Laser devices and methods for producing thereof

Abstract

A semiconductor laser device includes a first metamaterial element, a semiconductor substrate having a main surface, and a multijunction active region arranged over the main surface of the semiconductor substrate between the first metamaterial element and the semiconductor substrate. The multijunction active region includes a plurality of active regions each comprising a multiple-quantum-well (MQWs), and a plurality of tunnel junction layers providing electrical coupling and located between neighboring active regions along a vertical direction perpendicular to the main surface of the semiconductor substrate.

Description

[0001] LASER DEVICES AND METHODS FOR PRODUCING THEREOF

[0002] Field

[0003] This present disclosure relates to photonic-based lasers and methods for producing thereof.

[0004] Background

[0005] The higher optical gain available in multijunction VCSELs enables scaling the output power without increasing the lasing threshold current density. The output light beam from a multijunction VCSEL is typically wider than that of a single-junction VCSEL, primarily due to the presence of multiple oxide layers. In a conventional VCSEL, the oxide layer provides lateral electrical and optical confinement. However, in a multijunction VCSEL, the presence of multiple oxide layers (one per active junction) within the laser cavity structure generally increases the divergence angle of the output beam. This occurs for several reasons, including the irregular profiles of the oxide layers relative to one another and an increase in the effective refractive index step between the core and cladding regions of the VCSEL. Additionally, current crowding around the edges of the oxide aperture stimulates higher-order transverse modes, which emit at wider angles.

[0006] Multijunction VCSELs are particularly useful for various high-power sensing applications, such as automotive LiDAR and 3D sensing. A key requirement for these applications is a narrow divergence angle (typically, the l / eA2 divergence angle should be less than 20 degrees). However, multijunction VCSELs exhibit divergence angles greater than 35 degrees, which significantly exceeds this requirement.

[0007] Description

[0008] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the disclosure. In the following description, various aspects of the disclosure are described with reference to the following drawings, in which:

[0009] FIG. 1A shows a cross-section of a semiconductor laser device according to at least one aspect of the present disclosure; FIG. IB shows a top view of a photonic crystal element for the device of FIG. 1A, according to at least one aspect of the present disclosure;

[0010] FIG. 2A shows a cross-section of a semiconductor laser device according to at least one aspect of the present disclosure;

[0011] FIG. 2B shows a top view of a chiral photonic crystal element for the device of FIG. 2A, according to at least one aspect of the present disclosure;

[0012] FIG. 2C shows a perspective view of the chiral photonic, a perspective view of a unit cell section of the chiral photonic crystal, and a cross-sectional view of a hole of the chiral photonic crystal.

[0013] FIGS. 2D and 2E shows alternative structures or alternative realizations or of chiral photonic crystals;

[0014] FIG. 3 shows a cross-section of a semiconductor laser device according to at least one aspect of the present disclosure;

[0015] FIG. 4A shows a cross-section of a semiconductor laser device according to at least one aspect of the present disclosure;

[0016] FIGS. 4B and 4C each shows a top view of a metamaterial element for the device of FIG. 4A, according to at least one aspect of the present disclosure;

[0017] FIG. 5 shows a cross-section of a semiconductor laser device according to at least one aspect of the present disclosure;

[0018] FIG. 6 shows flow diagram of a method according to at least one aspect of the present disclosure.

[0019] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and aspects in which the disclosure may be practiced. One or more aspects are described in sufficient detail to enable those skilled in the art to practice the disclosure. Other aspects may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the disclosure. The various aspects described herein are not necessarily mutually exclusive, as some aspects can be combined with one or more other aspects to form new aspects. Various aspects are described in connection with methods and various aspects are described in connection with devices. However, it may be understood that aspects described in connection with methods may similarly apply to the devices, and vice versa. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. Throughout the drawings, it should be noted that proportions are not necessary to scale and that the size of features may be emphasized for ease of illustration.

[0020] FIG. 1 A a cross-section of a semiconductor laser device, namely a multijunction Photonic Crystal Surface Emitting Laser (PCSEL) 100 according to at least one aspect of the present disclosure. The PCSEL 100 includes a multijunction active region 150 which is formed over a main or first surface 105a of a semiconductor substrate 105. The active region 150 includes a plurality of multiple quantum-wells (MQWs) or MQW regions 155. The active region 150 also includes tunnel junctions 160 which can provide electrical coupling between junctions in the active region 150.

[0021] A metamaterial element or metamaterial layer 170 can be formed over the semiconductor substrate and on or over the active region 150.

[0022] In FIG. 1A, an n-doped semiconductor layer 110 is arranged between the semiconductor substrate 105 and the active region 150. Further, a p-doped semiconductor layer 120 or a cladding layer 120 is arranged over the metamaterial element 170. An anode 180 can be arranged on the p-doped layer 120 and a second contact / cathode 185 can be arranged on the semiconductor substrate 105.

[0023] In at least one example, the semiconductor substrate 105 can be or include layer gallium arsenide, e.g., n-doped gallium arsenide, n-doped GaAs. The n-doped semiconductor layer 110 can be or include a layer of n-doped aluminum gallium arsenide, n-doped AlGaAs. Further, p-doped semiconductor layers described herein can be p-doped aluminum gallium arsenide, p-doped AlGaAs.

[0024] In at least one example, the metamaterial element 170 can be configured to linear polarization and configured to operate at one or more gamma ( ) points. In such cases, the semiconductor laser device or the PCSEL 100 is configured to produce an optical standing wave so that the peak of the optical standing wave overlaps with one or more of the active regions of the multijunction active region 150 and so that the null of the optical standing wave occurs at one or more of the tunnel junctions 160.

[0025] Further, in at least one example, the metamaterial element 170 can be a linearly polarized photonic crystal that operates at the gamma points. To achieve this type of operation, the photonic crystal lacks or breaks in-plane symmetry with respect to a plane parallel to the vertical direction. More specifically, as shown in FIG. IB, the photonic crystal would lack or break in-plane symmetry in the XY plane.

[0026] The metamaterials, such as, photonic crystal elements described herein can include a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region.

[0027] In one example, the photonic crystal can be a semiconductor layer, e.g., p-doped AlGaAs in one instance, that has a plurality of holes 175. In at least one example, such holes may be free of solid material and instead may be filled, at least partially with air. Referring to FIG. 1A and IB the holes may be through holes that extend through a thickness of the photonic crystal (thickness measured along the Z-direction), e.g., from a first main surface to a second mian surface of the photonic crystal. The photonic crystal can realize a lack or a break the in-plane symmetry (XY-plane symmetry in FIG. IB) by the arrangement of the holes 175. That is, the holes may lack symmetry from a top view, e.g., view facing the XY plane. As shown, the shape (e.g., the trapezoidal-like shape in this example) of the holes 175 results in the holes 175are asymmetric in the XY-plane. That is, the holes 175cannot create two mirror-image halves by being divided into two mirror-image halves by lines drawn through its center along the X-axis and the y-axis.

[0028] FIG. 2A shows another semiconductor laser device or PSCEL 200 according to another aspect of the present disclosure. The PCSEL 200 may be in several respects be similar to the PCSEL 100 of FIG. 1. Hence, herein the same elements being referred to with the same reference number. Therefore, a duplicated description of such elements is not provided.

[0029] The PCSEL 200, unlike the PCSL 100, includes a chiral metamaterial element 270. In one or instances, the chiral metamaterial element 270 is a chiral photonic crystal. In other cases, the metamaterial element 270 can be a chiral metasurface material.

[0030] As shown in FIG. 2A, the metamaterial element 270, like the metamaterial element 170 of FIG. 1, can be arranged vertically (e.g., along the z-direction) between the multijunction active region 150 and the p-doped layer 120.

[0031] In the case where the metamaterial element 270 is a chiral photonic crystal, it can be a chiral photonic crystal with broken in-plane and out-of-plane symmetries. That is, like described in connection with the photonic crystal of FIG. 1A and IB, the chiral photonic crystal can have lack in-plane (XY-plane) symmetry and further also lack out-of-plane symmetry (plane perpendicular or orthogonal to XY-plane).

[0032] For example, the chiral photonic crystal 270 may be a semiconductor layer with holes 275 as shown in FIG. 2B. The holes 275 can be through holes which again lack symmetry inplane symmetry (e.g., lack in the XY-plane). That is, the holes 275 lack symmetry with respect to a plane parallel to the vertical direction (in Z-direction).

[0033] In addition, FIG. 2C further shows views or aspects of the chiral photonic crystal 270. That is, FIG. 2C shows the holes 275 configured so that the chiral photonic crystal 270 further lacks out-of-plane symmetry. That is the chiral photonic crystal 270 lacks in-plane symmetry and out-of-plane symmetry.

[0034] FIG. 2C includes a perspective view of the chiral photonic crystal 270, a unit cell section 270a of the chiral photonic crystal 270 and a cross-sectional view of a hole 275 of the chiral photonic crystal 270. As shown, the hole 270 in this example are slanted or arranged at angle cp offset from vertical direction (e.g., Z-axis direction).

[0035] As shown, the sections of the chiral photonic crystal 270 can produce or excite a combination of both right-hand circle polarization (RCP) and left-hand circular polarization (LCP) radiation.

[0036] In general, the chiral photonic crystal or chiral metasurf aces / metamaterials 270 disclosed or employed herein can be configured or designed to break both in-plane and out-of-plane symmetries to achieve strong chirality. Such a chiral photonic crystal exhibits near unity circular dichroism and a very large Q-factor (Q~10A4).

[0037] In various examples, the chiral photonic crystal or metasurface 270 is subwavelength is the fricative index of the medium).

[0038] FIGS. 2D and 2E shows alternative structures for alternative realizations or of chiral photonic crystal for laser devices described herein. Therefore, the geometry of chiral photonic crystal is not necessarily unique. FIG. 2D shows a structure from Kuhner, Lucca, et al. "Unlocking the out-of-plane dimension for photonic bound states in the continuum to achieve maximum optical chirality." Light: Science & Applications 12.1 (2023) and FIG. 2E shows a structure from M.V. Gorkunov, et al. “Metasurfaces with maximum chirality empowered by bound states in the continuum” Physical Review Letters, 125, 093903.

[0039] In general, the chiral photonic crystal with strong chirality can be realized by breaking both in-plane and out-of-plane symmetries.

[0040] FIG. 3 shows another semiconductor laser device or PSCEL 300 according to another aspect of the present disclosure. The PCSEL 300 may be similar in some respects to other laser devices described herein, e.g., the PCSEL 200 of FIG. 2A. Hence, herein the same elements being referred to with the same reference number. Therefore, a duplicated description of such elements may not be provided.

[0041] The PCSEL 300, similar to the PCSEL 200, includes a chiral metamaterial element 270. The chiral metamaterial element 270 can be a chiral photonic crystal, e.g., including holes 275 and lacking in-plane and out-of-plane symmetry (e.g., see FIG 2B). In other cases, the metamaterial element 270 can be a chiral metasurface material also as described in other devices herein (e.g., see FIGS. 2C-2D).

[0042] Unlike the devices 100 or 200 of FIGS. 1 and 2, the laser device 300 includes a reflector structure 310. In the example of FIG. 3 A, the reflector structure 310 can be arranged over a side of chiral metamaterial element 270 facing away from the multijunction active region 150. In particular, the reflector structure 310 can be arranged vertically between the chiral metamaterial element 270 and the anode 180.

[0043] In at least one example, the reflector structure 310 is a distributed Bragg reflector (DBR) which can include alternating layers of materials with different refractive indices. For instance, reflector structures, e.g., DBRs or DBR mirrors, described herein can be based on AlGaAs / GaAs material system. That is, such DBR mirrors can include alternating layers. For a first layer 112 can be a layer of Aluminum Gallium Arsenide (AlGaAs) and a second layer 114 can be a layer of Gallium Arsenide (GaAs).

[0044] For the PCSEL or laser device 300, DBR 310 helps to minimize the absorption losses in the contact 180 and improve the WPE of the chiral PCSEL.

[0045] FIG. 4A shows another semiconductor laser device or PSCEL 400 according to another aspect of the present disclosure. The PCSEL 400 may be in several respects similar to other PCSELs or laser devices described herein. Hence, herein the same elements being referred to with the same reference number. Therefore, a duplicated description of such elements is not provided.

[0046] The PCSEL 400, like the PCSEL 100, includes a metamaterial element / metamaterial layer 170a formed over the semiconductor substrate 105 and on or over the active region 150. Further, like the laser device 300, the PCSEL or laser device 400 further also includes a reflector structure 310 arranged vertically between the metamaterial element 170a and the anode 180.

[0047] Also similar to the laser device 300, the device 400 includes a reflector structure 310 arranged between the metamaterial element 170a and the anode 180. The reflector structure can be a DBR, e.g., any DBR described herein.

[0048] Furthermore, the laser device 400 further includes a second metamaterial element 170b. As shown in the example of FIG. 4B, the second metamaterial element is arranged between the multijunction active region 150 and the cathode 185. That is, the second metamaterial element is arranged over a side of the multijunction active region 150 facing away from the first metamaterial element 170a.

[0049] In at least one example, the first and second metamaterial elements 170a, 170b are configured so that laser device 400 is configured to emit an arbitrary polarization. That the first and second metamaterial elements can cause the laser device to emit a linearly polarized, a circularly, polarized, or an elliptically polarized emission. That is, the laser device 400 can realize polarization control resulting from the configuration of the first and second metamaterial elements 170a, 170b.

[0050] FIGS 4B and 4C respectively show an example of the first metamaterial element 170a and the second metamaterial 170b as seen from a top view. In this example the first metamaterial element 170a and the second metamaterial 170b are each photonic crystals including a plurality of holes 175. The photonic crystals 170a, 170b can be any photonic crystals described herein e.g., p-doped AlGaAs in one instance.

[0051] In the example of FIG. 4A, the polarization control can be realized with photonic crystals 170a and 170b having holes 175 oriented (in the XY-plane) as shown in FIGS. 4B and 4C. For each of the first photonic crystal / first photonic crystal element 170a and in the second photonic crystal / second photonic crystal element 170b the holes 175 can be through-holes. As shown, the holes 175 in the first photonic crystal element 170a can have an orientation defined by angle 0_A. The angle 0_A can be measured with respect to a reference line L in the plane (e.g., the XY-plane) where the main surface of the first photonic crystal element 170a resides or is parallel to. The holes 175 in the second photonic crystal element 170b can have an orientation similarly defined by angle 0_B.

[0052] The PCSEL or laser device 400 can realize polarization control by adjusting the (relative) angle between the photonic crystal 170a and the photonic crystal 170b (6 A and 0_B). By adjusting the angles and changing the differences in angles between the holes of the first photonic crystal element 170a and the second photonic crystal element 170b, different polarizations (e.g., linear, chiral, and elliptical) can be produced by the laser device 400.

[0053] FIG. 5 shows another semiconductor laser device or PSCEL 500 according to another aspect of the present disclosure. The PCSEL or laser device 500 may be similar in some respects to other laser devices described herein. Hence, herein the same elements being referred to with the same reference number. Therefore, a duplicated description of such elements may not be provided.

[0054] In FIG. 5, the PCSEL or laser device 500, like the laser device 200, includes a chiral photonic metamaterial element 270. In the example of FIG. 5A, the chiral photonic metamaterial element 270 is arranged above a multijunction active region 150. As described in other examples, the chiral photonic metamaterial 270 lacks or breaks both inplane and out-of-plane symmetry. The chiral photonic metamaterial element 270 may be a chiral photonic element that includes holes 275, e.g., through holes.

[0055] In at least one case, as described in other examples, the chiral photonic element 270 may include a layer of p-doped semiconductor, e.g., p-doped AlGaAs. In one or more instances, the holes 275 of the chiral photonic element 270 may be filled with material. For instance, the holes 275 may be filled with one or more low-refractive index dielectric materials. Examples of such materials include silicon oxide (SiO2), silicon nitride (SiN), and aluminum oxide (A12O3), to name a few.

[0056] Further, in the example of FIG. 5, the contact 180 (e.g., anode 180) can be directly connected or electrically coupled to the photonic crystal element 270, e.g., to the non-hole regions, e.g., the semiconductor part of the photonic crystal element 270. As shown, the contact 180 includes vias 182 that directly connect the contact 180 to the photonic crystal element 270. In addition, a layer 190 may be included between a top portion of the contact 180 and the chiral photonic crystal element 270. The vias 182 of the contact 180 can extend from the contact 180 and through the layer 190 to contact the chiral photonic crystal element 270. In one or more instances, the layer 190 may be a layer of indium titanium oxide (ITO).

[0057] FIG. 6 shows a method 600 according to at least one example of the present disclosure. The method 600 may be used for forming at least a portion of the one or more devices described herein.

[0058] The method 600 includes at 610, forming semiconductor substrate.

[0059] Next, at 620, the method 600 includes forming a multijunction active region arranged over a main surface of a semiconductor substrate.

[0060] Forming the multijunction active region includes, at 622, forming a plurality of active regions each comprising a multiple-quantum-well (MQWs), and includes, at 624, forming a plurality of tunnel junction layers providing electrical coupling and located between neighboring active regions along a vertical direction perpendicular to the main surface of the semiconductor substrate.

[0061] At 630, the method 600 includes forming a first metamaterial element over the multijunction active region so that the multijunction active region is arranged between the semiconductor substrate and the first metamaterial element.

[0062] Additional processes or actions, familiar to those skilled in the art, may be employed to complete or further the formation of these or similar devices. See also, the example section.

[0063] For example, forming a multijunction active region and the first metamaterial element may include epitaxially growing a plurality of layers on or over the main surface of the semiconductor substrate. Epitaxially growing this plurality of layers may include epitaxially growing the layers using chemical vapor deposition (CVD), which may include using metal organic chemical vapor deposition (MOCVD).

[0064] In at least one example, the first metamaterial element is a photonic crystal element that lacks or breaks in-plane symmetry with respect to a plane parallel to the vertical direction. Further, forming such a photonic crystal element may include patterning at least one of the epitaxially grown layers by performing high-resolution lithography, and etching the patterned areas of the at least one of the epitaxially grown layers. Performing the high- resolution lithography technique may include performing electron-beam lithography or nano-imprint lithography. Etching the patterned areas may include performing inductively coupled plasma-reactive ion etching (ICP-RIE).

[0065] The same techniques for forming a first photonic crystal element may be applied to devices described herein that also include a second photonic crystal element.

[0066] The following examples concern or relate to aspects of the present disclosure.

[0067] Example 1 is a semiconductor laser device including: a first metamaterial element; a semiconductor substrate having a main surface; and a multijunction active region arranged over the main surface of the semiconductor substrate between the first metamaterial element and the semiconductor substrate, the multijunction active region includes: a plurality of active regions each comprising a multiple-quantum-well (MQWs), and a plurality of tunnel junction layers providing electrical coupling and located between neighboring active regions along a vertical direction perpendicular to the main surface of the semiconductor substrate.

[0068] Example 2 is the subject matter of Example 1, which may further include a first contact arranged over a surface of the first metamaterial element facing away from the multijunction active region; and a second contact arranged over a surface of the substrate facing away from the multijunction active region.

[0069] Example 3 is the subject matter of Example 1 or 2, wherein the first metamaterial element is optionally a photonic crystal element or a metasurface element.

[0070] Example 4 is the subject matter of Example 3, wherein the first metamaterial element may be configured for linear polarization and may be configured to operate at one or more gamma, T, points, and wherein the semiconductor laser device can be configured to produce an optical standing wave so that the peak of the optical standing wave overlaps with one or more of the active regions of the multijunction active region and so that the null of the optical standing wave occurs at one or more of the tunnel junctions. Example 5 is the subject matter of Example 4, wherein the first metamaterial element may be a photonic crystal element that lacks or breaks in-plane symmetry with respect to a plane parallel to the vertical direction.

[0071] Example 6 is the subject matter of Example 5, wherein the photonic crystal element may include a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the photonic crystal element includes a plurality of holes extending through the photonic crystal element from the first main surface to the main surface at an angle offset from the vertical direction, wherein the plurality of holes configure or cause the photonic crystal to lack in-plane symmetry with respect to the plane parallel to the vertical direction.

[0072] Example 7 is the subject matter of Example 6, wherein each of the plurality of holes may be filled at least partially with air.

[0073] Example 8 is the subject matter of Example 3, which may further include a second metamaterial element arranged on or over a side the multijunction active region opposite to a side facing the first metamaterial element; and a reflector structure arranged over a side of the first metamaterial element facing away from the multijunction active region.

[0074] Example 9 is the subject matter of Example 8, wherein the first metamaterial element and the second metamaterial element can be configured so that the semiconductor laser device is configured to emit an arbitrary polarization emission comprising a linearly polarized, a circularly polarized, or an elliptically polarized emission.

[0075] Example 10 is the subject matter of Example 9, wherein the first metamaterial element may include a first photonic crystal element and the second metamaterial element may include a second photonic crystal element, wherein the first photonic crystal element includes a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the first photonic crystal element includes a plurality of holes extending from the first main surface to the second main surface of the first photonic crystal element, wherein each of the plurality of holes have a first orientation with respect to a top view facing the first main surface of first the photonic crystal element, wherein the second photonic crystal element includes a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the second photonic crystal element includes a plurality of holes extending from the first main surface to the second main surface of the second photonic crystal element, wherein each of the plurality of holes have a second orientation with respect to a top view facing the first main surface of the second photonic crystal element, wherein the semiconductor device is configured to emit a linearly polarized emission, a circularly polarized emission, or an elliptically polarized emission based on the first orientation and the second orientation.

[0076] Example 11 is the subject matter of Example 10, wherein each of the plurality of holes of the first photonic crystal and the second photonic crystal may be filled at least partially with air and / or a low index material.

[0077] Example 12 is the subject matter of Example 3, wherein the first metamaterial element may optionally be a chiral metamaterial element.

[0078] Example 13 is the subject matter of Example 12, wherein the chiral metamaterial element may be a chiral photonic crystal element or a chiral metasurface element.

[0079] Example 14 is the subject matter of Example 12 or 13, wherein the chiral metamaterial element may be a chiral photonic crystal element having broken in-plane symmetry and broken out-of-plane symmetry with respect to a plane perpendicular to the vertical direction.

[0080] Example 15 is the subject matter of Example 14, wherein the chiral photonic crystal element may include a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the chiral photonic crystal element includes a plurality of holes extending through the chiral photonic crystal element from the first main surface to the main surface at angle offset from the vertical direction, wherein the plurality of holes configures the chiral photonic crystal to lack in-plane symmetry and out-of-plane symmetry with respect to the plane parallel to the vertical direction.

[0081] Example 16 is the subject matter of Example 15, wherein each of the plurality of holes may optionally be filled at least partially with air.

[0082] Example 17 is the subject matter of any of Examples 12 to 16, which may further include a reflector structure arranged over a side of the chiral metamaterial element facing away from the multijunction active region. Example 18 is the subject matter of Example 17, wherein the reflector structure may optionally include a distributed Bragg reflector (DBR).

[0083] Example 19 is the subject matter of Example 15, wherein each the plurality of holes may be filled (wholly or partially) with a dielectric material; wherein the semiconductor laser device may further include one or more vias electrically connecting the chiral photonic crystal element to the first contact, e.g., connecting a semiconductor material portion of the chiral photonic crystal element to the first contact.

[0084] Example 20 is the subject matter of Example 19, wherein the dielectric material may be a low-refractive index dielectric material.

[0085] Example 21 is the subject matter of Example 20, wherein the low-refractive index dielectric material may include silicon oxide, silicon nitride, and / or aluminum oxide.

[0086] Example 22 is the subject matter of any of Examples 1 to 21, wherein the substrate can be a n-doped semiconductor substrate.

[0087] Example 23 is the subject matter of Example 22, wherein the n-doped semiconductor substrate can be a n-doped gallium arsenide substrate.

[0088] Example 24 is the subject matter of any of Examples 2 to 23, wherein the first contact can be a p-contact and the second contact can be a n-contact.

[0089] Example 25 is the subject matter of any of Examples 2 to 24, which may further include a cladding layer arranged between the first contact and the first metamaterial element.

[0090] Example 26 is the subject matter of Example 25, wherein the cladding layer may include a p-doped semiconductor layer, e.g., p-doped aluminum gallium arsenide.

[0091] Example 27 is the subject matter of any of Examples 1 to 26, wherein the first metamaterial element may include p-doped semiconductor material, e.g., p-doped aluminum gallium arsenide.

[0092] Example 1 A is a method including: forming semiconductor substrate; forming a multijunction active region arranged over a main surface of a semiconductor substrate, wherein forming the multijunction active region includes: forming a plurality of active regions each comprising a multiple-quantumwell (MQWs), and forming a plurality of tunnel junction layers providing electrical coupling and located between neighboring active regions along a vertical direction perpendicular to the main surface of the semiconductor substrate; and forming a first metamaterial element over the multijunction active region so that the multijunction active region is arranged between the semiconductor substrate and the first metamaterial element.

[0093] Example 2A is the subject matter of Example 1 A, which may further include: forming a first contact over a surface of the first metamaterial element facing away from the multijunction active region; and forming a second contact arranged over a surface of the substrate facing away from the multijunction active region.

[0094] Example 3A is the subject matter of Example 1A or 2A, wherein forming the multijunction active region and the first metamaterial element may include epitaxially growing a plurality of layers on or over the main surface of the semiconductor substrate.

[0095] Example 4 A is the subject matter of Example 3 A, wherein epitaxially growing the plurality of layers may include epitaxially growing the layers using chemical vapor deposition (CVD).

[0096] Example 5 A is the subject matter of Example 4A, where the layers may be grown using metal organic chemical vapor deposition (MOCVD).

[0097] Example 6A is the subject matter of any of Examples 1 A to 4A, wherein the first metamaterial element may be a photonic crystal element or a metasurface element.

[0098] Example 7A is the subject matter of Example 6A, wherein the first metamaterial element is a photonic crystal element, wherein the photonic crystal element can lack or break in-plane symmetry with respect to a plane parallel to the vertical direction, and wherein forming the photonic crystal element may include: patterning at least one of the epitaxially grown layers by performing high-resolution lithography, and etching the patterned areas of the at least one of the epitaxially grown layers

[0099] Example 8 A is the subject matter of Example 7A, wherein performing the high-resolution lithography technique may include performing electron-beam lithography or nano-imprint lithography.

[0100] Example 9A is the subject matter of Example 7A or 8 A, wherein etching the patterned areas may include performing inductively coupled plasma-reactive ion etching (ICP-RIE)

[0101] Example 10A is the subject matter of any of Examples 7A to 9A, wherein the photonic crystal element may include a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the photonic crystal element may include a plurality of holes extending through the photonic crystal element from the first main surface to the main surface at an angle offset from the vertical direction, wherein the plurality of holes can configure the photonic crystal to lack in-plane symmetry with respect to the plane parallel to the vertical direction.

[0102] Example 11 A is the subject matter of Example 10A, wherein each of the plurality of holes can be filled with air and / or low index materials.

[0103] Example 12A is the subject matter of Example 6A, which may further include: forming a second metamaterial element arranged on or over a side the multijunction active region opposite to a side facing the first metamaterial element; and forming a reflector structure arranged over a side of the first metamaterial element facing away from the multijunction active region.

[0104] Example 13A is the subject matter of Example 12A, wherein the first metamaterial element may include a first photonic crystal element and the second metamaterial element comprises a second photonic crystal element, wherein forming each of the first and second photonic crystal elements may include: patterning at least one of the epitaxially grown layers by performing high-resolution lithography, and etching the patterned areas of the at least one of the epitaxially grown layers.

[0105] Example 14A is the subject matter of Example 13A, wherein performing the high- resolution lithography technique can include performing electron-beam lithography or nano-imprint lithography.

[0106] Example 15A is the subject matter of Example 13A or 14A, wherein etching the patterned areas comprises performing inductively coupled plasma- reactive ion etching (ICP-RIE)

[0107] Example 16A is the subject matter of any of Examples 13 A to 15 A, wherein the first photonic crystal element can include a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the photonic crystal element includes a plurality of holes in the first photonic crystal element extending from the first main surface to the second main surface of the first photonic crystal element, wherein each of the plurality of holes have a first orientation with respect to a top view facing the first main surface of first the photonic crystal element, wherein the second photonic crystal element includes a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein forming the second photonic crystal element includes forming a plurality of holes in the second photonic crystal element extending from the first main surface to the second main surface of the second photonic crystal element, wherein each of the plurality of holes have a second orientation with respect to a top view facing the first main surface of the second photonic crystal element.

[0108] Example 17A is the subject matter of Example 16A, wherein the second orientation can be different from the first orientation.

[0109] Example 18A is the subject matter of Example 16A or 17A, wherein each of the plurality of holes of the first photonic crystal and the second photonic crystal may be filled with at least with air and / or a low index material. Example 19A is the subject matter of Example 6A, wherein the first metamaterial element can be a chiral metamaterial element that is a chiral photonic crystal element or a chiral metasurface element.

[0110] Example 20A is the subject matter of Example 19A, wherein the first metamaterial element is a chiral photonic crystal element having broken in-plane symmetry and broken out-of-plane symmetry with respect to a plane perpendicular to the vertical direction, wherein forming the chiral photonic crystal element can include: patterning at least one of the epitaxially grown layers by performing high-resolution lithography, and etching the patterned areas of the at least one of the epitaxially grown layers

[0111] Example 21 A is the subject matter of Example 20A, wherein the chiral photonic crystal element can include a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein forming the first metal material element can include forming a plurality of holes in the chiral photonic crystal element extending through the photonic crystal element from the first main surface to the main surface at angle offset from the vertical direction, wherein the plurality of holes configures the chiral photonic crystal to lack in-plane symmetry and out-of-plane symmetry with respect to the plane parallel to the vertical direction.

[0112] Example 22A is the subject matter of Example 21 A, wherein each of the plurality of air holes can be filled at least partially with air.

[0113] Example 23A is the subject matter of any of Examples 19A to 21A, which may further include: forming a reflector structure arranged over a side of the chiral metamaterial element facing away from the multijunction active region.

[0114] Example 24A is the subject matter of Example 23 A, wherein the reflector structure can be a distributed Bragg reflector (DBR).

[0115] Example 25A is the subject matter of Example 21A, which may further include: filling each of the plurality of holes is filled with a dielectric material; and forming one or more vias electrically connecting one or more of the plurality of dielectric filled holes to the first contact.

[0116] Example 26A is the subject matter of Example 25 A, wherein the dielectric material can be a low-refractive index dielectric material.

[0117] Example 27A is the subject matter of Example 26A, wherein the low-refractive index dielectric material can include silicon oxide, silicon nitride, and / or aluminum oxide.

[0118] Example 28A is the subject matter of any of Examples 1A to 24A, wherein the substrate can be a n-doped semiconductor substrate.

[0119] Example 29A is the subject matter of Example 28 A, wherein the n-doped semiconductor substrate can be a n-doped gallium arsenide substrate.

[0120] Example 30A is the subject matter of any of Examples 2A to 26A, wherein the first contact can be a p-contact and the second contact can be a n-contact.

[0121] Example 31A is the subject matter of any of Examples 2A to 30A, which may further include: forming, by MOCVD or molecular beam epitaxy (MBE), a cladding layer between the first contact and the first metamaterial element.

[0122] Example 32A is the subject matter of Example 31 A, wherein the cladding layer can include a p-doped layer of aluminum gallium arsenide.

[0123] Example 33A is the subject matter of any of Examples 1A to 32A, wherein the first metamaterial element can include a p-doped aluminum gallium arsenide.

[0124] Example 34A is the subject matter of any of Examples 2A to 33A, which may further include: performing an etching process to form a circular mesa from layers extending from the substrate to first metamaterial element, wherein the first and second contacts are formed on the circular mesa. Example 35 A is the subject matter of any of Examples 2A to 34A, wherein forming each of the first contact and the second contact can include performing an electron beam evaporation.

[0125] Any of the aspects, examples, and / or embodiments described herein may be suitable or appropriately combined including combined with the embodiments or examples described herein.

[0126] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any example or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other examples or designs.

[0127] For the purposes of the present disclosure, the phrase "A and / or B" means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0128] Reference to "one embodiment" or "an embodiment" in the present disclosure means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" or "in an embodiment" are not necessarily all referring to the same embodiment. The appearances of the phrase "for example," "in an example," or "in some examples" are not necessarily all referring to the same example.

[0129] The words “plurality” and “multiple” in the description or the claims expressly refer to a quantity greater than one. The terms “group (of)”, “set [of]”, “collection (of)”, “series (of)”, “sequence (of)”, “grouping (of)”, etc., and the like in the description or in the claims refer to a quantity equal to or greater than one, i.e. one or more. Any term expressed in plural form that does not expressly state “plurality” or “multiple” likewise refers to a quantity equal to or greater than one.

[0130] The term “connected” can be understood in the sense of a (e.g. mechanical, optical and / or electrical), e.g. direct or indirect, connection and / or interaction. For example, several elements can be connected together mechanically such that they are physically retained (e.g., a plug connected to a socket) and electrically such that they have an electrically conductive path (e.g., signal paths exist along a communicative chain). As used herein, unless otherwise specified the use of the ordinal adjectives “first”, “second”, “third” etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

[0131] As utilized herein, terms "module", "component," "system," "circuit," "element," "slice," "circuitry," and the like are intended to refer to a set of one or more electronic components, a computer-related entity, hardware, software (e.g., in execution), and / or firmware. For example, circuitry or a similar term can be a processor, a process running on a processor, a controller, an object, an executable program, a storage device, and / or a computer with a processing device. By way of illustration, an application running on a server and the server can also be circuitry. One or more circuits can reside within the same circuitry, and circuitry can be localized on one computer and / or distributed between two or more computers. A set of elements or a set of other circuits can be described herein, in which the term "set" can be interpreted as "one or more."

[0132] Such electric or electronic circuitry can be operated by a software application or a firmware application executed by one or more processors. The one or more processors can be internal or external to the apparatus and can execute at least a part of the software or firmware application. As yet another example, circuitry can be an apparatus that provides specific functionality through electronic components without mechanical parts; the electronic components can include one or more processors therein to execute executable instructions stored in computer readable storage medium and / or firmware that confer(s), at least in part, the functionality of the electronic components. As another example, circuitry or similar term can be implemented in hardware such as application specific integrated circuit (ASIC), programmable gate array (PGA), discrete digital circuits, etc.) or in a combination of hardware and software (e.g., a software model executed by a corresponding processor).

[0133] The term "semiconductor substrate" can mean any construction comprising semiconductor material, for example, a silicon substrate with or without an epitaxial layer, a silicon-on- insulator substrate containing a buried insulator layer, or a substrate with a silicon germanium layer.

[0134] A lateral direction is understood to mean a direction that runs, in particular, parallel to a main extension surface of the component, in particular of a layer. A vertical direction is understood to mean a direction that is oriented, in particular, perpendicular to the main extension surface of the component and / or layer. The vertical direction and the lateral direction are approximately orthogonal to each other.

[0135] Further, spatially relative terms, such as "beneath," "below," "lower," "above," "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0136] The term "data" as used herein may be understood to include information in any suitable analog or digital form, e.g., provided as a file, a portion of a file, a set of files, a signal or stream, a portion of a signal or stream, a set of signals or streams, and the like. Further, the term "data" may also be used to mean a reference to information, e.g., in form of a pointer. The term data, however, is not limited to the aforementioned examples and may take various forms and represent any information as understood in the art.

[0137] As used herein, a signal that is "indicative of' a value or other information may be a digital or analog signal that encodes or otherwise communicates the value or other information in a manner that can be decoded by and / or cause a responsive action in a component receiving the signal. The signal may be stored or buffered in computer readable storage medium prior to its receipt by the receiving component and the receiving component may retrieve the signal from the storage medium. Further, a "value" that is "indicative of some quantity, state, or parameter may be physically embodied as a digital signal, an analog signal, or stored bits that encode or otherwise communicate the value.

[0138] Unless otherwise stated, the words “about” and “substantially” as used herein are to be construed as meaning the normal measuring and / or fabrication limitations related to the value or condition which the word “about” or “substantially” modifies. Unless expressly stated otherwise, the term “embodiment” is used herein to mean an embodiment of the present disclosure.

[0139] As used herein, a signal may be transmitted or conducted through a signal chain in which the signal is processed to change characteristics such as phase, amplitude, frequency, and so on. The signal may be referred to as the same signal even as such characteristics are adapted. In general, so long as a signal continues to encode the same information, the signal may be considered as the same signal. For example, a transmit signal may be considered as referring to the transmit signal in baseband, intermediate, and radio frequencies.

[0140] While the above descriptions and connected figures may depict device components as separate elements, skilled persons will appreciate the various possibilities to combine or integrate discrete features, functions into a single element. Such may include combining two or more components into a single component. Conversely, skilled persons will recognize the possibility to separate a single element into two or more discrete elements, such as splitting a single component into two or more separate components.

[0141] It is appreciated that implementations of methods detailed herein are exemplary in nature, and are thus understood as capable of being implemented in a corresponding device. Likewise, it is appreciated that implementations of devices detailed herein are understood as capable of being implemented as a corresponding method. It is thus understood that a device corresponding to a method detailed herein may include one or more components configured to perform each aspect of the related method.

[0142] All acronyms defined in the above description additionally hold in all claims included herein.

[0143] While embodiments of the present disclosure have been described above, it is obvious that further embodiments may be implemented. For example, further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above. Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.

[0144] While the disclosure has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims. The scope of the disclosure is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced. Reference Numeral List semiconductor laser device / PCSEL semiconductor substrate a semiconductor substrate surface n-doped semiconductor layer layer of reflector structure layer of reflector structure p-doped semiconductor layer active region MWW region tunnel junction / 170a / 170b metamaterial element hole(s) first contact / anode via(s) second contact / cathode layer semiconductor laser device / PCSEL metamaterial element a unit cell section of metamaterial element hole(s) semiconductor laser device / PCSEL reflector structure / DBR semiconductor laser device / PCSEL semiconductor laser device / PCSEL -630 method

Claims

1. CLAIMS1. A semiconductor laser device comprising: a first metamaterial element; a semiconductor substrate having a main surface; and a multijunction active region arranged over the main surface of the semiconductor substrate between the first metamaterial element and the semiconductor substrate, the multijunction active region comprising: a plurality of active regions each comprising a multiple-quantum-well (MQWs), and a plurality of tunnel junction layers providing electrical coupling and located between neighboring active regions along a vertical direction perpendicular to the main surface of the semiconductor substrate.

2. The semiconductor laser device of claim 1, further comprising: a first contact arranged over a surface of the first metamaterial element facing away from the multijunction active region; and a second contact arranged over a surface of the substrate facing away from the multijunction active region.

3. The semiconductor laser device of claim 1 or 2, wherein the first metamaterial element is optionally a photonic crystal element or a metasurface element.

4. The semiconductor laser device of claim 3, wherein the first metamaterial element is configured for linear polarization and configured to operate at one or more gamma, T, points, and wherein the semiconductor laser device is configured to produce an optical standing wave so that the peak of the optical standing wave overlaps with one or more of the active regions of the multijunction active region and so that the null of the optical standing wave occurs at one or more of the tunnel junctions.

5. The semiconductor laser of claim 4, wherein the first metamaterial element is a photonic crystal element, and wherein the photonic crystal element lacks or breaks in-plane symmetry with respect to a plane parallel to the vertical direction.

6. The semiconductor laser of claim 5, wherein the photonic crystal element comprises a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the chiral photonic crystal element includes a plurality of holes extending through the photonic crystal element from the first main surface to the main surface at an angle offset from the vertical direction, wherein the plurality of holes configures the photonic crystal to lack in-plane symmetry with respect to the plane parallel to the vertical direction.

7. The semiconductor laser of claim 6, wherein each of the plurality of holes are filled at least partially with air.

8. The semiconductor laser device of claim 3, further comprising a second metamaterial element arranged on or over a side the multijunction active region opposite to a side facing the first metamaterial element; and a reflector structure arranged over a side of the first metamaterial element facing away from the multijunction active region.

9. The semiconductor laser device of claim 8, wherein the first metamaterial element and the second metamaterial element are configured so that the semiconductor laser device is configured to emit an arbitrary polarization emission comprising a linearly polarized, a circularly polarized, or an elliptically polarized emission.

10. The semiconductor laser device of claim 9, wherein the first metamaterial element comprises a first photonic crystal element and the second metamaterial element comprises a second photonic crystal element, wherein the first photonic crystal element comprises a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the first photonic crystal element includes a plurality of holes extending from the first main surface to the second main surface of the first photonic crystal element, wherein each of the plurality of holes have a first orientation with respect to a top view facing the first main surface of first the photonic crystal element, wherein the second photonic crystal element comprises a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the second photonic crystal element includes a plurality of holes extending from the first main surface to the second main surface of the second photonic crystal element, wherein each ofthe plurality of holes have a second orientation with respect to a top view facing the first main surface of the second photonic crystal element. wherein the semiconductor device is configured to emit a linearly polarized emission, a circularly polarized emission, or an elliptically polarized emission based on the first orientation and the second orientation.

11. The semiconductor laser device of claim 10, wherein each of the plurality of holes of the first photonic crystal and the second photonic crystal are filled at least partially with air and / or a low index material.

12. The semiconductor laser device of claim 3, wherein the first metamaterial element is a chiral metamaterial element.

13. The semiconductor laser device of claim 12, wherein the chiral metamaterial element is a chiral photonic crystal element or a chiral metasurface element.

14. The semiconductor laser device of claim 12 or 13, wherein the chiral metamaterial element is a chiral photonic crystal element having broken in-plane symmetry and broken out-of-plane symmetry with respect to a plane perpendicular to the vertical direction.

15. The semiconductor laser device of claim 14, wherein the chiral photonic crystal element comprises a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the chiral photonic crystal element includes a plurality of holes extending through the photonic crystal element from the first main surface to the main surface at angle offset from the vertical direction, wherein the plurality of holes configures the chiral photonic crystal to lack in-plane symmetry and out-of-plane symmetry with respect to the plane parallel to the vertical direction.

16. The semiconductor laser device of claim 15, wherein each of the plurality of holes is filled at least partially with air.

17. The semiconductor laser device of claim 12 or 13, further comprising:a reflector structure arranged over a side of the chiral metamaterial element facing away from the multijunction active region.

18. The semiconductor laser device of claim 17, wherein the reflector structure comprises a distributed Bragg reflector (DBR).

19. The semiconductor laser device of claim 15, further comprising: wherein each the plurality of holes is filled with a dielectric material; wherein the semiconductor laser device further comprises one or more vias electrically connecting chiral photonic crystal element to the first contact.

20. The semiconductor laser device of claim 19, wherein the dielectric material comprises a low- refractive index dielectric material.

21. The semiconductor laser device of claim 20, wherein the low-refractive index dielectric material comprises silicon oxide, silicon nitride, and / or aluminum oxide.

22. The semiconductor laser device of claim 1, wherein the substrate comprises an n-doped semiconductor substrate.

23. The semiconductor laser device of claim 22, wherein the n-doped semiconductor substrate comprises n-doped gallium arsenide substrate.

24. The semiconductor laser device of claim 2, wherein the first contact comprises a p-contact and the second contact comprises an n-contact.

25. The semiconductor laser device of claim 2, further comprises a cladding layer arranged between the first contact and the first metamaterial element.

26. The semiconductor laser device of claim 25, wherein the cladding layer comprises a p-doped semiconductor layer.

27. The semiconductor laser device of claim 1, wherein the first metamaterial element comprises a p-doped semiconductor material.

28. A method comprising:forming semiconductor substrate; forming a multijunction active region arranged over a main surface of a semiconductor substrate, wherein forming the multijunction active region comprises: forming a plurality of active regions each comprising a multiple -quantum-well (MQWs), and forming a plurality of tunnel junction layers providing electrical coupling and located between neighboring active regions along a vertical direction perpendicular to the main surface of the semiconductor substrate; and forming a first metamaterial element over the multijunction active region so that the multijunction active region is arranged between the semiconductor substrate and the first metamaterial element.

29. The method of claim 28, further comprising: forming a first contact over a surface of the first metamaterial element facing away from the multijunction active region; and forming a second contact arranged over a surface of the substrate facing away from the multijunction active region.

30. The method of claim 28 or 29, wherein forming the multijunction active region and the first metamaterial element comprises epitaxially growing a plurality of layers on or over the main surface of the semiconductor substrate.

31. The method of claim 30, wherein epitaxially growing the plurality of layers comprises epitaxially growing the layers using chemical vapor deposition (CVD).

32. The method of claim 31, where the layers are grown using metal organic chemical vapor deposition (MOCVD).

33. The method of claim 28 or 29, wherein the first metamaterial element may be a photonic crystal element or a metasurface element.

34. The method of claim 33, wherein the first metamaterial element is a photonic crystal element, wherein the photonic crystal element lacks or break in-plane symmetry with respect to a plane parallel to the vertical direction, and wherein forming the photonic crystal element comprises:paterning at least one of the epitaxially grown layers by performing high- resolution lithography, and etching the paterned areas of the at least one of the epitaxially grown layers35. The method claim 34, wherein performing the high-resolution lithography technique comprises performing electron-beam lithography or nano-imprint lithography.

36. The method claim 34 or 35, wherein etching the paterned areas comprises performing inductively coupled plasma-reactive ion etching (ICP-RIE)37. The method of claim 36, wherein the photonic crystal element comprises a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the photonic crystal element comprises a plurality of holes extending through the photonic crystal element from the first main surface to the main surface at an angle offset from the vertical direction, wherein the plurality of holes is configured so that the photonic crystal to lack in-plane symmetry with respect to the plane parallel to the vertical direction.

38. The method of claim 27, wherein each of the plurality of holes are filled with air and / or low index materials.

39. The method of claim 33, further comprising: forming a second metamaterial element arranged on or over a side the multijunction active region opposite to a side facing the first metamaterial element; and forming a reflector structure arranged over a side of the first metamaterial element facing away from the multijunction active region.

40. The method of claim 39, wherein the first metamaterial element comprises a first photonic crystal element and the second metamaterial element comprises a second photonic crystal element, wherein forming each of the first and second photonic crystal elements comprises: paterning at least one of the epitaxially grown layers by performing high- resolution lithography, and etching the paterned areas of the at least one of the epitaxially grown layers.

41. The method of claim 40, wherein performing the high-resolution lithography technique comprises performing electron-beam lithography or nano-imprint lithography.

42. The method of claim 40 or 41, wherein etching the patterned areas comprises performing inductively coupled plasma-reactive ion etching (ICP-RIE)43. The method of claim 40 or 41, wherein the first photonic crystal element comprises a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein the photonic crystal element includes a plurality of holes in the first photonic crystal element extending from the first main surface to the second main surface of the first photonic crystal element, wherein each of the plurality of holes have a first orientation with respect to a top view facing the first main surface of first the photonic crystal element, wherein the second photonic crystal element includes a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein forming the second photonic crystal element includes forming a plurality of holes in the second photonic crystal element extending from the first main surface to the second main surface of the second photonic crystal element, wherein each of the plurality of holes have a second orientation with respect to a top view facing the first main surface of the second photonic crystal element.

44. The method of claim 43, wherein the second orientation is different from the first orientation.

45. The method of claim 44, wherein each of the plurality of holes of the first photonic crystal and the second photonic crystal are filled with at least with air and / or a low index material.

46. The method claim 43, wherein the first metamaterial element comprises a chiral metamaterial element that is a chiral photonic crystal element or a chiral metasurface element.

47. The method of claim 46, wherein the first metamaterial element is a chiral photonic crystal element having broken in-plane symmetry and broken out-of-plane symmetry with respect to a plane perpendicular to the vertical direction, wherein forming the chiral photonic crystal element comprises:paterning at least one of the epitaxially grown layers by performing high- resolution lithography, and etching the paterned areas of the at least one of the epitaxially grown layers48. The method claim 47, wherein the chiral photonic crystal element comprises a first main surface and a second main surface which is opposite to the first main surface and faces toward the multijunction active region, wherein forming the first metal material element comprise forming a plurality of holes in the chiral photonic crystal element extending through the photonic crystal element from the first main surface to the main surface at angle offset from the vertical direction, wherein the plurality of holes configures the chiral photonic crystal to lack in-plane symmetry and out-of-plane symmetry with respect to the plane parallel to the vertical direction.

49. The method of claim 48, wherein each of the plurality of air holes are filled at least partially with air.

50. The method of claims 46 to 48, further comprising: forming a reflector structure arranged over a side of the chiral metamaterial element facing away from the multijunction active region.

51. The method of claim 50, wherein the reflector structure comprises a distributed Bragg reflector (DBR).

52. The method of claim 48, further comprising: filling each of the plurality of holes with a dielectric material; and forming one or more vias electrically connecting one or more of the plurality of dielectric filled holes to the first contact.

53. The method of claim 52, wherein the dielectric material comprises a low-refractive index dielectric material.

54. The method of claim 53, wherein the low-refractive index dielectric material comprises silicon oxide, silicon nitride, and / or aluminum oxide.

55. The method of claim 28, wherein the substrate comprises an n-doped semiconductor substrate.

56. The method of claim 55, wherein the n-doped semiconductor substrate comprises an n-doped gallium arsenide substrate.

57. The method of claim 29, wherein the first contact comprises a p-contact and the second contact comprises an n-contact.

58. The method of claim 29, further comprising: forming, by MOCVD or molecular beam epitaxy (MBE), a cladding layer between the first contact and the first metamaterial element.

59. The method of claim 58, wherein the cladding layer comprises a p-doped layer of aluminum gallium arsenide.

60. The method of claim 28, wherein the first metamaterial element comprises a p-doped aluminum gallium arsenide.

61. The method of claim 29, further comprising: performing an etching process to form a circular mesa from layers extending from the substrate to first metamaterial element, wherein the first and second contacts are formed on the circular mesa.

62. The method of claim 29, wherein forming each of the first contact and the second contact comprises performing electron beam evaporation.

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