.sub.2* with less energy. Here, R is an organic group, for example C.sub.4H.sub.9.

NH.sub.2R.fwdarw.NH.sub.2* +R

[0053] In a first reaction, the NH.sub.2* reacts exothermically with gallium chloride in accordance with the following reaction equation

3NH.sub.2*+2GaCl.sub.3.fwdarw.3N+2Ga+6HCl+energy

[0054] The energy released during this reaction drives the parallel reaction specified as follows

NH.sub.2*+energy.fwdarw.N+H.sub.2,

[0055] in which elemental nitrogen arises. The elemental gallium formed during the first exothermic reaction and the elemental nitrogen formed during the second endothermic reaction are disposed at the surface. The individual atoms can find the integration places in the layer that are most favourable in terms of energy, such that an epitaxial monocrystalline GaN layer is produced. The layer can be deposited on a sapphire substrate, a silicon substrate, or a substrate.

[0056] In another embodiment, the growth of GaN layer takes place in a process chamber of a CVD reactor, wherein a process gas comprising a Ga-component and an N-component is fed with a gas inlet element into the process chamber together with a carrier gas, which can be H.sub.2. The process gas and the carrier gas flow from the gas inlet element to the substrates, which have to be coated with a GaN layer. The flow velocity lies in a range of 0.1 to 10 ms. The total pressure in the process chamber lies in a range of 20 to 200 mbar (20 to 200 hPa). The substrate temperature lies in a range between 600 K (326.85 C.) and 950 K (676.85 C.). The partial pressure of the Ga-component or the N-component lies in a range of 1 to 3000 Pa. The Ga-component can be GaCl.sub.3. The N-component can be Tert-Butylhydrazine or Ammonium. The process chamber of the CVD reactor is designed that in a space upstream and away from the substrate GaCl.sub.3 is splitted into a radical. The radicals are transported to the substrate by the carrier gas. Whereas on the surface of the substrate an exothermic reaction of the radical takes place, wherein HCl is formed. The exothermic reaction gives an additional activation energy for driving a second endothermic reaction at the surface of the substrate.

[0057] In accordance with the invention, the radicals produced in the gas phase reaction reach the surface and only react with one another there.

[0058] The above embodiments serve to explain the inventions included on the whole by the application which, each independently, develop the prior art at least by the following combinations of features:

[0059] A method for depositing a monocrystalline semiconductor layer consisting of a first element A and a second element B, wherein the first element A is fed as part of a first gaseous starting material, in particular a hydride, and the second element B is fed as part of a second gaseous starting material, in particular a halide, together with a carrier gas formed by an inert gas, in particular N.sub.2, Ar, He, into a process chamber 3 of a CVD reactor, wherein radicals are produced from the first starting material, which radicals and the second starting material are brought to the surface of a semiconductor substrate heated to a substrate temperature which is lower than the decomposition temperature of the pure radical, wherein the radicals in a first reaction react exothermically with the second starting material, in particular the halide, at the surface, wherein atoms of the first element A and atoms of the second element B remain at the surface as reaction products and the radicals decompose endothermically in a second reaction, at the same time as the first reaction, by absorbing the heat released during the first reaction, wherein atoms of the first element A remain at the surface, wherein the substrate temperature is sufficiently high for the atoms of the first element A and of the second element B to be integrated into the surface in crystalline order.

[0060] A method which is characterised in that the first element A is an element of the V main group, for example arsenic, phosphorus, antimony or nitrogen, the second element B is an element of the III main group, for example aluminium, gallium or indium, or in that the first element is an element of the IV main group, for example carbon, silicon or germanium, and the second element (B) is an element of the IV main group, for example carbon, silicon, germanium or tin, or in that the first element (A) is an element of the VI main group and the second element (B) is an element of the II main group.

[0061] A method characterised in that the radicals are produced by pneumatic expansion of the first gaseous starting material when feeding into the process chamber from a pressure greater than 1,000 mbar to a process chamber pressure of less than 300 mbar.

[0062] A method for monolithically depositing a monocrystalline IV-IV layer that glows when excited and that is composed of a plurality of elements of the IV main group, in particular a GeSn or SiGeSn layer, having a dislocation density less than 10.sup.6 cm.sup.2, on an IV substrate, in particular a silicon or germanium substrate, in particular a silicon substrate or germanium substrate, comprising the following steps: [0063] providing a hydride of a first IV element (A), such as Ge.sub.2H.sub.6 or Si.sub.2H.sub.6; [0064] providing a halide of a second IV element (B), such as SnCl.sub.4; [0065] heating the substrate to a substrate temperature that is less than the decomposition temperature of the pure hydride or of a radical formed therefrom and is sufficiently high that atoms of the first element (A) and of the second element (B) are integrated into the surface in crystalline order, wherein the substrate temperature lies, in particular, in a range between 300 C. and 475 C.; [0066] producing a carrier gas flow of an inert carrier gas, in particular N.sub.2, Ar, He, which in particular is not H.sub.2; [0067] transporting the hydride and the halide and decomposition products arising therefrom to the surface at a total pressure of at most 300 mbar; [0068] depositing the IV-IV layer, or a layer sequence consisting of IV-IV layers of the same type, having a thickness of at least 200 nm, wherein the deposited layer is, in particular, a Si.sub.yGe.sub.1xySn layer, with x >0.08 and y1.

[0069] A method characterised in that the hydride is Ge.sub.2H.sub.6 and/or Si.sub.2H.sub.6 and is fed with a partial pressure of from 60 Pa to 120 Pa into the process chamber.

[0070] A method characterised in that the halide is SnCl.sub.4 and is fed with a partial pressure of from 0.1% to 5% of the partial pressure of the hydride, in particular with a partial pressure of from 0.03 Pa to 1.25 Pa into the process chamber.

[0071] A method characterised in that the layer or the layer sequence is deposited on a Ge buffer layer applied to an Si substrate.

[0072] A method characterised in that the substrate temperature lies in a range between 350 C. and 390 C.

[0073] A method characterised in that the layer or layer sequence is deposited with a growth rate in the range between 15 nm/min and 50 nm/min.

[0074] An optoelectronic component, for example laser, photodiode, photosensor, photoelement, optical waveguide, or the like, having a monocrystalline IV-IV layer that has been epitaxially deposited on an IV substrate, in particular a Ge or Si substrate, glows when excited, is composed of a plurality of elements of the IV main group, in particular a GeSn or SiGeSn layer, and has a dislocation density less than 10.sup.6 cm.sup.2, wherein the layer or a layer sequence comprising the layer and consisting of a plurality of identical IV-IV layers is at least 200 nm thick, preferably at least 300 nm thick.

[0075] A method or an optoelectronic component characterised in that the layer is a GeSn layer or an SiGeSn layer and the Sn proportion lies in the range between 8% and 20%, preferably is greater than 10%, and particularly preferably lies in the range between 10% and 14%.

[0076] A method or an optoelectronic component characterised in that the layer has a relaxation degree of more than 80% and/or the dislocation density is less than 10.sup.6cm.sup.2, and/or in that the lattice defects are limited to a region close to the boundary layer to the substrate or the buffer layer, in particular to a region between 10 nm and 20 nm away from the boundary layer.

[0077] A method or an optoelectronic component characterised in that the layer sequence is a GeSn layer which is arranged between two SiGeSn layers.

[0078] A monolithically applied integrated circuit, in particular a microprocessor, characterised by an optoelectronic component according to any one of claims 10 to 13 monolithically applied to the substrate or a buffer layer.

[0079] All of the disclosed features are essential to the invention (individually, but also in combination with one another). The content of the associated/appended priority documents (copy of the prior application) is hereby fully incorporated into the disclosure of the application by reference, in addition for the purpose of including features of these documents in claims of the present application. The features in the dependent claims characterise independent, inventive developments of the prior art, in particular so as to be able to produce divisional applications on the basis of these claims.