DE102012010926A1 - Photoconductive structure e.g. radiation source, for optical generation of field signals in terahertz- frequency range in bio analysis, has metallic layers formed from locations and provided in direct contact with semiconductor material - Google Patents

Abstract

The structure has metal semiconductor based arrangement, a photoconductive semiconductor material (11) with a surface provided with an arrangement of two lateral limited metallic layers i.e. strip conductors (12, 13). The metallic layers are formed from two different metal locations with different appearances. The metallic layers are laterally provided in direct contact with the semiconductor material. A material bond is provided within the metallic layers. One metallic layer of one metal location is partly covered by the other metallic layer of another metal location. An independent claim is also included for a method for manufacturing a photoconductive structure.

Description

The present invention relates to a photoconductive structure for generating electromagnetic field signals, in particular pulsed and continuous (so-called continuous wave) field signals in the frequency range of 1 GHz to 10 THz, in particular a semiconductor substrate on which at least two metal strips which at least two different metal types with different work functions are joined together and extend laterally, which is set by optical excitation in a photoconductive state, which causes the generation of an electromagnetic field signal in the frequency range of 1 GHz to 10 THz. Furthermore, the invention relates to the surface arrangement of a plurality of said photoconductive structures, a metrological arrangement in which the photoconductive structure according to the invention is used, and a method for generating electromagnetic field signals using the photoconductive structure according to the invention.

Such photoconductive structures can be used for emission and generation of electric field signals from the microwave range (0.3 to 300 gigahertz) to terahertz range (300 gigahertz to 10 terahertz) and are thus suitable as a signal source for measurements in these frequency ranges, their importance in recent years has increased sharply.

The generation of electromagnetic signals and radiation in the THz frequency range by means of compact, efficient, cost-effective and robust sources is a hitherto unsatisfactorily solved technical problem.

The development of a technical solution to this problem is of great economic importance, since a large number of new applications have been identified (for example in the field of safety engineering, bioanalysis, non-destructive materials testing or communication technology), whose commercial implementation is due to the aforementioned shortcomings of the previous THz signal sources is severely restricted.

In recent years, interest in photoconductive structures for generating THz radiation has greatly increased. Emitter approaches in particular, whose active emission surface can be scaled by a two-dimensional array arrangement, that is to say by a generally periodic structure multiplication, are becoming increasingly popular since, due to their surface size, they permit relatively high absolute THz output powers and saturation losses at high optical excitation intensity in the case of small-area emitters, even at low optical excitation powers, it is to be avoided. The state of the art for these large-scale scalable THz emitters, to which the present invention belongs, has recently been described by Winnerl in US Pat Scalable Microstructured Photoconductive Terahertz Emitters, J Infrared Milli Terahz Waves (2012) 33: 431-454 summarized.

The fundamental mechanism for THz signal generation in photoconductive semiconductor material structures is based on the emission of THz waves by optically excited charge carriers, which are accelerated in an electric field or have different electron-hole diffusion lengths. An acceleration field can, for. B. across two spaced on the semiconductor substrate surface placed stripline can be applied. High low-bias acceleration fields require small stripline pitches within such a metal-semiconductor-metal (MHM) structure. In the case of an array arrangement of these MHM structures, it must be taken into account that a distance must be maintained between all adjacent MHM emitter elements in order to avoid a short circuit, whereby further MHM intermediate elements with opposite acceleration field are formed. This can cause a large reduction or even complete extinction of THz emission by destructive far-field interference. To avoid this destructive interference, various approaches have been proposed.

From the international patent application WO2006 / 047975 For example, a method is known that provides an optically transparent insulating cover layer on which non-transparent masking elements are arranged to prevent optical excitation of the MHM intermediate elements. However, this method is very complex and moreover affected by a high parasitic dark current of the MHM intermediate elements, which limits the maximum bias voltage. In addition, there is a high susceptibility to short circuiting within the biased electrodes. A single short-circuit already completely destroys the operability of the entire component.

In the international patent application PCT / EP2007 / 002790 Another method is described which provides for the complete removal of the semiconductor material in the regions of the MHM interpositories, thereby reducing the dark current. However, the production cost is still comparatively high, since highly thinned semiconductor layers must be used, which must be transferred to stabilize on an insulating, optically transparent substrate. Furthermore, there is also a great risk of complete failure due to a short circuit. The same disadvantages with respect to production costs, dark current and susceptibility to defects also apply to the approach of the German patent application DE.10.2006.059573B3 is described and a microlens array for targeted avoidance of optical excitation of the MHM intermediate elements provides.

A first solution to the problem of high defect susceptibility to short circuits has recently been disclosed in the German patent application PCT / EP2009 / 004258 presented. The arrangement of specially shaped metal strips described therein enables the generation of a parallel to the semiconductor surface (ie lateral) photocurrent due to different diffusion speeds of the optically excited electrons and holes, the so-called Photo-Dember effect. This arrangement requires no biasing of the strip conductors and is therefore still functional in the case of even multiple short circuit defects, with only a marginal reduction in output power. A serious disadvantage, however, is the low efficiency of the Photo-Dember effect, whereby the achievable conversion efficiency is very low. The avoidance of destructive interference effects is also technically so complex in this approach that in the previous practice a relatively high proportion of destructive interference is accepted.

At this point, the invention is based, whose task is to provide a structure for THz signal generation, which allows the highest possible conversion efficiency with respect to the optical excitation power, has a low susceptibility to defects and can be manufactured as inexpensively.

This object is achieved by a metal-semiconductor structure according to claim 1 and by the metrological arrangement according to claim 13 and the manufacturing method according to claim 14. Advantageous developments of the invention are formulated in the subclaims and will be described in more detail below.

A key feature of the proposed structure is the lateral offset arrangement of at least two metal strips with different work functions on a semiconductor substrate surface. The generation of a lateral photocurrent for THz emission is accomplished in this approach not by the Photo-Dember effect, but by acceleration of optically excited charge carriers within the internal, instantaneous electrostatic fields at the metal-semiconductor (MH) transitions - ie within the so-called space charge zones.

A targeted arrangement of at least two metal strip conductors consisting of at least two different metal types with different work functions within an array is used to destructive interference effects in the ideal case - d. H. with a suitable combination of the semiconductor material and the different metals - completely avoided. This is done by a targeted unidirectional adjustment of the MH boundary fields as a function of the metal type at laterally successive MH edges.

For example, within the array arrangement, a laterally repeating "a-b-c" sequence may be used, consisting of directly adjacent regions of the following type: semiconductor metal type 1 metal type 2.

It is advantageous in this context that the THz emission by field-induced charge carrier acceleration at metal-semiconductor interface fields under typical excitation conditions is many times more efficient than the Photo-Dember effect, which, among other things, enables many times higher conversion efficiencies compared to the prior art can be.

The proposed structure does not require external bias, but utilizes the instantaneously occurring interface fields at metal-semiconductor junctions. The approach is therefore resistant to short-circuit defects. The production of the proposed structures is moreover, as will be described below, possible with minimal technical effort using self-aligning structuring processes.

Another advantage of the proposed structure is that suitable semiconductor materials do not necessarily have to have a pronounced photo-Dember effect. On the other hand, a strong Photo-Dember effect within the selected semiconductor material does not contribute to the improvement or deterioration of the THz generation efficiency of the proposed structure. Against this background, the selection of suitable semiconductor materials is significantly less limited compared to the photo-Dember effect-based THz generation. In a recent study of Reklaitis ( J. Appl. Phys. 109, 083108 (2011) ) also demonstrates that the photovoltaic effect of the optical stimulation radiation is significantly more effective than the band gap energy of the semiconductor material used, which also counteracts cost-effective use. The most important criteria for choosing the semiconductor material are the highest possible charge carrier mobility, a sufficiently short charge carrier lifetime and a sufficiently high absorption in the Wavelength range of the optical excitation. These criteria apply in the case of Photo-Dember effect based THz generation in addition to the above requirements. In the present case, for example, for the choice of the photoconductive material different III / V semiconductors such as GaAs, InGaAs, InAs, but also group IIII semiconductors such as Si, Ge or alternatively also semimetals such as graphene or graphite in question. If a THz signal decoupling is to take place through the substrate rear side, care must also be taken to minimize the absorption of the semiconductor material in the THz frequency range, which is generally the case with weakly or undoped semiconductors.

An important advantage of the proposed structure is further that the proportion of inactive to active area within the overall structure can be significantly smaller compared to the previous approaches, which also contributes significantly to improving the achievable conversion efficiency. This is justified by the fact that two adjacent MHM elements according to the invention may be in direct contact. So far disturbing MHM intermediate areas are thus completely eliminated, which not least results in a direct increase in the relative active area proportion. At the same time, destructive interference can also be completely avoided by completely avoiding MHM intermediate regions and with a suitable choice of the different metal types. The direct contact of two different metals is a characteristic feature of the proposed arrangement. To illustrate this, this structure will be referred to hereinafter as the metal-metal-semiconductor (MMH) structure.

The applications of the THz emitter structure are extremely diverse. In particular, it can be used as a THz signal source in the quality testing and development of integrated ultrahigh-frequency circuits, in the field of medical technology, in bioanalytics, in safety technology for spectroscopy for the detection of hazardous substances or for basic research in the field of novel photonic materials and structures.

Embodiments of the invention will now be described below with reference to the drawings. This is not necessarily to scale the embodiments, but the drawing, where appropriate for explanation, executed in a schematized and / or slightly distorted form. With regard to additions to the teachings directly recognizable from the drawing reference is made to the relevant prior art. It should be noted that various modifications and changes may be made in the form and detail of an embodiment without departing from the general idea of the invention. The disclosed in the description, in the drawing and in the claims features of the invention may be essential both individually and in any combination for the development of the invention. In addition, all combinations of at least two of the features disclosed in the description, the drawings and / or the claims fall within the scope of the invention. The general idea of the invention is not limited to the exact form or detail of the preferred embodiment shown and described below or limited to an article that would be limited in comparison with the subject matter claimed in the claims. For the given design ranges, values within the stated limits should also be disclosed as limit values and be arbitrarily usable and claimable. For simplicity, the same reference numerals are used below for identical or similar parts or parts with identical or similar function.

Further advantages, features and details of the invention will become apparent from the following description of the preferred embodiments and from the drawings; these show in:

1 a schematic representation of the top view of a single metal-metal-semiconductor structural element for optical signal generation in the terahertz frequency range according to a first preferred embodiment;

2 (a) a schematic representation of the cross section of a single metal-metal-semiconductor structural element for optical signal generation in the terahertz frequency range according to a first preferred embodiment and (b) the associated band model of this arrangement;

3 a schematic representation of the cross section of a single metal-metal-semiconductor structural element for optical signal generation in the terahertz frequency range according to a second preferred embodiment;

4 a schematic representation of the cross section of a single metal-metal-semiconductor structural element for optical signal generation in the terahertz frequency range according to a third preferred embodiment;

5 a schematic representation of the cross section of a single metal-metal-semiconductor structural element for optical signal generation in the terahertz frequency range according to a fourth preferred embodiment;

6 a schematic representation of an array arrangement of a metal-semiconductor-semiconductor structure element for optical signal generation in the terahertz frequency range according to the first and second preferred embodiment;

7 a schematic representation of an array arrangement of a metal-semiconductor-semiconductor structure element for optical signal generation in the terahertz frequency range according to the third and fourth preferred embodiment;

8 (a) Measured time course of the generated THz signal with different axial alignment of the metal-metal-semiconductor array structure to detect a unidirectional lateral photocurrent as the cause of the THz emission. (b) Schematic representation of the measuring arrangement.

9 Measured emission spectrum of a metal-metal-semiconductor-array structure.

In the 1 schematically illustrated arrangement shows a plan view of the surface of a single element of an MMH emitter structure 101 according to the concept of the invention, which is designed to generate a continuous and pulsed terahertz signal. The single element of the emitter structure 101 based on a semiconductor substrate 11 on which a strip conductor 12 a first type of metal a and a strip conductor 13 a second metal species b, whose work function is different from the work function of the metal species b, extend. Between stripline 12 and stripline 13 there is at least in part a material shortage. stripline 12 and stripline 13 are laterally offset immediately adjacent to one another on the semiconductor substrate 11 arranged in the form that direct contact areas between semiconductor substrate 11 and metal type a and semiconductor substrate 11 and metal grade b are formed. stripline 12 has a lateral width w1, strip conductor 13 has a lateral width w2, the width of the stripline assembly consisting of strip conductor 12 and 13 corresponds to w3, the single element of the emitter structure 101 has a width w4 and a length l1. To form an area for THz signal generation, w3 is set smaller than w4. In certain cases, integration of locally non-THz emitting regions may be desired; for example in an array of single emitters. In these cases, locally w3 can be chosen equal to w4, whereby the strip conductors can also deviate from a simple straight shape.

In 2 (a) is a single element of an emitter structure 101 shown in cross section. To generate an emission 161 and 162 in the THz frequency range, the single element 101 preferably from the one with the strip conductors 12 and 13 occupied side with an optical radiation 14 stimulated. With sufficiently thin semiconductor substrates, with a thickness smaller than the optical penetration depth of the exciting excitation signal, a rear optical excitation is possible. To clarify the basic THz emission process, is in 2 B) a ligament model 11 the arrangement 101 outlined. The optical excitation radiation 14 preferably has a photon energy 17 greater than the bandgap of the semiconductor material 11 is and thus is able to electrons 19 and hole 20 To generate couples efficiently. According to the respective work functions of the metal strip 12 and 13 arise in the semiconductor material 11 different Bandverbiegungen and thus different interface fields at the respective metal-semiconductor junctions 11 / 12 and 11 / 13 one. Ideally for THz generation with maximum efficiency, the metal types a and b will be according to the semiconductor material used 11 chosen so that at the two MH transition areas the Bandverbiegungen in amplitude magnitude and sign as much as possible differ from each other. Which metals are suitable depends on the chosen semiconductor material. With GaAs as the semiconductor material, for example, a combination of Ti and Au, Al and Au or Al and Pd can be used.

For the fundamental generation of a THz signal with the aid of the structure under consideration, there is also a smaller difference in the interfacial fields at the metal-semiconductor junctions 11 / 12 and 11 / 13 already effective. For identical metal types for the strip conductors 12 and 13 However, the THz emission disappears completely. This relationship can be explained as follows: At both metal-semiconductor junctions 11 / 12 and 11 / 13 become after optical excitation in the semiconductor material 11 due to the local presence of the interface fields, lateral photocurrents 151 and 152 generated. The photocurrents result from the lateral acceleration 18 the optically excited electrons 19 and holes 20 in the area of the interface fields. These lateral local photocurrents induce local THz emissions, which are superimposed with increasing distance from the emission areas to a total emission. In case of identical metal grades for the strip conductors 12 and 13 own the photocurrents 151 and 152 identical amounts, however, laterally opposite propagation directions. The resulting THz emissions are in this case completely destructive, ie they are extinguished. However, if the photocurrents have an identical propagation direction or at least a different amplitude strength, a constructive superimposition of the THz emissions or at least a non-completely destructive superposition takes place. The two latter states are inventively by the use of two different types of metal for the strip conductor 12 and 13 achieved which generate a lateral symmetry break in the band of the semiconductor material, which prevents the complete destructive superposition of the THz emissions or in a constructive overlay - ie an absolute emission gain - reversed. The use of interfacial field-induced photocurrents has changed from the previous ones in PCT / EP2009 / 004258 described approach based on diffusion-induced photocurrents, which requires metal strips of only one type of metal, but additionally requires locally varying transmission properties of these metal strips, as highlighted by several orders of magnitude more efficient approach. The additional technological effort due to the application of two different metal types is generally negligible given a suitable choice of the structuring processes (eg self-aligning processes).

In the following, further examples of the technical implementation of the basic invention, a THz emitting MMH structure are shown. In 3 is a cross section of an MMH structure which is likewise suitable for the purpose of the invention for THz emission 102 shown in which the strip conductor 13 the stripline 12 overlaps. The mandatory requirement of a direct at least lateral contact of the laterally adjacent strip conductors 12 and 13 In practice, this can often only be achieved by accepting a partial overlap of the two strip conductors. This applies in particular to various self-aligning structuring and deposition methods. The overlap of a stripline 12 through the other strip conductor 13 However, whether partial or complete, according to the invention it does not adversely affect the underlying emission mechanism, as it is only the lateral sequence of the metal types a and b that are in direct contact with the semiconductor substrate surface that is of importance. The overlap of the stripline 12 through the strip conductor 13 does not change the property and formation of the interface field at the metal-semiconductor junction 11 / 12 and consequently also not the THz emission process. However, in this example may the strip conductor 13 the stripline 12 not completely enclose (ie, a semiconductor contact on both sides of the strip conductor 12 form), since in this case again an undesirable symmetrical band profile would be generated.

In the 3 illustrated embodiment 102 For example, a THz-emitting MMH structure can be fabricated in a semiconductor technique using photolithography. After application of photoresist strips on the semiconductor surface, both types of metal can be deposited successively by vapor deposition under two different evaporation angles tilted towards the substrate surface. Subsequently, the photoresist strips, including the metal deposited above, are removed from the substrate in a suitable solvent ("lift-off process"). This production method requires only one lithography step and no time-consuming mask adjustment for the placement of the laterally offset strip conductors due to the self-adjusting sputtering process 13 ,

In 4 is another embodiment 103 a THz emitting MMH structure shown in which the strip conductor 12 the type of metal a during the manufacturing process itself to mask and form an uncoated semiconductor substrate during the deposition of the metal species b of the stripline 13 serves and completely by stripline 13 covered but not completely enclosed. stripline 13 is divided in the middle in this embodiment. In this embodiment, particularly small lateral spacings of the strip conductors can very efficiently 12 and 13 be realized in the range of a few nanometers. Strip conductor spacings in the range from about 10 nm to 200 nm can cause a drastic field elevation of the optical excitation radiation, for example, by an associated induction of plasmonic resonances in the strip conductors and thereby also contribute to increasing the THz emission efficiency. The small stripline pitches of this embodiment also result in the formation of a locally highly limited photocurrent 153 and thus a single point source for THz emission 163 , The embodiment 103 moreover allows the production of particularly small individual emitter structures and accordingly a very high areal density of individual emitters within the array arrangements explained below

Another embodiment 104 THz emitting MMH structure is in 5 outlined. An improvement of the THz radiation behavior is in this embodiment by the introduction of a trench-shaped recess 15 in the semiconductor substrate 11 reached. Furthermore, the recess 15 be used for masking during the metallization process in the already mentioned form as an alternative to masking by photoresist strips.

The size of the photocurrents 151 . 152 . 153 and the THz emission field strength 161 . 162 . 163 usually increases linearly with the intensity of the optical excitation 14 , However, for large excitation intensities and consequently high carrier densities, shielding effects of the interface field occur, resulting in a sublinear increase in THz emission field strength. As a result, the conversion efficiency decreases as the optical excitation intensity increases. To counteract this effect and to achieve maximum conversion efficiency is an array arrangement of the MMH Single emitter structures helpful. The available excitation power is distributed here over a larger area, whereby the intensity per single emitter decreases and each individual emitter can be operated in a degradation-free intensity range.

Each embodiment of the MMH single emitter ( 101 . 102 . 103 and 104 ) can be transferred to an array arrangement for conversion efficiency increase, in the form that the respective individual structures are placed several times side by side on the semiconductor substrate surface. Examples of array arrangements are in 6 and 7 outlined. The lateral multiplication may preferably occur periodically in a two-dimensional orthogonal or hexagonal array arrangement. However, aperiodic arrangements are also possible within the meaning of the invention. The spectral, temporal and spatial THz radiation behavior is in particular due to the lateral distances s1 and s2 of the individual structures 101 . 102 . 103 or 104 affected. The distances s1 and s2 are usually selected in a range between s1, s2 = 0 and at most a length in the region of the generated THz wavelength.

The optical excitation of the above MMH structures for THz signal generation can take place both with pulsed optical signals and with continuous optical excitation. With pulsed optical excitation, the lifetime should be that in the semiconductor material 11 optically excited charge carriers should be at least shorter than the duration used between two consecutive pulses in order to avoid field shielding effects due to accumulated charge carriers. The optical excitation with optical pulses allows the generation of a likewise pulsed THz emission. The generation of a continuous THz emission with the aid of the proposed structures is possible on the principle of photocoupling differential frequency generation, in which the output signals of two continuous optical excitation sources with different wavelengths on the surface of the single emitter 101 . 102 . 103 . 104 or array arrangements 201 . 202 be superimposed. The frequency of the generated THz emission in this case corresponds to the difference frequency of the optical excitation signals.

The high effectiveness of the proposed approach is demonstrated below on the basis of experimental investigations. An array arrangement was made ( 201 . 202 ) based on InGaAs as a semiconductor material and Ti and Au as the metal types for strip conductors 12 respectively. 13 , This structure was excited with optical pulses with a wavelength of 800 nm, pulse durations of 150 fs and a pulse repetition frequency of 78 MHz. in 8 (a) is the time profile of the emitted THz signal E _{x, THz} for different axial orientation angles of the emitter array arrangement ( 201 . 202 ). As in 8 (b) shown, the array arrangement ( 201 . 202 ) is rotated about the z axis and the THz field emitted in the k direction and the polarization thereof in the x direction is measured. The detection of the THz signal took place at a short distance (in the near field) to the back of the array arrangement. For the angle φ = 0 ° a positive THz field amplitude is measured, while for φ = 180 ° a negative THz field amplitude is detected and for φ = 90 ° the signal disappears. This result clearly confirms that THz signal generation is dominated by the generation of a laterally unidirectional photocurrent. A comparison structure with strip conductors consisting of only one type of metal and the semiconductor substrate without metal strips showed no measurable THz emission.

The amplitude spectrum of the measured THz emission is in 9 shown. The bandwidth of this emitter prototype already reaches the available bandwidth of the detection system used from about 10 GHz to 4 THz.

• – ein photoleitendes Halbleitermaterial 11 dessen Oberfläche mit einer Anordnung von mindestens zwei lateral begrenzten metallischen Schichten (12, 13) versehen ist,
• – die metallischen Schichten 12 und 13 aus mindestens zwei unterschiedlichen Metallsorten mit unterschiedlichen Auftrittsarbeiten gefertigt sind,
• – die metallischen Schichten (12, 13) sich lateral benachbart jeweils in direktem Kontakt mit dem Halbleitermaterial 11 befinden und ein Materialschluss innerhalb der Metallschichten (12, 13) besteht.

In summary, the invention relates to a photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) for the optical generation of electromagnetic field signals in the microwave, millimeter wavelength range and terahertz (THz) frequency range, consisting of a metal-semiconductor-based arrangement. According to the invention, it is provided that the metal-semiconductor-based arrangement ( 101 . 102 . 103 . 104 . 201 . 202 ) having:

• A photoconductive semiconductor material 11 its surface with an arrangement of at least two laterally delimited metallic layers ( 12 . 13 ),
• - the metallic layers 12 and 13 are made of at least two different types of metal with different performance work,
• - the metallic layers ( 12 . 13 ) laterally adjacent each in direct contact with the semiconductor material 11 and a material shortage within the metal layers ( 12 . 13 ) consists.

LIST OF REFERENCE NUMBERS

11

semiconductor

12

metal layer

13

metal layer

14

excitation radiation

15

Semiconductor recess

17

Optical excitation energy

18

Charge carrier transport

19

electron

20

hole

101

Single emitter structure

102

Single emitter structure

103

Single emitter structure

151

photocurrent

152

photocurrent

153

photocurrent

161

Microwave, millimeter wave and THz emission

162

Microwave, millimeter wave and THz emission

163

Microwave, millimeter wave and THz emission

201

Array arrangement

202

Array arrangement

L1

Metal Film length

W1

Metal layer width

W2

Metal layer width

W3

Metal layer width

W4

Metal layer width

S1

emitter spacing

S2

emitter spacing

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2006/047975 [0007]
• EP 2007/002790 [0008]
• DE 102006059573 B3 [0008]
• EP 2009/004258 [0009, 0033]

Cited non-patent literature

• Scalable Microstructured Photoconductive Terahertz Emitter, in J Infrared Milli Terahz Waves (2012) 33: 431-454 [0005]
• J. Appl. Phys. 109, 083108 (2011) [0017]

Claims (14)

Photoconductive structure, optoelectronic component - in particular radiation source - ( 101 . 102 . 103 . 104 ) for the optical generation of electromagnetic field signals in the microwave, millimeter wavelength range and terahertz (THz) frequency range, consisting of a metal-semiconductor based arrangement, characterized in that - a photoconductive semiconductor material 11 its surface with an arrangement of at least two laterally delimited metallic layers ( 12 . 13 ), - the metallic layers 12 and 13 are made of at least two different types of metal with different appearance work, - the metallic layers ( 12 . 13 ) laterally adjacent each in direct contact with the semiconductor material 11 and a material shortage within the metal layers ( 12 . 13 ) consists. Photoconductive structure ( 101 . 102 . 103 . 104 ) according to claim 1, characterized in that a metallic layer ( 12 ) of the metal grade a from the second metallic layer ( 13 ) of the metal type b is partially covered Photoconductive structure ( 101 . 102 . 103 . 104 ) according to claim 1 or 2, characterized in that a periodic array or matrix arrangement ( 201 . 202 ) of a plurality of photoconductive structures according to claim 1 is formed. Photoconductive structure ( 101 . 102 . 103 . 104 ) according to one of claims 1 to 3, characterized in that an aperiodische arrangement of a plurality of photoconductive structures according to claim 1 is formed. Photoconductive structure ( 101 . 102 . 103 . 104 ) according to one of claims 1 to 4, characterized in that a surface arrangement of a plurality of photoconductive structures is formed according to claim 1, which have a different axial orientation. Photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to one of claims 1 to 5, characterized in that as semiconductor material 11 GaAs, InGaAs, InAs, InSb, GaP, Si, CdHgTe, Ge, InN, ZnSe, Te, PbTe or CdTe. Photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to one of claims 1 to 6, characterized in that instead of a semiconductor material 11 the semi-metal graphite or graphene is used. Photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to one of claims 1 to 7, characterized in that as semiconductor material 11 an epitaxially grown layer is used. Photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to one of claims 1 to 8, characterized in that the semiconductor material 11 At low temperatures epitaxially grown GaAs is. Photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to one of claims 1 to 9, characterized in that one of the metallic layers ( 12 . 13 ) consists of Ti, Au, Al, Pd, Ag, Cu, Cr, Zr, Ni, W, Pt or Zn. Photoconductive structure ( 201 . 202 ) according to one of claims 1 to 10, characterized in that the lateral distance between two metal layers of two adjacent photoconductive structures ( 101 . 102 . 103 . 104 ) is less than 5 μm, in particular less than 200 nm. Use of a photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to one of claims 1 to 11 as a photovoltaic energy source or photodetector. Measuring and / or detection system with a photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to any one of the preceding claims. Process for the preparation of a photoconductive structure ( 101 . 102 . 103 . 104 . 201 . 202 ) according to one of the preceding claims, characterized in that - first a laterally delimited metal layer 12 a first type of metal on a semiconductor surface 11 is applied - then a second metal layer 13 a second type of metal is carried out by a vapor deposition process under a not perpendicular to the semiconductor surface evaporation direction.

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