Optoelectronic device comprising a III-V structure on a substrate comprising a silicon waveguide

Abstract

Optoelectronic device comprising a III-V structure on a substrate comprising a silicon waveguide. The invention relates to an optoelectronic device (1) comprising: a substrate (10) comprising a silicon waveguide (11), a III-V structure (12) forming a first waveguide and comprising: a first layer (13), for example n-doped, an optically active layer (14), a second layer (15) for example p-doped, and an intermediate layer (16) based on a III-V material configured to form a waveguide with an effective refractive index between the effective refractive index of the first waveguide and the effective refractive index of the silicon waveguide (11), so as to obtain optical coupling between the first waveguide (12) and the intermediate waveguide (16), and optical coupling between the intermediate waveguide (16) and the silicon-based waveguide (11). Figure for the abstract: Fig. 4A

Description

Title of the invention: Optoelectronic device comprising a III-V structure on a substrate comprising a silicon waveguide technical field

[0001] The present invention relates to the field of optoelectronics, and more particularly to optoelectronics on silicon substrates. Its particularly advantageous application is the integration of III-V hybrid structures on silicon with a silicon photon guide. STATE OF THE ART

[0002] In the field of silicon-based integrated optics, waveguides are important components. They form an optical circuit that allows the interconnection of different optoelectronic components. Sub-micrometer waveguides are notably used in applications related to optical telecommunications, photonics, nonlinear optics, and quantum computing.

[0003] Optoelectronic devices exist, for example illustrated in [Fig. 2A] and 2B, comprising an optically active structure 12' based on III-V materials and comprising a first layer 13' (for example, N-doped), a quantum well layer, also called the active layer 14', and a second layer 15' (for example, P-doped). The first layer 13', the quantum well layer, also called the active layer 14', and the second layer 15' form a first waveguide 12', which can also be referred to as the active waveguide. The optically active structure 12', also called the IILV structure, is integrated onto a substrate 10 comprising a silicon-based waveguide 11'. These devices are used, for example, as amplifiers, modulators, or for light generation purposes, such as in lasers.

[0004] Typically, for the integration of these IILV hybrid structures on silicon, the aim is to achieve optical coupling between the active waveguide and the silicon-based waveguide 11', for example buried in a substrate 10'. The substrate 10' can for example be an SOI substrate (from the English Silicon-On-Insulator, translated as silicon on insulator).

[0005] The optical coupling between the active waveguide and the silicon-based waveguide 11' is limited by the difference in effective refractive index between the active waveguide and the silicon-based waveguide 11'. Figure 1 illustrates the effective refractive index by way of example: - neff ( i5 ) of the active 12' guide as a function of the width of the 15' layer of p-InP (also called "bar" InP) in nm, - Aneff (si5oo)d'un waveguide 11' dit « pưươр« based on silicon having a core thickness of en' 500 nm and two lateral edges of 300 nm thickness, - Aneff ( si3oo)d of a more standard waveguide in photonics, silicon-based with a core 300 nm thick and two lateral edges of 150 nm.

[0006] Figure 1 shows a mismatch between the effective refractive indices of an InP bar with a width greater than 500 nm and a standard 300 nm core silicon-based waveguide used in photonics. The transition between the quantum well layer of the optically active InP structure and the silicon-based waveguide remains possible, but only for an InP bar width typically less than 200 nm. The InP bar must therefore be very narrow. This imposes excessively stringent manufacturing constraints that prevent the industrial-scale production of these devices.

[0007] To circumvent this problem, solutions exist in which a III-V structure is integrated onto a thick silicon-based waveguide. The paper Duan, GH, et al. (2014). Hybrid III—V on Silicon Lasers for Photonic Integrated Circuits on Silicon. IEEE Journal of selected topics in quantum electronics, 20(4), 158-120, describes an InP laser on a SOI substrate, with a so-called "thick" silicon waveguide having a thickness of 440 nm. Figure 1 indeed shows a good match between the effective refractive indices of an InP bar for a width greater than 750 nm and a thick silicon-based waveguide. However, the use of a thick silicon-based waveguide has some drawbacks. This type of waveguide is not a standard in photonics and the integration of III-V structure on this type of waveguide requires reviewing and modifying the silicon part of the manufacturing processes.This therefore complicates the fabrication of integrated III-V structures on silicon-based waveguides.

[0008] An object of the present invention is therefore to propose a solution facilitating the integration of a hybrid III-V optically active structure on silicon, and in particular so that the integration of the III-V structure is more compatible with industrial manufacturing constraints.

[0009] The other objects, features and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0010] To achieve this objective, according to a first aspect, an optoelectronic device is planned comprising: - a substrate comprising a silicon-based waveguide having an effective refractive index, - an optically active structure based on at least one III-V material, referred to as the "III-V structure", disposed on the substrate, the III-V structure comprising: • a first layer exhibiting a first conductivity of a first type of charge carrier, • an active layer configured to emit or receive light radiation, and placed above the first layer, • a second layer having a second type of charge carriers, and surmounting the active layer, the first layer, the active layer and the second layer being configured together to form a first waveguide, called an "active waveguide" having an effective refractive index.

[0011] Advantageously, the III-V structure further comprises an intermediate layer based on a III-V material configured to form an intermediate waveguide with an effective refractive index between the effective refractive index of the first waveguide and the effective refractive index of the silicon-based waveguide, the intermediate layer being disposed between the active layer and the silicon-based waveguide, so as to obtain optical coupling between the first waveguide and the intermediate waveguide, and optical coupling between the intermediate waveguide and the silicon-based waveguide.

[0012] The intermediate layer thus serves as an intermediate waveguide between the active waveguide and the silicon-based waveguide. The intermediate waveguide therefore has an intermediate effective refractive index in order to bridge the effective index difference between the active waveguide and the silicon-based waveguide.

[0013] The width constraint of the second layer is therefore relaxed. Furthermore, thanks to this intermediate optical coupling, it is possible to increase the thickness of the first layer. It is therefore possible to dimension the III-V structure in a way that is more compatible with industrial manufacturing. Moreover, this allows the III-V structure to be integrated onto a substrate comprising a silicon-based waveguide with dimensions more standard for photonic applications. Typically, the waveguide can be silicon-based and have a core thickness of 300 nm. This therefore facilitates the integration of the III-V structure by minimizing, and preferably avoiding, adaptations to the substrate fabrication processes.

[0014] A second aspect relates to a method for manufacturing an optoelectronic device according to the first aspect, the method comprising: - a supply of structure III-V, - integration by transferring the III-V structure onto the substrate including the silicon-based waveguide. BRIEF DESCRIPTION OF THE FIGURES

[0015] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0016] [Fig. 1] The [Fig. 1] represents the variation of the effective refractive index for elements of an optoelectronic device according to the prior art.

[0017] [Fig.2A] Figures 2A and 2B represent a longitudinal and transverse cross-sectional view respectively of an optoelectronic device according to the prior art.

[0018] [Fig.2B]

[0019] [Fig.3] Fig.3 represents the variation of the effective refractive index for elements of an optoelectronic device according to an example of an embodiment of the invention.

[0020] [Fig.4A] Figures 4A and 4B represent a longitudinal cross-sectional view and a top view respectively of an optoelectronic device according to an exemplary embodiment of the invention.

[0021] [Fig.4B]

[0022] [Fig.5A] Figures 5A and 5B are diagrams respectively of the gap energy as a function of the stress S, and of the refractive index as a function of the gap energy, in an InGaAsP layer.

[0023] [Fig.5B]

[0024] [Fig.6] Fig.6 represents a cross-sectional view of the optoelectronic device illustrated in figures 4A and 4B.

[0025] [Fig.7] Fig.7 represents a top view of the optical transition zones of the optoelectronic device illustrated in Figures 4A and 4B, as well as the distribution of the optical mode obtained by simulation of the corresponding device, according to several planes in cross-section.

[0026] [Fig.8] Fig.8 represents a longitudinal cross-sectional view of the optical transition zones of the optoelectronic device illustrated in Figures 4A and 4B.

[0027] [Fig.9A] Figures 9A and 9B represent the distribution of the optical mode obtained by simulation of the optoelectronic device according to the example of [Fig.8], along a longitudinal section plane, and for two bar widths p-InP.

[0028] [Fig.9B]

[0029] [Fig. 10] Fig. 10 represents the confinement factor CF of the optical mode in the active layer comprising the MQW quantum wells (for multi quantum wells) and in an intermediate layer of InGaAsP, depending on the thickness of the intermediate layer and according to an example of the device implementation.

[0030] [Fig. 11 A] Figures 11A and 11IB represent the distribution of the optical mode obtained by simulation of the optoelectronic device according to the example of [Fig. 10] along a transverse section plane, and for two thicknesses of the intermediate layer.

[0031] [Fig.llB]

[0032] [Fig.12A] Figures 12A and 12B represent the percentage of transmission by optical coupling in the first and second optical transition zones respectively, as a function of the length of the transition zones, according to an example.

[0033] [Fig.12B]

[0034] [Fig.13A] Figures 13A to 13C represent optimization graphs of geometric parameters of the optoelectronic device, according to an example.

[0035] [Fig.l3B] [Fig.l3C]

[0036] [Fig.14A] Figures 14A to 14C represent top, cross-section and longitudinal section views respectively of the device according to another embodiment.

[0037] [Fig.l4B] [Fig.l4C]

[0038] [Fig.15A] Figures 15A to 15D represent longitudinal cross-sectional views of steps in the manufacturing process of the optoelectronic device, according to an example.

[0039] [Fig.l5B] [Fig.l5C] [Fig.l5D]

[0040] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the relative dimensions of the layers, portions, structure, substrate or other elements of the device are not representative of reality. DETAILED DESCRIPTION

[0041] Before beginning a detailed review of embodiments of the invention, optional features which may possibly be used in association or alternatively are stated below.

[0042] According to one example, the second layer extends in a principal extension plane and has at least one dimension in said plane greater than or equal to 500 nm, preferably greater than or equal to 700 nm, and preferably 1 pm. According to another example, the second layer extends in a principal extension plane and has at least one dimension in said plane less than or equal to 4 pm. More preferably, this dimension is substantially equal to 2 pm. Thus, the width of the second layer, or equivalently of bar III-V, can be compatible with the processes of industrial-scale manufacturing. This notably facilitates the transfer of the III-V structure onto the substrate.

[0043] According to one example, the intermediate layer is based on, or made of, a material having a refractive index between 3.2 and 3.5. During the development of the invention, it was shown that this range of refractive index limits the absorption of light by the intermediate layer, while allowing intermediate coupling of the active waveguide to the silicon-based waveguide.

[0044] According to one example, the intermediate layer has a thickness ei6 greater than or equal to 100 nm. With a thickness greater than 100 nm, the thickness of the intermediate layer is sufficient to perform the intermediate optical coupling and is reproducible with standard layer growth techniques.

[0045] According to one example, the intermediate layer has a thickness ei6 less than or equal to 250 nm. A thickness less than 250 nm allows light to be concentrated in the active layer comprising the quantum wells, rather than in the intermediate layer.

[0046] According to one example, the intermediate layer is based on, or made up of, InGaAsP. During the development of the invention, it was shown that this material limits the absorption of radiation, particularly in the infrared range.

[0047] According to one example, the first layer, the active layer and the second layer are based on or made of InP.

[0048] According to one example, FlnGaAsP has the formula Ini.xGaxAsyPi y with x between 0.1 and 0.4, preferably approximately 0.4, and y between 0.1 and 0.8, preferably approximately 0.8. This composition maximizes the refractive index of the intermediate layer while limiting its absorption, particularly in the infrared range, for an unconstrained layer. This material is therefore particularly well-suited for improving coupling by the intermediate waveguide.

[0049] According to one example, the first layer comprises a first sublayer and a second sublayer placed on top of the first sublayer, with the intermediate layer sandwiched between the first and second sublayers. The intermediate layer is located within the first layer, between the first and second sublayers. This arrangement allows for a better distribution of the distance between the active layer, the intermediate layer, and the silicon-based waveguide, thereby improving optical coupling. The fabrication of the device is simplified by limiting the need to adapt existing processes. In particular, the IILV structure is transferred to the substrate via the first layer, as is customary, and not via an intermediate layer that could be made of a different material.

[0050] According to an alternative example in which the intermediate layer is disposed at the interface between the first layer and the substrate.

[0051] According to one example, in which the intermediate layer is disposed between the active layer and the substrate.

[0052] According to one example, the first sub-layer has a thickness eno, the second sub-layer has a thickness em, eni being strictly greater than ei30. Thus, the intermediate layer is off-center with respect to the first layer. It has been shown that this limits light loss compared to a centered configuration (where eni is approximately equal to eno) for the same thickness of the first layer.

[0053] According to one example, between a first interface between the active layer and the first layer and a second interface between the first layer and the substrate, the first layer has a thickness of between 500 nm and 1500 nm, and preferably approximately 1 pm. This thickness notably affects the distance between the active layer, the intermediate layer, and the silicon-based waveguide. This thickness allows for good optical coupling between the active waveguide, the intermediate waveguide, and the silicon-based waveguide, while limiting light loss. In addition, this thickness improves heat dissipation and reduces the access resistance of the optically active structure. This thickness facilitates the fabrication of the III-V structure, notably by relaxing the constraints on the etching parameters of the initial stack.

[0054] According to one example, a first portion of the intermediate layer is at least partly superimposed with a portion of the active layer at the level of a first optical transition zone, the first portion of the intermediate layer and the portion of the active layer each having a width Li6, LM, in their main extension plane, decreasing along the first optical transition zone, in a coupling direction parallel or coincident with the main extension direction of the silicon-based waveguide moving away from the III-V structure, the first optical transition zone having a length L1 greater than or equal to 100 pm in the coupling direction.

[0055] According to one example, a second portion of the intermediate layer is at least partially superimposed with a portion of the silicon-based waveguide at a second optical transition zone, the second portion of the intermediate layer and the portion of the silicon-based waveguide each having a width Li6, Lu, in their principal extension plane, such that: - the width Li6 of the second portion of the intermediate layer is decreasing, and - the width Lu of the portion of the silicon-based waveguide is increasing, along the second optical transition zone moving away from the III-V structure in the coupling direction, the second optical transition zone having a length L2 greater than or equal to 200 pm in the coupling direction.

[0056] Within the framework of this so-called "pointed" geometry, these lengths allow a transmission, by successive optical couplings, of more than 99% of the light.

[0057] According to one example, the device is a laser, an optical amplifier or an optical modulator or a photodetector.

[0058] According to one example, the device is configured to emit or receive radiation in the infrared light range, and for example with a wavelength between 800 nm and 2 pm.

[0059] According to one example, the first layer has an "n" type conductivity, the charge carriers being electrons.

[0060] According to one example, the second layer has a conductivity of type "p", the charge carriers being holes.

[0061] According to one example, the process includes dimensioning the intermediate layer, dimensioning comprising: - a determination of a dimension L of the second layer in its principal extension plane (x,y), said dimension being greater than or equal to 500 nm, preferably between 700 nm and 20 pm, - the intermediate layer having a thickness ei6, a determination of the thickness ei6 as a function of the dimension L^ of the second layer in its principal extension plane, and the supply of structure III-V includes: - an epitaxial growth of the intermediate layer so that the intermediate layer has the determined thickness ei6. - an etching of the second layer so that the second layer has the determined dimension Li5.

[0062] Note that outside of transition zones or equivalently of optical coupling, the III-V bar can be much wider, typically the III-V bar can have a width of a few tens of pm.

[0063] According to one example, the process includes dimensioning the first layer, dimensioning comprising: - a determination of the thickness of the first layer, measured between a first interface between the active layer and the first layer and a second interface between the first layer and the substrate, allowing the transfer of at least 90% of the light between the active waveguide and the waveguide intermediate waveguide and between the intermediate waveguide and the silicon-based waveguide, and in which the supply of structure III-V includes: - an epitaxial growth of the first layer so that, after transfer, the active layer and the substrate are separated by the determined thickness.

[0064] In a perfectly classical manner, a structure based on a III-V material is a structure comprising, or made up of, a material comprising at least one species from column III of the periodic table and at least one species from column V of that table.

[0065] Similarly, the following abbreviations relating to a material M may be used: - uM, or equivalently iM, refers to intrinsic or unintentionally doped material M, according to the terminology usually used in the field of microelectronics for the prefix u- or equivalently i-, - nM refers to the N-, N+ or N++ doped material M, according to the terminology usually used in the field of microelectronics for the prefix n-, - pM refers to the P-, P+ or P++ doped material M, according to the terminology usually used in the field of microelectronics for the prefix p-,

[0066] A substrate, film, or layer "based" on a material M is understood to mean a substrate, film, or layer comprising only that material M or that material M and possibly other materials, for example, alloying elements, impurities, or dopant elements. Where applicable, the material M may have different stoichiometries.

[0067] Several embodiments of the invention implementing successive steps of the manufacturing process are described below. Unless explicitly stated, the adjective "successive" does not necessarily imply, although this is generally preferred, that the steps follow each other immediately; intermediate steps may separate them.

[0068] Furthermore, the term "step" refers to the execution of a part of the process, and can designate a set of sub-steps.

[0069] Furthermore, the term "step" does not necessarily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step may, in particular, be followed by actions related to a different step, and other actions from the first step may be repeated later. Thus, The term step does not necessarily refer to unitary actions that are inseparable in time and in the sequence of phases of the process.

[0070] It is specified that, within the framework of the present invention, the thickness of a layer or substrate is measured along a direction perpendicular to the surface along which this layer or substrate has its maximum extent. The thickness is thus taken along a direction perpendicular to the principal faces of the substrate on which the various layers rest. Thus, a layer typically has a thickness along z when it extends primarily along an xy plane. The relative terms "on," "under," and "substrate" preferably refer to positions taken along the z direction.

[0071] In the following, the length is taken along the x direction, the width is taken along the y direction, and the height and depth of engraving are taken along the z direction.

[0072] It is specified that, within the scope of the present invention, the terms "on," "overcomes," "covers," "underlying," "opposite," and their equivalents do not necessarily mean "in contact with." Thus, for example, the deposition, transfer, bonding, assembly, or application of a first layer onto a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer, either by being directly in contact with it or by being separated from it by at least one other layer or element. By "in contact" or "in contact with," it is understood that a thin interface may exist, for example, caused by manufacturing variability.

[0073] It is specified that, within the framework of the present invention, a third layer intercalated between a first layer and a second layer does not necessarily mean that the layers are directly in contact with each other, but means that the third layer is either directly in contact with the first and second layers, or separated from them by at least one other layer or at least one other element, unless otherwise arranged.

[0074] By "superimposed" layers, portions, or zones, it is understood here that the layers, portions, or zones are in contact along their main extension plane and arranged one above the other along the direction of stacking, this direction being perpendicular to the main extension plane.

[0075] Dimensional values ​​are understood to be within manufacturing and measurement tolerances.

[0076] The terms "approximately", "about", "on the order of" mean "within 10%" or, when referring to an angular orientation, "within 10°". Thus, a direction substantially normal to a plane means a direction having an angle of 90+10° with respect to the plane.

[0077] Within the framework of the invention, energies are given in electronvolts, for which 1 eV ~ 1.602.10 19 J, in the international system of units.

[0078] For plane light waves in homogeneous media (for example in optical materials), the refractive index n can be used to quantify the increase in wavenumber (phase change per unit length) caused by the medium: the wavenumber is n times higher than in a vacuum.

[0079] The effective refractive index has an analogous meaning for the propagation of light in a waveguide with restricted transverse extent: the value [3 (phase constant) of the waveguide (for a certain wavelength) is the effective refractive index multiplied by the wavenumber in vacuum, according to the following expression:

[0080]

[0081] The expression "A and / or B" means (A), (B), or (A and B). The expression "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0082] The invention will now be described in detail through a few non-limiting embodiment examples. The optoelectronic device 1 according to the invention can, for example, be used as an amplifier, modulator, for light detection purposes as a photodetector, or for light generation purposes, for example, for a laser.

[0083] Figures 3, 4A and 4B illustrate an example of an optoelectronic device according to the invention.

[0084] The optoelectronic device 1 comprises a substrate 10. The substrate 10 may, for example, be a silicon-on-isothiazolinone (SOI) substrate. The substrate 10 includes a waveguide 11 based on, or made of, silicon (Si). Hereafter, this waveguide is referred to as the "Si waveguide 11". The Si waveguide 11 may be embedded in a portion 100 based on, or made of, SiO2 of the substrate 10 (as illustrated in [Fig. 15D]). As is known, the Si waveguide may have reliefs 112, and / or at least one filter, and / or a diffraction grating, and / or elements for total internal reflection.

[0085] The Si 11 waveguide typically extends continuously along a direction x. It then guides the propagation of light radiation along x. The Si 11 waveguide can have different cross-sectional shapes. In the following, a waveguide with an edge is described. Note that other waveguide geometries, for example, slotted or periodic grating, are possible. The dimensioning methods described below can be adapted to other waveguide geometries. In the accompanying drawings, only a cross-section of the Si 11 waveguide in the yz and xz planes is shown. However, this cross-section is not necessarily constant along x, along the Si 11 waveguide.

[0086] The optoelectronic device 1 further comprises an optically active structure 12 based on, or composed of, at least one III-V material. The III-V structure 12 comprises a first layer 13 exhibiting a first conductivity of a first type of charge carrier. For example, the first layer is N-doped, the charge carriers being electrons. The III-V structure 12 comprises a second layer 15 exhibiting a second conductivity of a second type of charge carrier. For example, the second layer is P-doped, the charge carriers being holes. The III-V structure 12 comprises an active layer 14 configured to emit or receive light radiation. The active layer 14 comprises quantum wells for this purpose. The active layer 14 may also be designated by the acronym MQW (from the English "multi-quantum wells"). The layer 14 is sandwiched between the first 13 and second 15 layers.Layers 13, 14, and 15 form a first waveguide, which can be referred to as the active waveguide. In the III-V structure, the second layer 15 and the active layer 14 generally have at least one dimension in the xy plane, and in particular the width Li5 along the y direction, smaller than the corresponding dimension of the first layer 13. The second layer 15 and the active layer 14 can thus form what is called a III-V bar.

[0087] According to one example, the optoelectronic device 1 is configured to operate in the infrared range. For example, the working wavelength of the electronic device 1 is substantially between 800 nm and 2 pm, and preferably substantially equal to 1.55 pm.

[0088] In order to bridge the gap between the effective refractive index range Aneff (sisoo) of a Si waveguide, particularly one with a thickness of approximately 300 nm according to photonics standards, and the effective refractive index of the III-V bar neff (15), the optoelectronic device 1 comprises an intermediate layer 16 forming an intermediate waveguide. This intermediate waveguide enables optical coupling between the active waveguide and the intermediate waveguide 16, and also between the intermediate waveguide 16 and the Si waveguide 11. As illustrated in [Fig. 3], the waveguide formed by the intermediate layer 16, also referred to as the intermediate waveguide 16, can have an effective refractive index range within an Aneff range (intermediate to the effective refractive indices of the Si waveguide 11 and the III-V bar). This allows for a relaxation of the dimensioning constraints on the width Li 5du bar IILV.

[0089] For these optical couplings, the intermediate layer 16 is arranged between the active layer 14 and the waveguide Si 11. As illustrated in [Fig. 4B], for the coupling between the intermediate waveguide 16 and the active waveguide, a first portion 16a of the intermediate layer 16 can be at least partially superimposed along the z-direction with a portion 14a of the active layer 14. This forms a first transition zone 1a. For the coupling between the intermediate waveguide 16 and the waveguide Si 11, a second portion 16b of the intermediate layer 16 and a portion 11b of the waveguide Si 11 can be at least partially superimposed along the z direction. This forms a second transition zone 1b.

[0090] The layers of structure III-V 12 are at least partly superimposed on each other.

[0091] According to one example, the III-V structure 12 is InP-based. According to this example, the first layer 13 is a layer based on or composed of n-InP, and the second layer 15 is a layer based on or composed of p-InP. The active layer 14 may be an i-InP-based layer. The active layer 14 may be based on or composed of at least one ternary or quaternary alloy comprising InP and another element selected from Ga, As, Al, and / or P, for example. The layer 14 may, for example, be based on or composed of InGaAsP or InGaAsAl. The layer 14 may be intrinsic and therefore undoped. In the following, the III-V structure 12 is considered, for non-limiting purposes, to be InP-based. Note that other III-V materials are possible. In particular, the material selection and dimensioning procedures described below can be applied to other IILV materials.

[0092] The materials of the intermediate layer 16 preferably have a lattice match with the IILV material of the IILV structure 12. The material of the intermediate layer 16 preferably exhibits limited absorption at the working wavelength. In the case of InP, the InGaAsP material is chosen because it exhibits low absorption at the working wavelength of 1.55 pm (and in particular compared to the InGaAs material, for example).

[0093] The composition of InGaAsP can be chosen according to the following procedure. Using the diagrams illustrated in Figures 5A (Adachi - 2009 - Properties of Semiconductor Alloys Group-IV, III-VandII-VI semiconductors) and 5B (Minch Park - 1999 - Theory and experiment of InGaAsP and InGaAlAs long-wavelength strained), one first positions oneself at the 0% abscissa of [Fig. 5A] in order to have an unstrained intermediate layer. For a working wavelength of 1.55 pm, the corresponding band gap energy Eg is preferably greater than or equal to 0.8 eV to avoid absorption. According to [Fig. 5A], the intersection between an Eg = 0.8 eV and the value of y for an abscissa of 0% therefore implies y less than or equal to approximately 0.8. With [Fig. 5B], the refractive index n of the material can be determined according to the composition of the material and the energy E of the photon. By plotting this value of y on the graph of [Fig.5B] (for which the values ​​of y and Ly are reversed with respect to [Fig.5A]), we obtain y greater than or equal to 0.2. On [Fig.5B], the intersection between the composition line y = 0.2 and E = 0.8 eV, and the intersection between the composition line y = 1 and E = 0.8 eV give a refractive index approximately between approximately 3.17 and 3.5.

[0094] The intersection between the 0% stress abscissa in [Fig.5A], and the corresponding composition line y can give the value of x. For example, for y=0.8 we ax approximately equal to 0.4.

[0095] According to the Ini xGaxAsyPi y composition as described in [Fig.5A], we have: - x not zero and preferably between 0 and 0.4, and / or - y not zero and less than or equal to 0.8, and preferably between 0.1 and 0.8.

[0096] To maximize the band gap energy and limit light absorption at the working wavelength, it may be preferable to limit the refractive index of the material. If a high band gap energy is desired, the refractive index of FlnGaAsP will, for example, be minimized (n would tend towards 3.2, for example). However, using a low refractive index implies thickening the intermediate layer 16, which can make optical coupling with the other waveguides more difficult. Optimizing the device dimensions may depend on the intended applications.

[0097] To maintain thin film thicknesses, a high refractive index is preferable. In order to find a compromise between these effects, the intermediate layer 16 preferably has a refractive index approximately equal to 3.5. This promotes coupling while keeping the thickness of the intermediate layer 16 reasonable.

[0098] Preferably, the composition is Ino,6Gao,4Aso,8Po,2 to exhibit a refractive index substantially equal to 3.5.

[0099] Particular examples of dimensioning and geometry are then described with reference to Figures 6 to 13C.

[0100] According to a first example illustrated in Figures 6 and 7, the device 1 comprises the SiO2-based substrate 10, in which a Si waveguide 11 is embedded. The Si waveguide 11 has a central portion 110 with a thickness approximately equal to 300 nm. The central portion 110 is framed along the y-direction by two edges 111 with a thickness approximately equal to 150 nm. The central portion 110 can be surmounted by a portion of the substrate 10 with a thickness ei0 approximately equal to 100 nm.

[0101] The IILV structure 12 is disposed on the substrate 10. In the IILV structure 12, the intermediate layer 16 is preferably disposed within the first layer 13. Thus, the first layer 13 comprises a first sublayer 130 and a second sublayer 131, the intermediate layer 16 being intercalated between the first sublayer 130 and the second sublayer 131.

[0102] As illustrated in [Fig. 7], to achieve optical coupling at the first 1a and second 1b transition zones, the optoelectronic device 1 can have a so-called "pointed" configuration. In a pointed configuration, at least one The dimension in the xy plane, and for example the width y, of the active layer 14, the intermediate layer 16, and the waveguide Si 11, is increasing or decreasing at each transition zone la, 1b, along a coupling direction A and away from the III-V structure (x-direction in [Fig. 7]). The coupling direction may be parallel, and preferably coincident, with the main extension direction of the waveguide Si 11. In the following, we consider the notions of increasing or decreasing along the coupling direction A and away from the III-V structure (x-direction in [Fig. 7]).

[0103] More specifically, at the first transition zone 1a, the active layer 14, and optionally the second layer 15, has a width Li5 that decreases linearly between a first width and a second width, for example from 2 pm to 500 nm. According to this example, the intermediate layer 16 has a width Lie that decreases linearly between a first width and a second width, for example from 6 pm to 2 pm. Preferably, the intermediate layer 16 and the active layer 14 are centered along the coupling direction A, at least at the first transition zone 1a. The width variation zone of the active layer 14 and the intermediate layer 16 can extend along the x direction over a length LL

[0104] According to one example, at the second transition zone 1b, the intermediate layer 16 has a width Li6 that decreases linearly between a first and a second length, for example from 2 pm to 500 nm. According to another example, the decrease in the width Li6 of the intermediate layer 16 is continuous from the first transition zone 1a to the second transition zone 1b. The waveguide Si 11 can, according to this example, have a width Lii that increases linearly between a first and a second width, for example from 500 nm to 2 pm. Preferably, the intermediate layer 16 and the waveguide Si 11 are centered along the coupling direction A at least at the first transition zone 1b. The width variation zone of the waveguide Si 11 and the intermediate layer 16 can extend along the x direction over a length L2.

[0105] As illustrated by Figures 7 and 8, the optical coupling between the active waveguide and the intermediate waveguide 16 and then between the intermediate waveguide 16 and the Si waveguide 11, has been modeled for the geometry illustrated in Figures 6 and 7. In [Fig. 7], several transverse section planes in the yz plane can be seen, showing the successive passages of light from the active layer 14 to the Si waveguide 11. [Fig. 8] illustrates this along a longitudinal section plane xz.

[0106] The second layer 15 and the active layer 14 are generally etched to form the III-V bar. The second layer 15 can therefore have a width Scope along the y-direction. The optical transitions in the active layer 14 are typically governed by the width Li5, as illustrated in Figures 9A and 9B for Li5 = 4 pm and Li5 = 0.5 pm, respectively. As an example, to concentrate the light in the active layer 14, the second layer 15 has a width Li5 greater than 500 nm, and preferably between 2 pm and 4 pm. Here, the width Li5 is considered at the widest point of the III-V bar, outside the optical transition zone. The active layer 14 can have the same width as the second layer 15. Alternatively, as illustrated in [Fig. 6], the active layer 14 can have an overhang, preferably on either side of the second layer 15. This overhang can extend over a distance from the scope along the y-direction, for example, approximately 200 nm.

[0107] The width Li5 is interdependent with the thickness ei6 of the intermediate layer 16. The aim is to concentrate the light in the active layer 14. As illustrated in Figures 10 and 1 IA, depending on the width Li5 chosen, the maximum thickness of the intermediate layer 16 can be fixed. For a width Li5 of the second layer 15 p-InP approximately equal to 4 pm, and an intermediate layer 16 of InGaAsP with refractive index n = 3.5 located 200 nm from the lower interface 13b between the substrate 10 and the first sublayer 130, a prevalence of light in the intermediate layer 16 can be observed from a thickness ei6 greater than 250 nm (for example, as illustrated in [Fig. 1 IB] for a thickness ei6 of 350 nm). We therefore choose a thickness ei6 less than or equal to 250 nm, and preferably approximately equal to 175 nm, in order to concentrate the light in the active layer 14. The [Fig.11 A] shows as an example a prevalence of light in the active layer 14 for a thickness Ci6 of 100 nm). .

[0108] The more we want to reduce the thickness ei6 of the intermediate layer, the more its effective refractive index will decrease and therefore the more we will have to reduce the width Li5 of the second layer 15. We understand therefore that a compromise can be found because of this interdependence.

[0109] Furthermore, the active layer 14 and the intermediate layer 16 are preferably sufficiently far apart to allow maximum optical coupling and minimize coupling losses. This can limit the width Li5 of the second layer 15. This also allows for a relaxation of the constraints on the etching step of the III-V bar. Indeed, a frequently encountered problem is over-etching of the IILV bar, resulting in etching of the first layer 13. With a greater thickness of the first layer 13, etching this layer 13 will have a more moderate impact, particularly on the access resistance of the optoelectronic device. For this reason, and with reference to [Fig. 6], for example, the total thickness of the first layer, taken between a first interface 13a with the active layer 14 and a second interface 13b with the substrate 10, can be substantially equal to 1 pm.

[0110] The active layer 14 and the waveguide Si 11 can be separated by a distance, taken along the direction z substantially perpendicular to the main extension plane of the active layer 14, of between 800 nm and 1200 nm, and preferably substantially equal to 1100 nm.

[0111] Furthermore, it has been observed that coupling losses are further reduced by shifting the intermediate layer 16 downwards within the first layer 13. For example, the thickness ratio ei3i / ei30 can be between 2.5 and 3.5. As an example, the thickness eno of the first sublayer 130 is approximately 200 nm. Thus, with a thickness ei0 approximately 100 nm, the distance between the intermediate layer 16 and the Si waveguide 11 can be approximately 300 nm. As an example, the thickness eni of the second sublayer 131 can be approximately 625 nm.

[0112] According to one example, the thickness eu of the active layer 14 can be substantially between 200 nm and 500 nm. According to another example, the thickness ei 5 of the second active layer 15 can be substantially between 1 pm and 3 pm.

[0113] For example, and with reference to Figures 7, 12A and 12B, the length, taken along x, of the optical transition zones la, 1b can be adapted to maximize the transmission of light between respectively the active layer 14 and the intermediate layer 16, and the intermediate layer 16 and the waveguide Si 11. By modeling according to the geometric characteristics previously presented, it has been shown that a transmission of at least greater than or equal to 95% and preferably greater than or equal to 99% could be obtained with L1 greater than or equal to 100 pm and L2 greater than or equal to 200 pm.

[0114] As can be seen from the preceding description, the geometric parameters can be determined to optimize the light transmission by successive couplings in the optoelectronic device 1. The interdependencies between these parameters can be studied by modeling. To illustrate this, Figures 13A to 13C show dimensioning optimizations of the device 1. The simulations presented in Figures 13A, 13B, 13C and the associated diagrams (Figures 14A, 14B, 14C) concern the first transition between the active waveguide and the intermediate waveguide 16 (transition zone α in [Fig. 7]), according to an example. For example, [Fig. 13A] represents the transmission of the first transition α as a function of the thickness ε of the first layer 13 and the length L1 of the first transition zone α, for a geometry including a smaller width Li5 of the p-InP layer, at the level of the zone between the two transitions of a pointed geometry, approximately equal to 500 nm.

[0115] [Fig. 13A] shows the transmission value of the transition as a function of its length (L1) and the thickness of n-InP (en) for an optimal value of InGaAsP which can be read from [Fig. 13B]. For example, for the value shown in the inset (transmission of 82.41% for a transition 400 pm long and an n-InP thickness of 1.5 pm), the corresponding InGaAsP thickness is 1.05 pm.

[0116] Figure 13B shows the optimal thickness of the InGaAsP intermediate layer (between 0.1 and 0.9) as a function of the n-InP thickness (en) and the transition length L1. For example, for a transition 400 pm long and an n-InP thickness of 1.5 pm, the optimal simulated InGaAsP thickness is 1.05 pm (inset in figure).

[0117] For example, [Fig. 13C] illustrates the confinement obtained as a function of the thickness ei3 of the first layer 13 and the length L1 of the first transition zone la, according to an example. [Fig. 13C] shows the fraction of the electric field covering the stack of wells and their barriers. In particular, an overlap of 10.61% is obtained for a length Li of 400 pm and an n-InP thickness of 1.5 pm (inset in the figure). Since the wells and their barriers have approximately identical thicknesses, the field confinement in the quantum wells alone is about half the value shown, or 5.3% under these conditions. This is the value used in the calculation of the laser gain.

[0118] Many other geometries are possible in addition to those described previously. By way of example, Figures 14A to 14C describe another example of geometry. In this geometry, the width Li5 of the second layer is approximately equal to 6 pm. The tip of the second layer 15 has a width Li5 approximately equal to 500 nm. The active layer 14 may have an overhang on either side of the second layer 15 over a distance d[4 approximately equal to 1 pm. The length L1 may be between 100 pm and 500 pm. The total thickness ei3 of the first layer 13 may be between 0.2 pm and 1.8 pm. The intermediate layer 16 may have a thickness ei6 approximately equal to 0.1 ei3 and 0.9 ei3.

[0119] The manufacturing process is now described according to a particular embodiment with reference to Figures 15A to 15D. As illustrated by Figures 15A and 15B, a stack 18 intended to form the III-V structure 12 can be fabricated on a support substrate 17 by epitaxial growth. The process may include sizing steps to determine the thickness of the layers of the III-V structure formed, according to the modalities described above. It is therefore understood that the steps Epitaxial growth patterns can therefore be configured to achieve the determined thicknesses.

[0120] The process can then include at least one step of etching the stack 18 to obtain the III-V structure 12. During this or these etching steps, the second layer 15 and the active layer 14 are etched to form the III-V bar of width Li5. Several etching steps can be carried out so that the active layer has an overhang.

[0121] The process may then include transferring the IILV structure 12 onto the substrate 10 comprising the Si waveguide 11, as illustrated in [Fig. 15D]. The substrate 10 may include an upper portion 100 based on, or composed of, SiO2. The substrate 10 may include a lower portion 101 based on, or composed of, silicon. The process may include so-called "backside" steps for integrating functionalities or components onto the lower portion 101 of the substrate 10. These steps preferably take place prior to the transfer.

[0122] To this end, the fabrication of the substrate portion 10 can be carried out upstream. All of these steps can be performed upstream. These steps can, for example, include the fabrication of the metal layers above the Si waveguide(s), particularly for electrically connecting the optoelectronic device(s) such as modulators or photodetectors. Thus, the Si waveguides 11 may no longer be accessible from the front (upper) face of the substrate 10. Therefore, instead of transferring the IILV structure 12 onto the upper surface of the substrate 10 (as seen in [Fig. 2A] for example), the front face of the substrate 10, including the Si waveguide 11, can be bonded to a support substrate (typically silicon-based) allowing manipulation of the substrate 10.The substrate 10 can be partially etched, thus allowing access to the back of the Si waveguide and integration of the IILV structure coupled to the silicon waveguide, as illustrated for example in [Fig. 15D]. The main advantage of this approach is that it enables the realization of a complete photonic technology (including, among other things, electrical routing), while remaining compatible with the integration of IILV components (via the back side).

[0123] The invention is not limited to the embodiments described above and extends to all embodiments covered by the invention. The present invention is not limited to the examples described above. Many other embodiments are possible, for example by combining features described above, without departing from the scope of the invention. For example, in the preceding description, examples of IILV InP structures are described. Other IILV materials can be considered, and in particular structures not based on InP but on GaAs and utilizing alloys such as AlGaAs or InGaAs. Furthermore, the features described in relation to one aspect of the invention can be combined with another aspect of the invention.

Claims

Demands

1. An optoelectronic device (1) comprising: • a substrate (10) including a silicon-based waveguide (11) having an effective refractive index, • an optically active structure based on at least one III-V material, referred to as the "III-V structure" (12), disposed on the substrate (10), the III-V structure (12), the III-V structure (12) comprising: • a first layer (13) having a first conductivity of a first type of charge carrier, • an active layer (14) configured to emit or receive light radiation, and surmounting the first layer (13), • a second layer (15) having a second type of charge carrier, and surmounting the active layer (14), the first layer (13), the active layer (14) and the second layer (15) being configured together to form a first waveguide having an effective refractive index,the optoelectronic device (1) being characterized in that the III-V structure (12) further comprises an intermediate layer (16) based on a III-V material configured to form an intermediate waveguide with an effective refractive index between the effective refractive index of the first waveguide and the effective refractive index of the silicon-based waveguide (11), the intermediate layer (16) being disposed between the active layer (14) and the silicon-based waveguide (11), so as to obtain optical coupling between the first waveguide (12) and the intermediate waveguide (16), and optical coupling between the intermediate waveguide (16) and the silicon-based waveguide (11).

2. Optoelectronic device (1) according to the preceding claim, wherein the second layer (15) extends in a principal extension plane (x,y) and has at least one dimension (Li5) in said plane greater than or equal to 500 nm, preferably between 700 nm and 20 pm.

3. Optoelectronic device (1) according to any one of the preceding claims, wherein the intermediate layer (16) is based on a material having a refractive index between 3.2 and 3.

5.

4. Optoelectronic device (1) according to any one of the preceding claims, wherein the intermediate layer (16) has a thickness ei6 between 100 nm and 250 nm.

5. Optoelectronic device (1) according to any one of the preceding claims, wherein the intermediate layer (16) is based on InGaAsP.

6. Optoelectronic device (1) according to the preceding claim, wherein FlnGaAsP is of formula Ini xGaxAsyPi y with x between 0.1 and 0.4, preferably substantially equal to 0.4, and y between 0.1 and 0.8, preferably substantially equal to 0.

8.

7. Optoelectronic device (1) according to any one of the preceding claims, wherein the first layer (13) comprises a first sublayer (130) and a second sublayer (131) overlying the first sublayer (130), the intermediate layer (16) being intercalated between the first (130) and second (131) sublayers.

8. Optoelectronic device (1) according to the preceding claim, wherein the first sublayer (130) has a thickness eno and the second sublayer (131) has a thickness eni, eni being strictly greater than eno.

9. Optoelectronic device (1) according to any one of the preceding claims, wherein, between a first interface (13a) between the active layer (14) and the first layer (13) and a second interface (13b) between the first layer (13) and the substrate (10), the first layer (13) has a thickness of between 500 nm and 1500 nm.

10. An optoelectronic device (1) according to any one of the preceding claims, wherein: • a first portion (16a) of the intermediate layer (16) is at least partially superimposed with a portion (14a) of the active layer (14) at the level of a first optical transition zone (la), the first portion (16a) of the intermediate layer (16) and the portion (14a) of the active layer (14) each having a width Li6, LM, in their principal extension plane, decreasing along the first optical transition zone (la), in a coupling direction (A) parallel to or coinciding with the principal extension direction of the silicon-based waveguide (11) away from the III-V structure (12), the first optical transition zone (la) having a length L1 greater than or equal to 100 pm in the coupling direction (A), • a second portion (16b) of the intermediate layer (16) is at least partially superimposed with a portion (11b) of the silicon-based waveguide (11) at the level of a second optical transition zone (1b), the second portion (16b) of the intermediate layer (16) and the portion (11b) of the silicon-based waveguide (11) each having a width Li6, Lu,in their principal extension plane, such that: • the width Li6 of the second portion (16b) of the intermediate layer (16) is decreasing, and • the width Lu of the portion (11b) of the silicon-based waveguide (11) is increasing, along the second optical transition zone (1b) away from the III-V structure (12) in the coupling direction (A), the second optical transition zone (1b) having a length L2 greater than or equal to 100 pm in the coupling direction (A).

11. Optoelectronic device (1) according to any one of the preceding claims, wherein the device (1) is a laser, an optical amplifier or an optical modulator or a photodetector.

12. Optoelectronic device (1) according to any one of the preceding claims, configured to emit or receive radiation in the infrared light range, and for example with a wavelength between 800 nm and 2 pm.

13. A method for manufacturing an optoelectronic device (1) according to any one of the preceding claims, the method comprising: • supplying the III-V structure (12), • integrating by transferring the III-V structure (12) onto the substrate (10) comprising the silicon-based waveguide (H).

14. A manufacturing method according to the preceding claim, further comprising dimensioning the intermediate layer (16) including: • determining a dimension Li5 of the second layer (15) in its principal extension plane (x,y), said dimension being greater than or equal to 500 nm, preferably between 700 nm and 20 pm, • the intermediate layer (16) having a thickness ei6, determining the thickness ei6 as a function of the dimension Li5 of the second layer (15) in its principal extension plane, and wherein the provision of the III-V structure (12) includes: • epitaxial growth of the intermediate layer (16) such that the intermediate layer (16) has the determined thickness ei6, • etching of the second layer (15) such that the second layer (15) has the determined dimension Li5.

15. A manufacturing method according to any one of the two preceding claims, further comprising dimensioning the first layer (13) including: • determining a thickness in μ of the first layer (13), taken between a first interface (13a) between the active layer (14) and the first layer (13) and a second interface (13b) between the first layer (13) and the substrate (10), allowing the transfer of at least 90% of the light between the active waveguide and the waveguide intermediate (16) and between the intermediate waveguide (16) and the silicon-based waveguide (11), and in which the supply of structure III-V (12) comprises: • an epitaxial growth of the first layer (13) so that, after transfer, the active layer (14) and the substrate (10) are separated by the determined thickness ei3.

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