Graphene Photodetector

Abstract

The graphene photodetector comprises a first graphene absorber layer (2) connected to first and second metal electrodes (3, 4), the first and second metal electrodes defining a channel (5) on the first graphene layer (2) that operates as a plasmonic waveguide; a gate dielectric layer (6) sandwiched between the first graphene layer (2) and a second graphene layer (7), the second graphene layer being used for electrical gating and comprising first and second gate electrodes (8, 9) in close proximity to the first metal electrode (3) and the second metal electrode (4), respectively; and a photonic dielectric waveguide (10) having a planarized cladding (11) disposed beneath the gate dielectric layer (6), wherein first and second gate electrodes (8, 9) remain interposed between the gate dielectric layer (6) and the cladding (11), the spacing defining a width of a channel cross-section, the distance between the first metal electrode (3) and the second metal electrode (4) being in the range of 100 nm to 600 nm, and the distance between the first gate electrode (8) and the second gate electrode (9) being at least 60% of the distance between the first metal electrode (3) and the second metal electrode (4).

Description

[Technical field]

[0001] The present invention relates to graphene photodetectors, and in particular to graphene photodetectors that utilize light conversion mechanisms based on the photothermoelectric effect and the photovoltaic effect. [Background technology]

[0002] Graphene photodetectors offer several advantages in various applications due to the properties of graphene, particularly in high speed data and telecommunications applications.

[0003] Graphene is sp 2 The valence and conduction bands of this material intersect at six points in reciprocal space called Dirac points.

[0004] Graphene has a low density of states that varies linearly with the energy of the electronic states and vanishes at the Dirac point. Such a feature allows for easy tunability of the chemical potential (low gate voltages required to shift the chemical potential when compared to other materials such as silicon) and all its associated material properties (e.g. electrical conductivity, Seebeck coefficient, optical absorption, etc.) by the electric field effect. This feature is called electrostatic doping.

[0005] The optical absorption spectrum of graphene spans from the UV to the far IR, and the mobility of charge carriers in graphene is as high as 100.000 cm even at room temperature if the material is properly encapsulated (e.g., in hBN). 2 / Vs may be exceeded.

[0006] Fast carrier dynamics of photoexcited carriers upon photoexcitation due to short relaxation times (on the order of picoseconds) and small electronic thermal capacitance allows the realization of photodetectors with optoelectronic bandwidths greater than 100 GHz.

[0007] Furthermore, graphene can be grown on a suitable substrate (e.g., copper) by chemical vapor deposition (CVD) and transferred onto virtually any photonic substrate.

[0008] The use of graphene photodetectors based on the photothermoelectric effect primarily enables direct optical power-to-voltage conversion, zero dark current, and ultrafast operation.

[0009] The photothermal effect (PTE) is based on the increase in temperature of an electronic system following the absorption of optical power. In PTE-based graphene photodetectors, an electromotive force is generated by the Seebeck effect, which is caused by a spatial gradient of the electron temperature within the graphene in the presence of a spatially inhomogeneous Seebeck coefficient.

[0010] To better understand this concept, assume that a laser beam excites an active graphene layer with a spatially homogeneous chemical potential and thus a constant Seebeck coefficient (a property that depends on the chemical potential) along the channel. Optically excited hot carriers in the laser spot area (i.e., electrons and holes that are found at a higher temperature relative to the lattice after irradiation) diffuse radially from the center of the excited area to the side. In this condition, hot electrons (or holes, depending on the sign of the Seebeck coefficient) diffuse in the opposite direction, resulting in a net photocurrent of zero. Conversely, if a step change in the chemical potential (and consequently the Seebeck coefficient) is induced in the center of the excited area, hot electrons or holes diffuse in the same direction, resulting in a net photocurrent. Since the photoresponse is generated directly by the thermoelectric effect, unlike other effects (e.g., the photoconductive effect and the photobolometric effect), the photothermoelectric effect does not require a bias applied to the active graphene layer and thus operates in the absence of dark current.

[0011] Both the photovoltaic and photothermoelectric effects require a non-uniform chemical potential, i.e. a p-n junction, for different reasons. There is a notable difference between a graphene p-n homojunction (where the junction is made entirely of graphene) and a conventional semiconductor-based diode.

[0012] The first difference is that conventional semiconductors require physical doping to realize a pn junction. In contrast, the easy tunability of the graphene chemical potential by the field effect allows the realization of an electrostatically induced pn homojunction by using an appropriate gate structure. Several gate configurations have been reported in the literature, combining a top-gate configuration (where the gate electrode is placed above the active graphene layer) and a bottom-gate configuration (where the gate electrode is placed below the active graphene layer). As merely an example, the top split-gate and bottom split-gate configurations are referred to below.

[0013] In the split-gate configuration, two gate electrodes separated by a small gap (typically less than 300 nm) are used to induce a spatial doping profile in the active layer with opposite signs on either side of the junction. Two examples of top and bottom split-gate configurations relevant for waveguide-integrated graphene photodetectors are shown in Figure 1a-d.

[0014] In Fig. 1a (bottom-gate configuration, zero-bias detector operation) and Fig. 1c (bottom-gate configuration, unbiased operation), two pieces of doped silicon slot waveguide are used as gate electrodes below the active graphene channel. This solution avoids the deposition of dielectrics on top of the active layer, preventing the degradation of its electrical properties. However, the bottom-gate constrains the design to the use of doped silicon for the realization of the gate electrode. Other photonic platforms such as SiN cannot be used. The use of chemical doping removes the advantage of graphene that it does not require doping. The conductive layer interposed between the waveguide and the active graphene layer absorbs a larger amount of optical power for the active channel, so other possible bottom-gate configurations of the waveguide-integrated photodetector are not feasible. The optical power absorbed by the gate does not contribute to the photocurrent, resulting in a reduced responsivity.

[0015] In the top split-gate configurations of Figure 1b (top-gate configuration, zero-bias operation) and Figure 1d (top-gate configuration, unbiased operation), two graphene gate electrodes are placed on a thick gate dielectric (thickness >100 nm) deposited on top of the active channel. Since the graphene gate is placed far away from the waveguide, the optical power absorbed in the gate layer accounts for about 10% of the total absorption. However, the mobility of the charge carriers is affected by the deposition process as outlined in the article by Giambra et al. (Optics express 27(15), 20145-20155).

[0016] The second notable difference between graphene pn homojunctions and conventional semiconductor pn junctions is that due to the semimetallic nature of graphene, graphene pn homojunctions do not have a rectifying behavior. When a bias is applied to a graphene pn junction, a large current (even a current in mA, depending on the sample resistance and the applied bias) flows regardless of the polarity of the bias relative to the p- or n-side, i.e., there is no reverse bias condition where the diode dark current is suppressed. Therefore, the only possibility to realize a photodetector that operates with low or zero dark current is to use the photovoltaic or photothermoelectric effect, since these effects do not require a bias.

[0017] Figures 1a, 1b and 1c, 1d show the difference between two photodetector operations: zero-bias operation and unbiased operation. In 1a, 1b the integrated photodetector operates in zero-bias condition, i.e. the drain electrode (right metal electrode) is grounded via an inductor. In 1c, 1d the photodetector is directly connected to the electronics for data readout (amplifier in the figure) without applying an external bias. In both cases only photocurrent is present (zero dark current operation). In unbiased operation it is preferable to express the responsivity by the voltage responsivity (V / W) which corresponds to the ratio of the photovoltage to the incident light power. Summary of the Invention [Problem to be solved by the invention]

[0018] The main object of the present invention is to provide a graphene photodetector that overcomes the limitations highlighted with reference to known solutions. [Means for solving the problem]

[0019] This object, and others which will become more apparent hereinafter, are achieved by a graphene photodetector made in accordance with the appended claims.

[0020] According to one aspect of the disclosed subject matter, the present invention provides a method for producing a cellular membrane comprising: a first graphene absorber layer connected to a first metal electrode at a first end of the first graphene layer and connected to a second electrode at a second end of the first graphene layer opposite the first end, the first and second metal electrodes being referred to as a source and a drain, respectively; a first graphene absorbing layer, the first and second metal electrodes defining a channel and a plasmonic waveguide on the first graphene layer; a gate dielectric layer interposed between the first graphene layer and the second graphene layer, located on an opposite side of the channel to the first graphene layer; a second graphene layer is used for electrical gating and comprises first and second gate electrodes proximate to the first and second metal electrodes, respectively; a gate dielectric layer, the first and second gate electrodes being centered on the channel; a photonic dielectric waveguide having a planarized cladding disposed below a gate dielectric layer, with first and second gate electrodes remaining interposed between the gate dielectric layer and the cladding; The distance between the first metal electrode and the second metal electrode that defines the width of the channel cross section is in the range of 100 nm to 600 nm; The graphene photodetector, wherein the distance between the first gate electrode and the second gate electrode is at least 60% of the distance between the first metal electrode and the second metal electrode.

[0021] In some embodiments, the width of the channel may more preferably be in the range of 250 nm to 450 nm.

[0022] In some embodiments, the thickness of the first and second metal electrodes, which defines the height of the channel cross section, ranges from 70 nm to 200 nm.

[0023] In some embodiments, the thickness of the first and second metal electrodes is preferably 100 nm.

[0024] In some embodiments, the thickness of the gate dielectric layer ranges from 10 nm to 40 nm.

[0025] In some embodiments, the thickness of the dielectric layer is preferably 20 nm.

[0026] In some embodiments, the first and / or second metal electrodes are made from one or more of gold, silver, aluminum, titanium nitride (TiN), or alloys thereof.

[0027] In some embodiments, the distance between the first and second metal electrodes, which defines the width of the channel cross-section, is constant in the longitudinal extension of the channel.

[0028] In some embodiments, the constant width of the channel cross section is in the range of 250 nm to 450 nm.

[0029] In some embodiments, the width of the channel varies periodically in the longitudinal extension of the channel, with sections having a minimum width alternating with sections having a maximum width, and the width varying gradually between the minimum and maximum values ​​along the longitudinal direction, or vice versa.

[0030] In some embodiments, the minimum width is in the range of 100 nm to 250 nm and the maximum width is in the range of 450 nm to 600 nm.

[0031] In some embodiments, the number of channel sections having the smallest width ranges from two to five.

[0032] In some embodiments, the channel is provided with three sections having a minimum width.

[0033] In some embodiments, between two adjacent sections of smallest and largest width, the opposing sides of the channel form an angle of between 4° and 23° with respect to the direction of longitudinal extension of the channel.

[0034] In some embodiments, the optical mode of the dielectric waveguide should be a quasi-transverse electric (quasi-TE) mode.

[0035] In some embodiments, the channel can be realized by using more than one graphene layer, preferably two graphene layers, preferably two graphene layers stacked on top of each other.

[0036] Further characteristics and advantages of the present invention will become more apparent from the following detailed description of some of its preferred embodiments, given as non-limiting examples, with reference to the attached drawings, in which: [Brief description of the drawings]

[0037] [Figure 1a] 1A-1D are schematic diagrams showing cross-sections of respective graphene photodetector embodiments according to the prior art; [Figure 1b] 1A-1D are schematic diagrams showing cross-sections of respective graphene photodetector embodiments according to the prior art; [Figure 1c] 1A-1D are schematic diagrams showing cross-sections of respective graphene photodetector embodiments according to the prior art; [Figure 1d] 1A-1D are schematic diagrams showing cross-sections of respective graphene photodetector embodiments according to the prior art; [Diagram 2] FIG. 1 is a schematic cross-sectional view of a graphene photodetector realized in accordance with the present invention. [Diagram 3]2A-2C are schematic top views of respective embodiments of a photodetector implemented in accordance with the present invention; [Figure 4] 2A-2C are schematic top views of respective embodiments of a photodetector implemented in accordance with the present invention; [Diagram 5] 5 is a schematic enlarged top view of a specific part shown in FIG. 4. [Figure 6] 1 is a graph showing the ratio of the power absorbed by the active graphene layer to the power absorbed by the graphene gate electrode versus the gate dielectric thickness in a photodetector of the present invention. [Figure 7] FIG. 2 is a schematic top view showing an enlarged area of ​​the gap between the metal electrodes in the active graphene channel of the photodetector of the present invention. [Figure 8] 1 is a graph showing optical power density absorbed at the gold / graphene interface for selected gap widths in a photodetector of the present invention. [Figure 9] 4 is a graph showing voltage response in a photodetector of the present invention as a function of gap width. [Figure 10] 1 is a graph showing the power absorbed in the metal contacts and in the active graphene channel of a photodetector as a function of the thickness of the respective metal electrodes. [Figure 11] 1 is a graph showing optical absorption in the active graphene channel of a photodetector versus the distance between the dielectric layer and the dielectric waveguide. [Figure 12] 1 is a graph showing optical absorption in the active graphene channel of a photodetector versus the thickness of the dielectric layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Referring initially to Figure 2, a graphene photodetector implemented in accordance with an embodiment of the present invention is generally designated 1. In Figure 2, a schematic diagram of a cross-section of the photodetector 1 is shown.

[0039] The photodetector 1 comprises a first graphene absorber layer 2 (having a planar configuration depicted by a dashed line) connected at a first end 2a of the first graphene layer 2 to a first metal electrode 3 and at a second end 2b of the first graphene layer 2 opposite to the first end 2a to a second metal electrode 4. The first and second metal electrodes 3, 4 are referred to as source and drain, respectively.

[0040] The contact between the graphene layer 2 and each of the metal electrodes 3, 4 ensures proper electrical connection for conducting and detecting the photocurrent generated in the photodetector.

[0041] The first metal electrode 3 and / or the second metal electrode 4 are preferably made from one or more of gold, silver, aluminum, titanium nitride (TiN), or alloys thereof.

[0042] The first metal electrode 3 and the second metal electrode 4 further define a channel 5 on the first graphene layer 2 that operates as a plasmonic waveguide, as will be explicitly disclosed below.

[0043] The first metal electrode 3 and the second metal electrode 4 are spaced apart, and the distance between the first and second metal electrodes, designated d1, defines the width of the channel cross section.

[0044] t m The thickness of the first metal electrode and the second metal electrode, denoted by x, defines the height of the channel cross section and is preferably in the range of 70 nm to 200 nm, more preferably 100 nm.

[0045] The distance d1 between the first metal electrode 3 and the second metal electrode 4 is preferably in the range of 100 nm to 600 nm, and more preferably in the range of 250 nm to 450 nm.

[0046] The photodetector 1 further comprises a gate dielectric layer 6 interposed between the first graphene layer 2 and a second graphene layer 7 (also depicted by dashed lines), such a configuration realizing a capacitor, the dielectric layer 6 being located on an opposite side of the channel 5 to the first graphene layer 2. Preferably, the dielectric layer 6 is made of SiN or Al2O3.

[0047] The first graphene layer 2 and the second graphene layer 7 are preferably planar and parallel to each other, the distance between them being defined by the thickness of the dielectric layer 6, t diel As shown in the figure.

[0048] The second graphene layer 7 is used for electrical gating and comprises first and second gate electrodes, indicated at 8, 9, at least partially overlapping the first graphene layer 2 and located adjacent to the first metal electrode 3 and the second metal electrode 4, respectively.

[0049] Preferably, the first gate electrode 8 and the second gate electrode 9 are spaced apart by a distance d2 and have a central configuration with respect to the channel 5, as is clearly shown in Figure 2. Central configuration means that the gate electrodes 8, 9 are arranged in mirror symmetry with respect to an imaginary median plane of symmetry of the cross section of the channel 5, identified in Figure 2 with the axis denoted Z.

[0050] Preferably, the distance d2 between the gate electrodes 8, 9 is at least 60% of the distance between the first metal electrode 3 and the second metal electrode 4, and more preferably, the distance d2 is in the range of 100 nm to 300 nm. In this range, more preferably, the value of d2 is 150 nm.

[0051] As disclosed further below, metal electrodes 3, 4 on top of the first graphene layer 2 defining the active channel 5 are provided for either collecting the photocurrent and confining the light at the metal-graphene interface. Control of the electrostatic doping in the active channel by varying the graphene chemical potential (applying an external voltage to the gate electrodes) is achieved by using a so-called bottom split gate geometry provided by gate electrodes 8, 9 of the second graphene layer 4.

[0052] The photodetector 1 further comprises a photonic dielectric waveguide 10 with a planarized cladding 11 disposed beneath the dielectric layer 6, with the first and second gate electrodes 8, 9 remaining interposed between the dielectric layer 6 and the cladding 11. The waveguide 10 comprises a core 12, preferably a silicon core, embedded in the cladding 11, preferably a SiO2 cladding.

[0053] The waveguide 10, preferably of rectangular cross section, is centrally located with respect to the active graphene channel 5. The thickness of the dielectric spacer between the waveguide 10 and the graphene gate electrode is defined as t clad Preferably, the waveguide 10 has a rectangular cross section of 220 nm by 480 nm.

[0054] 3, the active channel 5 and the waveguide 10 extend along a predominant longitudinal direction identified by the Y-axis of the diagram. X denotes a direction perpendicular to the Y-axis and parallel to the first graphene layer 2. The distance d1 defining the gap between the metal electrodes 3, 4 in the active graphene channel 5 is measured along the transverse direction X.

[0055] According to one embodiment of the invention shown in a top view in Figure 3, the distance d1 between the first 3 and second 4 metal electrodes, which defines the width of the active graphene channel 5, is constant along the longitudinal extension Y of the channel. This configuration is obtained by having the opposing edges of each metal electrode 3, 4 parallel to each other and spaced apart by a gap distance d1 with respect to the prevailing longitudinal extension.

[0056] According to another embodiment of the invention, shown in a top view in Figure 4, the distance d1 defining the width of the channel 5 may vary periodically in the longitudinal extension of the channel, such that channel sections having a minimum width, indicated as d1', alternate with sections having a maximum width, indicated as d1'', and the width varies gradually along the longitudinal direction Y between a minimum value d1' and a maximum value d1'', and vice versa.

[0057] Preferably, the minimum width d1' is in the range of 100 nm to 300 nm, and the maximum width d1'' is in the range of 450 nm to 600 nm.

[0058] Preferably, the number of channel sections having the smallest width d1' may range from two to five, and more preferably, three channel sections having the smallest width d1' may be provided in the longitudinal extension of the channel.

[0059] Figure 5 shows an enlarged view of the tapered configuration of the channel section of Figure 4. In the tapered configuration, opposing faces of the channel form an angle α with the direction of longitudinal extension of the channel.

[0060] A small taper angle α (see Fig. 5) is desirable to efficiently convert the mode of the dielectric waveguide into the plasmonic mode of the detector structure. However, a too small taper angle would result in a long taper section (in the propagation direction y). This would be detrimental since it would increase the metal losses and, as a result, reduce the responsivity. The preferred angle α is defined in the range of 4° to 23°.

[0061] Gate electrode and dielectric waveguide (t clad , see Fig. 2) must be small enough to ensure good coupling between the dielectric waveguide and the detector stack. However, the gate electrode is electrically isolated. For this reason, t clad ≠0.

[0062] The thickness of the gate dielectric layer, t dielis chosen to be small enough to maximize the optical absorption in the active graphene channel. However, the thickness t diel is preferably selected to be at least 20 nm to prevent current leakage between the active channel and the gate electrode.

[0063] The graphene-based photodetectors of the claimed subject matter are proposed to exploit the photoconversion mechanisms (photovoltaic and photothermoelectric effects) occurring at the metal / graphene interface. The photovoltaic and photothermoelectric mechanisms at the metal / graphene interface can be exploited to generate a photocurrent. Unlike prior art devices where a graphene homojunction is used, described with reference to Figures 1a-1d, the photovoltaic effect is expected to give a relevant contribution in addition to the photothermoelectric effect. The basic idea behind the claimed photodetectors is to use plasmonic waveguides to confine the optical field to the edges of the metal electrodes (source and drain) that are used to collect the photocurrent. The photodetector structure is designed to be integrated on top of a photonic dielectric waveguide 10 with a planarized cladding 11 and consists of a stack of two graphene layers 2, 7 separated by a dielectric layer 6. The metal electrodes 3, 4 on top of the first graphene layer 2 (active channel 5) are used either to collect the photocurrent and to confine the light to the metal / graphene interface. Control of the doping of the active channel 5 (first graphene layer 2 ) is achieved by using a bottom split gate geometry provided by the second graphene layer 7 .

[0064] The geometry of the photodetector is shown in Figures 2-4, where the device stack is integrated on top of a photonic waveguide 10 with a core 12 and a planarized cladding 11. The source and drain electrodes 3 and 4 act both as electrodes to collect the photocurrent and as plasmonic waveguides to confine the light at the metal / graphene interface.

[0065] To excite a plasmonic mode, the optical mode of the dielectric waveguide needs to be a quasi-transverse electric (quasi-TE) mode.

[0066] Light from a dielectric waveguide 10 is coupled into the plasmonic modes of a metal-insulator-metal (MIM) waveguide on an active graphene channel 5. Most of the optical power is absorbed at the graphene / metal interface at the edges of the metal contacts. With reference to Figure 3, the width d1 of the MIM before the metal absorption spreads to the graphene absorption is 300 nm.

[0067] In FIG. 4, where the intermetallic distance varies periodically, regions of the MIM with large width (d1 greater than 300 nm) alternate with regions with small width (d1 less than 300 nm).

[0068] As mentioned above, referring to the prior art solutions, the graphene layer interposed between the dielectric waveguide and the active graphene layer is detrimental since it absorbs a large amount of optical power that reduces the responsivity of the photodetector. In the proposed invention, this problem is significantly reduced. In fact, the use of a plasmonic waveguide enhances the electric field in the active graphene layer. Moreover, the optical absorption of graphene is proportional to the number of layers. By using two graphene layers, the active channel has a greater absorption relative to the gate.

[0069] In the graph of Figure 6, the power absorbed by the active graphene layer (P active channel ) and the power absorbed by the graphene gate electrode (P gate ) is the gate dielectric thickness (t diel ) as a function of t clad is always 20 nm. The ratio of power absorbed by the active layer to the graphene gate electrode ranges from just over 400% for a 20 nm thick layer to just under 200% for an 80 nm thick gate dielectric. The graph has a monotonically decreasing trend and increases with gate dielectric thickness (t diel ) increases, indicating that the graphene gate absorbs a significantly larger fraction of the optical power.

[0070] For graphene active channels, the main drawbacks of a small gap between metal electrodes are the large absorption in the metal and the non-trivial control of the graphene chemical potential between the two metal electrodes.

[0071] For small gaps, as observed by the applicant for a gap of 20 nm, the chemical potential in the gap is approximately constant and does not change from the left contact to the right contact. If the chemical potential in the gap cannot be controlled, the PTE and PV photoresponse cannot be maximized, since the gap region of the channel is the region where the largest part of the optical power is absorbed. This results in poor voltage response. However, due to the electric field enhancement obtained in the gap, the embodiment with tapered section has the advantage of increasing the amount of optical power absorbed in the active graphene channel. Two embodiments of photodetectors can be compared: 1 - a realization of a photodetector with a constant width of 300 nm, and 2 - a photodetector with a tapered section with a minimum width d1' equal to, for example, 250 nm and a maximum width d1'' equal to 600 nm. In the realization, in a photodetector with a constant width, the absorbed optical power is smaller compared to the case of a photodetector with a periodically tapered width. Moreover, thanks to the smallest gap width (>100 nm), in periodically tapered realizations the optical power is not only confined within the gap, but a relevant part of the absorption also occurs in tapered sections with larger widths. Figure 8, which shows the optical power absorbed at the metal-graphene interface as a function of the Y coordinate, highlights this concept. In this coordinate system, Y=0 corresponds to the center of the structure shown in Figure 7. For the taper with the smallest gap width of 20 nm, the optical power is almost completely absorbed in the gap region. For devices with the smallest gap widths of 250 nm and 70 nm, the power is absorbed more uniformly along Y.

[0072] Optical power absorption in a region larger than 100 nm wide allows for more precise control of the chemical potential, which allows for better optimization of the PTE and PV effects and therefore the responsivity of the detector.

[0073] For this reason, a solution with a tapered section and a relatively large gap (>100 nm) represents the optimal design, which consequently defines the optimal range for d1' and d1'' (FIG. 4).

[0074] The graph in FIG. 9 shows the simulated voltage response as a function of gap width.

[0075] Figure 10 shows the thickness of the metal electrode, t m 1 is a graph showing the power absorbed in the metal contacts and in the active channel as a function of t clad is 20 nm, and t diel The thickness of the metal is also 20 nm. It has been observed that the power absorption in the metal decreases as the metal thickness increases.

[0076] Figure 11 shows the distance t clad 1 is a graph showing the optical absorption in an active graphene channel versus t diel is 20 nm, and t m is 70 nm. Distance t clad must be chosen as thin as possible to maximize the light absorption in the active graphene channel. clad For t = 50 nm, the power absorbed in the active channel is clad A 54% reduction was observed for .lambda.=20 nm.

[0077] FIG. 12 shows the thickness of the dielectric layer, t diel 1 is a graph showing the optical absorption in the active channel versus t clad is 20 nm, and t m is 70 nm. diel For t = 50 nm, the power absorbed in the active channel is dielA 60% reduction was observed for .gtoreq.20 nm.

Claims

1. 1. A graphene photodetector, comprising: a first graphene absorber layer (2) connected to a first metal electrode (3) at a first end (2a) of the first graphene absorber layer (2) and connected to a second metal electrode (4) at a second end (2b) of the first graphene absorber layer opposite to the first end (2a); the first metal electrode (3) and the second metal electrode (4) are a source and a drain, respectively; the first metal electrode (3) and the second metal electrode (4) define a channel (5) on the first graphene absorbing layer (2) that acts as a plasmonic waveguide; a first graphene absorber layer (2); a gate dielectric layer (6) interposed between the first graphene absorber layer (2) and the second graphene layer (7), the gate dielectric layer (6) is disposed on an opposite side of the channel (5) to the first graphene absorber layer (2); the second graphene layer (7) is used for electrical gating and comprises a first gate electrode (8) and a second gate electrode (9) in close proximity to the first metal electrode (3) and the second metal electrode (4), respectively; - said first gate electrode (8) and said second gate electrode (9) are centered on said channel (5); a gate dielectric layer (6); a photonic dielectric waveguide (10) having a planarized cladding (11) disposed below the gate dielectric layer (6), wherein the first gate electrode (8) and the second gate electrode (9) remain interposed between the gate dielectric layer (6) and the cladding (11); Equipped with the distance between the first metal electrode (3) and the second metal electrode (4), which defines the width of the channel cross section, is in the range of 100 nm to 600 nm; the distance between the first gate electrode (8) and the second gate electrode (9) is at least 60% of the distance between the first metal electrode (3) and the second metal electrode (4); Graphene photodetector.

2. The graphene photodetector of claim 1, wherein the width of the channel (5) is in the range of 250 nm to 450 nm.

3. 3. The graphene photodetector according to claim 1, wherein the thickness of the first metal electrode (3) and the second metal electrode (4), which defines the height of the channel cross section, is in the range of 70 nm to 200 nm.

4. Graphene photodetector according to claim 3, wherein the thickness of the first metal electrode (3) and the second metal electrode (4) is 100 nm.

5. The graphene photodetector of claim 1, wherein the thickness of the gate dielectric layer (6) is in the range of 10 nm to 40 nm.

6. Graphene photodetector according to claim 1, wherein the thickness of the gate dielectric layer (6) is 20 nm.

7. 2. The graphene photodetector of claim 1, wherein the first metal electrode (3) and / or the second metal electrode (4) are made from one or more of the following metals: gold, silver, aluminum, titanium nitride (TiN), or alloys thereof.

8. The distance (d) between the first metal electrode (3) and the second metal electrode (4) that defines the width of the channel cross section １ 2. The graphene photodetector of claim 1, wherein the θ is constant in the longitudinal extension (Y) of the channel (5).

9. 9. The graphene photodetector of claim 8, wherein the constant width of the channel cross section is in the range of 250 nm to 450 nm.

10. The width of the channel (5) varies periodically in the longitudinal extension (Y) of the channel, with a minimum width (d １ The section with the maximum width (d １ 2. The graphene photodetector of claim 1, wherein the widths vary gradually along the longitudinal direction between the minimum width value and the maximum width value, and vice versa.

11. The minimum width (d １ The maximum width (d ′) is in the range of 100 nm to 250 nm, １ 11. The graphene photodetector of claim 10, wherein the wavelength λ / 2′ is in the range of 450 nm to 600 nm.

12. The minimum width (d １ 12. The graphene photodetector of claim 10 or 11, wherein the number of sections of the channel having a first electrode and a second electrode is in the range of 2 to 5.

13. The minimum width (d １ 13. The graphene photodetector of claim 12, wherein three sections having a first section and a second section are provided.

14. The minimum width (d １ ') and the maximum width (d １ 11. The graphene photodetector according to claim 10, wherein between two adjacent sections having a lateral cross section (a) of 1000 nm and a lateral cross section (b) of 1000 nm, the opposite surfaces of the channel (5) form an angle (α) of 4° to 23° with respect to the direction of longitudinal extension of the channel (5).

15. The graphene photodetector of claim 1, wherein the optical mode of the photonic dielectric waveguide is a quasi-transverse electric (quasi-TE) mode.

16. Graphene photodetector according to claim 1, wherein said channel (5) can be realized by using two or more graphene layers, preferably two graphene layers.

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