WO2010043200A1 - Method for producing a (oo1)-textured crystal layer from a photoactive layered semiconductor on a metal conductive layer using a metal promoter - Google Patents

Abstract

Layered semiconductors have a significantly higher absorption coefficient for visible light than silicon and are therefore of particular interest as absorber materials in thin-film solar cells. In the presence of a metal promoter, (OO1)-textured crystal layers having two-dimensional crystal growth parallel to the basal plane can presently only be produced by epitaxial growth in sufficient quality on isolator or extremely expensive metal substrates or layers. According to the invention, in a first alternative method (FIG. 4E) the grain boundaries acting as diffusion paths in the polycrystalline metal conductive layer (02) are inactivated by a saturation material, preferably a metal promoter or oxygen. The metal conductive layer (09) to be saturated can thus have any surface quality. As a second alternative method (FIG. 6C), indirect crystallization of the layered semiconductor layer, with partial chalcogenization, of a precursor metal layer (10) suited for producing layered semiconductors is proposed, wherein a thin precursor metal layer (11) is not converted and thus - including the saturated metal layer (09) - can be used as a cost-effective rear contact in a thin-film solar cell.

Description

 APPLICANT

Helmholtz Center Berlin for Materials and Energy GmbH

DESCRIPTION

A method of forming a (OOI) textured crystal layer of a photoactive lattice semiconductor on a metallically conductive layer involving a metal promoter.

DESCRIPTION

The invention relates to methods for producing a (001) -textured crystal layer of a photoactive, chalcogen-based layered lattice semiconductor on a chemically resistant, metallically conductive layer involving a metal promoter for exciting two-dimensional crystal growth parallel to the surface of the metallic layer and on a crystal layer produced by the method on a metallically conductive layer and its application.

Layered lattice semiconductors (or (transitional) metaldichalcogenides) have an approximately 10 to 50 times higher absorption coefficient for visible light than silicon and are thus of particular interest as absorber materials in thin-film solar cells. The van der Waals surface (vdW surface) in these layered lattice semiconductors (parallel to the basal plane) is characterized by low surface state concentrations (no unsaturated bonds as recombination centers), providing an ideal surface for the formation of electronically high-quality interfaces in pn heterojunction. For polycrystalline layers, this leads to the Demands to produce layers with large crystallites with the vdW surface parallel to the substrate ((OOI) texture).

STATE OF THE ART

The production of chalcogen-based layered lattice semiconductors from a melt is known from DE 35 26 908 A1. The exploitation of the oriented growth of layered lattice semiconductors for layer separation is known from DE 102 47 735 B3 and WO 2004/033769 A1. The use of Ni as a metal promoter in crystal growth is described for example in US 6,479,329 B2, US 2005/0245053 A1 and DE 101 41 090 A1. In addition to Ni, EP 0 656 644 B1 also discloses Pd, Pt, Cu, Ag, Au, In, Sn, Pb, P, As and Sb as promoters (including semiconductors and nonmetals) for the crystallization. It is described that the application and subsequent annealing of a thin promoter layer on amorphous silicon leads to its crystallization.

Basic preparatory work for the textured growth of laminated semiconductors in the presence of a metal promoter (Ni) as a crystallization nucleus are known from [1], [2] and [3], in particular the good growth on insulators is reported. From [4] it is known that metallic conductive, highly oriented pyrolytic graphite (HOPG) can be used as the substrate, but without the use of a metal promoter and at high temperatures (> 900 ° C). As a result, it is recognized that the substrate has a significant influence the crystallization has. The crystallization on the expensive, metallically conductive HOPG substrate, however, did not show the quality as the crystallization on a non-conductor. In the present context, a "metallically conductive layer" is understood as meaning a layer which has the electrical conductivity of a metal, which may be directly a metal, but may also be a nonmetal, for example Graphite or plastic, act. However, all previous attempts to fabricate textured layers of a layered lattice semiconductor on a low cost metal layer failed, see [5] where metal layers of Ni, Cr, or NiCr compounds were tested on a quartz substrate, and [6] here became initially used a non-conductive quartz substrate. In the preparation of metallic substrates, the choice of material was extremely problematic because the metal either reacted (AI) or diffused (Au) with the metal promoter. As a solution, an alkali metal-induced crystallization, for example by means of Na, was considered, but not further investigated.

The known approach to producing a layered lattice semiconductor on a low surface area metal has been to use a chemically resistant, conductive material such as titanium nitride (TiN) as the contact layer, which is known to be very temperature stable and chemically resistant and also acts as a diffusion barrier, eg the contacting of silicon components. However, TiN did not show the required (OOI) growth of WS ₂ , etc., even with the Ni-induced crystallization that was so successful on insulators (see above and [9]). This could be clearly done with the help of in situ, time-resolved

X-ray diffraction measurements (EDXRD, see [7]) can be detected. The crystallographic quality of these layers crystallized on TiN corresponds to that of WS ₂ layers, which were produced without a nickel promoter, but which are not suitable for electronic applications. Even when using other chemically resistant metal layers (Pt, WN, TiW, TiWN, TiNSi ₂ , TiSi ₂ ), no pronounced (001) growth could be observed despite the use of a thin film (5 nm) of nickel as metal promoter. This means that these materials were not a sufficient barrier against Ni diffusion. However, this is the prerequisite for the promoter effect of the metal layer (eg Ni, Co), see [8], which consists of a metal-chalcogen eutectic with an elec- tic temperature Tεu _t e _kt i _k forms, which is liquid and leads to the crystal growth of the Schichtgitter- semiconductors from the liquid phase, see [9].

In [9] the mechanism of nickel-induced fast crystallization of highly textured WS ₂ thin films is described in detail. (OOI) -textured tungsten disulfide thin films (layered semiconductor SHG) were prepared by nickel sulfide-induced (nickel sulfide promoters) rapid crystallization of amorphous, sulfur-rich tungsten sulfide (WS _{3 + X} ) layers. Growth was observed in situ by energy dispersive X-ray diffraction. Non-conductive quartz was used as the substrate, which was vapor-deposited with an electrically conductive metal layer of chemically stable Cr as an adhesion layer and a thin film of nickel sulfide as a metal promoter. In the sulfuric acid rich tungsten disulfide layer, a rapid crystallization with a crystallization rate greater than 20 nm / s was observed in a sulphurous atmosphere (H ₂ S, 10 Pa). The crystallization took place at about 650 ⁰ C, ie just above the eutectic temperature of the metal-chalcogen alloy nickel-sulfur at 637 ° C. After crystallization, hexagonal nickel sulfide crystallites isolated on the surface of the tungsten sulfide could be observed by electron microscopy. These results led to the model that rapid crystallization occurs by liquid phase crystal growth from nickel sulfide droplets floating on the surface of tungsten sulfide. The produced crystallized tungsten sulfide layers show (001) texture with crystallite sizes up to 3 μm.

FIG. 1 shows the time dependence of the intensity of the (001) scatter signal of an amorphous, sulfur-rich WS _{3 + x} layer during the heating process. The initial Ni layer is 5 nm thick. A temperature ramp of 400 k / min was run. A rapid crystallization at a rate of more than 20 nm / s is recognizable at 650 ⁰ C ± 50 ⁰ C. FIG. 2, which is also taken from FIG. 9, shows the dependence of the crystal quality of an WS ₂ layer on the basis of the detected X-ray diffraction the thickness of the nickel promoter layer. It can be seen that a 5 nm Ni layer results in very strongly (OOI) -textured WS ₂ layer growth. In contrast, a further layer thickness increase leads to a gradual increase in the (002) diffraction peak intensity. FIGURE 2 further shows that without the Ni layer no crystallization takes place, demonstrating the essential role of the nickel promoter in crystal formation. The SEM image according to FIG. 3 from [9] shows a rapidly crystallized WS ₂ -FiIm. Large (OOI) -oriented WS ₂ crystals (parallel to the basal plane) with a diameter of up to 3 μm are clearly visible. The small hexagonal crystals are NiS _x crystallites.

[10] provides a current, comprehensive overview of the prior art sputtering-based process options for producing tungsten disulfide layers, which details the principles of the present invention. For example, [10] gives a table of possible metal promoters with their most important parameters. So far, however, strongly (OOI) -textured, photoactive Dichalkogenidschichten (WS ₂ , MoS ₂ , WSe ₂ , MoSe ₂ and others) in the presence of a Metällpromoters as a seed crystal only on non-conductive substrates (mica, sapphire, quartz, oxidized silicon, Si ₃ N ₄ et al.) or very expensive conductive substrates (HOPG, platinum) are deposited or crystallized. Methods for producing the abovementioned strongly (001) -textured absorber layers on metallically conductive thin layers or cheaper metal sheets with a lower surface quality have not been described in the prior art.

TASK

Starting from the state of the art closest to the invention according to [9] with the knowledge according to [5] and [6], that so far none are sufficiently good textured crystal layers could be grown from a photoactive layer-grid semiconductor on a low-cost chemically resistant, metallically conductive layer despite interposition of a thin layer of a metal promoter, the TASK for the invention therefore is to provide a generic method of the type described above, generally guaranteed a fast and good (OOI) -textured crystal growth independent of the metal layer used. Accordingly, the layered lattice semiconductors produced should have a good (OOI) crystal structure and be suitable for a variety of applications. The solution according to the invention for this task can be found in the two alternative method claims and the related product and use claims. Advantageous modifications are shown in the respective associated subclaims and explained in more detail below in connection with the invention.

The first method alternative according to the invention is characterized by a pretreatment step before the application of a metal promoter layer in the form of a saturation of the metallically conductive layer with a saturation material. By this simple, but extremely efficient measure, the grain boundaries acting as diffusion paths in the polycrystalline metallically conductive layer are occupied by deliberately introduced saturation material, so that the grain boundaries are inactivated. For the subsequently applied metal promoter there is thus no possibility to diffuse into the metallically conductive layer, since the diffusion paths are blocked. The saturation of the metallically conductive layer thus ensures that the entire metal promoter used is available for crystal formation, resulting in a correspondingly fast and high-quality crystallization with a - desired - pronounced (001) texture. As a result of the decoupling of the metallic conductive layer used according to the invention in its surface quality from the metal promoter used, it is thus also possible to obtain cheaper metallic conductive layers, including metal thin layers, for example, from low-grade alloys, metal sheets or foils or metallically conductive plastics or mixtures or compounds for the construction of layered lattice semiconductors are used in the invention.

Advantageously, in the first method alternative according to the invention, the saturation of the metallically conductive layer can be carried out with a metal promoter as the saturation material. For reasons of process economy, this may preferably be the same metal promoter which is also used for the subsequent crystallization. The saturation with a metal promoter can preferably be carried out in the process steps listed below:

Providing a metallically conductive layer with a predetermined temperature stability limit T _G in the form of a metallic substrate or by coating a substrate with a metallically conductive

Component, compound or alloy,

Applying a saturation layer of a metal promoter with a layer thickness di on the metallically conductive layer,

• Annealing the saturation layer at a tempering temperature T _τ <T _G)

Application of a metal promoter layer with a given eutectic temperature T _eu tectikum in a metal chalcogen eutectic with a layer thickness d ₂ on the saturated metallically conductive layer, application of a chalcogen-rich, X-ray amorphous Schichtgitter-

Semiconductor layer with a layer thickness d ₃ in a chalcogen-containing gas atmosphere at a process pressure p _P and

• heating the dangling metallic conductive layer on a process temperature T _H to T _eut ek _t ikum <TH <T _G in the chalcogen-containing gas atmosphere in at least one process pressure PT. As an alternative to saturating the metallically conductive layer with a metal promoter, it is also possible to saturate the metallically conductive layer with oxygen as the saturation material. In this case, the diffusion of the metal promoter into the metallically conductive layer can be suppressed or at least drastically reduced by sputtering the metallically conductive compound or alloy or component reactively with a small addition of oxygen (O 2). In this case, the grain boundaries are saturated with the oxide, so that the known as diffusion paths grain boundaries are also blocked. In this case, however, it is important to precisely control the oxygen content of the sputtering atmosphere in order to avoid an excessive increase in the resistance of the metallically conductive layer, since a sufficiently good electrical conductivity must be maintained. Preferably, the process can be carried out in the following steps:

Reactive sputtering of a metallically conductive component, compound or alloy onto a substrate with the addition of oxygen at such a low level that a saturated, metallically conductive layer having a predetermined temperature stability limit T _{G is} formed,

Application of a metal promoter layer with a given eutectic temperature T _eu tectikum in a metal chalcogen eutectic with a layer thickness d ₂ on the saturated, metallically conductive layer, application of a chalcogen-rich X-ray amorphous layer lattice

Semiconductor layer with a layer thickness d ₃ in a chalcogen-containing gas atmosphere and

• Heating the saturated, metallically conductive layer to a process temperature T _H with T _eu tektikum <T _H <T ₀ in the chalcogen-containing gas atmosphere. Reactive sputtering of TiN _x Oy with 0.3 ≦ x <0.45 and 0.1 <y <0.3 can preferably take place here. This leads to specific resistances of the saturated metal layer in the range of 1x10 ^"4 Ωcm to 1x10 ^{" 2} Ωcm. In this case, the specific resistance increases with the oxygen content, ie with increasing y.

For the formation of the metallically conductive layer, a pure metal component or a metal compound or alloy or a metallically conductive non-metal compound or alloy may be used. Legie- are approximations as eutectic (Greek .: melt) designated when its components to each other, in such a proportion that they (t melting point eutectic temperature T _{Eu e} k _t ikum) as a whole at a certain temperature are liquid or solid , Metallically conductive non-metal compounds may be based on graphite or plastic, for example. Plastic mixtures are also referred to as alloys. Decisive for the possible use of non-metals in the form of compounds or alloys as a metallically conductive layer is their electrical conductivity (as in a metal), chemical resistance and resistance to the occurring process temperatures.

The second method alternative according to the invention is characterized by a direct crystallization of the layered lattice semiconductor layer by a partial conversion of a suitable precursor metal layer, eg Mo or W. This process can also be referred to as "incomplete chalcogenation." If a thin promoter layer is applied to a lattice layer Semiconductor formation is applied to a suitable precursor metal layer and then annealed in an H ₂ S atmosphere, so that an (OOI) -textured layer forms from the surface of the precursor metal layer from the corresponding layered lattice semiconductor. For example, metal layers that are annealed without a promoter layer form only extremely thin, superficial chalcogenide layers, again detected by in situ EDXRD The invention thus provides the possibility of converting a suitable precursor metal layer in a predetermined layer thickness directly into a strongly (001) (desired) textured layered lattice semiconductor.

In a simple way, the crystallization of a layered lattice semiconductor can be carried out directly on a metal contact. Thus, simple metal bands or bands coated with metal can be used as a metal reservoir in order to produce layered lattice semiconductors in the chalcogen gas atmosphere. However, care must be taken that the precursor metal layer is provided in such a layer thickness and the chalcogenation time is adjusted in such a time that after incomplete chalcogenation an unconverted precursor metal layer of sufficient strength remains as a metallically conductive layer. Preferably, a direct crystallization can be carried out with the process steps listed below:

Providing a precursor metal layer by coating a substrate having a predetermined temperature stability limit T _G with a metal or metal alloy having a layer thickness s suitable for forming a layered lattice semiconductor

• Aufheizen der Vorläufer-Metallschicht über eine Prozesszeit t auf eineApplying a metal _promoter layer with a given eutectic temperature Teut _ekt ikum in a metal-chalcogen eutectic with a layer thickness d ₂ on the precursor metal layer with

• Heating the precursor metal layer over a process time t on a

Process temperature T _H with T _eu tektikum <TH <TG in a chalcogen-containing gas atmosphere at least one process pressure p _τ, wherein the layer thickness s and the process time t are related in such a way that a thin precursor metal layer in a range of s / 2 above of the non-metallic substrate does not react with the chalcogen-containing gas atmosphere and remains as a metallically conductive layer. Both mentioned process agents according to the invention lead in the end result to a high-grade (OOI) -textured (desired) layer-lattice semiconductor layer on a metallically conductive layer. In the first alternative method, the diffusion of the metal promoter into the metallically conductive layer is deliberately suppressed by its saturation (by the metal promoter itself or by oxygen), in the second method alternative, the diffusion of the metal promoter into the metallically conductive layer is selectively utilized by a partial , direct crystallization is induced in a precursor metal layer. For this, the metal or metal alloy used must be capable of forming a layered lattice semiconductor in response to the chalcogen-containing atmosphere. In the first method alternative, the saturation layer and / or the metal promoter layer may preferably be applied by vapor deposition or magnetron sputtering. In the second method alternative, this applies to the application of the metal promoter layer. The precursor metal layer and the metallically conductive layer may preferably be deposited by vapor deposition.

In general, a metallically conductive substrate, here preferably a metal substrate, or a metallically conductive compound or alloy on a substrate, here correspondingly preferably a non-metallic substrate, can be used directly for the process alternatives according to the invention as a metallically conductive layer. The prerequisite for the suitability of the substrate used is its temperature stability as a function of the temperature stability of the metallically conductive layer used. Preferably, a non-metallic substrate may be oxidized silicon, quartz, ceramic or sapphire. However, it may also be a metallic substrate in the form of a simple metal sheet. Suitable metallic conductive layers must be electrically conductive and chemically resistant. They should preferably have a high temperature stability (and a moderate melting point for alloys used) and already act as a diffusion barrier by nature. As metallic conductive layer are therefore particularly suitable metal compounds TiN, TiW, TiSi ₂ , Ta, TaN, TaN: O, WN or WN: O. The metal component, which is crystallized directly and therefore must be capable of forming layered lattice semiconductors with chalcogenation, may preferably be Mo or W. Suitable metal _promoters preferably have a low eutectic temperature T _eutekt i _k um in a metal-chalcogen eutectic (eg Ni-S, Toni _k um (Co: 680 ° C, Ni: 637 ⁰ C, Pd: 623 ⁰ C), others see [10], Table 1) and show a good solubility with layer-lattice semiconductor-forming metals (see also [10], in particular with Mo and W. Therefore, Ni, Co or Pd can preferably be used as the metal promoter

Gas atmosphere of inert Ar gas can preferably H ₂ S, H ₂ Se or H ₂ Te are used as chalcogen-containing gas. Sulfides, selenides and tellurides have the necessary band gaps to crystallize as a layer lattice. After choosing these materials, the process alternatives according to the invention may be used to prepare WS ₂ , WSe ₂ , WTe ₂ , MoS ₂ , MoSe ₂ or MoTe ₂ as layered lattice semiconductors ((transitional) metaldichalcogenide).

If these materials are selected, the preferred process parameters are: a temperature stability limit T _G > 700 ^° C.

A tempering temperature T _τ > 600 ⁰ C,

• a eutectic temperature T _eu te _kt ikum <700 ⁰ C,

• a layer thickness di ~ d ₂ between 5 nm and 50 nm

• a layer thickness d ₃ between 100 nm and 500 nm • a layer thickness s between 0.5 μm and 1 μm

Sulfur-rich WS _{3 + 2} as a chalcogen-rich X-ray amorphous layer lattice semiconductor,

• H ₂ S + Ar as chaikogenhaltige gas atmosphere with a H ₂ S content in a range of 50%, • a process pressure p _P in a range of 2 Pa and

• a process pressure p _τ in a range of 10 Pa. Further details of the usable materials and process parameters in the invention can be found in the specific description part.

With the alternative fabrication methods of the invention, a strong (OOI) textured crystal layer of a photoactive layered lattice semiconductor may be formed on an electrically conductive metal layer. Such a layer structure is particularly advantageous for use in a thin-film solar cell with a metallic back contact as an essential functional element. In this case, the layered lattice semiconductor forms the photoactive part and the electrically conductive metal layer forms the metallic back contact

Embodiment

The process for producing a photoactive, (OOI) -textured crystal layer of a photoactive, chalcogen-based layered lattice semiconductor on a chemically metallic conductive layer involving a Metallpromoters for stimulating two-dimensional crystal growth parallel to the surface of the metallically conductive layer (basal plane) is in its variants explained in more detail below with reference to exemplary embodiments in the schematic FIGURES. Showing:

FIGURE 1 of the prior art, a diagram for

Crystallization, FIGURE 2 of the prior art, a diagram for

Dependence of the crystallization on the metal promoter, FIG. 3 on the prior art, an SEM image of a crystal layer, FIG. 4A to 4F the method according to the invention in variant A -

(Saturation of the metal layer by the metal promoter),

FIG. 5A to 5D show the method according to the invention in variant A - (saturation of the metal layer by oxidation) and

FIG. 6A to 6D the method according to the invention in variant B -

(direct crystallization of the layered lattice semiconductor layer with partial conversion of the metal layer).

For individual FIGURES not mentioned or shown in the description

Reference signs are to be taken from the preceding FIGURES or their description. FIGS. 1 to 3 serve to illustrate the principles of the present invention and are taken from the prior art according to [9]. They have already been explained in the introduction to the description. Further explanations can be found in [9].

The experiments were carried out in a magnetron sputtering system equipped with a lock to ensure constant process conditions in the coating chamber. This portable measuring and coating chamber was specially designed to be used at the synchrotron radiation source HASYLAB at DESY (Hamburg) for in situ and time-resolved measurements of energy-dispersive X-ray diffraction (EDXRD).

VARIANT A - ABSORPTION OF THE METALLIC CONDUCTIVE LAYER First embodiment: Saturation of the metallically conductive layer by the metal promoter

FIG. 4A Coating of a substrate 01 with a metallically conductive layer 02, in the selected exemplary embodiment TiN, which is electrically conductive, chemical is resistant and thermally stable and is known as a diffusion barrier. The substrate 01 must withstand temperatures up to at least the temperature stability limit T _{G of} the metallically conductive layer 02 (TG (TJN) ~ 700 ° C. used), in the selected embodiment oxidized Si.

FIG. 4B

Introducing a coated layer 01 into a sputtering chamber 03. Applying a saturation layer 04 to the metallically conductive layer 02. In the selected exemplary embodiment, a metal promoter (Ni) is likewise used as the saturation material. The saturation layer 04 is applied with a layer thickness di between 5 nm and 50 nm by vapor deposition or magnetron sputtering.

FIGURE 4C Eintempern the Absättigungsschicht 04 at an annealing temperature T _τ> 600 ⁰ C and <T _G 02. By this operation, which act as diffusion paths grain boundaries in the metal conductive layer 05 in the polycrystalline metallic conductive layer 02 with the metal promoter (in this case Ni ) and blocked for the diffusion of further atoms (see inset in FIG. 4C). The saturation layer 04 acts as a sacrificial layer and is dissolved after annealing in the metallically conductive layer 02 (TiN). The metallically conductive layer 02 is transformed into a saturated, metallically conductive layer 09 (indicated in FIG. 4C by a dotted line, nickel attachment).

FIG. 4D

Applying a metal promoter layer 06 (here Ni) with a layer thickness d ₂ of 5 nm - 50 nm by vapor deposition or magnetron sputtering on the saturated, metallically conductive layer 09. The metal promoter has a predetermined eutectic temperature T _eu tectikum in a metal chalcogen - Eutectic (Ni: T _eutect i _k um = 637 ° C) FIGURE 4E

Coating the metal promoter layer 06 with a sulfur-rich, X-ray amorphous layer-grid semiconductor layer 07, in the selected embodiment WS _{3 + X} , with a layer thickness d ₃ of about 100 nm to 500 nm in a chalcogen-containing gas atmosphere 08, in the selected embodiment H ₂ Sn-Ar Atmosphere, at a process pressure Pp of about 2 Pa and a H ₂ S content of about 50%.

Solid amorphous materials, in contrast to the anisotropic layered lattice crystals, are isotropic. They do not have a definite melting point, but gradually go over slow softening in the liquid state. Their experimental differentiation from crystalline phases can be made by X-ray diffraction, which gives them no sharp, but only a few diffuse interferences at small diffraction angles. Substances with such an X-ray diffraction pattern are referred to as "X-ray amorphous".

FIG. 4F heating of the saturated, metallically conductive layer 09 to a

Process temperature TH with T _eut ekti _k by <T _H <T _G (at TiN 700-800 ⁰ C) in the chalcogen-containing gas atmosphere 08 at at least one process pressure PT of> 10 Pa. This step serves to convert the amorphous layered lattice semiconductor layer 07 into a textured crystal layer 12 with large (001) -oriented crystallites 13 in the micrometre range (see

Inset FIGURE 4F, indicated by vertical dashes in FIGURE 4F). Saturated metal layer 09 was saturated with saturation material (here Ni) by tempered saturation layer 04 up to the solubility limit at approx. 700 ° C., so that metal promoter layer 06 was retained during heating and did not diffuse into saturated metal layer 09 but completely the crystallization was available (see arrows in FIGURE 4E). Upon crystallization of the amorphous layered lattice semiconductor layer 07, the metal promoter layer 06 changes, leaving metal promoter crystallites 14 behind.

VARIANT A-ABSOLUTE METAL LAYER Second Embodiment: Saturation of the Metallic Conductive Layer by Oxidation

FIG. 5A

Introducing the substrate 01 into a sputtering chamber 03. Reactive sputtering of a metal compound, here TiN, on the substrate 01 with the addition of oxygen O ₂ with such a low content that an electrically conductive but saturated metallically conductive layer 09 with a predetermined temperature stability limit T _G is formed. It is sputtered TiN _x Oy with 0.3 <x <0.45 and 0.1 <y <0.3 reactively, ie by chemical reaction. As a result, the grain boundaries 05 are saturated with TiO _x (see inset in FIG. 5A), so that they are blocked for diffusion (indicated in FIG. 5A by a dotted line, TiO _x deposition). To adjust the electrical resistance of the saturated metallic conductive layer 09, the oxygen content of the sputtering atmosphere must be precisely controlled.

FIG. 5B

Applying a metal promoter layer 06 (here Ni) with a layer thickness d ₂ of 5 nm - 50 nm to the saturated metallically conductive layer 09 by vapor deposition or magnetron sputtering. The metal _promoter has a given eutectic temperature T _eutectic in a metal-chalcogen eutectic (Ni: T _eu tectic = 637 ° C) FIG. 5C

Coating of the metal promoter layer 06 with a sulfur-rich, X-ray amorphous layer-grid semiconductor layer 07, in the selected embodiment WS _{3 + X} , with a layer thickness d ₃ of about 100 nm to 500 nm in a chalcogen-containing gas atmosphere 08, in the selected

Embodiment H ₂ S + Ar atmosphere, at a process pressure Pp of about 2 Pa and a H ₂ S content of about 50%.

FIG. 5D Heating the saturated metallic conductive layer 09 to a

Process temperature T _H with T _eu tekti _k by <TH <T _G (at TiN ~ 700-800 ⁰ C) in the chalcogen-containing gas atmosphere 08 at least one process pressure PT of> 10 Pa. This step serves to convert the amorphous layered lattice semiconductor layer 07 into a textured crystal layer 12 with large (001) -oriented crystallites 13 in the micrometre range (see

Inset FIGURE 5D, indicated by vertical dashes in FIGURE 5D). The saturated, metallically conductive layer 09 is saturated with saturation material (here O ₂ to form TiO _x ), so that the metal promoter layer 06 was retained during heating and not diffused into the saturated, metallically conductive layer 09, but completely available for the crystallization stood (see arrows in FIG. 5C). Upon crystallization of the amorphous layered lattice semiconductor layer 07, the metal promoter layer 06 changes, leaving metal promoter crystallites 14 behind.

VARIANT B - DIRECT CRYSTALLIZATION OF THE LAYER SEMI-FINISHED LAYER

UNDER PARTIAL CONVERSION OF THE METALLIC CONDUCTIVE LAYER

FIGURE 6A coating of the substrate 01, in the exemplary embodiment selected, oxidized silicon with a temperature stability limit T _G above 700 ⁰ C, with a precursor metal layer 10, here made of the metal tungsten W (metal component), at a predetermined temperature stability limit T _G and a layer thickness s, here 0.5 μm to 1 μm.

FIGURE 6B

Introducing the coated substrate 01 into a sputtering chamber 03 and applying a metal promoter layer 06 (here Ni) with a layer thickness cfe on the precursor metal layer 10 with cb "s (here d ₂ = 5 nm to 50 nm) by means of vapor deposition or magnetron sputtering , The metal _promoter has a given eutectic temperature T _eutek ti _k in a metal-chalcogen eutectic (Ni: T _E utektikum = 637 ° C)

FIG. 6C heating the precursor metal layer 10 over a process time t (duration see below) to a process temperature T _H with T _eut ek _t i _k by <T _H <T _G (at Ni and W ~ 700-800 ° C) in _FIG Chalkogenhaltigen gas atmosphere 08 (here H ₂ S in Ar) at least one process pressure PT (here> 10 Pa).

FIGURE 6D

The above-mentioned step serves to partially chalkogenize the precursor metal layer 10, in this case sulphurizing, in order to include large (OOI) -oriented crystallites 13 in the micrometer range (with insertion of the metal promoter layer 06 indicated by arrows in FIG. 6C) (see inset in FIGURE 6D) in a textured crystal layer 12. The combination of thickness of the thin precursor metal layer 10 and the process time t is chosen in this case, that only part of the precursor metal layer 10 is converted to the chalcogenide (in this case sulfide), so that a thin precursor metal layer 11 in a range of about s / 2 above the substrate (here layer thickness 0.2 .mu.m to 0.5 .mu.m ) remains as electrically conductive metal layer 02. This thin precursor metal layer 11 can then be used as back contact in a solar cell, so that thin-film solar cells based on chalcogen-based layer lattice semiconductors with particularly inexpensive back contacts can be produced particularly advantageously with the methods described above. In particular, metal sheets or foils can be used in roll-to-roll production.

QUOTED LITERATURE

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LIST OF REFERENCE NUMBERS

01 substrate

02 metallic conductive layer 03 sputtering chamber

04 saturation layer

05 grain boundary

06 metal promoter layer

07 layered semiconductor layer 08 chalcogen-containing gas atmosphere

09 saturated, metallically conductive layer

10 precursor metal layer (suitable for forming a layered lattice semiconductor layer)

11 thin precursor metal layer 12 textured crystal layer

13 (OOI) -oriented crystallite

14 metal promoter crystallite

di layer thickness of 04 d ₂ layer thickness of 06 d ₃ layer thickness of 07

PP process pressure at 07

P ₁ - process pressure s layer thickness of 10 t process time

T _E u _TEKT ikum eutectic temperature (melting point) of an alloy

T _G temperature stability limit

TH process temperature crystallization

T _τ annealing temperature

Claims

A method of forming a (OOI) textured crystal layer of a photoactive chalcogen-based layered lattice semiconductor on a chemically resistant, metallically conductive layer involving a metal promoter for exciting two-dimensional crystal growth parallel to the surface of the metallically conductive layer Characterized by a saturation of the metallically conductive layer (02) with a saturation material prior to the application of a metal promoter layer (06). 2. The method according to claim 1, Characterized by a saturation of the metallically conductive layer (02) with a metal promoter as a saturation material with the method steps: Providing a metallically conductive layer (02) having a predetermined temperature stability limit T _G in the form of a metallic substrate or by coating a substrate (01) with a metallically conductive component, compound or alloy, Applying a saturation layer (04) made of a metal promoter with a layer thickness di onto the metallically conductive layer (02), Tempering the saturation layer (04) at a tempering temperature T _τ <T _G , applying a metal _{promoter layer} (06) with a predetermined eutectic temperature T _eut e _kt i _k to the saturated one in a metal chalcogen eutectic with a layer thickness d ₂ metallic conductive layer (09), Applying a chalcogen-rich X-ray amorphous layer-lattice semiconductor layer (07) with a layer thickness d ₃ in a chalcogen-containing gas atmosphere (08) at a process pressure p _P and • heating the saturated metallic conductive layer (09) to a process temperature T _H with T _eu tekti _k by <T _H <T _G in the chalcogen-containing gas atmosphere (08) at least one process pressure p _τ . 3. The method according to claim 1, Characterized by a saturation of the metallically conductive layer (02) with oxygen as a saturation material with the method steps: Reactive sputtering of a metallically conductive component, compound or alloy onto a substrate (01) with the addition of Oxygen having such a low content that a saturated but metallically conductive layer (09) having a predetermined temperature stability limit TQ is formed, Applying a metal promoter layer (06) with a predetermined eutectic temperature T _eu tectikum in a metal chalcogen Eutectic with a layer thickness äΣ on the saturated, metallically conductive layer (09), Applying a chalcogen-rich X-ray amorphous layer-lattice semiconductor layer (07) with a layer thickness d ₃ in a chalcogen-containing gas atmosphere (08) and • Heating the saturated, metallically conductive layer (09) to a process temperature T _H with T _βu tektikum <T _H <T _G in the chalcogen-containing gas atmosphere (08). 4. The method according to claim 3, MARKED BY Reactive sputtering of TiN _x Oy at 0.3 <x <0.45 and 0.1 <y <0.3. 5. A method of forming a (OOI) -textured crystal layer of a photoactive layered lattice semiconductor on a chemically resistant, metallically conductive layer involving a metal promoter for exciting two-dimensional crystal growth parallel to the surface of the metallic-conductive layer. Characterized by a direct crystallization of the layered lattice semiconductor layer (07) with the method steps: Providing a precursor metal layer (10) by coating a substrate (01) with a predetermined temperature stability limit TQ with a metal or metal alloy having a layer thickness s suitable for forming the layer grid semiconductor layer (07) Applying a metal promoter layer (06) with a given eutectic temperature T _eu tektikum in a metal chalcogen eutectic with a layer thickness d ₂ on the precursor metal layer (10) with d ₂ «s and • Heating the precursor metal layer (10) over a process time t to a process temperature TH with T _eu tektikum <TH <TQ in a chalcogenic gas atmosphere (08) at least one process pressure pr, wherein the layer thickness s and the process time t so related in that a thin precursor metal layer (11) in a range of s / 2 above the substrate (01) does not react with the chalcogen-containing gas atmosphere (08) and remains as a metallically conductive layer (02). 6. The method according to claim 2, 3 or 5, MARKED BY Applying the saturation layer (04) and / or the metallically conductive layer (02) and / or the metal promoter layer (06) and / or the precursor metal layer (10) by vapor deposition or Magnetron sputtering 7. The method according to claim 1 or 5, MARKED BY A USE OF • oxidized silicon, quartz, ceramics or sapphire as substrate (01), • TiN, TiW, TiSi ₂ , Ta, TaN, TaN: O, WN or WN: O as metal compound, Mo or W as metal component, • Ni, Co or Pd as Metailpromoter H ₂ S, H ₂ Se or H ₂ Te as chalcogen gas, • Ar as atmospheric gas and • WS ₂ , WSe ₂ , WTe ₂ , MoS ₂ , MoSe ₂ or MoTe ₂ as chalcogen-based Layered lattice semiconductors ((transition) metal dichalcogenide). 8. The method according to claim 6 and 7, CHARACTERIZED BY • a temperature stability limit T _G > 700 ⁰ C A tempering temperature T _τ > 600 ° C, • a eutectic temperature T _eu tektikum <700 ⁰ C, • a layer thickness di "d ₂ between 5 nm and 50 nm • a layer thickness d ₃ between 100 nm and 500 nm • a layer thickness s between 0.5 μm and 1 μm Sulfur-rich WS3 _{+ Z} as a chalcogen-rich, X-ray amorphous layer-lattice semiconductor, • H ₂ S + Ar as a chalcogen-containing gas atmosphere with an H ₂ S content in a range of 50%, • a process pressure p _P in a range of 2 Pa and • a process pressure p _τ in a range of 10 Pa. 9. (OOI) -textured crystal layer (12) of a photoactive Schichtgitter- semiconductor on a chemically resistant, metallically conductive layer (02), prepared by the method according to one of claims 1 to 8. 10. Application of a (OOI) -textured crystal layer (12) of a photoactive layered lattice semiconductor of a chemically resistant, metallically conductive layer (02) according to claim 9 in a thin film solar cell based on a chalcogen-based layered lattice semiconductor with the metallically conductive layer (02 ) as back contact.