Semiconductor structure for forming a vertical cavity laser diode

Abstract

The present invention provides a stack of semiconductor layers based on III-V components defining an upper Bragg mirror arranged on an active layer constituted by at least one quantum well enabling laser emission at a defined wavelength, said active layer being arranged on a lower Bragg mirror, the stack being designed so that the laser emission leaves the stack via the lower Bragg mirror; a semiconductor contact film disposed directly below the bottom Bragg mirror, the semiconductor contact film having a first thickness and a first complex refractive index n1′=n1+i.k1; a semi-insulating gallium arsenide support substrate; an oxide layer in contact with the front surface of the support substrate and disposed between the front surface and the contact film, the oxide layer having a second thickness and a second complex refractive index n2′=n2+i.k2; The present invention relates to a semiconductor structure for forming a vertical cavity laser diode, comprising:

Description

FIELD OF THE INVENTION

[0001] The field of the invention is that of semiconductors, in particular that of optoelectronics. The invention relates to semiconductor structures forming one or more vertical cavity laser diodes. Technical background of the invention

[0002] Vertical-cavity surface-emitting lasers (VCSELs) are increasingly being developed for emerging mass-market applications, particularly in face recognition in the mobile phone sector, and LIDAR ("light detection and ranging") remote sensing for the automotive industry.

[0003] The VCSEL 100 is fabricated by successive epitaxial growth from a stack of III-V semiconductor layers (FIG. 1). The composition, doping, and thickness of each layer are precisely controlled to form, on the one hand, the active region 2, composed of one or more quantum wells in which a laser beam can be generated, and, on the other hand, two Bragg mirrors 3a, 3b, composed of alternating layers of high and low refractive index, that sandwich the active region 2.

[0004] As shown in FIG. 1 , it is known to form a layer stack for a VCSEL 100 on a bulk substrate 1, which is made of, for example, gallium arsenide (GaAs) for laser wavelengths between 650 nm and 1300 nm, or indium phosphide (InP) for laser wavelengths between 1300 nm and 2000 nm. The bulk substrate 1 must be of excellent quality to ensure the epitaxy seed function and the quality of the layer stack. However, if the VCSEL(s) are intended to emit through the backside, i.e., if the laser beam passes through the bulk substrate 1, a problem arises: signal absorption by the substrate 1. For example, to fabricate a layer stack for a VCSEL 100, an n-type GaAs substrate is conventionally used as the bulk substrate 1. However, this type of substrate has too much absorption in the laser emission wavelength range (typically 0.5 μm to 1.5 μm) to ensure a high performance level of the VCSEL 100.

[0005] To address this problem, document WO 2021 / 125005 proposes performing a transfer of layer(s) from the bulk substrate 1 to a support substrate whose properties are more suited to the radiation constraints on the back surface of the VCSEL 100.

[0006] To perform the layer transfer, an assembly step is required. The assembly must be able to maintain the quality of the transferred layer(s), and the assembly must also avoid disturbing the operation of the VCSEL 100.

[0007] The present invention proposes a solution that simplifies and increases the reliability of the manufacture of vertical cavity laser diodes (VCSELs). In particular, the present invention relates to a semiconductor structure comprising a semi-insulating support substrate made of gallium arsenide, on which there is present a stack of semiconductor layers based on III-V components that define a lower Bragg mirror, an active laser layer, and an upper Bragg mirror. The semiconductor contact films and oxide layers interposed between the stack of layers and the support substrate have specific characteristics in terms of thickness and optical absorption in order to provide the laser diode with a high level of performance while ensuring a simple and robust manufacture of the semiconductor structure. BRIEF DESCRIPTION OF THE INVENTION

[0008] The present invention provides a stack of semiconductor layers based on III-V components defining an upper Bragg mirror arranged on an active layer constituted by at least one quantum well enabling laser emission at a defined wavelength, said active layer being arranged on a lower Bragg mirror, the stack being designed so that the laser emission leaves the stack of semiconductor layers via the lower Bragg mirror; a semiconductor contact film disposed directly below the bottom Bragg mirror, the semiconductor contact film having a first thickness and a first complex refractive index known as n1′=n1+i.k1, where n1 is the first refractive index and k1 is a first extinction coefficient for a defined wavelength; a semi-insulating gallium arsenide support substrate having a front surface and a back surface; an oxide layer in contact with the front surface of the support substrate and disposed between said front surface and the contact film, said oxide layer having a second thickness and a second complex refractive index known as n2'=n2+i.k2, where n2 is the second refractive index and k2 is a second extinction coefficient for a defined wavelength; The present invention relates to a semiconductor structure for forming one or more vertical cavity laser diodes, comprising:

[0009] The semiconductor structure comprises: the oxide layer is in direct contact with the contact film opposite the bottom Bragg mirror; the first damping coefficient and the second damping coefficient are equal to or less than 1; the first thickness and the second thickness are defined by h1=m1*λ / (4n1) and h2=m2*λ / (4n2), respectively, where m1 and m2 are integers; It stands out in this respect.

[0010] According to advantageous characteristics of the invention, taken alone or according to any combination that can be made, the first damping coefficient and the second damping coefficient are 0.1 or less, the contact layer and the oxide layer have an extinction coefficient of 1 or less, preferably 0.1 or less, in the wavelength range of 0.5 μm to 2 μm; the oxide layer is formed of silicon oxide, glass, or zinc oxide; the lower Bragg mirror comprises fewer than seven alternating layers of gallium arsenide and aluminum arsenide for wavelengths λ between 800 μm and 950 μm; the semiconductor structure includes a direct bond interface between the oxide layer and the contact film; the semiconductor structure includes a direct bond interface between the oxide layer and the supporting substrate; The semiconductor structure includes a direct adhesive interface to the oxide layer.

[0011] The present invention also relates to a method for manufacturing the above-described semiconductor structure.

[0012] According to a first variant, the manufacturing method comprises the following steps: - fabricating a stack of semiconductor layers on an initial substrate provided with a layer of van der Waals material in the following order: an upper Bragg mirror formed on the layer of van der Waals material, an active layer formed on the upper Bragg mirror, and a lower Bragg mirror formed on the active layer; fabricating a contact film on the bottom Bragg mirror, thereby forming a donor structure comprising an initial substrate, a layer of van der Waals material, a stack of semiconductor layers, and a contact film; forming all or part of an oxide layer on the contact film and / or the supporting substrate; assembling by direct bonding of the donor structure to a support substrate along a bonding interface that includes a surface of or is included in the oxide layer; separating at least one layer of van der Waals material to produce a semiconductor structure; Includes:

[0013] According to a second variant, the manufacturing method comprises the following steps: - fabricating a contact film on the initial substrate, thereby forming a donor structure; forming all or part of an oxide layer on the contact film and / or the supporting substrate; assembling by direct bonding of the donor structure to a support substrate along a bonding interface that includes a surface of or is included in the oxide layer; removing at least a portion of the initial substrate to create a free surface for the contact film; fabricating a stack of semiconductor layers on a free surface of the contact film in the following order: a lower Bragg mirror disposed on the contact film, an active layer disposed on the lower Bragg mirror, and an upper Bragg mirror disposed on the active layer; Includes:

[0014] Advantageously, the removing step comprises separating along an embedded plane of weakness parallel to the bond interface and recovering some or all of the initial substrate.

[0015] Other features and advantages of the present invention will become apparent from the following detailed description, which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B illustrate semiconductor structures for fabricating a VCSEL according to the prior art. [Figure 2a] 1 illustrates a semiconductor structure according to the present invention; [Figure 2b] 1 illustrates a semiconductor structure according to the present invention; [Figure 3a]1 is a table of contact film thicknesses for an example semiconductor structure according to the present invention. [Figure 3b] 1 is a table of oxide layer thicknesses for an example semiconductor structure in accordance with the present invention. [Figure 4a] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a first variant embodiment of the invention; [Figure 4b] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a first variant embodiment of the invention; [Figure 4c] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a first variant embodiment of the invention; [Figure 4d] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a first variant embodiment of the invention; [Figure 4e] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a first variant embodiment of the invention; [Figure 4f] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a first variant embodiment of the invention; [Figure 5a] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the invention; [Figure 5b] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the invention; [Figure 5c] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the invention; [Figure 5ca] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the invention; [Figure 5d] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the invention; [Figure 5e] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the invention; [Figure 5f] 5A-5C are steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the invention; [Figure 6]1 is a graph showing the reflectivity as a function of the number of alternating layers of gallium arsenide and aluminum arsenide for a prior art Bragg mirror and for the lower Bragg mirror of a semiconductor structure according to the present invention.

[0017] Certain figures are schematic and not to scale for clarity, in particular the layer thicknesses along the z-axis are not to scale relative to the lateral dimensions along the x- and y-axes.

[0018] In the figures, the same reference numerals may be used to refer to elements of the same nature.

[0019] The present invention relates to a semiconductor structure 150 specifically designed for optoelectronic applications to form one or more vertical cavity laser diodes.

[0020] The semiconductor structure 150 may be in the form of a small plate, for example 50 mm to 200 mm in diameter, where the semiconductor structure is designed to accommodate multiple optoelectronic components (VCSELs) that can then be singulated, or the semiconductor structure may be in the form of a smaller sized vignette that accommodates a single optoelectronic component or group of components.

[0021] As shown in FIG. 2a, the structure 150 includes a stack E of semiconductor layers based on III-V components, which defines an upper Bragg mirror 30b, an active layer 20 composed of at least one quantum well that enables laser emission at a defined wavelength λ, and a lower Bragg mirror 30a. The active layer 20 has two faces: one in contact with the upper Bragg mirror 30b and the other in contact with the lower Bragg mirror 30a. The terms "upper" and "lower" of the Bragg mirrors 30a, 30b of the stack E are used with reference to the reference system (x, y, z) shown in FIG. 2a, where the z-axis direction indicates "upward." According to the z-axis, the reference mirror 30a is at a lower level in the structure 150, and the reference mirror 30b is at a higher level. These terms are also used with reference to mirrors designed to emit laser radiation having a wavelength λ. This is so-called backside emission, i.e., the laser wave exits through the lower Bragg mirror 30a, i.e., the mirror closest to the support substrate 10, which will be described later.

[0022] The layers 30b, 20, 30a of the stack E, and generally the layers or substrates described below, extend parallel to the major plane (x, y) and have a thickness along the z axis.

[0023] As is already known, the active layer 20 can be made of gallium arsenide (GaAs) and / or its ternary or quaternary compounds (e.g., AlGaAs, InGaAsN, etc.), or the active layer 20 can be made of indium phosphide (InP) and / or its ternary or quaternary compounds (e.g., InAsP, GaAlInP, etc.). Bragg mirrors, constituted by alternating layers of low and high refractive index, are also known multilayers that can be made of gallium arsenide (GaAs), aluminum arsenide (AlAs) and their compounds, or of indium phosphide (InP) and its compounds, depending on the nature of the active layer 20. It should be remembered that, in practice, the stack E is produced by epitaxy, so that materials with perfectly matched lattice constants and chemical properties must be used.

[0024] The thickness of the stack E can be 1 to 15 μm.

[0025] As mentioned above, the semiconductor structure 150 comprises a support substrate 10 made of semi-insulating gallium arsenide, transparent at the wavelength of the laser, and having a front surface 10' and a back surface 10''. A stack of layers E is arranged on the front surface 10'. Laser radiation having a wavelength λ is designed to exit through the back surface 10'' of said substrate 10. Semi-insulating gallium arsenide, with its high level of optical transparency, has low absorption of the laser wave, which is a prerequisite for the high performance function of VCSELs. Its thickness is, for example, between 200 and 2,000 μm.

[0026] The structure 150 also includes a semiconductor contact film 40 disposed directly below and in contact with the lower Bragg mirror 30a of the stack E. The contact film 40 has a first thickness h1 and a first complex refractive index n1′, known as n1′=n1+i.k1, where n1 is the first refractive index and k1 is a first extinction coefficient for wavelength λ.

[0027] Finally, the structure 150 comprises an oxide layer 50 arranged on one side in contact with the front surface 10' of the support substrate 10 and on the other side in contact with the contact film 40. As will be described below with reference to the method for manufacturing the structure 150, the oxide layer 50 offers great advantages in the assembly step, since its surface treatment is easy and proven and this type of layer ensures excellent quality of direct bonding (low level of defects and high energy) (without additional adhesive materials). The material of the oxide layer 50 is advantageously amorphous in order to limit the stress fields associated with the addition of two materials with misaligned crystalline networks and / or different lattice constants, as well as to avoid the formation of nanobubbles at the bonding interface.

[0028] The oxide layer 50 has a second thickness h2 and a second complex refractive index n2', known as n2'=n2+i.k2, where n2 is the second refractive index and k2 is the second extinction coefficient for wavelength λ.

[0029] The materials of the contact film 40 and the oxide layer 50 are selected so that the first and second attenuation coefficients k1 and k2 are less than 10, less than 1, or less than 0.1 (relative to the wavelength λ). Advantageously, the attenuation coefficients of the contact film 40 and the oxide layer 50 are less than 10, less than 1, or less than 0.1 in the wavelength range [0.5 μm to 2 μm]. These attenuation coefficients are selected to be as close to zero as possible (at least at the wavelength λ) in order to minimize attenuation of the optical signals designed to pass through said layers 40, 50.

[0030] In particular, the contact film 40 can be made of n-type or p-type GaAs to function as an electrical contact layer, the contact film 40 then having an extinction coefficient k1 equal to 0 at a wavelength λ of 940 nm. In the wavelength range λ=1.55 μm, the contact film 40 can be made of n-type or p-type InP for an InP-based stack.

[0031] The oxide layer 50 is partially made of silicon oxide (SiO x , SiO2), and its extinction coefficient k2 is 1.1 10 at λ = 940 nm. -3 Other materials are zinc oxide (k2=7.10 for λ=0.94 μm) -3 , and k2=2.10 for λ=1.55μm -3 ) or glass, etc.

[0032] It will be understood that the examples of materials provided for the contact film 40 and oxide layer 50 are not exhaustive.

[0033] Furthermore, according to the present invention, the first thickness h1 and the second thickness h2 of the contact layer 40 and the oxide layer 50, respectively, are h1=m1*λ / (4n1), and h2=m2*λ / (4n2), wherein m1 and m2 are integers which may be the same or different.

[0034] These thickness rules applied to the two layers 40, 50 interposed between the lower Bragg mirror 30a and the support substrate 10 allow the contact film 40 and the oxide layer 50 to be integrated into the layers of the mirror 30a. This offers the advantage, firstly, that the laser radiation is not disturbed, since the wave, in fact, only encounters the Bragg mirror before entering and passing through the support substrate 10, and not any intervening disturbing layers. Secondly, the number of layers required to manufacture the lower Bragg mirror 30a can be reduced, since the contact film 40 and the adhesive layer 50 are involved in the reflection of the laser wave.

[0035] For example, the bottom Bragg mirror 30a can include fewer than 7 alternating layers (GaAs / AlAs) instead of 13 to achieve 95% reflectivity (FIG. 6). By way of another example, the bottom Bragg mirror 30a formed from InP and / or its compounds can include fewer than 10 alternating layers instead of more than 30 to achieve 95% reflectivity.

[0036] While design rules relating thickness to wavelength and refractive index ratio are conventionally applied to the layers forming a Bragg mirror, the prior art does not anticipate applying these same rules to the layers below the bottom mirror. Indeed, in contrast to the layers that make up the Bragg mirror, these layers are conventionally selected to have no refractive index contrast and therefore do not contribute to the reflection of light.

[0037] For example, in the case of a stack E based on GaAs or its compounds (laser wavelength λ=940 nm) with a contact film 40 made of n-type GaAs and an oxide layer 50 made of SiO2, The thickness h1 of the contact film 40 can be selected from the thicknesses shown in the table of Figure 3a. Recall that the refractive index n1 is 3.5060 for λ = 940 nm. The thickness h2 of the oxide layer 50 can be chosen from the thicknesses shown in the table of Figure 3b. Recall that the refractive index n2 is 1.4512 for λ = 940 nm.

[0038] The semiconductor structure 150 according to the present invention is therefore particularly suitable for forming very good quality vertical cavity laser diodes (VCSELs) because of the simplified and reliable assembly steps (necessary to perform the transfer of the useful layers to the support substrate 10) and because the laser wave is not disturbed after it leaves the bottom Bragg mirror 30a.

[0039] The semiconductor structure 150 according to the invention also comprises a direct bonding interface 60 extending in a major plane (x, y), said interface 60 being contained in the oxide layer 50 or being adjacent to the oxide layer 50. The bonding interface 60 can also be located between the oxide layer 50 and the contact film 40, between the oxide layer 50 and the support substrate 10, or in the oxide layer 50.

[0040] "Direct bonding" means bonding based on molecular adhesion between the assembled surfaces without the need for adhesive materials. There are many types of direct bonding, which differ in particular in the temperature conditions, pressure conditions, atmosphere, or treatments performed before bringing the surfaces into contact. Reference can be made to molecular bonding at ambient temperature with or without prior plasma activation of the surfaces to be assembled, atomic diffusion bonding (ADB), or surface activated bonding (SAB), etc.

[0041] The oxide layer 50, which is particularly preferred for bonding, can be chosen to be thicker or thinner depending on the requirements, as long as its thickness h2 complies with the rules relating it to the ratio of the wavelength λ and the refractive index n2 of said layer 50. This provides flexibility in carrying out assembly steps, which are often easier if the oxide layer thickness is 150 nm or more.

[0042] 2b shows a semiconductor structure 150 according to the invention, which has undergone additional steps for producing an optoelectronic component (VCSEL): a second contact film 41 is formed on the upper Bragg mirror 30b, electrical contacts 80, 81 are formed on each of the two contact films 40, 41, and a dielectric layer 90 is provided around the stack E for electrical insulation. These steps are known and will not be further described here.

[0043] The method for manufacturing the semiconductor structure 150 is based on the techniques of layer transfer by adhesion and thinning according to the prior art. In particular, reference can be made to the Smart Cut™ process, which is particularly suitable for the transfer of thin layers. For the transfer of thicker layers, the 2DLT ("two-dimensional material-based layer transfer") technique can also be used.

[0044] Next, two variations of the manufacturing method according to the present invention will be described.

[0045] First variant of the method The first step of the method involves the provision of an initial substrate 70 suitable for the manufacture of a stack E of semiconductor layers, for example an n-type substrate GaAs for the stack, based on GaAs and / or compounds thereof (FIG. 4a). The first step also involves the provision of a support substrate 10. Each of the substrates 10, 70 has a front surface 10′, 70′ and a back surface 10″, 70″.

[0046] This first variant is based on the 2DLT transfer technique, which involves a material known as a 2D (two-dimensional) or van der Waals material (2D because it is substantially two-dimensional) interposed between the layer or stack to be transferred and the initial substrate on which said stack is formed, at the level of which subsequent release is possible. In this case, the van der Waals material is used to separate the stack of semiconductor layers E from the initial substrate 70.

[0047] A layer 75 of van der Waals material is formed on the initial substrate 70. A van der Waals material is defined as a material composed of atoms that are strongly bonded to each other by covalent or ionic bonds only in the plane of the material's formation (in this case, the (x,y) plane) and do not have strong bonds perpendicular to this plane. Materials such as graphite, graphene, MoS2, WSe2, and h-BN are van der Waals or 2D materials. From a practical point of view, it is therefore possible to use one or more layers, preferably a single layer, of graphene (or another 2D material), as described, for example, in Celesta Chang et al., "Remote Epitaxy," Nature Methods, June 2022, or in the document WO 2017 / 044577. A graphene layer can be obtained, for example, by wet transfer of a layer obtained by CVD onto a catalytic metal substrate. It should be noted that the crystalline pattern of the initial substrate 70 can guide the crystalline growth of the layers of stack E through the layers of graphene if this crystalline pattern is sufficiently fine and preferably consists of less than 1-10 layers of graphene, preferably 1-3 layers.

[0048] The second step corresponds to the fabrication of a stack E of semiconductor layers, at least on the side of the front surface 70' of the initial substrate 70, in the following order: a layer 75 of van der Waals material, an upper Bragg mirror 30b formed on said layer 75, an active layer 20 formed on the upper Bragg mirror 30b, and a lower Bragg mirror 30a formed on the active layer 20 (FIG. 4b). This stack is fabricated by successive epitaxy using the initial substrate 70 as an epitaxy seed. These steps are known in the prior art and will not be described here.

[0049] The third step consists in fabricating a contact film 40 on the lower Bragg mirror 30a, thereby forming a donor structure 130 comprising an initial substrate 70, a layer of van der Waals material 75, a stack of semiconductor layers E, and a contact film (FIG. 4c). Again, the contact film 40 can be fabricated by epitaxy. This contact film complies with the conditions previously described regarding thickness and optical properties.

[0050] During a fourth step, an oxide layer 50 is wholly or partially formed on the contact film 40 and / or the supporting substrate 10 (FIG. 4d). In other words, the oxide layer 50 can be fabricated completely on the donor structure 130 side, or completely on the supporting substrate 10 side as shown in FIG. 4d, or the oxide layer 50 can be formed partially on the donor structure 130 side and partially on the supporting substrate 10 side, and after assembly (which occurs in the next step of the method), the two parts of the oxide layer 50 will be bonded along the bonding interface 60 to together constitute the oxide layer 50 of the semiconductor structure 150.

[0051] The oxide layer 50 can be formed by any known deposition technique, such as chemical vapor deposition (CVD), optionally using a PECVD plasma ("plasma-enhanced chemical vapor deposition"), chemical vapor deposition (CVD), optionally using a high-density plasma (HDP), physical vapor deposition (PVD), or atomic layer deposition (ALD). The deposition is typically carried out at temperatures between 100°C and 700°C. The oxide layer 50 complies with the aforementioned conditions regarding thickness and optical properties.

[0052] The fifth step involves assembling by direct bonding the donor structure 130 and the support substrate 10 on their respective front surfaces 10′, 70′ along the bonding interface 60 to form a bonded assembly 140. In the example shown in FIG. 4e, the direct bonding is performed by bringing the free surfaces of the contact film 40 and the oxide layer 50 into close contact.

[0053] As mentioned above, direct bonding by molecular adhesion can be performed at ambient temperature or under controlled temperature and atmosphere (ADB or SAB type). It will be understood that cleaning or surface activation (e.g., using plasma) can be performed before the surfaces to be assembled are brought into contact. These surface treatments are known and proven for oxide layers, so it can be advantageous to form portions of an oxide layer 50 on each of the surfaces to be assembled. Furthermore, the fact that the bonding interface 60 includes or is included in the oxide layer surface 50, which can be relatively thick (typically greater than 150 nm), ensures better control of the chemical species involved in the molecular adhesion bonding and, therefore, a better quality of the interface 60.

[0054] The bonded assembly 140 can be advantageously subjected to a heat treatment to strengthen the bond interface 60, typically at a temperature between 150° C. and 600° C. for a period of a few minutes to a few hours.

[0055] The sixth step of the method corresponds to separating the bonded assembly 140 at the layer of van der Waals material 75 to provide a semiconductor structure 150 according to the invention (FIG. 4f). Separation can be caused by mechanical stress applied at the layer of van der Waals material 75 in the peripheral region of the bonded assembly 140, for example, and / or by the addition of a top layer (not mentioned) that provides stress allowing delamination.

[0056] Once the sixth step is completed, first the semiconductor structure 150 is obtained, and then the initial substrate 70 (FIG. 4f).

[0057] Although this first variant has been described with particular reference to the 2DLT technique, it will be understood that any other known transfer technique compatible with the stack of layers to be transferred can be used in the method according to the invention.

[0058] Second variant of the method The first step of the method according to this second variant involves the provision of an initial substrate 70 designed for the manufacture of a stack E of semiconductor layers (FIG. 5a). The first step also involves the provision of a support substrate 10. Each of the substrates 10, 70 has a front surface 10′, 70′ and a back surface 10″, 70″.

[0059] The second step corresponds to the fabrication of the contact film 40 directly on the initial substrate 70, thereby forming the donor structure 130' (FIG. 5b). The contact film 40 is fabricated by epitaxy and is subsequently used in the method as a seed for the epitaxial growth of the stack E.

[0060] During the third step, an oxide layer 50 is formed wholly or partially on the contact film 40 and / or on the support substrate 10 (FIG. 5c). The explanations given for the fourth step of the first variant of the method apply here. In the example shown in FIG. 5c, a portion 51 of the oxide layer 50 is formed on the contact film 40 and another portion 52 is formed on the support substrate 10; after assembly, these two portions 51, 52 constitute the oxide layer 50, which must comply with the thickness and optical property requirements mentioned above.

[0061] The fourth step of this second variant involves assembling by direct bonding, on their respective front sides, donor structure 130' and support substrate 10 along bonding interface 60, to form bonded assembly 140'. In the example shown in Fig. 5d, direct bonding is performed by bringing the free faces of portions 51, 52 of oxide layer 50 into close contact. The explanations provided for the fifth step (assembly) of the first variant of the method also apply here.

[0062] The fifth step of the second variant of the method corresponds to the total or partial removal of the initial substrate 70 from the bonded assembly 140' to produce an intermediate structure 145' comprising the support substrate 10, the oxide layer 50, the contact film 40 and potentially a residual layer 72 of the initial substrate 70 (Figure 5e).

[0063] Advantageously, the removing step comprises separating along a buried weak plane 71 parallel to the adhesive interface 60 and recovering all or part of the initial substrate 70. To this end, as known from the Smart Cut™ process, before the assembly step (fourth step), it is possible to carry out an additional step comprising introducing light ions into the initial substrate 70 (or alternatively into the contact film 40) in order to form, together with the front surface of the donor structure 130′, a buried weak plane 71 that defines the layers to be transferred, i.e., part 51 of the adhesive layer, all or part of the contact film 40, and potentially a residual layer 72 of the initial substrate 70 (FIG. 5c). Typically, in an initial substrate made of GaAs, 1 E +16at / cm 2 ~5 E +17at / cm 2 Ion implantation of helium or hydrogen or these two ions at a dose of 0.1 MPa and an energy of about 100 keV can form a buried weak surface 71 that allows the transfer of layers with thicknesses of 500 nm (He implant) to 700 nm (H implant). Note that cleaning and surface treatments can be performed before and / or after implantation, such as to eliminate potential specific organic and / or metallic contamination.

[0064] Returning to the fifth step of the method according to the second variant, said step involves separation along the buried weak surface 71 as a result of the presence and / or growth of cavities and microcracks in said surface. As is already known, this type of separation occurs, for example, during a heat treatment capable of generating the generation of cavities and their pressurization, as well as the spontaneous propagation of fracture waves in the buried weak surface 71. The separation heat treatment typically corresponds to an annealing at 200°C lasting, for example, between 30 minutes and 2 hours. Alternatively or in combination with the heat treatment, separation can be induced by mechanical stress applied to the buried weak surface 71.

[0065] Upon completion of the fifth step, first the intermediate structure 145' is obtained, and then the remaining part 73 of the initial substrate (Fig. 5e). This step can then be completed by a surface treatment (cleaning, polishing, etching) or other smoothing treatment to improve the surface quality of the contact layer 40 or the residual layer 72, or even to remove this layer 72.

[0066] Although the fifth step of removal has been described with particular reference to the Smart Cut™ process, it will be understood that any other known technique for transferring a thin monocrystalline layer may be used in the method according to the invention.

[0067] The sixth step of the second variant of the method corresponds to the fabrication of a stack E of semiconductor layers on the intermediate structure 145'. Although a residual layer 72 of the initial substrate 70 was transferred in the previous step, it is possible to choose to eliminate this residual layer before fabricating the stack E. The stack is then formed in the following order: the lower Bragg mirror 30a is formed on the contact film 40, the active layer 20 is formed on the lower Bragg mirror 30a, and the upper Bragg mirror 30b is formed on the active layer 20 (FIG. 5f). This stack is produced by successive epitaxy using the contact film 40 as an epitaxy seed. These steps are known in the prior art and will not be described here.

[0068] Upon completion of this sixth step, a semiconductor structure 150 according to the present invention is obtained.

[0069] The first and second variants of the manufacturing method can include additional steps of deposition and etching, which in particular allow for isolating the multiple laser diodes collectively formed in a single structure 150 from one another, forming a contact film 41 on the upper Bragg mirror 30b, and making electrical contacts 80, 81 on each of the two contact films 40, 41, as shown in Figure 2b.

[0070] The semiconductor structure 150 according to the invention is advantageous because, as a result of the presence of the oxide layer 50 at the bonding interface 60, it significantly facilitates pre-assembly surface treatment steps and provides superior quality adhesion. Additionally, this layer 50 eliminates the risk of dislocation formation between the crystals of the assembled materials. The thickness and absorption characteristics of the contact film 40 and the oxide layer 50, which are defined as design rules, prevent these layers, interposed between the lower Bragg mirror 30a and the support substrate 10, from reducing the performance level of the VCSEL by blocking or absorbing the outgoing laser radiation before it passes through the support substrate 10. The contact film 40 and the oxide layer 50 according to the invention also participate in the mirror function and allow a smaller number of alternating layers to be used for the manufacture of the lower Bragg mirror 30a, thus constituting another simplification of the manufacturing method.

[0071] It will be understood that the invention is not limited to the described embodiments, but that variant embodiments can be provided without departing from the context of the invention as defined by the claims.

Claims

1. A semiconductor structure (150) for forming one or more vertical cavity laser diodes, comprising: a stack (E) of semiconductor layers based on III-V components defining an upper Bragg mirror (30b) arranged on an active layer (20) constituted by at least one quantum well enabling laser radiation at a defined wavelength (λ), said active layer (20) being arranged on a lower Bragg mirror (30a) and said laser radiation being designed to exit said stack of semiconductor layers (E) via said lower Bragg mirror (30a); A semiconductor contact film (40) disposed directly below the lower Bragg mirror (30a) has a first thickness (h １ ) and n １ '=n １ + i.k １ The first complex refractive index (n １ '), wherein n １ is the first refractive index, and k １ is a first attenuation coefficient for the wavelength (λ) defined above; a semi-insulating gallium arsenide support substrate (10) having a front surface (10') and a back surface (10''); an oxide layer (50) in contact with the front surface (10') of the support substrate (10) and disposed between the front surface (10') and the contact film (40), the oxide layer having a second thickness (h ２ ) and n ２ '=n ２ + i.k ２ The second complex refractive index (n ２ '), wherein n ２ is the second refractive index, and k ２ is a second extinction coefficient for the wavelength (λ) defined above; and A semiconductor structure (150) comprising: the oxide layer (50) is in direct contact with the contact film (40) on the opposite side of the lower Bragg mirror (30a); The first damping coefficient (k １ ) and the second damping coefficient (k ２ ) is less than or equal to 1, The first thickness (h １ ) and the second thickness (h ２ ) is h １ = m １ *λ / (4n １ ) and h ２ = m ２ *λ / (4n ２ ) where m １ and m ２ is an integer, A semiconductor structure (150) comprising:

2. The first damping coefficient (k １ ) and the second damping coefficient (k ２ 10. The semiconductor structure of claim 1, wherein .gamma.

3. The semiconductor structure (150) according to claim 1 or 2, wherein said contact layer (40) and said oxide layer (50) have an extinction coefficient of less than or equal to 1, preferably less than or equal to 0.1 in the wavelength range from 0.5 μm to 2 μm.

4. The semiconductor structure (150) of any one of claims 1 to 3, wherein said oxide layer (50) is formed from silicon oxide, glass or zinc oxide.

5. The semiconductor structure (150) of any one of claims 1 to 4, wherein said lower Bragg mirror (30a) comprises fewer than seven alternating layers of gallium arsenide and aluminum arsenide for wavelengths λ between 800 μm and 950 μm.

6. The semiconductor structure (150) of any one of claims 1 to 5, comprising a direct bond interface (60) between said oxide layer (50) and said contact film (40).

7. The semiconductor structure (150) of any one of claims 1 to 5, comprising a direct bond interface (60) between said oxide layer (50) and said support substrate (10).

8. The semiconductor structure (150) of any one of claims 1 to 5, comprising a direct bond interface (60) in said oxide layer (50).

9. The following steps: fabricating the stack of semiconductor layers (E) on an initial substrate (70) provided with a layer of van der Waals material (75), in the order of the upper Bragg mirror (30b) formed on the layer of van der Waals material (75), the active layer (20) formed on the upper Bragg mirror (30b), and the lower Bragg mirror (30a) formed on the active layer (20); fabricating the contact film (40) on the lower Bragg mirror (30a), thereby forming a donor structure (130) comprising the initial substrate (70), the layer of van der Waals material (75), the stack of semiconductor layers (E), and the contact film (40); forming all or part of the oxide layer (50) on the contact film (40) and / or the support substrate (10); assembling the donor structure (130) and the support substrate (10) by direct bonding along an adhesive interface (60) comprising a surface of or included in the oxide layer (50); separating the layer of van der Waals material (75) to yield the semiconductor structure (150); A method for manufacturing the semiconductor structure (150) of any one of claims 1 to 8, comprising:

10. The following steps: fabricating said contact film (40) on an initial substrate (70), thereby forming a donor structure (130'); forming all or part of the oxide layer (50) on the contact film (40) and / or the support substrate (10); assembling the donor structure (130') and the support substrate (10) by direct bonding along an adhesive interface (60) comprising a surface of or included in the oxide layer (50); removing at least a portion of the initial substrate (70) to create a free surface of the contact film (40); fabricating the stack (E) of semiconductor layers on the free surface of the contact film (40) in the following order: the lower Bragg mirror (30a) arranged on the contact film (40), the active layer (20) arranged on the lower Bragg mirror (30a), and the upper Bragg mirror (30b) arranged on the active layer (20); A method for manufacturing the semiconductor structure (150) of any one of claims 1 to 8, comprising:

11. 11. The method of claim 10, wherein the removing step comprises separating along an embedded plane of weakness (71) parallel to the adhesive interface (60) and recovering some or all (73) of the initial substrate (70).

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