(19)
(11)EP 2 005 229 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
26.06.2019 Bulletin 2019/26

(21)Application number: 07732214.7

(22)Date of filing:  30.03.2007
(51)International Patent Classification (IPC): 
G02B 6/12(2006.01)
H01L 31/0304(2006.01)
H01L 31/101(2006.01)
H01L 31/0232(2014.01)
(86)International application number:
PCT/GB2007/001160
(87)International publication number:
WO 2007/113502 (11.10.2007 Gazette  2007/41)

(54)

PHOTODETECTOR

PHOTODETEKTOR

PHOTODÉTECTEUR


(84)Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC MT NL PL PT RO SE SI SK TR

(30)Priority: 31.03.2006 GB 0606540

(43)Date of publication of application:
24.12.2008 Bulletin 2008/52

(73)Proprietor: UCL Business PLC
London W1T 4TP (GB)

(72)Inventors:
  • SEEDS, Alwyn, John
    London SW3 6BU (GB)
  • RENAUD, Cyril
    London W2 4BG (GB)
  • ROBERTSON, Michael
    Suffolk IP1 4LT (GB)

(74)Representative: J A Kemp 
14 South Square Gray's Inn
London WC1R 5JJ
London WC1R 5JJ (GB)


(56)References cited: : 
EP-A2- 1 049 177
  
  • MADJAR A ET AL: "Design Considerations for a Uni-Traveling Carrier Traveling Wave Photo Detector for Efficient Generation of Millimeter Wave and Sub-MM Wave Signals" 2005 EUROPEAN MICROWAVE CONFERENCE CNIT LA DEFENSE, PARIS, FRANCE OCT. 4-6, 2005, PISCATAWAY, NJ, USA,IEEE, 4 October 2005 (2005-10-04), pages 597-600, XP010903352 ISBN: 2-9600551-2-8
  • BELING A ET AL: "Inp-based 1.55 /spl mu/m high-speed photodetectors for 80 Gbit/s systems and beyond" TRANSPARENT OPTICAL NETWORKS, 2005, PROCEEDINGS OF 2005 7TH INTERNATIONAL CONFERENCE BARCELONA, CATLONIA, SPAIN JULY 3-7, 2005, PISCATAWAY, NJ, USA,IEEE, 3 July 2005 (2005-07-03), pages 303-308, XP010834406 ISBN: 0-7803-9236-1
  • BELING A ET AL: "Inp-based 1.55 /spl mu/m high-speed photodetectors for 80 Gbit/s systems and beyond", TRANSPARENT OPTICAL NETWORKS, 2005, PROCEEDINGS OF 2005 7TH INTERNATIO NAL CONFERENCE BARCELONA, CATLONIA, SPAIN JULY 3-7, 2005, PISCATAWAY, NJ, USA,IEEE, vol. 1, 3 July 2005 (2005-07-03), pages 303-308, XP010834406, DOI: 10.1109/ICTON.2005.1505811 ISBN: 978-0-7803-9236-6
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description


[0001] This invention concerns a photodetector for converting light signals into electrical signals.

[0002] There is an increasing demand for photodetectors able to detect efficiently optical signals modulated at frequencies above 40 GHz for applications such as millimetre-wave over optical fibre communication, high data rate optical networking, millimetre-wave and THz signal generation and radio-astronomy.

[0003] Conventionally, two main approaches for high speed photodetectors have emerged. One is to match the optical velocity and the electrical velocity in a waveguide photodiode structure in order to overcome the frequency response limitation arising from the device capacitance. Such a travelling wave (TW) structure offers a 3dB bandwidth of 50 GHz with a responsivity of 0.2 A/W. EP 1 049 177 A2 discloses a high power and large bandwidth travelling-wave photodetector. The second approach is the use of an electron-only transfer structure because the electron transfer is faster than that for holes. An example of this approach is the Uni-Travelling Carrier structures (UTC) in which the electrons act as the only active carriers and determine the photoresponse. This UTC structure allows a 3dB bandwidth of as high as 310 GHz with 0.07 A/W responsivity. The two techniques have also been combined by coupling a number of individual UTC photodiodes to an optical waveguide, their spacing and electrical interconnection being adjusted in an attempt to match the optical velocity along the waveguide to the electrical velocity of signals travelling along such interconnection, achieving a 115 GHz 3dB bandwidth and 0.075 A/W responsivity.

[0004] A. Beling et al: "InP-Based 1.55 µm High-Speed Photodetectors for 80 Gbit/s Systems and Beyond", ICTON 2005, pages 303-308 volume 1, reports on a fully packaged highly efficient photodetector with 100GHz bandwidth, suitable for 160 Gbit/s return-to-zero detection.

[0005] However, in realising a high-speed photodetector, there are a number of competing requirements. In a waveguide photodetector, the absorption length for greater than 90% absorption in an absorber such as InGaAs is 3 µm. With a typical waveguide width of 4 µm to 6 µm wide, absorption in such a small area imposes a limit on the saturation power of the photodetector. The natural answer would be to increase the area of the absorber, e.g. by increasing the length of the waveguide. However, any depletion photodetector has an associated electrical capacitance, also known as depletion capacitance. The larger the junction area, the greater the capacitance. With a given load resistance, increased capacitance leads to proportionately lower device bandwidth. For bandwidths below 300 GHz the interaction length with the absorption layer in a waveguide photodetector could be kept sufficiently short (e.g. 10 µm) to have a low parasitic capacitance and still offer adequate responsivity and saturation power (but the maximum length will be limited by the parasitic capacitance of the device). However to obtain higher responsivity and saturation power a longer waveguide absorption section will be required thus increasing substantially the parasitic capacitance of the detector which will strongly limit its bandwidth.

[0006] The present invention seeks to alleviate the problem of simultaneously providing high bandwidth, high responsivity and high saturation power in a photodetector.

[0007] According to one aspect of the invention there is provided a photodetector comprising:

an active waveguide comprising an absorber for converting photons conveying an optical signal into charge carriers conveying a corresponding electrical signal;

a carrier collection layer for transporting the charge carriers conveying the electrical signal; and

a secondary waveguide immediately adjacent to the carrier collection layer, which supports fewer than 5 modes, for receiving the photons conveying the optical signal, and which is evanescently coupled to the active waveguide.



[0008] According to a preferred aspect of the invention, fast transport of said charge carriers away from said active waveguide is enabled, for example by using a uni-travelling carrier (UTC) structure.

[0009] According to another preferred aspect of the invention the photodetector comprises a travelling wave structure comprising a further waveguide arranged such that the phase velocity of the electrical signal along the further waveguide is substantially matched to the phase velocity of the optical signal in the active waveguide.

[0010] The photodetector according to the above aspects of the invention incorporates an extra waveguide in the structure, referred to as the secondary waveguide or equivalently as the passive waveguide. This additional passive waveguide allows for evanescent coupling with the active absorber waveguide, and the design also enables one or both of fast carrier transfer (like in UTC structure) and a travelling wave (TW) structure to be achieved. A travelling wave structure is a structure such that the optical signal travels at a velocity (phase velocity) comparable to that of the electrical signal along the waveguide/electrode.

[0011] The secondary waveguide receives the light to be detected, which light may be equivalently referred to herein as photons or electromagnetic radiation. The terms "light" or "photons" used herein do not imply limitation to any particular part of the electromagnetic spectrum, for example the terms are not limited to the visible part of the spectrum, and they explicitly include infrared radiation, near-infrared radiation, mid-infrared radiation, far-infrared radiation, terahertz wave radiation (THz wave) and millimetre wave radiation. The evanescent coupling enabled by the extra waveguide allows for higher saturation power because it increases the length over which absorption takes place, and also increases the responsivity of the detector.

[0012] Depending on the parameters of the structure, the evanescent coupling could imply a relatively long waveguide photodetector, and thus a relatively high parasitic capacitance. However, according to one aspect of the invention, the fact that the secondary waveguide is immediately adjacent to the depletion or carrier collection layer means that this can be overcome by matching the optical and electrical phase velocity (Travelling Wave technique). Effectively the capacitance is made part of a transmission line (further waveguide) formed by the capacitance per unit length of the detector and the inductance per unit length of the electrodes. If the travelling wave structure is well designed the main bandwidth limitation of the detector will be the electron transit time through the absorber (active waveguide) and not the capacitance of the device. The use of travelling wave (TW) techniques with evanescent coupling from a secondary waveguide allows the thickness of the absorber, which determines the electron transit time, to be reduced, thus increasing the bandwidth further.

[0013] Optionally the secondary waveguide is designed with dimensions so as to support only a few modes such that the detector can realise velocity matched travelling wave operation, so as to avoid the capacitance limitation, in order to reach the highest bandwidth possible while retaining compatibility with the added layer in the structure. For example the secondary waveguide may be single-moded or slightly multi-moded, such as supporting 2 or 3 modes, while remaining within the scheme of an evanescently coupled device.

[0014] The photodetector according to another aspect of the invention is designed to enhance the intrinsic bandwidth of the material by using structure-optimised fast carrier travel (such as a Uni Travelling Carrier structure, for example utilising only electron transport across the depletion or carrier collection region) thus offering a shorter transit time, i.e. charge carriers generated in the absorption layer are rapidly transported away.

[0015] According to a further aspect of the invention, mode converters are used to couple light more efficiently from a fibre into the secondary passive waveguide. The device according to the invention has the advantage that the coupling can be optimised without changing the parameters of the active part of the photodetector because of the use of the secondary passive waveguide. A polarisation-independent detector can also be fabricated through the use of an appropriately designed mode converter.

[0016] Embodiments of the present invention will now be now described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows schematically a typical epitaxial design for a photodetector according to an embodiment of the invention;

Figure 2 shows a typical travelling wave structure for a photodetector according to an embodiment of the invention;

Figure 3 is a schematic illustration explaining the evanescent coupling used in the invention;

Figure 4 illustrates evanescent coupling and is a graph of length of waveguide required for 90% absorption against thickness of the absorption layer in a device according to an embodiment of the invention; and

Figures 5a and 5b show two graphs of results obtained with a device embodying the invention.



[0017] An example of a UTC epitaxial design for a photodetector according to an embodiment of the invention is shown in Figure 1. It comprises the following layers from top to bottom: a p-doped Q1.3 diffusion barrier 1 to block the electrons and which is also the top contact layer; a p-doped InGaAs absorption layer 2 (which in the final device constitutes the active waveguide); an n-doped Q1.3 grading layer 3 which blocks the holes; an n-doped InP depletion layer which constitutes a carrier collection layer 4; an n-doped Q1.3 waveguide layer 5 (which in the final device constitutes the added passive secondary waveguide); an n-doped InP buffer layer 6; and a semi-insulating substrate 7. Other layers, such as a p-doped InGaAs top contact layer, may optionally be added above barrier layer 1. Note that Qx.x denotes a quaternary material (in this case InGaAsP) with a bandgap corresponding to an intrinsic absorption edge at a wavelength of x.x µm (in this embodiment 1.3 µm). Depending on the strain in the material, the bandgap defines the proportion of Indium, Gallium, Arsenic and Phosphorus in the quaternary material.

[0018] The choice of the materials and dimensions of some of the layers will now be explained. The bandwidth BW of a travelling wave detector according to an embodiment of the invention can be described, to a first order approximation, by the following equation:



[0019] Where Γ is the confinement factor, α is the absorption coefficient, νe is the electrical phase velocity, dd is the absorption region thickness and νd is the uniform electron drift velocity. There is no limitation due to parasitic capacitance because the first term of the equation (the travelling wave term) replaces the parasitic capacitance limitation. The second term is the carrier drift velocity limitation which is optimised in the structures proposed here as embodiments of the invention. The travelling wave term is dependent on the structure and device design. The structure will determine capacitance and conductance of the equivalent circuit for the device as well as the optical coupling characteristic. In a device embodying the invention, the secondary waveguide is placed adjacent to the depletion or carrier collection layer in order to retain control of the capacitance, resistance and the optical coupling. The device design will determine the series resistance and inductance (dependent of the width of the waveguide and the type of contact). Finally the parallel resistance is determined by the material, and the spacing of the electrodes. The control on the capacitance, resistance and the optical coupling in conjunction with the last term enables one to obtain velocity match at high frequency. Typically it implies that the combined thickness of the layers above the layer or layers comprising the secondary passive waveguide layer and the secondary passive waveguide layer itself should be between 0.9 µm and 1.3 µm for typical levels of doping, and typical InGaAsP/InP structures. This thickness includes: layer or layers comprising the secondary passive waveguide layer which should be between not greater than 0.5 µm, preferably between 0.05 µm and 0.5 µm, more preferably between 0.25 µm and 0.5 µm, for efficient coupling of the incident light and efficient evanescent coupling; the absorption layer which should be between 0.03 µm and 0.3 µm for both high intrinsic bandwidth and efficient evanescent coupling; and the layers in between which should be between 0.15 µm and 0.35 µm for efficient evanescent coupling, appropriate capacitance per unit length and short carrier transit time.

[0020] One aspect of a UTC detector (the invention is embodied as a UTC detector according to one aspect) is that its speed is enhanced over that of an ordinary PIN diode by using only a single fast carrier type (electron) in the charge transport (holes with a low velocity do not contribute). Electrons are faster than holes at thermal equilibrium and can travel short distances ballistically, i.e. faster than thermal equilibrium saturated velocity. With a suitable bias applied to the device the electrons can travel at up to 6 times their thermal equilibrium velocity.

[0021] In order to enable fast carrier transport by UTC operation to be achieved, the photon absorption layer 2 and carrier collection layer 4 are arranged to be separate. The absorption layer 2 is highly p-doped, and electrons generated drift to the low doped depletion layer comprising the carrier collection layer 4 where they are accelerated away. The interface between the absorber layer 2 and depletion or carrier collection layer 4 is very important because it should not enhance recombination or impede the flow of electrons (as would occur as a result of any heterobarrier). Conventionally an abrupt transition between highly doped absorption layer and low doped depletion or carrier collection layer has been achieved using a dopant such as beryllium in the absorber layer, because this has a low diffusion coefficient, and the elimination of a heterobarrier by use of a quaternary grading layer between the absorption and collection layers. In this description, the terms depletion layer and carrier collection layer are generally used synonymously. A depletion layer is an example of a layer that provides the function of carrier collection.

[0022] It might be expected that zinc would not be a suitable dopant, because it is known to have a very high diffusion coefficient. However, in some embodiments of this invention, it has been found that zinc is a very suitable dopant, because it is less soluble in InP than InGaAs, and even less soluble in sulphur doped InP. Figure 1 shows a structure using light sulphur doped InP (1016 cm-3) for the depletion or carrier collection layer 4, an n-doped Q1.3 layer for the grading layer 3, and highly Zn-doped (> 2 x 1018 cm-3) InGaAs for the absorption layer 2. During growth a very limited amount of zinc diffusion takes place through the Q1.3 layer into the InP. This actually reduces any residual heterobarriers between InGaAs and Q1.3, and Q1.3 and InP. This results in the desired high speed UTC devices with high quantum efficiency.

[0023] Figure 2 shows a typical travelling wave structure for a photodetector embodying the invention. After the layered structure depicted in Figure 1 has been grown, for example by epitaxy, it is then processed, for example by etching, to define the width and length of the layers of the device such that the absorption layer 2 constitutes an active waveguide, and the Q1.3 waveguide layer 5 constitutes a secondary, passive waveguide, as shown on the substrate in Figure 2. For example, the waveguide width may be 4 to 6 µm, and the length 15 µm or more. Metal is also deposited using conventional lithographic techniques to provide a top p-type contact 8, and a pair of n-type contacts 9. In this structure, the electrical and optical phase velocity are matched in order to overcome the limitation of the parasitic capacitance for the electrical bandwidth. The travelling wave structure is defined by the spacing of the electrodes which can be calculated from the characteristics of the detector material and the metal deposition used for contact. Therefore to define the travelling wave device one will typically have to define the type of p-contact 8, the type of n-contact 9, the width 10 of the waveguide and the spacing 11 of the electrodes.

[0024] In this embodiment of the invention, the material of the contacts 8 and 9 would be gold or alloys containing gold as a principal component, such as Ti-Au, Pt-Au, Cr-Au, or any suitable material giving ohmic (non-rectifying) contacts to the underlying semiconductor material. The centre electrode 9 would be in the range of 2 to 8 µm wide; the side electrode width would be >5 µm, and the inter-electrode spacing 11 would be from 5 to 25 µm typically). The thickness of the contacts 8,9 is between 300 nm and 800 nm

[0025] In use, the incoming light L is coupled into the secondary passive waveguide 5 to then be evanescently coupled into the active waveguide (absorption layer) 2.

[0026] Figure 3 shows a schematic cross-section describing evanescent coupling between the secondary passive waveguide 5 and the active waveguide 2. The light is coupled from the passive waveguide to the active waveguide through the interaction of the evanescent field 12 of the mode(s) in the passive waveguide 5 with the active waveguide 2. The length over which the light is substantially absorbed (e.g. 90% absorbed) into the passive waveguide depends on the spacing 14 between the two waveguides 2,5, the thickness 15 of the passive waveguide 5, the thickness 16 of the active waveguide 2, and the absorption coefficient of the material of the active waveguide. The secondary waveguide in this embodiment of the invention is designed to support one or only a few guided modes in order to enhance the coupling length and the homogeneity of the coupling. The number of modes is determined by the width and thickness of the waveguides as well as the difference of refractive indexes between the core and the cladding (surrounding material). The refractive index is dependent on the material, and in the case of InP is 3.17 and for Q1.3 is about 3.4. These materials are chosen to enable good detection, therefore the dimensions of the waveguide can be chosen to achieve the desired performance. The width of the secondary waveguide is determined by the width of the active waveguide (absorption layer) which needs to be relatively small to reduce the device capacitance; for example in the range of from 1 to 8 µm. Thus the thickness of the secondary waveguide is the principal free parameter for defining a waveguide supporting only one or a few modes, and in the structure according to this embodiment, the thickness is selected to be not greater than 0.5 µm, preferably in the range of from 0.05 to 0.5 µm, more preferably in the range of from 0.25 to 0.5 µm.

[0027] Figure 4 shows the result from two dimensional simulations for an evanescent coupled detector where the detector is as in Figures 2 and 3 with the other parameters being: 4 µm for the width 10 of the waveguide 2, thickness 15 of the passive waveguide of 0.4 µm, spacing 14 between the waveguides of 0.33 µm, and the thickness 16 of the active waveguide ranging from 0.05 µm to 0.25 µm, although this thickness is not critical provided it is thick enough to give small contact resistance and the change in contact resistance, inductance and parasitic capacitance is taken into account in designing the device. The graph shows the length of the waveguide necessary to absorb 90% of the incoming light as the thickness of the active waveguide (absorption layer 2) is varied.

[0028] An additional tapered waveguide, functioning as a mode-converter, not shown, can be provided to couple light efficiently from a cleaved optical fibre into the secondary passive waveguide 5. The mode-converter waveguide can also be of the design that makes the device polarisation independent. Further details regarding suitable mode-converters and polarization independence can be gleaned from Chee-Wei Lee, Mee-Koy Chin, Mahadevan K. Iyer, and Alexandre Popov, "Asymmetric Waveguides Vertical Couplers for Polarization-Independent Coupling and Polarization-Mode Splitting", Journal of Lightwave Technology, vol. 23, pp. 1818-1827, 2005.

[0029] Figure 4 shows the importance of the absorption layer thickness (i.e. the thickness 16 of the active waveguide 2), as it plays an important role in the determination of the absorption length. One can notice that reducing the thickness of the absorption layer implies a shorter absorption length until a value (in this case around 0.12 µm thick) at which the absorption length starts to increase again on further reduction in thickness of the absorption layer. A longer absorption length is desirable to extract all the advantages of using a travelling wave structure. However, achieving this at reduced thickness has the further advantage of increasing the intrinsic bandwidth because the electrons will have less distance to travel. Therefore the absorption layer 2 typically has a thickness of less than 0.1 µm. This also increases the parasitic capacitance, but in the device embodying one aspect of the present invention this can be overcome by the use of the travelling wave structure.

[0030] Figures 5a and 5b show results obtained from a sample photodetector device embodying the invention. Note that in this case only 40% of the incoming light from a single mode fibre could be coupled into the photodetector. One can see that this non-optimized device already offers a high 3 dB bandwidth as seen on the graph of Fig. 5a of more than 110 GHz, and a high responsivity of 0.2 A/W at 110 GHz as seen in the graph of Fig. 5b. This device has a 15 µm long active waveguide in which the light is absorbed, limiting the saturation power, yet already achieves a saturation power of more than 100 mW. The saturation power can be enhanced further by the use of longer active waveguides.


Claims

1. A photodetector comprising:

an active waveguide (2) comprising an absorber for converting photons conveying an optical signal into charge carriers conveying a corresponding electrical signal;

a carrier collection layer (4) for transporting the charge carriers conveying the electrical signal; and

a secondary waveguide (5) immediately adjacent to the carrier collection layer (4), which supports fewer than 5 modes, for receiving the photons conveying the optical signal, and which is evanescently coupled to the active waveguide (2);

wherein the active waveguide (2) thickness is less than 0.1 µm.


 
2. A photodetector according to claim 1, wherein fast transport of said charge carriers away from said active waveguide (2) is enabled.
 
3. A photodetector according to claim 1 or 2, wherein the photodetector comprises a travelling wave structure comprising a further waveguide arranged such that the phase velocity of the electrical signal along the further waveguide is substantially matched to the phase velocity of the optical signal in the active waveguide (2).
 
4. A photodetector according to any of the preceding claims, wherein the secondary waveguide (5) is within an intentionally doped layer of an epitaxial structure.
 
5. A photodetector according to any of the preceding claims, comprising a uni-travelling carrier structure for charge carrier transport from the active waveguide (2).
 
6. A photodetector according to any of the preceding claims, wherein the structure is layered and where the total thickness of the layers comprising the active waveguide (2), the secondary waveguide (5), and any intervening layers (3, 4) combined is in the range of from 0.9 µm to 1.3 µm.
 
7. A photodetector according to claim 6, wherein the secondary waveguide (5) layer thickness is not greater than 0.5 µm.
 
8. A photodetector according to claim 6 or 7, wherein the active waveguide (2) layer thickness is in the range of from 0.03 µm to 0.3 µm.
 
9. A photodetector according to claim 6, 7 or 8, wherein the thickness of the intervening layers (3, 4) is in the range of from 0.15 µm to 0.35 µm.
 
10. A photodetector according to any of the preceding claims, wherein the width of the secondary waveguide (5) is in the range of from 1 to 8 µm.
 
11. A photodetector according to any of the preceding claims, wherein the active waveguide (2) comprises a semiconductor doped with zinc.
 
12. A photodetector according to any of the preceding claims, wherein the active waveguide (2) comprises InGaAs.
 
13. A photodetector according to any of the preceding claims, wherein the secondary waveguide (5) comprises n-type InGaAsP.
 
14. A photodetector according to any of the preceding claims, wherein said carrier collection layer (4) comprises an InP depletion layer between the active waveguide (2) and secondary waveguide (5), and/or wherein the active waveguide (2) and secondary waveguide (5) are at least 15 µm long.
 
15. A photodetector according to any of the preceding claims, further comprising a mode converter for coupling photons to be detected from an optical fibre into the secondary waveguide (5).
 


Ansprüche

1. Photodetektor, umfassend:

einen aktiven Wellenleiter (2), umfassend einen Absorber zum Umwandeln von Photonen, die ein optisches Signal übertragen, in Ladungsträger, die ein entsprechendes elektrisches Signal übertragen;

eine Trägersammelschicht (4) zum Transportieren der Ladungsträger, die das elektrische Signal übertragen; und

einen sekundären Wellenleiter (5) unmittelbar angrenzend an die Trägersammelschicht (4), der weniger als 5 Modi unterstützt, zum Empfangen der Photonen, die das optische Signal übertragen, und der evaneszent mit dem aktiven Wellenleiter (2) gekoppelt ist;

wobei die Stärke des aktiven Wellenleiters (2) weniger als 0,1 µm ist.


 
2. Photodetektor nach Anspruch 1, wobei ein schneller Transport der Ladungsträger weg von dem aktiven Wellenleiter (2) ermöglicht ist.
 
3. Photodetektor nach Anspruch 1 oder 2, wobei der Photodetektor eine Wanderwellenstruktur umfassend einen weiteren Wellenleiter umfasst, die so angeordnet ist, dass die Phasengeschwindigkeit des elektrischen Signals entlang des weiteren Wellenleiters im Wesentlichen an die Phasengeschwindigkeit des optischen Signals in dem aktiven Wellenleiter (2) angeglichen ist.
 
4. Photodetektor nach einem der vorherigen Ansprüche, wobei sich der sekundäre Wellenleiter (5) innerhalb einer absichtlich dotierten Schicht einer epitaxischen Struktur befindet.
 
5. Photodetektor nach einem der vorherigen Ansprüche, umfassend eine Uni-Travelling-Carrier-Struktur für Ladungsträgertransport von dem aktiven Wellenleiter (2).
 
6. Photodetektor nach einem der vorherigen Ansprüche, wobei die Struktur geschichtet ist und wo die Gesamtstärke der Schichten, die den aktiven Wellenleiter (2), den sekundären Wellenleiter (5) und alle zwischenliegenden Schichten (3, 4) kombiniert umfassen, in dem Bereich von 0,9 µm bis 1,3 µm ist.
 
7. Photodetektor nach Anspruch 6, wobei die Schichtstärke des sekundären Wellenleiters (5) nicht größer als 0,5 µm ist
 
8. Photodetektor nach Anspruch 6 oder 7, wobei die Schichtstärke des aktiven Wellenleiters (2) in dem Bereich von 0,03 µm bis 0,3 µm ist.
 
9. Photodetektor nach Anspruch 6, 7 oder 8, wobei die Stärke der zwischenliegenden Schichten (3, 4) in dem Bereich von 0,15 µm bis 0,35 µm ist.
 
10. Photodetektor nach einem der vorherigen Ansprüche, wobei die Breite des sekundären Wellenleiters (5) in dem Bereich von 1 bis 8 µm ist.
 
11. Photodetektor nach einem der vorherigen Ansprüche, wobei der aktive Wellenleiter (2) einen mit Zink dotierten Halbleiter umfasst.
 
12. Photodetektor nach einem der vorherigen Ansprüche, wobei der aktive Wellenleiter (2) InGaAs umfasst.
 
13. Photodetektor nach einem der vorherigen Ansprüche, wobei der sekundäre Wellenleiter (5) n-leitendes InGaAsP umfasst.
 
14. Photodetektor nach einem der vorherigen Ansprüche, wobei die Trägersammelschicht (4) eine InP-Depletionsschicht zwischen dem aktiven Wellenleiter (2) und dem sekundären Wellenleiter (5) umfasst, und/oder wobei der aktive Wellenleiter (2) und der sekundäre Wellenleiter (5) mindestens 15 µm lang sind.
 
15. Photodetektor nach einem der vorherigen Ansprüche, ferner umfassend einen Moduswandler zum Koppeln von Photonen, die von einer optischen Faser erfasst werden sollen, in den sekundären Wellenleiter (5).
 


Revendications

1. Photodétecteur comprenant :

un guide d'ondes actif (2) comprenant un absorbeur destiné à convertir des photons acheminant un signal optique en porteurs de charge acheminant un signal électrique correspondant ;

une couche de collecte de porteurs (4) destinée à transporter les porteurs de charge acheminant le signal électrique ; et

un guide d'ondes secondaire (5) immédiatement adjacent à la couche de collecte de porteurs (4), qui prend en charge moins de 5 modes, destiné à recevoir les photons acheminant le signal optique, et qui est couplé de manière évanescente au guide d'ondes actif (2) ;

l'épaisseur du guide d'ondes actif (2) étant inférieure à 0,1 µm.


 
2. Photodétecteur selon la revendication 1, dans lequel un transport rapide desdits porteurs de charge en éloignement dudit guide d'ondes actif (2) est activé.
 
3. Photodétecteur selon la revendication 1 ou 2, le photodétecteur comprenant une structure d'onde de déplacement comprenant un guide d'ondes supplémentaire agencé de sorte que la vitesse de phase du signal électrique le long du guide d'ondes soit sensiblement mise en correspondance avec la vitesse de phase du signal optique dans le guide d'ondes actif (2).
 
4. Photodétecteur selon l'une quelconque des revendications précédentes, dans lequel le guide d'ondes secondaire (5) se trouve dans une couche intentionnellement dopée d'une structure épitaxiale.
 
5. Photodétecteur selon l'une quelconque des revendications précédentes, comprenant une structure de porteur à déplacement unilatéral pour un transport de porteurs de charge depuis le guide d'ondes actif (2).
 
6. Photodétecteur selon l'une quelconque des revendications précédentes, dans lequel la structure est en couches et où l'épaisseur totale des couches comprenant le guide d'ondes actif (2), le guide d'ondes secondaire (5) et des couches intermédiaires quelconques (3, 4) combinés se trouve dans la plage de 0,9 µm à 1,3 µm.
 
7. Photodétecteur selon la revendication 6, dans lequel l'épaisseur de couche de guide d'ondes secondaire (5) n'est pas supérieure à 0,5 µm.
 
8. Photodétecteur selon la revendication 6 ou 7, dans lequel l'épaisseur de couche de guide d'ondes actif (2) se trouve dans la plage de 0,03 µm à 0,3 µm.
 
9. Photodétecteur selon la revendication 6, 7 ou 8, dans lequel l'épaisseur des couches intermédiaires (3, 4) se trouve dans la plaque de 0,15 µm à 0,35 µm.
 
10. Photodétecteur selon l'une quelconque des revendications précédentes, dans lequel la largeur du guide d'ondes secondaire (5) se trouve dans la plaque de 1 à 8 µm.
 
11. Photodétecteur selon l'une quelconque des revendications précédentes, dans lequel le guide d'ondes actif (2) comprend un semi-conducteur dopé au zinc.
 
12. Photodétecteur selon l'une quelconque des revendications précédentes, dans lequel le guide d'ondes actif (2) comprend de l'InGaAs.
 
13. Photodétecteur selon l'une quelconque des revendications précédentes, dans lequel le guide d'ondes secondaire (5) comprend de l'InGaAsP de type n.
 
14. Photodétecteur selon l'une quelconque des revendications précédentes, dans lequel ladite couche de collecte de porteurs (4) comprend une couche de déplétion d'InP entre le guide d'ondes actif (2) et le guide d'ondes secondaire (5), et/ou dans lequel le guide d'ondes actif (2) et le guide d'ondes secondaire (5) ont au moins 15 µm de longueur.
 
15. Photodétecteur selon l'une quelconque des revendications précédentes, comprenant en outre un convertisseur de mode destiné à coupler des photons à détecter depuis une fibre optique dans le guide d'ondes secondaire (5).
 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



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Patent documents cited in the description




Non-patent literature cited in the description