Photoconductive antenna for terahertz waves, method for manufacturing such photoconductive antenna, and terahertz time-domain spectroscopy system

Abstract

A comb-shaped photoconductive antenna (10) for generating and / or detecting terahertz radiation, comprising a substrate (SB) made of a compound semiconductor and a plurality of comb-shaped electrodes (DE) and two contact pads (CP) on the front surface of the substrate (SB), - The comb-shaped photoconductive antenna (10) includes a metallization layer (ML) made on the front surface of the substrate (SB) for the comb-shaped electrode (DE) and the contact pad (CP), - The comb-shaped electrodes (DEs) are arranged at equal intervals with a distance Δ between them, and each comb-shaped electrode is linked to another comb-shaped electrode by a portion of the metallization layer, which is called the integrated resistance (IR) and exhibits intrinsic electrical resistance. - The contact pads are linked to their respective comb-shaped electrodes by the metallization layer portion (MP) so that they adapt to the application of voltage across the comb-shaped electrodes, A comb-shaped photoconductive antenna (10) characterized by the above.

Description

Technical Field

[0001] The present invention generally relates to photoconductive antennas, methods of manufacturing photoconductive antennas, and terahertz time-domain spectroscopy systems.

Background Art

[0002] The terahertz (THz) frequency range, which lies between the microwave and mid-infrared ranges, offers unique opportunities in a variety of application fields including medical and security imaging, non-destructive testing, submillimeter-wave astronomy, and gas detection.

[0003] Over the past decade, highly promising technical solutions have emerged to cover the shortage of devices in this area of the electromagnetic spectrum. One of the most important and widespread technologies is terahertz time-domain spectroscopy (THz-TDS). This technology is associated with ultrafast optical lasers for the generation and detection of THz pulses. The generation of THz pulses is usually performed by the ultrafast excitation of photoconductive antennas.

[0004] Referring to FIG. 1, generally, a photoconductive antenna has a specific substrate (1) on which semiconductors are generally used, and is accompanied by two electrodes (2) on the substrate (1). The mechanism is as follows: while a voltage is applied between the electrodes (2), an ultrashort pulse laser light is irradiated onto the gap between the electrodes (2) to generate a time-varying current in the excited optical carriers between the electrodes (2). The time profile of this current is related to both the optical excitation pulse length and the recombination time of the carriers in the substrate. This current causes the emission of terahertz waves with a wide frequency spectrum through the photoconductive antenna. It should be noted that a THz-TDS system can also use another photoconductive antenna or an electro-optic crystal as a detector for terahertz waves.

[0005] In typical semiconductor antennas, the specific semiconductor can be selected from compound semiconductors such as GaAs, InGaAs, AlGaAs, GaAsP, and InGaAsP. Furthermore, low-temperature grown GaAs (LT-GaAs) films grown in crystalline form are very commonly used due to their short carrier lifetime and high resistance (Non-Patent Literature 1). LT-GaAs is usually grown as a crystal on a semi-insulating GaAs (SI-GaAs) substrate. This leads to various problems such as reduced power utilization efficiency of THz waves and spectral narrowing as THz waves pass through the SI-GaAs substrate.

[0006] THz-TDS characteristics, including dynamic range, bandwidth, signal-to-noise ratio, and frequency resolution, are closely related to pulse specifications, and consequently, their performance is primarily linked to the characteristics of the pulse emitter.

[0007] More specifically, THz-TDS has a frequency resolution limited by the total scanning time, which is primarily limited by undesirable interference echoes (3) of the emitted THz pulses (see Figure 2). In fact, discontinuities such as changes in refractive index along the beam path cause echoes when the original signal is reflected.

[0008] If the majority of the echoes are controllable (for example, by using a sample, window, or electro-optic detection crystal with thicker or wedge-shaped dimensions), then in the case of this photoconductive antenna, the echoes will arise from the reflection of the original pulse within its own substrate. Due to the short distance of a standard-sized wafer, it is these echoes that actually limit the spectral resolution of the system. In the case of a photoconductive antenna made from a 500 μm GaAs wafer (refractive index n=3.64 in the THz range), a THz echo will occur after only 12 ps, and typically the resolution will be limited to the lower limit of 90 GHz (3 cm). -1 ) is restricted.

[0009] While this resolution is sufficiently low for many applications, higher performance is required in some cases. For example, spectroscopic methods for gas sensing and identification are considered very promising due to their high selectivity as well as their inherent non-invasiveness. Compared to mid-infrared spectra, which consist of complex signatures of vibrational and rotational transitions, the THz fingerprints of many polar molecules consist of simple rotational spectra with unique spectral signatures, which can provide more efficient and accurate detection of many gases. For the resolution of such spectra, most of the spacing between pure rotational spectra is typically 0.1 cm. -1 ~10cm -1 The range (for example, in the case of a CO molecule, the rotation constant B = 2 cm) -1 Because it is located in a specific area, a higher resolution is required.

[0010] To achieve higher spectral resolution in THz-TDS systems, several methods have been proposed to address the echo problem. THz anti-reflective coatings have been developed, but they have several drawbacks: dielectric coatings are wavelength-dependent (Non-Patent Literature 2), while broadband designs may be achieved using thin metal coatings (Non-Patent Literature 3), this is difficult to realize and leads to significant losses.

[0011] An alternative approach involves applying numerical analysis methods through either deconvolution using a reference signal or echo cancellation using a deconvolution algorithm.

[0012] Patent Document 1 describes a photoconductive antenna that generates and / or detects terahertz waves and suppresses echoes, which normally arise from substrate reflection of the antenna, without any numerical post-processing and without being affected by loss. The antenna comprises a substrate (1) and at least two electrodes (2) on the front surface of the substrate (1). The photoconductive antenna further comprises a layer (4) obtained from a material that reflects terahertz waves, the layer extending below the front surface of the substrate (1) at a distance d = λ / 2, where λ corresponds to the maximum frequency at which radiation / detection is required.

[0013] Since there is no possibility of THz pulses propagating beyond the inserted metal surface, echoes originating from the interface between the substrate and air are eliminated. Furthermore, the absence of echoes from this system means that all THz power is contained within the original THz pulse, resulting in a higher extraction of the generated power.

[0014] The antenna in Figure 3 is satisfactory, but the method for manufacturing this type of antenna is complex.

[0015] More specifically, this manufacturing method involves a first step of forming a first metallization layer for the comb-shaped electrodes (2). Next, a second step is required to form a layer of SiO2 (5) on top of the first metallization layer. This method involves a third step of forming a second metal layer consisting of metal fingers (6) covering the gap with twice the periodicity of the first metallization layer. This makes it possible to photoexcite every two periods of the gap of the first metallization, and thus excite only one bias field direction, thereby avoiding destructive interference of the generated THz far-field. The antenna structure shown in Figure 3 is based on an electrode geometry called "comb-shaped geometry," which is known to be an efficient method for generating THz pulses. In addition, a strong radiation field with good directivity is delivered because it allows for irradiation of a large area of ​​electrodes (approximately 500 μm in diameter) and the required bias is lower due to the possibility of closely spaced electrodes. The term "comb-shaped" refers to the spatial arrangement of the electrodes (2) with respect to the metal fingers.

[0016] This third step requires deposition and patterning substeps and therefore cannot be performed immediately after the second step in the same environment. Consequently, precise repositioning is required to properly position the metal fingers (6) relative to the electrodes (2). This results in a complex manufacturing process, low manufacturing yield, and higher costs. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] International Publication No. 2016 / 097975 [Non-patent literature]

[0018] [Non-Patent Document 1] "IEEE Journal of Quantum Electronics," 28, p. 2464, 1992. [Non-Patent Document 2] A.J. Gatesman, J. Waldman, M. Ji, C. Musante, and S. Yngvesson, "An anti-reflection coating for silicon optics at terahertz frequencies," IEEE Microwave and guided wave letters, Column 10, No. 7, July 2000. [Non-Patent Document 3] Andreas Thoman, Andreas Kern, Hanspeter Helm, and Markus Walther, "Nanostructured gold films as broadband terahertz antireflection coatings," Physical Review B 77, 195405, 2008. [Overview of the Initiative] [Problems that the invention aims to solve]

[0019] To overcome the limitations mentioned above, new antenna designs and related manufacturing processes that improve production yield are needed. [Means for solving the problem]

[0020] For this reason, an object of the present invention is a comb-shaped photoconductive antenna that generates and / or detects terahertz radiation, including a substrate made of a compound semiconductor and including a plurality of comb-shaped electrodes and two contact pads on the front surface of the substrate, the photoconductive antenna including a metallization layer formed on the front surface of the substrate for the comb-shaped electrodes and the contact pads, wherein the comb-shaped electrodes are arranged at a distance Δ, each comb-shaped electrode being linked to another comb-shaped electrode by a respective part of the metallization layer called the integrated resistance and exhibiting a specific electrical resistance, and the contact pads being linked to the respective comb-shaped electrodes by parts of the metallization layer so as to adapt to the application of a voltage across the comb-shaped electrodes, characterized in that it is a comb-shaped photoconductive antenna.

[0021] The comb-shaped electrodes can be equidistantly spaced at a fixed distance Δ or separated at a variable distance Δi.

[0022] The comb-shaped electrodes have a geometry such that all of them exhibit the same polarity when the voltage is applied, and each integrated resistance is adapted to induce a potential difference between the two electrodes to which it is respectively linked when the voltage is applied, so that the comb-shaped photoconductive antenna can generate and / or detect terahertz radiation. The same polarity creates an electric field E with the same direction between each gap Δ.

[0023] According to one embodiment, the metallization layer is made of a material having an electrical resistivity greater than 100 μΩ·cm, preferably greater than 200 μΩ·cm. Preferably, the metallization layer is made of β-tantalum or titanium.

[0024] According to one embodiment, each integrated resistance exhibits a specific resistance included in 0.1 to 10 kΩ. Preferably, the metallization layer has a thickness included in 100 nm to 300 nm.

[0025] According to one embodiment, the distance Δ is less than 2 μm. Preferably, the distance Δ is less than 0.2 μm.

[0026] According to one embodiment, the comb-shaped photoconductive antenna includes at least one layer called a reflective layer, made of a material that reflects terahertz radiation, the reflective layer extending below the front surface of the substrate at a distance d = λ / 2, where λ corresponds to the maximum frequency at which radiation / detection is required. Preferably, the reflective layer is a metal layer.

[0027] According to one embodiment, the substrate is a semiconductor substrate selected from GaAs, InGaAs, AlGaAs, GaAsP, Si, quartz, InGaAsP, LT-GaAs, ErAs:GaAs, Fe:InGaAs, or InGaAsN and Group II-VI materials.

[0028] Another object of the present invention is a method for manufacturing a comb-shaped photoconductive antenna according to the present invention, which includes at least, - The step of forming a metallization layer on the front surface of a substrate made from a compound semiconductor, - A step of patterning the metallization layer to form a plurality of comb-shaped electrodes and two contact pads on the front surface of the substrate, The comb-shaped electrodes are arranged at equal intervals with a distance Δ between them, and each comb-shaped electrode is linked to another comb-shaped electrode by a portion of the metallization layer, which is called the integrated resistance and exhibits intrinsic electrical resistance. The metallization layer portion is configured such that each contact pad is linked to its respective comb-shaped electrode so that the contact pad adapts to the application of voltage across the comb-shaped electrode. Steps and It is a method that encompasses this.

[0029] According to the present invention, the method does not involve a further step of forming an additional metallization layer on top of the metallization layer.

[0030] According to one embodiment, the comb-shaped electrodes and contact pads are formed by photolithography and / or electron beam lithography or lift-off techniques.

[0031] Another object of the present invention is a terahertz time-domain spectroscopy system comprising a generating unit that generates terahertz radiation and a detection unit that detects terahertz waves, wherein at least one of the generating unit and the detection unit comprises a comb-shaped photoconductive antenna according to the present invention.

[0032] Further features, details, and advantages of the present invention will become apparent from the following description with reference to the following accompanying drawings, which are shown as examples. [Brief explanation of the drawing]

[0033] [Figure 1] This is a schematic diagram showing a conventional optical conduction antenna. [Figure 2] This is a time-domain terahertz pulse generated by a conventional photoconductive antenna. [Figure 3] This is a schematic diagram showing a conventional optical conduction antenna. [Figure 4A] This is a schematic diagram showing a photoconductive antenna according to the present invention. [Figure 4B] This is a schematic diagram showing a photoconductive antenna according to the present invention. [Figure 5A] This is a time-domain terahertz pulse generated by a photoconductive antenna according to the present invention. [Figure 5B] This is the spectral response of a terahertz pulse generated by a photoconductive antenna according to the present invention. [Figure 6] This is a schematic cross-sectional view of one embodiment of a photoconductive antenna according to the present invention. [Figure 7] This is a flowchart illustrating a method for manufacturing a photoconductive antenna according to the present invention. [Figure 8A]This is a schematic diagram showing various steps of a method for manufacturing a photoconductive antenna according to the present invention. [Figure 8B] This is a schematic diagram showing various steps of a method for manufacturing a photoconductive antenna according to the present invention. [Figure 8C] This is a schematic diagram showing various steps of a method for manufacturing a photoconductive antenna according to the present invention. [Figure 8D] This is a schematic diagram showing various steps of a method for manufacturing a photoconductive antenna according to the present invention. [Figure 8E] This is a schematic diagram showing various steps of a method for manufacturing a photoconductive antenna according to the present invention. [Figure 8F] This is a schematic diagram showing various steps of a method for manufacturing a photoconductive antenna according to the present invention. [Figure 9] This is a schematic diagram showing a terahertz time-domain spectroscopy system that includes at least one photoconductive antenna according to the present invention. [Modes for carrying out the invention]

[0034] Unless otherwise stated, elements in drawings are not necessarily accurate to scale.

[0035] Figures 4A and 4B are schematic front and side views, respectively, of a comb-shaped photoconductive antenna 10 adapted for the generation and / or detection of terahertz waves according to the present invention.

[0036] The photoconductive antenna 10 includes a substrate SB made from a compound semiconductor, and can be selected from compound semiconductors such as GaAs, InGaAs, AlGaAs, GaAsP, Si, quartz, InGaAsP, LT-GaAs, ErAs:GaAs, Fe:InGaAs, or InGaAsN, and Group II-VI materials.

[0037] The antenna 10 further includes multiple comb-shaped electrodes DE and two contact pads CP on the front surface of the substrate SB. The comb-shaped electrodes DE and contact pads CP are patterned from the same metallization layer ML.

[0038] The comb-shaped electrodes DE are arranged at equal intervals with a distance Δ between them, and each comb-shaped electrode is linked to another comb-shaped electrode by a portion of the metallization layer ML called the integrated resistance IR.

[0039] Furthermore, each contact pad CP is linked to the corresponding comb-shaped electrode DE by a portion of the metallization layer ML (referred to as MP). Thus, the contact pad CP is adapted to the application of a voltage across the comb-shaped electrodes DE. Given the geometry of this antenna 10, the comb-shaped electrodes exhibit the same polarity when such a voltage is applied.

[0040] Antenna 10 can be operated as shown in Figure 4A. An ultrafast laser source (e.g., a Ti:sapphire femtosecond laser) generates a laser pulse IL. For example, the pulse IL typically has a duration of 100 fs and a repetition rate of 77 MHz. The pulse IL then generates approximately 500 W / cm². 2 The irradiance is focused onto the photoconductive antenna 10. While the pulse IL is irradiating the antenna, a voltage bias is applied to the electrode DE via the contact pad CP.

[0041] Each integrated resistor IR separating each pair of comb-shaped electrodes DE induces a potential difference between the electrodes, which subsequently generates an electric field between them. This causes excited photocarriers generated by pulsed photons IL absorbed by the substrate to produce a time-varying current between electrodes DE. This induces a radiated electric field, i.e., a THz pulsed IG, proportional to its time derivative. The time profile of this current is related to both the photoexcitation pulse length and the carrier recombination time in the substrate. Since each electrode pair exhibits the same polarity, there is no destructive interference of the generated THz far-field. This is a clear difference in comparison to the antenna shown in Figure 3, and requires metal fingers (6) with twice the periodicity of the first metallization layer covering the gap between electrodes to enable photoexcitation every two periods of the gap of the first metallization, and thus to excite only one bias field direction, thereby avoiding destructive interference of the generated THz far-field.

[0042] Typically, applying a voltage generates an electric field of approximately 10 kV / cm between the electrodes. This strength is suitable for providing sufficiently strong acceleration of photoexcited carriers within the substrate SB to induce the generation of a THz pulse IG.

[0043] As will be further described with reference to Figures 8A to 8F, the antenna 10 according to the present invention has a structure that is far simpler than conventional antennas using comb-shaped geometry (for example, the antenna in Figure 3), and therefore can be manufactured through a more cost-effective process.

[0044] In one specific embodiment (referred to as SE), the laser pulse IL has a wavelength of 800 nm, and the antenna comprises 20 comb-shaped electrodes DE patterned from a layer ML of β-tantalum deposited on a 500 μm thick GaAs substrate SB. Each electrode DE has a width w = 8 μm and is separated from adjacent electrodes by a distance Δ = 1.5 μm. Therefore, the total width w of the comb-shaped electrodes DE is tThe thickness is approximately 200 μm. A voltage bias of 28.5 V applied between the contact pad CP induces a bias electric field of 10 kV / cm between the electrodes.

[0045] In another specific embodiment, the antenna comprises comb-shaped electrodes DE patterned from a layer ML of titanium deposited on a 500 μm thick GaAs substrate SB. Each electrode DE has a width of w = 100 nm and is spaced Δ = 100 nm apart from adjacent electrodes. The metal used here is titanium, which has a higher resistivity compared to gold, and is further structured in a loop to realize integrated resistors perpendicular to the comb-shaped electrodes. A 60 nm thick layer of titanium is deposited using electron beam lithography. Each integrated resistor connected to the antenna has an estimated resistance of 1800 Ω, and the electric field between the electrodes is approximately E = 2 kV·cm⁻¹ for a total voltage of approximately 10 V applied across the entire structure, in this case across an antenna width of 100 μm, i.e., a gap Δ of 480. The integrated resistors are connected in series to function as voltage dividers for the comb-shaped electrodes.

[0046] Figures 5A and 5B show the time profile and spectrum of a THz pulse IG generated by antenna 10 according to a specific embodiment SE, respectively. More precisely, Figure 5A is a typical time scan of the radiated THz field obtainable for antenna 10, and Figure 5B is the spectrum obtained from the same time scan (Fourier transform of the time scan) in the spectral range of 0 THz to 5 THz. As can be seen from Figure 5B, the radiated THz spectrum extends up to 5 THz. These figures demonstrate the feasibility of the present invention.

[0047] Preferably, the metallization layer ML is made from a material exhibiting an electrical resistivity greater than 100 μΩ·cm, preferably greater than 200 μΩ·cm. This helps reduce the area of ​​each integrated resistor IR to achieve a given resistivity, and therefore increases the number of comb-shaped electrodes DE in this design according to Figures 4A and 4B for a given area of ​​antenna 10. This increases the efficiency of THz pulse generation IG.

[0048] In one preferred embodiment, the metallization layer ML is made from β-tantalum. This metal is advantageous because it can be easily deposited (sputtered) at a thin film resistivity of 170-230 μOhm·cm. As a result, the IR resistance of an ML with a thickness of approximately 200 nm is approximately several kΩ. Furthermore, it is stable over time and durable.

[0049] To further improve the efficiency of THz pulse IG generation, the metallization layer preferably has a thickness of 50 nm to 1 μm, and more preferably 100 to 300 nm. Making the metallization layer thickness less than 50 nm is not advisable because the integrated resistor IR may melt when a voltage bias is applied between the contact pad CP. As explained above, the value of the integrated resistor IR also depends on the resistivity of the deposited material ML. Furthermore, making the metallization layer thickness greater than 500 nm is not advisable because the resistance of IR decreases as the thickness increases, and therefore the current for the same voltage increases, which has the disadvantage of requiring a more powerful power supply and carries the risk of the IR resistor overheating.

[0050] To further increase the number of comb-shaped electrodes DE of an antenna 10 of a predetermined area, it is possible to reduce the distance Δ between adjacent electrodes DE. It is also possible to reduce the width w of the electrodes DE. Therefore, the distance Δ is preferably less than 2 μm. The advantage of having a relatively small Δ is that a large electric field is supplied at low voltages.

[0051] In a preferred embodiment, the distance Δ is less than 0.2 μm. Indeed, when the distance Δ between adjacent electrodes DE is this small, coupling of surface plasmons excited by the laser pulse IL between two adjacent electrodes DE begins. This coupling enhances the electric field in the gap between the electrodes. This coupling also increases the absorption of the laser pulse IL near the electrodes. This leads to an improvement in the generation efficiency of the THz pulse IG.

[0052] This invention makes sample preparation easier or simpler, thereby enabling the exploration of new research topics such as plasmonic effects. In fact, observing this effect requires electrodes with a width W and a gap delta of 100 nanometers. In previous methods, which involve more manufacturing steps, including electrode alignment, manufacturing becomes very complex. The plasmonic enhancement of absorption and electric field depends, of course, on the geometry and dimensions of the electrodes. In a more basic approach, given the geometry shown in Figure 4B, it is possible to optimize the plasmonic enhancement using parameters w and Δ. In a specific embodiment SE, first-order optimization of plasmonic enhancement is achieved when w=Δ=100nm. In a more general approach, it is possible to optimize the plasmonic enhancement (and therefore THz generation efficiency) for any given geometry using FDTD simulation tools.

[0053] According to one preferred embodiment, each integrated resistor IR exhibits an intrinsic electrical resistance preferably in the range of 0.1 to 10 kΩ. Preferably, each integrated resistor IR has an intrinsic electrical resistance in the range of 0.5 to 1.5 kΩ. Assuming the dimensions of a specific embodiment SE, this resistance value is particularly suitable for inducing a bias electric field of 10 kV / cm between electrodes DE using a moderate voltage bias (e.g., 28.5 V to the contact pad, or 1.5 V to each gap between electrodes).

[0054] Figure 6 is a schematic side view of a photoconductive antenna 10 according to one embodiment of the present invention. In this embodiment, the antenna 10 further includes a layer called a reflective layer RL, made of a material that reflects terahertz radiation. The reflective layer RL extends below the front surface of the substrate SB at a distance d = λ / 2, where λ corresponds to the maximum frequency at which radiation / detection is required. As fully explained in International Publication No. 2016 / 097975, the reflective layer RL eliminates echoes arising from the interface between the substrate and air. The absence of echoes in this configuration means that all THz power is contained within the original THz pulse IG, resulting in higher extraction of generated power and higher THz generation efficiency.

[0055] Preferably, the reflective layer RL is a metallic layer, such as a metal selected from the list of gold, and / or titanium, and / or silver, and / or copper.

[0056] Figure 7 is a flowchart of a method according to the present invention for manufacturing a comb-shaped photoconductive antenna 10 according to the present invention. The method of the present invention comprises a first step A, which involves forming a metallization layer ML on the front surface of the substrate SB. This step can be carried out using any suitable method well known to those skilled in the art (e.g., sputtering) without departing from the scope of the present invention. It is also possible to have several steps to have an integrated resistor IR made from a different material than the electrode DE.

[0057] Next, in the second step B, the metallization layer ML is patterned to form a comb-shaped electrode DE and two contact pads CP on the front surface of the substrate SB. In this case as well, this step can be carried out using any suitable method such as photolithography and / or electron beam lithography, or any lift-off technique, which are well known to those skilled in the art, without departing from the scope of the present invention.

[0058] As those skilled in the art will understand, this process can be carried out using the lift-off technique. In this case, a first lithography step on the resist is required to achieve the desired antenna design, followed by a lift-off step of metal deposition and removal of the resist.

[0059] Figures 8A to 8F illustrate various steps of a method for manufacturing a comb-shaped photoconductive antenna 10 according to a particular embodiment of the present invention, wherein the second step B of the method uses a photolithography technique. Figures 8A to 8B illustrate the first step A, in which a metallization layer ML is formed on a substrate SB using, for example, a metal deposition or sputtering technique. In Figure 8C, a photoresist layer PR is deposited on the metallization layer ML, for example, by spin coating. Subsequently, the photoresist layer PR is patterned, typically by exposure and the subsequent use of a developer (Figure 8D). This substep can be performed by suitable methods well known to those skilled in the art, such as a laser writer or an optical photomask, without departing from the scope of the present invention. Thereafter, any portion of the metallization layer ML not covered by the residual photoresist layer PR is removed by any suitable method, such as mechanical and / or chemical etching (Figure 8E). Finally, the residual photoresist layer PR is removed, typically using a liquid solution, solvent, or plasma called a “resist stripper,” to obtain the antenna 10 according to the present invention (Figure 8F).

[0060] As can be seen from Figures 7 and 8A to 8F, the method according to the present invention requires a single metal deposition step to obtain both the electrode DE and the contact pad CP, and the IR. Therefore, this is faster and less complex than the method for manufacturing the antenna according to Figure 3, which requires two separate metal deposition steps and precise realignment between those two steps. This suggests that the antenna 10 according to the present invention will be less expensive than the antenna according to Figure 3.

[0061] Referring to Figure 9, the photoconductive antenna 10 according to the present invention is intended for use in a terahertz time-domain spectroscopy system 16, which comprises at least a generating unit 17 for generating terahertz waves and a detection unit 18 for detecting terahertz waves, and at least one of the generating unit 17 and the detection unit 18 has the photoconductive antenna 10 according to the present invention. In this embodiment, the generating unit 17 has the photoconductive antenna according to the present invention.

[0062] It should be noted that the photoconductive antenna according to the present invention can also be used for continuous wave THz systems such as continuous wave THz spectrometers without departing from the scope of the present invention.

[0063] While embodiments of this disclosure have been described in detail, those skilled in the art should understand that various changes, substitutions, and modifications can be made herein without departing from the spirit and scope of this disclosure. Accordingly, any such changes, substitutions, and modifications are intended to fall within the scope of this disclosure as defined in the following claims.

[0064] For example, a photoconductive antenna according to the present invention may have a layer of SiO2 or other dielectric material directly above the electrode DE.

[0065] In the claims, the means-plus-function clause is intended to encompass not only structures and structural equivalents that perform the enumerated functions described herein, but also equivalent structures.

[0066] This invention is essentially based on integrated IR resistors and has several benefits, such as process simplification, and future prospects, such as demonstration of plasmonic effects. [Explanation of Symbols]

[0067] 1 circuit board 2 electrodes 4 layers 5 layers 6 Metal Fingers 10. Photoconductive antenna 16 Terahertz time-domain spectroscopy system 17. Occurrence site 18 Detection unit CP Contact Pads DE comb-shaped electrodes IG THz pulse IL laser pulse IR integrated resistor ML metallization layer PR Photoresist Layer RL reflective layer SB board

Claims

1. A comb-shaped photoconductive antenna (10) for generating and / or detecting terahertz radiation (IG), comprising a substrate (SB) made of a compound semiconductor, and comprising a plurality of comb-shaped electrodes (DE) and two contact pads (CP) on the front surface of the substrate (SB), - The photoconductive antenna includes a metallization layer (ML) made on the front surface of the substrate (SB) for the comb-shaped electrodes (DE) and the contact pads (CP), - The comb-shaped electrodes (DEs) are arranged at equal intervals with a distance Δ between them, and each comb-shaped electrode is linked to another comb-shaped electrode by a portion of the metallization layer, which is called the integrated resistance (IR) and exhibits intrinsic electrical resistance. - Each contact pad is linked to its respective comb-shaped electrode by a portion of the metallization layer (MP) so that the contact pad adapts to the application of a voltage across the comb-shaped electrode, wherein the comb-shaped electrodes (DE) have a geometry such that they all exhibit the same polarity when the voltage is applied, and each integrated resistor is adapted to induce a potential difference between the two electrodes that are linked when the voltage is applied, thereby enabling the comb-shaped photoconductive antenna (10) to generate and / or detect terahertz radiation. A comb-shaped photoconductive antenna (10) characterized by the above.

2. The comb-shaped photoconductive antenna according to claim 1, characterized in that the metallization layer is made of a material exhibiting an electrical resistivity greater than 100 μΩ·cm, preferably greater than 200 μΩ·cm.

3. The comb-shaped photoconductive antenna according to claim 2, characterized in that the metallization layer is made of β-tantalum or titanium.

4. A comb-shaped photoconductive antenna according to any one of claims 1 to 3, characterized in that each integrated resistance (IR) exhibits an intrinsic resistance within the range of 0.1 to 10 kΩ.

5. The comb-shaped photoconductive antenna according to claim 4, characterized in that the metallization layer has a thickness that is included in the range of 100 nm to 300 nm.

6. The comb-shaped photoconductive antenna according to claim 4, characterized in that the distance Δ is less than 2 μm.

7. The comb-shaped photoconductive antenna according to claim 4, characterized in that the distance Δ is less than 0.2 μm.

8. A comb-shaped photoconductive antenna according to any one of claims 1 to 7, comprising at least one layer called a reflective layer (RL) made of a material that reflects terahertz radiation, wherein the reflective layer (RL) extends below the front surface of the substrate (SB) at a distance d = λ / 2, where λ corresponds to the maximum frequency at which radiation / detection is required.

9. The comb-shaped photoconductive antenna according to claim 6, characterized in that the reflective layer (RL) is a metal layer.

10. The comb-shaped photoconductive antenna according to any one of claims 1 to 9, characterized in that the substrate (SB) is a semiconductor substrate selected from GaAs, InGaAs, AlGaAs, GaAsP, Si, quartz, InGaAsP, LT-GaAs, ErAs:GaAs, Fe:InGaAs, or InGaAsN, and group II-VI materials.

11. A method for manufacturing a comb-shaped photoconductive antenna (10), wherein at least, A. The step of forming a metallization layer (ML) on the front surface of a substrate (SB) made from a compound semiconductor, B. A step of patterning the metallization layer (ML) to form a plurality of comb-shaped electrodes (DE) and two contact pads (CP) on the front surface of the substrate (SB), The comb-shaped electrodes (DE) are arranged at equal intervals with a distance Δ between them, and each comb-shaped electrode is linked to another comb-shaped electrode by a portion of the metallization layer (ML) that is called the integrated resistance (IR) and exhibits intrinsic electrical resistance. The metallization layer portion links each contact pad to its respective comb-shaped electrode so that the contact pad adapts to the application of a voltage across the comb-shaped electrode, and the comb-shaped electrodes (DE) have a geometry such that they all exhibit the same polarity when the voltage is applied, and each integrated resistor is adapted to induce a potential difference between the two electrodes that are linked to each other when the voltage is applied, so that the comb-shaped photoconductive antenna (10) can generate and / or detect terahertz radiation. Steps and A method for manufacturing a comb-shaped photoconductive antenna (10) according to any one of claims 1 to 10, comprising the above.

12. A method for manufacturing a photoconductive antenna according to claim 11, characterized in that it does not include a further step of forming an additional metallization layer on the metallization layer (ML).

13. A method for manufacturing a photoconductive antenna according to claim 11 or 12, characterized in that the comb-shaped electrodes (DE) and the contact pad are formed by photolithography and / or electron beam lithography or lift-off technique.

14. A terahertz time-domain spectroscopy system (16) comprising a generating unit (17) that generates terahertz radiation and a detection unit (18) that detects terahertz waves, wherein at least one of the generating unit (17) and the detection unit (18) comprises the comb-shaped photoconductive antenna (10) described in claim 1.

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