Semiconductor structure for forming vertical cavity laser diode

Abstract

The present invention relates to a semiconductor structure for forming one or more vertical cavity laser diodes, comprising:-a stack of semiconductor layers based on a Group III-V composition, defining an upper Bragg mirror arranged on an active layer consisting of at least one quantum well allowing laser emission at a defined wavelength, and-a lower Bragg mirror arranged on an active layer consisting of at least one quantum well allowing laser emission at a defined wavelength; the active layer is arranged on the lower Bragg mirror, and the laser emission is intended to be emitted from the stack via the lower mirror; -a semiconductor contact film arranged directly below the lower Bragg mirror, the contact film having a first thickness and a first complex refractive index n1 '= n1 + i. K1, n1 being the first refractive index, and k1 being a first extinction coefficient for a defined wavelength; a support substrate made of semi-insulating gallium arsenide; -an oxide layer in contact with the front surface of the support substrate and arranged 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, n2 being the second refractive index, k2 being a second extinction coefficient for the defined wavelength. In the structure, the oxide layer is in direct contact with the contact film, and the first and second extinction coefficients are less than or equal to 1; and the first and second thicknesses are defined by h1 = m1 * lambda / (4n1) and h2 = m2 * lambda / (4n2), respectively, m1 and m2 being integers.

Description

Technical Field

[0001] The field of the present invention is the field of semiconductors, in particular the field of optoelectronics, and relates to a semiconductor structure for forming one or more vertical cavity laser diodes. Background Art

[0002] Vertical-cavity surface-emitting lasers (VCSELs) are increasingly being developed for emerging mass-market applications including facial recognition, particularly in mobile phones, and lidar (“light detection and ranging”) long-range detection in the automotive industry.

[0003] VCSEL 100 is grown by continuous epitaxial growth ( Figure 1 ) is made of a stack of III-V semiconductor layers. The composition, doping, and thickness of each layer are precisely controlled to form, on the one hand, an active region 2 consisting of one or more quantum wells that allow the generation of a laser beam, and, on the other hand, two Bragg mirrors 3a, 3b that sandwich the active region 2 and are composed of an alternation of layers with high and low refractive indices.

[0004] It is known to form a stack of layers for a VCSEL 100 on a bulk substrate 1, such as Figure 1 As exemplified, bulk substrate 1 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 functionality of the epitaxial seeds and the quality of the layer stack. However, when the VCSEL is intended to emit via the back side, i.e., when the laser beam is to pass through the bulk substrate 1, the problem of signal absorption by the substrate 1 arises. For example, an n-type GaAs substrate is commonly used as the bulk substrate 1 to produce the layer stack for the VCSEL 100; this type of substrate is too absorptive in the laser emission wavelength range (typically 0.5 μm to 1.5 μm) to guarantee the high performance level of the VCSEL 100.

[0005] In order to solve this problem, document WO 2021 / 125005 proposes to perform a transfer of layers from a bulk substrate 1 to a support substrate whose characteristics are better suited to emission confinement on the back side of the VCSEL 100 .

[0006] In order to perform the transfer of the layers, an assembly step is required. This assembly must be such that the quality of the transferred layers can be maintained; it must also avoid adding disturbances to the operation of the VCSEL 100.

[0007] Purpose of the Invention

[0008] The present invention proposes a solution for simplifying and reliably manufacturing vertical cavity laser diodes (VCSELs). Specifically, it relates to a semiconductor structure comprising a semi-insulating support substrate made of gallium arsenide, on which a stack of semiconductor layers based on III-V components is located, defining a lower Bragg mirror, an active laser layer, and an upper Bragg mirror. The semiconductor contact film and oxide layer inserted between the layer stack and the support substrate have specific properties in terms of thickness and light absorption to provide a high level of performance for the laser diode while ensuring simple and robust manufacturing of the semiconductor structure. Summary of the Invention

[0009] The present invention relates to a semiconductor structure for forming one or more vertical cavity laser diodes, the semiconductor structure comprising:

[0010] a stack of semiconductor layers based on a III-V composition, defining an upper Bragg mirror situated on an active layer consisting of at least one quantum well allowing laser emission at a defined wavelength, said active layer being situated on a lower Bragg mirror, said laser emission being designed to emerge from the stack of semiconductor layers via said lower Bragg mirror;

[0011] a semiconductor contact film located directly below the lower Bragg mirror, the contact film having a first thickness and a first complex refractive index expressed as n1′=n1+i.k1, where n1 is the first refractive index and k1 is the first extinction coefficient for a defined wavelength;

[0012] - a semi-insulating gallium arsenide support substrate having a front side and a back side;

[0013] - an oxide layer in contact with the front side of the supporting substrate and located between the front side and the contact film, the oxide layer having a second thickness and a second complex refractive index expressed as n2'=n2+i.k2, where n2 is the second refractive index and k2 is the second extinction coefficient for a defined wavelength.

[0014] The semiconductor structures described differ in that:

[0015] - the oxide layer is in direct contact with the contact film on the side opposite to the lower Bragg mirror;

[0016] - the first extinction coefficient and the second extinction coefficient are equal to or less than 1; and

[0017] - 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.

[0018] According to the advantageous characteristics of the invention, individually or in any combination that can be created:

[0019] - the first extinction coefficient and the second extinction coefficient are equal to or less than 0.1;

[0020] - the extinction coefficient of the contact layer and the oxide layer in the wavelength range of 0.5 μm to 2 μm is equal to or less than 1, preferably equal to or less than 0.1;

[0021] - the oxide layer is formed of silicon oxide, glass or zinc oxide;

[0022] - for a wavelength λ between 800 μm and 950 μm, the lower Bragg mirror comprises fewer than seven alternating gallium arsenide and aluminum arsenide layers;

[0023] - the semiconductor structure comprises a direct adhesion interface between the oxide layer and the contact film;

[0024] - the semiconductor structure comprises a direct adhesion interface between the oxide layer and the supporting substrate;

[0025] - the semiconductor structure comprises a direct adhesion interface in the oxide layer.

[0026] The present invention also relates to a method for manufacturing a semiconductor structure as described above.

[0027] According to a first variant, the manufacturing method comprises the following steps:

[0028] - manufacturing a stack of semiconductor layers on an initial substrate provided with a van der Waals material layer in the following order: an upper Bragg mirror formed on the van der Waals material layer, an active layer formed on the upper Bragg mirror, and a lower Bragg mirror formed on the active layer;

[0029] - fabricating a contact film on the lower 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;

[0030] - forming all or part of an oxide layer on the contact film and / or on the supporting substrate;

[0031] - assembly by direct adhesion between the donor structure and the supporting substrate, along an adhesion interface involving a face of the oxide layer or an adhesion interface comprised in the oxide layer;

[0032] - Separation is performed at the van der Waals material layer to produce a semiconductor structure.

[0033] According to a second variant, the manufacturing method comprises the following steps:

[0034] - Fabrication of a contact film on an initial substrate, thereby forming a donor structure;

[0035] - forming all or part of an oxide layer on the contact film and / or on the supporting substrate;

[0036] - assembly by direct adhesion between the donor structure and the supporting substrate, along an adhesion interface involving a face of the oxide layer or comprised in the oxide layer;

[0037] - removing at least a portion of the initial substrate to create a free surface of the contact film;

[0038] - manufacturing the stack of semiconductor layers on the free surface of the contact film in the following order: the lower Bragg mirror on the contact film, the active layer on the lower Bragg mirror and the upper Bragg mirror on the active layer.

[0039] Advantageously, the removal step involves separation along embedded fragile planes parallel to the adhesion interface, as well as recovery of some or all of the original substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings, in which:

[0041] [ Figure 1 ] Figure 1 A semiconductor structure for manufacturing a VCSEL according to the prior art is shown;

[0042] [ Figure 2a ]

[0043] [ Figure 2b ] Figure 2a and Figure 2b shows a semiconductor structure according to the present invention;

[0044] [ Figure 3a ]

[0045] [ Figure 3b ] Figure 3a and Figure 3b A table showing thicknesses of a contact film and an oxide layer, respectively, in an example of a semiconductor structure according to the present invention;

[0046] [ Figure 4a ]

[0047] [ Figure 4b ]

[0048] [ Figure 4c ]

[0049] [ Figure 4d ]

[0050] [ Figure 4e ]

[0051] [ Figure 4f ] Figure 4a 、 Figure 4b 、 Figure 4c 、 Figure 4d 、 Figure 4e 、 Figure 4f The steps of a method for producing a semiconductor structure according to a first variant embodiment of the present invention are shown;

[0052] [ Figure 5a ]

[0053] [ Figure 5b ]

[0054] [ Figure 5c ]

[0055] [ Figure 5c' ]

[0056] [ Figure 5d ]

[0057] [ Figure 5e ]

[0058] [ Figure 5f ] Figure 5a 、 Figure 5b 、 Figure 5c 、 Figure 5c' 、 Figure 5d 、 Figure 5e 、 Figure 5f The steps of a method for manufacturing a semiconductor structure according to a second variant embodiment of the present invention are shown;

[0059] [ Figure 6 ] Figure 6 Graphs illustrating the reflectivity as a function of the number of alternations of gallium arsenide layers and aluminum arsenide layers for a Bragg mirror according to the prior art and for a lower Bragg mirror of the semiconductor structure according to the present invention are shown.

[0060] Some of the figures are schematic representations that are not drawn to scale for the sake of legibility. In particular, the thickness of the layers along the z axis is not to scale relative to the lateral dimensions along the x and y axes.

[0061] In the figures, the same reference numerals may be used for elements of the same nature. DETAILED DESCRIPTION

[0062] The present invention relates to a semiconductor structure 150 specifically designed for optoelectronic applications to form one or more vertical cavity laser diodes.

[0063] The semiconductor structure 150 can be in the form of a small plate, for example with a diameter between 50 mm and 200 mm: in this case, it is designed to receive a plurality of optoelectronic components (VCSELs) that can then be picked out. Alternatively, it can take the form of a vignette of smaller dimensions, housing one optoelectronic component or a group of components.

[0064] like Figure 2a As illustrated, the structure 150 comprises a stack E of semiconductor layers based on III-V components, which defines an upper Bragg mirror 30b, an active layer 20 consisting of at least one quantum well allowing 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" for the Bragg mirrors 30a, 30b of the stack E refer to the upper Bragg mirror 30b and the lower Bragg mirror 30a. Figure 2a The reference system (x, y, z) shown above is used, in which the direction of the axis z indicates "upwards"; with respect to the axis z, the reference mirror 30a is therefore at a lower level, and the reference mirror 30b is at a higher level in the structure 150. They also serve as a reference for the mirror through which the laser emission with a wavelength λ is intended to be emitted; this is the so-called back emission, i.e. the laser wave will be emitted via the lower Bragg mirror 30a (i.e. the lower Bragg mirror 30a closest to the supporting substrate 10), as will be described later.

[0065] The layers 30b, 20, 30a of the stack E and generally the layers or substrates described below extend parallel to the main planes (x, y) and have a thickness along the axis z.

[0066] As is known, the active layer 20 can be formed of gallium arsenide (GaAs) and / or its ternary or quaternary compounds (e.g., in particular AlGaAs, InGaAs, InGaAsN, etc.); alternatively, it can be formed of indium phosphide (InP) and / or its ternary or quaternary compounds (e.g., such as InAsP, GaAlInP, etc.). Multilayers are also known, consisting of alternating layers of low and high refractive index, which can be formed of gallium arsenide (GaAs), aluminum arsenide (AlAs), and their compounds, or of indium phosphide (InP), and their compounds, depending on the nature of the active layer 20. In fact, it should be remembered that the stack E is produced by epitaxial growth, which makes it necessary to use materials whose lattice parameters and chemical properties are completely compatible.

[0067] The thickness of the stack E may be between 1 μm and 15 μm.

[0068] As previously mentioned, semiconductor structure 150 includes a supporting substrate 10 made of semi-insulating gallium arsenide, transparent at the wavelength of the laser light, having a front side 10' and a rear side 10". A stack of layers E is located on front side 10'. Laser emission with a wavelength λ is designed to exit via rear side 10" of substrate 10. Semi-insulating gallium arsenide, with its high level of optical transparency, has a low absorption rate of laser waves, a prerequisite for the high-performance function of VCSELs. Its thickness is, for example, between 200 μm and 2,000 μm.

[0069] The structure 150 further includes a semiconductor contact film 40 located directly below and in contact with the lower Bragg mirror 30 a of the stack E. The contact film 40 has a first thickness h1 and a first complex refractive index n1′, expressed as n1′=n1+i.k1, where n1 is the first refractive index and k1 is the first extinction coefficient for wavelength λ.

[0070] Finally, the structure 150 comprises an oxide layer 50 which is in contact on one side with the front side 10 ′ of the support substrate 10 and is positioned 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 significant advantages during the assembly steps, since its surface preparation is easy and proven, and this type of layer ensures excellent quality (low level of defects and high energy) of direct adhesion (without the addition of adhesive materials). Advantageously, the material of the oxide layer 50 is amorphous, such as to limit the stress fields associated with the addition of two materials, the misalignment of the crystal networks of the two materials, and / or the different lattice parameters of the two materials, thereby avoiding the formation of nanobubbles at the adhesion interface.

[0071] The oxide layer 50 has a second thickness h2 and a second complex refractive index n2′, expressed as n2′=n2+i.k2, where n2 is the second refractive index and k2 is the second extinction coefficient for the wavelength λ.

[0072] The materials of the contact film 40 and the oxide layer 50 are selected so that the first extinction coefficient k1 and the second extinction coefficient k2 are lower than 10, equal to or less than 1, or equal to or less than 0.1 (for wavelength λ). Advantageously, the extinction coefficients of the contact film 40 and the oxide layer 50 are lower than 10, equal to or less than 1, or equal to or less than 0.1 in the wavelength range [0.5 μm-2 μm]. They are selected to be as close to zero as possible (at least at wavelength λ) in order to limit the attenuation of the optical signal designed to pass through the layers 40, 50.

[0073] In particular, the contact film 40 can be made of n-type or p-type GaAs to serve as an electrical contact layer; it then has an extinction coefficient k1 equal to 0 at a wavelength λ of 940 nm. In the wavelength range λ=1.55 μm, and on an InP-based stack, the contact film 40 can be made of n-type or p-type InP.

[0074] Part of the oxide layer 50 may be made of silicon oxide (SiO x , SiO2), and its extinction coefficient k2 is equal to 1.1 10 at λ = 940nm. -3 Other materials may constitute the oxide layer 50, for example, zinc oxide (for λ = 0.94 μm, k2 = 7.10 -3 , and for λ = 1.55 μm, k2 = 2.10 -3 ) or glass.

[0075] It should be understood that the examples of materials given for the contact film 40 and the oxide layer 50 are not exhaustive.

[0076] 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 are defined by the following formula:

[0077] h1=m1*λ / (4n1) and h2=m2*λ / (4n2),

[0078] Wherein m1 and m2 are integers which may be the same or different.

[0079] These thickness rules applied to the two layers 40 and 50 interposed between lower Bragg mirror 30a and support substrate 10 allow contact film 40 and oxide layer 50 to be incorporated into the layers of mirror 30a. This offers the advantage of not interfering with laser emission, as the wave encounters only the Bragg mirror, not the intervening interfering layer, before entering and passing through support substrate 10. Secondly, since contact film 40 and adhesion layer 50 participate in the reflection of the laser wave, the number of layers required to fabricate lower Bragg mirror 30a can be reduced.

[0080] For example, the lower Bragg mirror 30a may include fewer than seven alternating layers (GaAs / AlAs) to achieve a reflectivity of 95%, rather than thirteen alternating layers ( Figure 6 According to another example, the lower Bragg mirror 30a formed of InP and / or its compounds may include less than ten alternating layers to achieve a reflectivity of 95%, rather than more than thirty alternations.

[0081] Design rules relating thickness to the ratio between wavelength and refractive index are customarily applied to the multiple layers forming the Bragg mirror. On the other hand, the prior art never envisioned applying these same rules to the lower layers of the lower mirror. In fact, these are customarily chosen so that they have no refractive index contrast and therefore do not contribute to the reflection of light, unlike the layers that make up the Bragg mirror.

[0082] For example, in the case of a stack E based on GaAs or its compound (laser wavelength λ=940 nm), in the case of a contact film 40 made of n-type GaAs and an oxide layer 50 made of SiO 2 :

[0083] - The thickness h1 of the contact film 40 can be Figure 3a It should be remembered that for λ = 940 nm, the refractive index n1 is 3.5060.

[0084] - The thickness h2 of the oxide layer 50 can be Figure 3b It should be remembered that for λ = 940 nm, the refractive index n2 is 1.4512.

[0085] The semiconductor structure 150 according to the invention is therefore particularly suitable for forming a vertical cavity laser diode (VCSEL) of very good quality, since the assembly steps (which require the transfer of the useful layers to the supporting substrate 10) are simplified and made reliable, and since the laser wave is not disturbed after exiting the lower Bragg mirror 30a.

[0086] The semiconductor structure 150 according to the present invention further comprises a direct adhesion interface 60 extending on the main plane (x, y), said interface 60 being included in the oxide layer 50 or adjacent to the oxide layer 50. The adhesion interface 60 may be located between the oxide layer 50 and the contact film 40, between the oxide layer 50 and the supporting substrate 10, or may also be located in the oxide layer 50.

[0087] "Direct adhesion" refers to adhesion that does not require an adhesive material and is based on molecular adhesion between the assembly surfaces. There are various types of direct adhesion, which differ, inter alia, in the temperature conditions, pressure conditions, atmosphere, or treatments performed before the surfaces are brought into contact. Reference may be made to molecular adhesion at ambient temperature (whether or not the surfaces to be assembled have been previously plasma-activated), atomic diffusion bonding (ADB), or surface activated bonding (SAB), among others.

[0088] The oxide layer 50, which is particularly favorable for adhesion, can be chosen to be thicker or thinner as required, as long as its thickness h2 complies with the rule relating it to the ratio between the wavelength λ and the refractive index n2 of said layer 50. This provides great flexibility in carrying out the assembly steps, which are generally easier when the oxide layer thickness is 150 nm or more.

[0089] Figure 2b A semiconductor structure 150 according to the present invention is shown, which has undergone additional steps for manufacturing 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 described further here.

[0090] The method for producing the semiconductor structure 150 is based on the technology of transferring layers by adhesion and thinning according to the prior art. Reference may be made in particular to the Smart Cut technology which is particularly suitable for the transfer of thin layers. TM For the transfer of thicker layers, 2DLT (“2-D material-based layer transfer”) technology can also be used.

[0091] Two variants of the manufacturing method according to the invention will now be described.

[0092] First variant of the method:

[0093] The first step of the method comprises supplying an initial substrate 70 suitable for producing a stack E of semiconductor layers, for example an n-type GaAs substrate ( Figure 4a The first step also comprises the provision of a support substrate 10. Each substrate 10, 70 has a front side 10', 70' and a back side 10", 70".

[0094] This first variant is based on the 2DLT transfer technology, which involves a material known as a 2-D material or van der Waals material (2-D, because it essentially has two dimensions) that is inserted between the layer or stack to be transferred and the initial substrate on which it is formed, and at the level at which subsequent separation will be possible. In the present case, the van der Waals material is used to separate the stack E of semiconductor layers from the initial substrate 70.

[0095] A layer 75 of van der Waals material is formed on the initial substrate 70. Van der Waals materials are defined as materials consisting of atoms that are strongly bonded to each other by covalent or ionic bonds only in the plane in which the material is formed (in this case the plane (x, y)), without strong bonds perpendicular to this plane. Materials such as graphite, graphene, MoS2, WSe2, h-BN, etc. are van der Waals materials or 2-D materials. From a practical point of view, one or more layers of graphene (or another 2-D material), preferably a single layer, can therefore be used, such as described by Celesta Chang et al. in "Remote Epitaxy" in Nature Methods, June 2022, or also in document WO 2017 / 044577 A1. The 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 when the graphene layer is sufficiently fine, the crystal pattern of the initial substrate 70 can guide the crystal growth of the layers of the stack E through the graphene layer, preferably consisting of 1 layer to less than 10 layers, and most preferably 1 layer to 3 layers of graphene.

[0096] The second step corresponds to manufacturing, at least on the side of the front side 70 ′ of the initial substrate 70 , a stack E of semiconductor layers on the layer 75 of van der Waals material in the following order: an upper Bragg mirror 30 b formed on said layer 75 , an active layer 20 formed on the upper Bragg mirror 30 b and a lower Bragg mirror 30 a formed on the active layer 20 ( Figure 4b ). The stack is manufactured by successive epitaxies using the initial substrate 70 as epitaxial seeds. These steps known in the art will not be described here.

[0097] The third step comprises fabricating a contact film 40 on the lower Bragg mirror 30a, thereby forming a donor structure 130 comprising an initial substrate 70, a van der Waals material layer 75, a stack E of semiconductor layers and a contact film ( Figure 4c In this case, the contact film 40 can also be produced by epitaxial growth. It meets the conditions described previously in terms of thickness and optical properties.

[0098] During the fourth step, an oxide layer 50 is formed entirely or partially on the contact film 40 and / or on the support substrate 10 ( Figure 4d In other words, the oxide layer 50 can be entirely fabricated on the donor structure 130 side, or entirely fabricated on the support substrate 10 side, such as Figure 4d as illustrated; it can also be formed partly on the side of the donor structure 130 and partly on the side of the supporting substrate 10: after assembly (which takes place in a subsequent step of the method), the two parts of the oxide layer 50 will be glued along the adhesion interface 60 to together constitute the oxide layer 50 of the semiconductor structure 150.

[0099] The oxide layer 50 can be formed by any known deposition technique, such as, in particular, chemical vapor deposition (CVD) (optionally using a PECVD plasma (“plasma-enhanced chemical vapor deposition”), optionally using a high-density plasma (HDP)), physical vapor deposition (PVD), or atomic layer deposition (ALD). Deposition is typically carried out at a temperature between 100° C. and 700° C. The oxide layer 50 complies with the conditions previously described in terms of thickness and optical properties.

[0100] The fifth step consists in assembling by direct adhesion between the donor structure 130 and the support substrate 10 along the adhesive interface 60 on the side of their respective front faces 10 ′, 70 ′, to form a glued assembly 140 . Figure 4e In the illustrated example, direct adhesion occurs by bringing the free faces of the contact film 40 and the oxide layer 50 into close contact.

[0101] As previously mentioned, direct adhesion can be performed by molecular adhesion at ambient temperature, or alternatively, direct adhesion can be performed under controlled temperature and atmosphere (ADB or SAB type). It should be understood that cleaning or surface activation (for example, using plasma) can be performed before the surfaces to be assembled are brought into contact. These surface preparations are known and have been demonstrated on oxide layers, which is why it may be advantageous to form a portion of an oxide layer 50 on each surface to be assembled. In addition, the fact that the adhesion interface 60 involves an oxide layer 50 or is included in an oxide layer 50 (wherein the layer can be relatively thick (typically greater than 150 nm)) ensures better control of the chemical species involved in the gluing by molecular adhesion, and therefore ensures a better quality of the interface 60.

[0102] The glued assembly 140 may advantageously be subjected to a heat treatment to consolidate the bonding interface 60 , typically at a temperature between 150° C. and 600° C. for a period of several minutes to several hours.

[0103] The sixth step of the method corresponds to separating the glued assembly 140 at the van der Waals material layer 75 to provide a semiconductor structure 150 ( Figure 4f ). The separation may be caused by mechanical stress applied in the peripheral region of the glued assembly 140 (eg at the van der Waals material layer 75) and / or by adding an upper layer (not mentioned) that provides stress allowing separation.

[0104] After the sixth step is completed, the semiconductor structure 150 is first obtained, and then the initial substrate 70 is obtained. Figure 4f ).

[0105] It will be appreciated that, although this first variant has been described with particular reference to the 2DLT technique, any other known transfer technique compatible with the layer stack to be transferred may be used in the method according to the invention.

[0106] Second variant of the method:

[0107] The first step of the method according to this second variant consists in supplying an initial substrate 70 ( Figure 5a The first step also comprises the provision of a supporting substrate 10. Each substrate 10, 70 has a front side 10', 70' and a back side 10", 70".

[0108] The second step corresponds to the production of the contact film 40 directly on the initial substrate 70, thereby forming a donor structure 130' ( Figure 5b ). The contact film 40 is produced by epitaxial growth and will subsequently serve as a seed for the epitaxial growth of the stack E in the method.

[0109] During the third step, an oxide layer 50 is formed entirely or partially on the contact film 40 and / or on the support substrate 10 ( Figure 5c ). The description provided for the fourth step of the first variant of the method applies here. Figure 5c In the example illustrated, 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 will constitute the oxide layer 50 , which must comply with the conditions of thickness and optical properties previously described.

[0110] The fourth step of this second variant consists in assembling by direct bonding between the donor structure 130' and the supporting substrate 10 along the bonding interface 60 on the side of their respective front faces, so as to form a glued assembly 140'. Figure 5d In the example illustrated, direct adhesion occurs by bringing the free faces of the portions 51, 52 of the oxide layer 50 into close contact. The description provided for the fifth step (assembly) of the first variant of the method also applies here.

[0111] The fifth step of the second variant of the method corresponds to the total or partial removal of the initial substrate 70 from the glued assembly 140 ′, so as to produce an intermediate structure 145 ′ ( ) comprising the support substrate 10 , the oxide layer 50 , the contact film 40 and possibly a residual layer 72 of the initial substrate 70 . Figure 5e ).

[0112] Advantageously, the removal step involves separation along the embedded fragile plane 71 parallel to the adhesion interface 60, and recovery of all or part of the initial substrate 70. For this purpose, and as described in Smart Cut TMAs is known in the art, before the assembly step (fourth step), an additional step may be performed, which consists in introducing light ions into the initial substrate 70 (or alternatively into the contact film 40), such as to form an embedded fragile face 71 which, together with the front face of the donor structure 130 ′, defines the layers to be transferred, i.e., part 51 of the adhesion layer, all or part of the contact film 40 and possibly a residual layer 72 of the initial substrate 70 ( Figure 5c '). Typically, in an initial substrate made of GaAs, helium or hydrogen or both ions are present at a rate of 1 E +16at / cm 2 to 5 E +17at / cm 2 Ion implantation with a dose of 100 keV and an energy of about 100 keV makes it possible to form an embedded fragile surface 71, which will allow a shift in layer thickness from 500 nm (He implantation) to 700 nm (H implantation). It should be noted that cleaning and surface preparation can be performed before and / or after the implantation, for example to eliminate potential specific organic and / or metallic contaminants.

[0113] Returning to the fifth step of the method according to the second variant, this step involves separation along the embedded fragile plane 71 due to the presence and / or growth of cavities and microcracks in this fragile plane. As is already known, this type of separation occurs, for example, during a heat treatment, which can cause the development of cavities and their stress, and induce the spontaneous propagation of fracture waves in the embedded fragile plane 71. The separation heat treatment typically corresponds to annealing at 200°C for a duration of, for example, 30 minutes to 2 hours. Alternatively or in combination with a heat treatment, separation can be induced by mechanical stress applied to the embedded fragile plane 71.

[0114] After completing the fifth step, firstly the intermediate structure 145' is obtained and secondly the remaining part 73 of the initial substrate ( Figure 5e ). This step may then be completed by surface treatment (cleaning, polishing, etching) or other smoothing treatments to improve the surface quality of the contact layer 40 or the residual layer 72 , or also to remove this layer 72 .

[0115] It should be understood that although specific reference has been made to Smart Cut TM The method describes the fifth step of removal, but any other known thin single-crystal layer transfer technique can be used in the method according to the invention.

[0116] The sixth step of the second variant of the method corresponds to the production of a stack E of semiconductor layers on the intermediate structure 145 ′. Although the residual layer 72 of the initial substrate 70 was transferred in the previous step, it can optionally be removed before producing the stack E. The stack is then formed in the following order: the lower Bragg mirror 30 a is formed on the contact film 40 , the active layer 20 is formed on the lower Bragg mirror 30 a , and the upper Bragg mirror 30 b is formed on the active layer 20 ( Figure 5f ). The stack is created by successive epitaxies using the contact film 40 as epitaxial seeds. These steps known in the art will not be described here.

[0117] After completing the sixth step, the semiconductor structure 150 according to the present invention is obtained.

[0118] The first and second variants of the manufacturing method may include additional deposition and etching steps, making it possible in particular to isolate a plurality of laser diodes formed together on a single structure 150 from one another, to form a contact film 41 on the upper Bragg mirror 30 b and to produce an electrical contact 80 , 81 on each of the two contact films 40 , 41 , as Figure 2b exemplified.

[0119] The semiconductor structure 150 according to the invention is advantageous because it greatly facilitates the surface preparation steps prior to assembly and provides excellent adhesion qualities due to the presence of the oxide layer 50 at the adhesion interface 60. Furthermore, this layer 50 eliminates the risk of dislocation formation between the crystals of the assembled materials. The design rules defining the thickness and absorption characteristics of the contact film 40 and the oxide layer 50 prevent these layers, inserted between the lower Bragg mirror 30 a and the support substrate 10, from degrading the VCSEL's performance level by interfering with or absorbing the emitted laser emission 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 the lower Bragg mirror 30 a can be manufactured using a smaller number of layer alternations, thus constituting a further simplification of the manufacturing method.

[0120] It will be understood that the invention is not limited to the embodiments described and 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, the semiconductor structure (150) comprising: a stack (E) of semiconductor layers based on a III-V composition, defining an upper Bragg mirror (30b) situated on an active layer (20) consisting of at least one quantum well allowing laser emission at a defined wavelength (λ), said active layer (20) being situated on a lower Bragg mirror (30a), said laser emission being designed to exit the stack (E) of semiconductor layers via said lower Bragg mirror (30a); a semiconductor contact film (40) located directly below the lower Bragg mirror (30a), the contact film (40) having a first thickness (h1) and a first complex refractive index (n1'), expressed as n1'=n1+i.k1, wherein n1 is a first refractive index and k1 is a first extinction coefficient for the defined wavelength (λ); - a semi-insulating gallium arsenide support substrate (10), said semi-insulating gallium arsenide support substrate (10) having a front side (10') and a back side (10"); an oxide layer (50) in contact with the front side (10') of the support substrate (10) and located between the front side (10') and the contact film (40), the oxide layer (50) having a second thickness (h2) and a second complex refractive index (n2'), expressed as n2'=n2+i.k2, wherein n2 is the second refractive index and k2 is the second extinction coefficient for the defined wavelength (λ), The semiconductor structure (150) is characterized by: - the oxide layer (50) is in direct contact with the contact film (40) on the side opposite to the lower Bragg mirror (30a); - the first extinction coefficient (k1) and the second extinction coefficient (k2) are equal to or less than 1; and - The first thickness (h1) and the second thickness (h2) are defined by: h1 = m1*λ / (4n1) and h2 = m2*λ / (4n2), respectively, where m1 and m2 are integers.

2. The semiconductor structure (150) of claim 1, wherein The first extinction coefficient (k1) and the second extinction coefficient (k2) are equal to or less than 0.

1.

3. The semiconductor structure (150) according to claim 1, wherein The extinction coefficients of the contact layer (40) and the oxide layer (50) in the wavelength range of 0.5 μm to 2 μm are equal to or less than 1, preferably equal to or less than 0.

1.

4. The semiconductor structure (150) according to claim 1, wherein The oxide layer (50) is formed of silicon oxide, glass or zinc oxide.

5. The semiconductor structure (150) according to claim 1, wherein For a wavelength λ between 800 μm and 950 μm, the lower Bragg mirror (30a) comprises less than seven alternating gallium arsenide layers and aluminum arsenide layers.

6. The semiconductor structure (150) according to one of the preceding claims, comprising a direct adhesion interface (60) between the oxide layer (50) and the contact film (40).

7. The semiconductor structure (150) according to one of claims 1 to 5, comprising a direct adhesion interface (60) between the oxide layer (50) and the supporting substrate (10).

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

9. A method for producing a semiconductor structure (150) according to one of the preceding claims, comprising the following steps: - manufacturing the stack (E) of semiconductor layers on an initial substrate (70) provided with a van der Waals material layer (75) in the following order: the upper Bragg mirror (30b) formed on the van der Waals material layer (75), the active layer (20) formed on the upper Bragg mirror (30b), and the lower Bragg mirror (30a) formed on the active layer (20); - manufacturing the contact film (40) on the lower Bragg mirror (30a), thereby forming a donor structure (130), the donor structure (130) comprising the initial substrate (70), the van der Waals material layer (75), the stack (E) of semiconductor layers and the contact film (40); - forming all or part of the oxide layer (50) on the contact film (40) and / or the supporting substrate (10); - assembly by direct adhesion between the donor structure (130) and the supporting substrate (10) along an adhesion interface (60) involving a face of the oxide layer (50) or an adhesion interface (60) included in the oxide layer (50); - performing separation at the van der Waals material layer (75) to produce the semiconductor structure (150).

10. A method for producing a semiconductor structure (150) according to one of claims 1 to 8, the method comprising the following steps: - manufacturing the 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 supporting substrate (10); - assembly by direct adhesion between the donor structure (130') and the supporting substrate (10) along an adhesion interface (60) involving a face of the oxide layer (50) or an adhesion interface (60) 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); - manufacturing the stack (E) of semiconductor layers on the free surface of the contact film (40) in the following order: the lower Bragg mirror (30a) located on the contact film (40), the active layer (20) located on the lower Bragg mirror (30a), and the upper Bragg mirror (30b) located on the active layer (20).

11. The manufacturing method according to claim 10, wherein: The removal step involves separation along the embedded fragile plane (71) parallel to the adhesion interface (60) and recovery of some or all (73) of the initial substrate (70).

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