A photonic device for providing optical radiation including an optical mode located in a waveguide

Abstract

The present invention relates to a photonic device (DP) for providing optical radiation, the photonic device comprising a waveguide (2), an N-type semiconductor layer (1n) covering the waveguide (2), and an active region (QW) formed by a stack made of III-V materials. The photonic device further comprises a plurality of P-type semiconductor pillars (1p, 1'p) provided on and in contact with the active region (QW). At least a first metal pad (3n, 3'n) is in ohmic contact with a free portion of the N-type layer (1n), and at least a second metal pad (3p, 3'p) is in ohmic contact with the P-type pillars (1p, 1'p).

Description

Technical Field

[0001] The technical field of the present invention is that of integrated photonic devices which use both the properties of semiconductor materials capable of emitting light and the properties of semiconductor materials conventionally used in integrated circuits for implementing logic and / or analog functions. The present invention specifically relates to a photonic device for establishing a light radiation including an optical mode located in a waveguide. It may in particular be a heterogeneous laser on silicon. Background Art

[0002] Optical transceivers generally consist of active optical devices (such as lasers, modulators, photodiodes) and passive optical devices (such as waveguides, filters), optionally supplemented with electronic circuits. These blocks can be integrated into a photonic device using the techniques and materials commonly used for manufacturing integrated electronic circuits.

[0003] In such a photonic device, and in a manner known per se, an active region formed by a stack of III-V materials forms the optical amplification medium of the laser. The active region may include at least one quantum well, quantum dot or quantum box, or a plurality of such wells, dots or boxes. It is made of materials selected from the following non-exhaustive list: InP, AsGa, InGaAlAs, InGaAsP, InAsP, InAs.

[0004] The active region is arranged to be sandwiched between an N-type semiconductor layer and a P-type semiconductor layer. These layers, which are generally based on InP or AsGa, make it possible to circulate an electric current in the active region and to electrically pump the amplification medium to allow the generation of light. In order to inject and extract charges in the active region and allow this pumping, conductive metal pads are respectively provided in ohmic contact with the P-type and N-type semiconductor layers. These pads are also electrically connected to electrical interconnect traces which allow the charges to circulate in the device.

[0005] The active region is arranged to be aligned with a part of the waveguide, called the "hybrid part", formed for example of silicon. The optical mode generated in this arrangement is called "hybrid" because the mode is partly located in the active region and partly in the waveguide. The waveguide extends on at least one side of the hybrid part to allow the generated mode to propagate. The paper "Monolithically Integrated CMOS-Compatible III-V on Silicon Lasers" by M. Seifried et al., IEEE Journal of Selected Topics in Quantum Electronics, vol. 24, no. 6, pp. 1-9, Nov.-Dec. 2018, Art no. 8200709 reviews that the greater the overlap of the optical mode with the current injection region in the active region, the greater the amplification.

[0006] To allow for such a lasing effect, the photonic device further includes an optical feedback structure such that a resonant cavity for the amplifying medium can be formed. This structure can be produced by a distributed reflector (such as a Bragg grating) provided in the active region or preferably in the waveguide.

[0007] Generally, we are interested in optical radiation having a useful wavelength in the selected application area. Thus, in the telecommunications field, such a wavelength is typically between 1200 nm and 1600 nm. The various elements of the just-proposed photonic device are configured to emit radiation within the selected wavelength range.

[0008] Figure 1 An embodiment of a photonic device according to the prior art is shown. In a thin layer DL (the thin layer is here placed on a support (not shown)), a waveguide 2 made of silicon is formed. The latter extends longitudinally in a plane in the main direction X in the coordinate system (X, Y, Z). Figure 1 of the coordinate system (X, Y, Z) in a plane in the main direction X.

[0009] The waveguide has a profile at the edges (i.e., its profile in a plane perpendicular to the main propagation direction of the guided light). Thus, the waveguide consists of a strip 2a having an extended lateral dimension (in the Y direction) and a rib 2b having a smaller lateral dimension, the rib 2b being provided under the strip 2a and being laterally centered on the strip 2a. The thicknesses (in the Z direction) of the strip 2a and the rib 2b are each about 100 nm, typically between 50 nm and 500 nm. An N-type semiconductor layer 1n is provided on the thin layer DL, covering the waveguide 2. An electrical insulator, such as a silicon oxide layer, can be provided between the waveguide 2 and the N-type semiconductor layer 1n. This layer 1n has a thickness on the order of 100 nm.

[0010] On the N-type semiconductor layer 1n there is an active region QW, and a P-type semiconductor layer 1p is placed on the active region QW. This assembly is arranged to be in contact with the N-type layer 1n and to be aligned with the hybrid portion 2h of the waveguide 2, in particular with the rib 2b of the waveguide 2. The hybrid portion of the waveguide is configured to define a Bragg grating, which defines the optical feedback structure of the device, for example, by lateral corrugations of the waveguide 2 as Figure 1 shown.

[0011] The assembly formed by the active region QW and the P-type semiconductor layer 1p takes the form of a slab whose lateral dimension is smaller than the lateral dimension of the N-type semiconductor layer 1n such that the free portions of the layer 1n provided on both sides of the active region QW are neither covered by the active region QW nor by the P-type semiconductor layer 1p. The active region QW has a relatively small thickness of about 200 nm and extends along the hybrid portion 2h of the waveguide, which can have a longitudinal distance of about 500 microns.

[0012] On the free part of the N-type semiconductor layer 1n, metal pads are provided that are in ohmic contact with this layer, here two vias 3n, 3'n provided on both sides of the active region QW. The metal vias 3n, 3'n provide an electrical connection between the N-type semiconductor layer 1n and the electrical interconnect traces IC suspended above the component. Similarly, a metal pad 3p in the form of another via is in ohmic contact with the P-type semiconductor layer 1p to ensure an electrical connection between this layer and another interconnect trace IC (these traces are not shown in the Figure 1 top view in order to maintain the readability of this view).

[0013] The optical mode M generated by the photon device when current is injected into the active region QW via the P-type semiconductor layer 1p is shown as a dashed line in the Figure 1 cross-sectional view. It can be observed that this mode has a very large extent in the direction perpendicular to the plane (X, Y) defining the waveguide. In order to prevent this mode from intercepting the metal elements of the device, in particular the second metal pad 3p, the thickness of the P-type layer 1p is particularly large, greater than 1 micron and up to several microns. In this way, the metal pads 3n, 3'n, 3p are sufficiently separated from the active region QW, thus avoiding the absorption of light radiation in the metal constituting the pads.

[0014] However, this configuration is not advantageous. It first requires a significant thickness of the material forming the P-type semiconductor layer 1p, which is disadvantageous during the manufacture of the photon device. In fact, the etching of such a significant thickness is long and also produces a high surface topology, which is troublesome for the remaining manufacturing operations, in particular for the formation of the metal pads. In addition, the P-type semiconductor layer 1p, typically formed of InP doped with, for example, approximately 2 E 18 at / cm 3 of zinc, has a particularly high absorption coefficient (especially in the useful wavelength range in the field of optical communication), which is on the order of -40 dB / cm to -70 dB / cm. This factor should be compared with the factor (about -15 dB / cm) of an N-type semiconductor layer of InPN doped with sulfur, for example, at 2 E 18 / cm 3 and with the factor of silicon (about -2 dB / cm).

[0015] Therefore, Figure 1 the structure of the photon device shown is not optimal because, on the one hand, the generated radiation is significantly absorbed in the P-type semiconductor layer 1p and, on the other hand, its manufacture is troublesome when aiming to provide a flat surface.

[0016] To remedy this, the above-mentioned document proposes to provide a lateral dimension extension of the active region QW and the P-type semiconductor layer 1p in the Y direction, which makes it possible to broaden the optical mode generated in this direction and flatten it in the Z direction perpendicular to the plane defining the waveguide 2. For the injection of current and thus the electrical pumping to overlap with the optical mode, this solution requires the presence of a lateral blocking layer provided between the active region QW and the P-type semiconductor layer 1p. The current injection is thus located at the center of the structure because it is laterally blocked by the blocking layer. In this way, the light radiation has a mode that does not extend to the metal forming the metal pad. The drawback of this method is that it requires epitaxial growth to form the P-type semiconductor layer covering the lateral blocking layer. This step is performed at a very high temperature, generating stress in the active region QW, which leads to its degradation.

[0017] An object of the present invention is to provide an alternative to the prior art to remedy the problems caused by the presence of an absolutely thick P-type layer. Summary of the Invention

[0018] To achieve one of these objects, an object of the present invention proposes a photonic device for providing light radiation including an optical mode located in a waveguide, the device comprising:

[0019] - a waveguide extending in a plane along the main propagation direction of the optical mode;

[0020] - an N-type semiconductor layer provided to cover the waveguide;

[0021] - an active region formed by a stack of III-V materials, the active region being provided on and in contact with a portion of the N-type layer aligned with a portion of the waveguide, and another portion of the N-type layer, called the free portion, not being in contact with the active region;

[0022] - a plurality of P-type semiconductor pillars provided on and in contact with the active region, the P-type semiconductor material having a first optical index and the P-type pillars being separated from each other by a wrapping material having a second optical index lower than the first optical index;

[0023] - at least one first metal pad in ohmic contact with the free portion of the N-type layer and at least one second metal pad in ohmic contact with the P-type pillars.

[0024] By forming the P-type layer in the form of a plurality of pillars laterally separated from each other by a cladding material of lower optical index, the optical mode generated by the photonic device can be shaped to prevent it from extending (or limiting the range) in the Z direction perpendicular to the plane in which the waveguide lies, overlapping with the metal pads where it would be strongly absorbed. At the same time, compared with the thickness of the P-type layer of the prior art, the thickness of the P-type pillars can be limited, and a blocking layer is not required. This improves the efficiency of the photonic device.

[0025] According to other advantageous and non-limiting features of the present invention, considered individually or in any technically feasible combination:

[0026] - The waveguide is configured to form an optical feedback structure;

[0027] - The optical feedback structure is a laterally corrugated or longitudinally corrugated Bragg grating;

[0028] - The photonic device includes a component layer made of a dielectric material disposed between the N-type layer and the waveguide;

[0029] - The photonic device includes at least three P-type pillars;

[0030] - At least one of the P-type pillars does not make an ohmic contact with the second metal pad;

[0031] - The cladding material includes air, silica, silicon nitride, or alumina;

[0032] - The P-type pillars have different widths or are laterally separated from each other at different spacings.

[0033] - The P-type pillars are aligned with the lateral centering region of the active region;

[0034] - The P-type pillars have a height of less than 1 micrometer;

[0035] - The active layer has a width between 0.5 micrometers and 5 micrometers;

[0036] - The photonic device includes two first metal pads disposed on both sides of the active region QW;

[0037] - The active region includes a breakdown region disposed between two P-type pillars. Description of the Drawings

[0038] Other features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings, in which:

[0039] - Figure 1 A prior art photonic device is shown;

[0040] - Figure 2Shows a first embodiment of a photonic device DP according to the present invention;

[0041] - Figures 3a to 3c Shows three simulation architectures of the photonic device so that the advantages of the photonic device according to the present invention become apparent.

[0042] - Figure 4 Shows the absorption losses in the metal pads of the three simulation architectures according to the thickness of the P-type semiconductor material.

[0043] - Figure 5 Shows a summary of the results of simulations carried out within the framework of the preparation of the present invention.

[0044] - Figure 6 and Figure 7 Shows other embodiments of the photonic device according to the present invention. Detailed Description

[0045] To simplify the following description, the same reference numerals are used for the same elements or for elements that perform the same functions in the prior art or in different embodiments of the described photonic device.

[0046] Figure 2 Shows a first embodiment of the photonic device DP according to the present specification.

[0047] In a substrate S, which may be a silicon-on-insulator type substrate, there is a silicon waveguide 2 provided in a thin layer DL of the substrate S. The waveguide 2 extends longitudinally along the main direction ( Figure 2 the X direction in Figure 2 ), for example to guide light to other components of the photonic device 1, such as a modulator. In the

[0048] example, the waveguide 2 includes a strip 2a. It has a maximum width (in the Y direction, transverse to the main direction) that can be between 2 and 500 microns. The shown waveguide also includes a rib 2b, which is laterally centered on the strip 2a and extends from one end of the strip 2a to the other end in the main direction. The width of the rib 2b can be between 0.05 microns and 20 microns. The waveguide has a thickness (in the Z direction) that can be between 5 nm and 5 microns. Figure 2 In this example, the combination of the strip 2a and the rib 2b constitutes the waveguide 2, the profile of which is an edge. It is constructed in a manner known per se to form an optical feedback structure. As can be seen from the

[0049] The waveguide 2 is embedded in a dielectric material which is typically silica, and the optical confinement in the waveguide 2 is obtained from the difference in optical index between the silicon of the waveguide 2 and the dielectric material having an optical index lower than that of silicon. The assembly composed of this dielectric and the waveguide 2 forms a thin layer DL of the substrate S.

[0050] Of course, the present invention is in no way limited to Figure 2 the waveguide 2 having the shape shown, which may have a profile different from that given here by way of example. The substrate S does not have to be of the silicon-on-insulator type either, although the use of such a substrate greatly facilitates the fabrication of the waveguide 2. The waveguide 2 does not have to be made of silicon either. For example, it is conceivable that the waveguide 2 is formed of silicon nitride deposited on a silicon substrate having a surface oxide layer, and this nitride waveguide is encapsulated by a deposited silicon oxide layer. Thus, the waveguide does not have to be entirely encapsulated by a dielectric material, and the thin layer DL may have a surface topology which results in the formation of cavities in the structure when complementing the photon device DP, as is the case, for example, in document US8110823.

[0051] Continuing with the description Figure 2 of the embodiment, the top of the waveguide 2 is an emission structure constituted by an active region QW sandwiched between an N-type semiconductor material layer 1n and a P-type semiconductor material layer 1p.

[0052] More specifically, Figure 2 the photon device includes an N-type semiconductor layer 1n arranged to overlap the waveguide 2, that is to say, extending transversely on both sides of the waveguide over at least a part of its length. It has a width which is typically between 20 micrometers and 200 micrometers (along the Y direction). When the waveguide 2 is made of silicon, the N-type semiconductor layer may be formed of InP doped with sulfur, and it may have a thickness which is typically between 50 nm and 500 nm. The N-type semiconductor layer 1n may be in direct contact with the waveguide 2, and more generally with the thin layer DL, or as Figure 2 in the case of

[0053] a component layer BL may be provided between the thin layer DL and the N-type semiconductor layer 1n. This component layer is preferably thin, with a thickness between a few nanometers and 150 nm.

[0054] On the N-type layer 1n there is an active region QW formed by a stack of III-V materials. The active region QW is only provided on and in contact with the part of the N-type layer 1n which is aligned with the longitudinal part 2h (referred to as the hybrid part) of the waveguide 2. Thus, the so-called "free" part of the N-type layer 1n is not in contact with the active layer QW, and this free part (transversely arranged here on both sides of the active region QW) can be used to form ohmic contacts.

[0055] The active region QW has a thickness generally included between 10 nm and 500 nm, typically on the order of 50 nm, and extends along the hybrid portion 2h of the waveguide 2 over a length generally included between 100 microns and 2000 microns. Its width can be between 0.5 microns and 30 microns, for example equal to 5 microns.

[0056] The photonic device DP according to the present specification also includes at least one first metal pad in contact with the free portion of the N-type layer 1n. In the example shown, two through-holes 3n, 3'n filled with a metallic material (such as tungsten) are provided on either side of the active layer QW. These metal through-holes ensure the electrical connection between the N-type layer 1n and the interconnecting traces IC of the photonic device DP (the traces are not shown in the Figure 2 top view so as to preserve the readability of this view).

[0057] Finally, Figure 2 the photonic device DP of includes a plurality of pillars made of a P-type semiconductor material 1p provided on and in contact with the active region QW. In the remainder of the present specification, these pillars will be denoted by the expression "P-type pillars", it being understood that they are made of semiconductor material in all cases. Thus, the figure shows a first P-type pillar 1p and a second P-type pillar 1'p, the first P-type pillar 1p being made of P-doped InP provided along the first side of the active region QW and the second P-type pillar 1'p being provided along the other side of this region. The lower surfaces of these pillars 1p, 1'p are in contact with the active region QW and the upper surfaces are in ohmic contact with second metal pads 3p, 3'p respectively. The P-type pillars 1p, 1'p are separated from one another by a cladding material having an optical index lower than that of the semiconductor material forming the pillars. Thus, the cladding material can be a dielectric material based on silicon oxide, silicon nitride, a polymer dielectric based on benzocyclobutene, or even air. In all cases, the semiconductor material forming the P-type pillars has a first optical index while the cladding material separating the P-type pillars has a second index lower than the first index.

[0058] This arrangement in the P-type pillars makes it possible to shape the optical mode generated by the photonic device so as to prevent it from extending (or to limit its extent) in the Z direction perpendicular to the plane in which the waveguide 2 lies.

[0059] The P-type pillars 1p and 1'p extend over the entire length of the active region QW, or at least over the major part of this length. The width Wb of each pillar and the spacing e between each of the pillars 1p, 1'p of course depend on the width of the active layer QW and the number of pillars. The width of the pillars or the spacing between two pillars do not have to be the same. By way of example, and depending on the width of the active region QW in which they are located, the width Wb of the pillars can be between 0.5 microns and 3 microns and the spacing e between two pillars can be between 0.1 microns and 2 microns.

[0060] As already mentioned, the N-type layer 1n, the active region QW, and the P-type pillars 1p are embedded in a cladding material, typically silicon oxide. The first and second metal pads are provided in this material to electrically connect the respective components to electrical interconnect traces IC provided on the cladding material and suspended above the assembly.

[0061] Figure 2 The optical mode M generated in a hybrid manner in the active layer QW and the waveguide 2 in the shown photonic device DP is shown by a dashed line in the cross-section of this figure. The plurality of P-type pillars 1p, 1'p enable shaping of the optical mode M such that the optical mode Figure 2 extends laterally in a preferential manner in the Y direction and is prevented from extending in the Z direction perpendicular to the plane in which the active region QW is located. This reduces the risk of the optical mode covering metal regions, in particular the metal pads 3p, 3'p in ohmic contact with the P-type pillars 1p, 1'p.

[0062] Typically, the number of P-type pillars, the width Wb of these pillars, and the spacing e between two P-type pillars are adapted to the width of the waveguide 2. They are selected to shape the hybrid optical mode such that the optical mode extends laterally.

[0063] Thus, the height of these pillars 1p, 1'p can be reduced compared to the thickness of 1 or 2 microns or more encountered in prior art devices. This feature is particularly advantageous since the P-type semiconductor material forming these pillars has a particularly high optical absorption coefficient. Since the structure does not have any blocking layer, the formation of these pillars is easily achieved, does not require an epitaxial recovery step, and it is easy to provide a photonic device with a flat surface. As will become apparent from the results presented in the next part of this specification, P-type pillars 1p, 1'p with a height less than 1 micron, or even 500 nm, or 300 nm can be formed while limiting the absorption loss in the metal pads to below 0.1 dB.

[0064] To show all the benefits obtained by replacing the continuous P-type layer of the prior art with a plurality of P-type pillars 1p, 1'p separated by a cladding material of lower index, the applicant continued the simulation of the structures in Figures 3a to 3c the plurality of structures DP1, DP2, DP3 shown.

[0065] Figure 3a The first structure DP1 corresponds to a prior art photonic device formed based on InP. The active layer QW extends over a width of 3 microns. A continuous P-type InP layer 1p centered on the active layer and aligned with the rib of the waveguide 2 has a width of 2 microns. The layer has a thickness of 1 micron and is covered by a metal pad 3p of 500 nm. The component layer BL is placed between the N-type layer 1n and the waveguide 2.

[0066] Figure 3bThe second structure DP2 is according to the present invention. The active region QW is 2 micrometers wide and is suspended over the rib of waveguide 2. In this second structure DP2, two P-type pillars 1p made of P-doped InP are also provided, each P-type pillar having a width Wb of 0.5 micrometers and spaced a distance e of 0.5 micrometers apart. The P-type pillars are each disposed 0.25 micrometers from the edge of the active layer QW. The two P-type pillars 1p of this second structure have a height of 500 nm.

[0067] Figure 3c The third structure DP3 is also according to the present invention and is similar in structure to the second structure DP2, but this time four P-type pillars made of P-doped InP are provided, each P-type pillar having a width of 0.25 micrometers. Spaced a distance e of 0.25 micrometers apart from each other. The four P-type pillars of this third structure DP3 have a height of 250 nm.

[0068] For each of these structures, the overlap of the generated optical mode M with the various elements (waveguide 2, active region QW, P-type layer or pillar 1p) constituting the structure is measured by simulation. The following table summarizes the results obtained.

[0069] [Table 1]

[0070]

[0071] It can be observed that by introducing pillars separated by encapsulating material into the structure of the device, the increased portion of mode M can be restricted to waveguide 2 and active region QW. At the same time, the confinement of this radiation by the P-type semiconductor material forming the continuous layer of the first structure DP1 or the P-type pillars of the second structure DP2 and the third structure DP3 is restricted. Remember that P-doped InP has an optical radiation absorption factor of approximately 50 dB / cm, the active region QW has an absorption factor of approximately 15 dB / cm when formed of InN, and the silicon waveguide has a factor of approximately 2 dB / cm. Therefore, restricting the coverage of the generated radiation by the P-type semiconductor material is highly advantageous, as observed when this material is constructed in the form of pillars.

[0072] In a second series of simulations, for each of the three structures DP1, DP2, DP3, the height of the P-doped InP pillars 1p is changed. Then the absorption loss in the metal pad 3p suspended over the P-doped semiconductor material is estimated as a function of this thickness. Figure 4The figure therein shows these results. The thickness (nm) of the P-type semiconductor material of the pillar 1p forming the first structure DP1 or the P-type pillar 1p of the second structure DP2 and the third structure DP3 is arranged along the x-axis of the figure. The y-axis represents the absorption loss (in dB) in the metal pads 3p of these structures. It is observed on this figure that in order to reduce these losses to a level below 0.1 dB in a conventional structure such as the first DP1 structure, a thickness greater than 1 micron must be provided for the P-type layer 1p, as reported in the prior art. For the structures DP2, DP3 according to the present invention, when two P-type pillars 1p are provided as in the second structure DP2, the thickness of this semiconductor material can be reduced to less than 650 nm, and when four P-type pillars 1p are provided as in the case of the third structure DP3, this thickness can be reduced to less than 300 nm.

[0073] Finally, Figure 5 shows a summary of the simulation results that have been performed, and for Figures 3a to 3b each of the three structures DP1, DP2, DP3 shown, the absorption losses are compared. As Figure 5 shown, each of the structures DP1, DP2, DP3 has a P-type semiconductor material of sufficient thickness to limit the absorption loss in the metal pads 3p, so that for each of these structures, these losses are limited to well below 1 dB / cm. In the case of the first structure DP1 where the generated optical mode extends widely in the relatively thick P-type material, the absorption loss in this material is close to 10 dB / cm. This is not the case in the second structure DP2 and the third structure DP3, where the extension of the optical mode and the reduced thickness of the P-type semiconductor material in the pillar 1p limit the absorption loss in this material to less than 5 dB / cm.

[0074] When we observe Figure 5 the total losses shown, we measure all the advantages of the present invention.

[0075] Without departing from the scope of this specification, many variations can be made to Figure 2 the embodiments shown. Thus, as has been noted in connection with the presentation of the simulation results, it can be advantageous to provide more than two P-type pillars 1p, 1'p. Thus, we can provide any number of P-type pillars 1p, even or odd, such as 3, 4, 5 or more. It is advantageous to arrange the P-type pillars substantially centered along the Y direction on the active region QW. This promotes the dissipation of heat through heat conduction in the pillars, which is significantly generated in this central region of the active region QW. For example, this can be achieved by selecting an odd number of P-type pillars 1p and then aligning one of the pillars with this central region. This configuration is Figure 7 the configuration shown in the example of, but of course other configurations are also possible.

[0076] As already described, the pillars can have a variable width Wb and a spacing e therebetween. When at least 3 P-type pillars 1p are provided, it is also conceivable that only a plurality of these pillars 1p are in electrical contact with at least one second metal pad, while the remaining P-type pillars 1p are not electrically connected to the interconnect trace IC. By providing pillars that are not electrically connected and made of semiconductor material embedded in the encapsulating material, it helps to confine and shape the optical mode M so that the optical mode spreads laterally.

[0077] Figure 6 Thus, a cross-sectional view of a photonic device DP' having 4 P-type pillars 1p is shown. The outer P-type pillars are not connected to the second metal pad 3p and thus not connected to the interconnect trace IC. The distance e between the middle P-type pillars is greater than the distance e' between the outer pillars and the middle pillars.

[0078] Generally, conventional simulation devices can be used to determine the geometric parameters, their number, and their relative positions of the plurality of P-type pillars to impart a suitable shape to the optical mode.

[0079] It is also conceivable to flip the setting of the waveguide 2 relative to Figure 2 as in the case of the photonic device DP' shown in Figure 6 In this configuration, the strip 2a is disposed between the N-type layer 1n and the rib 2b. Figure 6 The component layer BL of the photonic device DP' of

[0080] To help confine and shape the optical mode so that it mainly extends laterally, it is conceivable to disrupt a part of the active region QW, especially the part of the region QW that is not covered by the P-type pillars 1p, to make it optically inert. This disruption of the crystal structure of the active region QW can be achieved by implanting heavy substances such as silicon.

[0081] The method for manufacturing the photonic devices DP, DP' according to the various embodiments just proposed is very similar to the methods of the prior art.

[0082] First, the waveguide 2 is formed in the substrate in a completely conventional manner by etching, deposition, oxidation, etc. This step can include transferring the waveguide 2 from the starting substrate to the substrate S, and then the substrate S will be used to form the photonic device. Alternatively, the waveguide 2 can be directly formed in the substrate S.

[0083] Transfer the label covering the waveguide 2 onto the substrate S where the waveguide 2 is located, and the label includes a stack formed by an N-type semiconductor layer, an active layer, and a P-type semiconductor layer. This label is used to form the emission structure of the photonic device. Thus, the thickness of this P-type semiconductor layer is substantially equal to the thickness of the P-type pillars of the target photonic device, for example, less than 1 micron, or less than 500 nm. Generally, the label has a small thickness of less than 2 microns.

[0084] The label forms slabs of these stacks and is disposed on the substrate S overlapping the waveguide 2, and the N-type semiconductor layer is disposed on the side of the waveguide 2. The component layer BL can be disposed between the waveguide 2 and the N-type semiconductor layer.

[0085] In a subsequent local etching step, the label is processed to precisely define the emission structure. To this end, a part of the P-type semiconductor layer is removed to form the P-type pillar 1p and expose the active layer. The sides of this layer are removed to define the active region QW and expose at least one free part of the N-type semiconductor layer. This free part can also be partially removed to form the N-type layer according to the final dimensions.

[0086] Then the component is encapsulated by depositing an encapsulating material, and then the encapsulating material is made flat, for example, using a mechanical-chemical polishing step. It should be noted that since the label initially has a relatively small thickness, the local etching steps are performed very quickly, the surface topology after these steps is small, reducing the thickness of the encapsulating material required to cover the emission structure and facilitating the polishing step aimed at making the final surface flat.

[0087] In a complementary step of the method for manufacturing a photonic device, depressions are generated by etching in the encapsulating material filled with a metal material to generate a first metal pad and a second metal pad that are in ohmic contact with the free part of the N-type layer 1n and with at least some of the P-type pillars 1p.

[0088] Of course, the present invention is not limited to the described embodiments, and different embodiments can be added without departing from the scope of the present invention defined by the claims.

[0089] Thus, although P-type semiconductor pillars completely separated from each other by an encapsulating material having a lower optical index have been presented here, this does not have to always be the case. Thus, it is conceivable that at least some of the P-type pillars are fixed to the pillars adjacent to them at the foot level only on a part of their height. In all cases, the P-type semiconductor material layer of the label is constructed on the waveguide to process the shape of the generated optical mode such that the optical mode extends preferentially in the transverse direction, as presented in detail in this specification.

Claims

1. A photonic device (DP, DP'), the photonic device being configured to provide optical radiation including an optical mode located in a waveguide, the device comprising: - a waveguide (2), the waveguide extending in a plane along a main propagation direction of the optical mode; - an N-type semiconductor layer (1n), the N-type semiconductor layer being arranged to cover the waveguide (2); - an active region (QW), the active region being formed by a stack made of III-V materials, the active region (QW) being arranged on and in contact with a portion of the N-type semiconductor layer (1n) that is aligned with a portion (2h) of the waveguide, another portion of the N-type semiconductor layer, referred to as the free portion, not being in contact with the active region (QW); - a plurality of P-type semiconductor pillars (1p, 1'p), the plurality of P-type semiconductor pillars being arranged on and in contact with the active region (QW), the semiconductor material of the plurality of P-type semiconductor pillars (1p, 1'p) having a first optical index and the plurality of P-type semiconductor pillars (1p, 1'p) being separated from each other by a cladding material having a second optical index lower than the first optical index; - at least one first metal pad (3n, 3'n) in ohmic contact with the free portion of the N-type semiconductor layer (1n) and at least one second metal pad (3p, 3'p) in ohmic contact with the plurality of P-type semiconductor pillars (1p, 1'p).

2. The photonic device (DP, DP') according to claim 1, wherein, the waveguide (2) is configured to form an optical feedback structure.

3. The photonic device (DP, DP') according to claim 2, wherein, the optical feedback structure is a lateral corrugation or a vertical corrugation Bragg grating.

4. The photonic device (DP, DP') according to claim 1, the photonic device comprising a component layer (BL) made of a dielectric material arranged between the N-type semiconductor layer (1n) and the waveguide (2).

5. The photonic device (DP, DP') according to claim 1, the photonic device comprising at least three P-type semiconductor pillars (1p, 1'p).

6. The photonic device (DP, DP') according to claim 5, wherein, at least one of the plurality of P-type semiconductor pillars (1p, 1'p) is not in ohmic contact with the second metal pad (3p, 3'p).

7. The photonic device (DP, DP') according to claim 1, wherein, the cladding material includes air, silica, silicon nitride, or alumina.

8. The photonic device (DP, DP') according to claim 1, wherein, the plurality of P-type semiconductor pillars have different widths or are laterally separated from each other at different spacings.

9. The photonic device (DP, DP') according to claim 1, wherein, the P-type semiconductor pillars (1p, 1'p) are arranged in alignment with a laterally centered region of the active region (QW).

10. The photonic device (DP, DP') according to claim 1, wherein, The plurality of P-type semiconductor pillars (1p, 1'p) have a height of less than 1 micrometer.

11. The photonic device (DP, DP') according to claim 1, wherein, the active region (QW) has a width between 0.5 micrometer and 5 micrometers.

12. The photonic device (DP, DP') according to claim 1, the photonic device comprising two first metal pads (3n, 3'n) disposed on both sides of the active region (QW).

13. The photonic device (DP, DP') according to claim 1, wherein, the active region (QW) includes a breakdown region disposed between two P-type semiconductor pillars (1p, 1'p).

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