Vertical cavity surface emitting laser for generating laser light

Abstract

A VCSEL (10) for generating laser light, having a base body (12), the base body (12) having first, second and third body parts (121, 122, 123) stacked in layers in an arrangement direction (1), the body parts (121, 122, 123) being connected to one another by a bonding process, the first body part (121) comprising a first Bragg reflector (141), the second body part (122) comprising a second Bragg reflector (142), the third body part (123) comprising an active layer (16), the first and second body parts (121, 122) form a resonant cavity (18) in which a third body part (123) is arranged between the first and second body parts (121, 122), the first and second body parts (121, 122) being free of indium and the third body part (123) containing indium, a photodetector (20), in particular in the form of a photodiode, being arranged in the resonant cavity (18), the photodetector is preferably arranged between the second Bragg reflector (142) and the active layer (16).

Description

Technical Field

[0001] The present invention relates to a vertical cavity surface emitting laser (VCSEL) for generating laser light. Background Art

[0002] A VCSEL is a semiconductor laser having an active region sandwiched between a stack of mirrors, which can be Bragg mirrors [NM Murgalit et al., Laterally Oxidized Long-Wavelength Continuous-Wave Vertical-Cavity Lasers, Applied Physics Letters, Vol. 69(4), July 22, 1996, pp. 471-472] or a combination of semiconductor and dielectric DBRs (Distributed Bragg Reflectors) [Y. Oshio et al., Wafer-Bonded InGaAsP / InP-GaAs / AlAs DBR Vertical-Cavity Surface-Emitting Lasers, Electronics Express, Vol. 32, No. 16, August 1996]. One of the mirror stacks is typically partially reflective, allowing a portion of the coherent light established in the resonant cavity formed by the mirror stack surrounding the active region to escape. The VCSEL is driven by a current flowing through the active region. The mirror stack is typically constructed from multiple pairs of layers made from a material system that typically contains two materials with different refractive indices that are easily lattice-matched to the rest of the VCSEL. For example, gallium arsenide (GaAs)-based VCSELs typically use aluminum arsenide / gallium arsenide (AlAs / GaAs) or aluminum gallium arsenide / aluminum arsenide (AlGaAs / AlAs) material systems, where the different refractive indices of each pair of layers are achieved by varying the aluminum content in the layers.

[0003] Conventional gallium arsenide (GaAs)-based VCSELs emit laser light at a wavelength of around 850 nm, a wavelength that is unsuitable for a range of applications requiring laser light transmission, particularly displays coated with organic light-emitting diodes, because most of the radiated energy is absorbed.

[0004] Furthermore, laser light having a wavelength of up to 850 nm may be critical in some cases in terms of eye safety and human perception.

[0005] VCSELs with longer wavelengths may solve this problem.

[0006] Gallium arsenide (GaAs)-based VCSELs can contain up to 30% indium (In) in the active layer that generates photons, enabling light wavelengths up to approximately 1100 nm. However, the indium content is limited by the lattice stress of the VCSEL's base material. Higher indium content leads to an increased concentration of lattice defects, which reduces the VCSEL's efficiency. Furthermore, only thin active layers less than 20 nm can be formed, resulting in low photon yields.

[0007] US6542531B2 discloses a VCSEL having an active layer containing InP. By using indium phosphide (InP) in the active layer, the laser wavelength can be shifted to a longer wavelength. However, this VCSEL is less sensitive to self-mixing interference, where self-mixing interference refers to the laser being reflected back into the resonant cavity of the VCSEL. This affects the standing wave of the light field in the resonant cavity. The effect on the standing wave can be measured by changes in the electrical characteristics of the VCSEL, and the light reflected back to the VCSEL can be inferred. However, the additional provision of an external sensor to detect the reflected laser light will result in spatial expansion and is not practical.

[0008] However, indium phosphide (InP)-based Bragg reflectors cannot provide sufficiently efficient resonant cavities for VCSELs. This appears to be an insurmountable problem, with no direct solution currently available.

[0009] European Patent EP2277245A1 discloses a vertical cavity surface emitting laser device comprising a VCSEL integrated with a monolithic photodiode. The photodiode is composed of a semiconductor material layer sequence of a first n-type doped region, a p-type doped region, an intrinsic region, and a second n-type doped region. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a VCSEL that can emit long-wavelength laser and has a compact structure.

[0011] It is proposed to provide a VCSEL for generating laser light, which comprises a base body having a first, a second and a third main body part stacked one after another in a layered manner along an arrangement direction. The main parts are connected to each other through a bonding process; the first main part includes a first Bragg reflector, the second main part includes a second Bragg reflector, and the third main part includes an active layer; the first and second main parts form a resonant cavity, and the third main part is arranged between the first and second main parts; the first and second main parts do not contain indium, and the third main part contains indium; and a photodetector is arranged in the resonant cavity, especially in the form of a photodiode, which is preferably arranged between the second Bragg reflector and the active layer.

[0012] Bonding is a process that connects materials with different lattice constants at the atomic level by applying pressure and heat to form a physical connection.

[0013] Each layer has a different function and corresponding composition. The properties of the VCSEL layers can be tuned by doping them with additional impurity atoms into the base material.

[0014] The layers are stacked and arranged in a matrix along the alignment direction. The layers are oriented perpendicular to the alignment direction. The Bragg reflectors are arranged parallel to each other, forming a resonant cavity where standing waves emerge. The reflectivity of the first Bragg reflector, at least on its outer surface, is slightly lower than that of the second Bragg reflector, allowing the laser light of the standing wave to be emitted from this emission region.

[0015] The photodetector detects the light of the standing wave within the resonant cavity. When laser light reflected from the outside reenters the resonant cavity, the standing wave is affected, and the photodetector detects this change. This allows for efficient detection of the light returning to the resonant cavity without the need for additional components. This results in a compact, highly integrated VCSEL with high detection sensitivity.

[0016] Due to the indium content in the active layer, the band edge of the electrons is lowered to an energy level at which light with a wavelength of 1300 nm to 1800 nm, in particular 1380 nm, can be emitted.

[0017] VCSELs with integrated photodetectors effectively suppress external interfering light. They are particularly suitable for sensors based on the principle of "self-mixing interference," enabling high-precision speed and distance measurement.

[0018] Further aspects of the invention are set out in the dependent claims.

[0019] In one embodiment of the present invention, the VCSEL includes a first tunnel contact between the first Bragg reflector and the active layer. This tunnel contact is located within the third main body. The tunnel contact is embedded in the material of the third main body. The tunnel contact is a conductive structure that confines current injected into the active layer via the electrode to a specific region of the active layer. Lateral structuring can be achieved through photolithography or ion implantation. Alternatively, ion implantation can be used to achieve lateral confinement of the tunnel contact.

[0020] Preferably, the VCSEL has a second tunnel contact between the photodetector and the active layer. When the tunnel contact contacts an external electrode, it provides a current path between the photodetector and the active layer. In this case, if the electrode of the first tunnel contact serves as the anode of the active layer, the electrode of the second tunnel contact can simultaneously serve as the cathode of the active layer and the anode of the photodetector. The current flowing through the substrate can be either electron or hole flow. The tunnel contact directs the current to the corresponding layer and preferably laterally confines the current to the region of the active layer aligned with the emission region of the first Bragg reflector. The electrode can be applied to the substrate surface and form an ohmic contact with the substrate material. The second tunnel contact can be manufactured in the same manner as the first tunnel contact. The tunnel contact can also be made directly through the electrode. To this end, this layer can be made relatively thick, for example, several hundred nanometers (e.g., 300-900 nanometers). This makes it easier to expose the tunnel contact layer because it is not immediately etched through during exposure. After the tunnel contact layer is exposed (for example, in the form of horizontal steps along the arrangement direction), a metal contact can be applied. Alternatively, the tunnel contact layer may comprise at least two materials, wherein the upper material acts as an etch stop layer. After etching is stopped in this plane by the etch stop layer, the etch stop layer is removed and the electrode is applied.

[0021] Through a bonding process, a bonding layer is formed between the third main body portion and the first and / or second main body portion, respectively, and the bonding layer forms a connection between the main body portions.

[0022] A standing laser wave forms within the resonator, with the active layer positioned at the antinode. This ensures that as much energy as possible from the electron excitation is transferred to the active layer for photon emission.

[0023] Preferably, the photodetector is arranged at a position between an antinode of the standing wave and a node directly adjacent to the antinode in the resonant cavity. This ensures that the photodetector does not enter the saturation range due to excessive light intensity and cannot generate a clear signal for evaluation through an evaluation unit connected to the photodetector. For example, the photodiode can be located at a position less than 102nm to less than 141nm, especially less than 108nm, from the antinode. In another embodiment, the photodetector can be directly arranged at the antinode of the standing wave. In this case, a bias voltage can be applied to the photodiode to reduce the detection energy, achieve photomultiplication, and thus evaluate weak light signals. In addition, by properly selecting the photodiode material, it can be used as an auxiliary active layer. When current passes through, the standing wave field can be enhanced and additional gain can be generated.

[0024] To reduce the interaction between the tunnel contact and the standing wave field, the tunnel contact can be located at the node of the standing wave. If there are multiple tunnel contacts, they can be arranged at different nodes.

[0025] The thickness of the absorption layer of the photodetector along the alignment direction is preferably 1 to 20 nm (preferably 10 nm). The absorption layer is preferably composed of undoped aluminum indium gallium arsenide (AlGaInAs). Layers containing indium phosphide (InP) may be provided before and after it.

[0026] The photodetector's absorption layer can be richer in indium and / or aluminum than the rest of the substrate to improve laser absorption efficiency. The photodetector can absorb 0.1% to 0.3% of the light intensity.

[0027] To facilitate single-sided access to at least some of the VCSEL's electrodes, steps are provided on the substrate. These steps expose the substrate's layers, allowing at least one electrode to be positioned on each step. In this case, the steps can be formed within a layer, or the surface of the steps can be located at the interface between two adjacent layers. In the first approach, the electrodes can be applied to the surfaces of the steps, which are aligned perpendicular to the alignment direction. In the second approach, the electrodes can be positioned on the surfaces of the steps, which are parallel to the alignment direction.

[0028] The Bragg reflector is particularly preferably bonded to the n-doped layer of the second body part. The polarity of the VCSEL and the current flow can thereby be set such that a cathode is applied to the n-doped layer adjacent to the first and second Bragg reflectors, respectively.

[0029] Furthermore, the VCSEL can be designed to have a total of three electrodes. In another embodiment, four electrodes can be provided, wherein the active layer and the photodetector each have an anode and a cathode.

[0030] In order to generate a sufficient number of photons in the active layer particularly efficiently, the active layer is provided with 2 to 6, in particular 5 or 6, quantum mechanical potential wells. In this case, indium phosphide (InP) is the base material of the active layer.

[0031] Preferably, the Bragg reflectors comprise layers that form mirror pairs within the respective Bragg reflectors, wherein the number of mirror pairs in the first Bragg reflector is approximately 20 and the number of mirror pairs in the second Bragg reflector is approximately 30 to 40. This results in a reduction in the reflection efficiency of the first Bragg reflector to approximately 99%, while the reflection efficiency of the second Bragg reflector is greater than 99.9%. Preferably, the layers of the Bragg reflectors do not contain indium phosphide (InP).

[0032] A method for manufacturing a VCSEL having first, second, and third body portions is advantageously provided, wherein a first wafer comprises a first body portion and a first substrate, a second wafer comprises a second body portion and a second substrate, and a third wafer comprises a third body portion and a third substrate. The method provides for connecting the first wafer to the third wafer such that the first body portion and the third body portion are bonded together. Furthermore, the method provides for removing the third substrate from the combination of the first and third wafers, thereby leaving the first substrate and a stack comprising the first and third body portions disposed thereon. Furthermore, the method provides for connecting a second wafer to the stack on the first substrate such that the second body portion is bonded to the third body portion. Finally, the method provides for removing the first substrate from the stack comprising the first, second, and third body portions.

[0033] In another alternative embodiment of the method, the second wafer is connected to the third wafer such that the second body portion is bonded to the third body portion. The third substrate is removed from the combination of the second and third wafers, thereby leaving the second substrate and the stack comprising the second and third body portions disposed thereon. Furthermore, the first wafer is connected to the stack on the second substrate such that the first body portion is bonded to the third body portion. Finally, the first substrate is removed from the stack comprising the first, second, and third body portions.

[0034] In a further development of the method, the substrate of the VCSEL is structured by a photolithographic etching process, after which electrodes are applied to the substrate surface.

[0035] Other features and advantages of the present invention will become apparent from the following description based on the embodiments and drawings. Although the present invention has been shown and disclosed in detail in the drawings and the above description, these drawings and descriptions should be considered to be purely illustrative or exemplary and not restrictive. It should be understood that the features mentioned above and to be described below can be used not only in the combination specified, but also in other combinations or alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings show:

[0037] Figure 1 A schematic diagram showing a VCSEL having three main parts,

[0038] Figure 2 Schematic diagram showing the arrangement of the layers in the laser standing wave field within the resonator,

[0039] Figure 3 Schematic diagram showing a first alternative of the basic process steps,

[0040] Figure 4 Schematic diagram showing a second alternative of the basic process steps. DETAILED DESCRIPTION

[0041] exist Figure 1 , a VCSEL 10 for generating laser light is shown. The VCSEL 10 has a substrate 12 having first, second and third body portions 121 , 122 , 123 .

[0042] The main body portions 121, 122, and 123 are stacked in layers along the arrangement direction 1 and connected to each other through a bonding process. Bonding is a process that physically connects materials with different lattice constants at the atomic level by applying pressure and heat. Through the bonding process, a bonding layer 24 is formed between the main body portions 121, 122, and 123. The bonding layer 24 is oriented perpendicular to the arrangement direction 1. The bonding layer 24 between the third main body portion 123 and the first and second main body portions forms a connection between the main body portions 121, 122, and 123.

[0043] Each main body 121, 122, and 123 comprises layers. Each layer has a different function and corresponding composition. The layers are composed of material combinations, for example, to adjust the energy excitation level of charge carriers or alter the efficiency of photon absorption. For example, an aluminum content of up to approximately 10% can be incorporated. The layers are arranged in the matrix 12 and stacked one after the other along the arrangement direction 1. The layers are oriented perpendicular to the arrangement direction 1.

[0044] The first body part 121 includes a first Bragg reflector 141, and the second body part 122 includes a second Bragg reflector 142. The Bragg reflectors 141 and 142 are formed in layers, with their main extension planes oriented perpendicular to the arrangement direction 1. The third body part 123 includes an active layer 16, which is also oriented perpendicular to the arrangement direction 1.

[0045] The first and second body portions 121, 122 form a resonant cavity 18. A third body portion 123 is arranged within the resonant cavity 18. The third body portion 123 is arranged between the first and second body portions 121, 122. Accordingly, the active layer 16 is located between the Bragg reflectors 141, 142 in the resonant cavity 18.

[0046] The first and second body parts 121, 122 do not contain indium, but are formed by a pair of mirrors, each of which has a gallium arsenide (GaAs) mirror and an aluminum gallium arsenide (AlGaAs) mirror. The Bragg mirrors 141, 142 are oriented parallel to each other and form a resonant cavity 18, in which a Figure 2 The standing wave 26 is shown. The reflectivity of the first Bragg reflector 141 is slightly lower than that of the second Bragg reflector 142. In addition, an emission region is formed on the outer surface of the first Bragg reflector 141, and the laser light of the standing wave 26 is emitted from the VCSEL from this region.

[0047] The number of mirror pairs in the first Bragg reflector 141 is about 20, and the number of mirror pairs in the second Bragg reflector 142 is about 30 to 40, so that the reflection efficiency of the first Bragg reflector 141 is reduced to about 99%, while the reflection efficiency of the second Bragg reflector 142 is greater than 99.9%.

[0048] Third main portion 123 comprises indium. It is preferably primarily composed of indium phosphide (InP). In particular, active layer 16 comprises indium in the form of aluminum gallium indium arsenide (AlGaInAs). The components in active layer 16 lower the so-called band edge of electrons to an energy level corresponding to light emission wavelengths of 1300 nm to 1800 nm, particularly 1380 nm.

[0049] Active layer 16 has five or six quantum mechanical potential wells. These are called quantum wells and, according to the present invention, are formed in aluminum indium gallium arsenide (AlInGaAs). The potential wells comprise aluminum gallium indium arsenide (AlGaInAs) layers, arranged between an upper p-doped layer 172 and a lower n-doped layer 173 relative to alignment direction 1. Layers 172 and 173 contain indium phosphide (InP).

[0050] Furthermore, a photodetector 20 , in particular in the form of a photodiode, is arranged in the resonant cavity 18 , which is preferably situated between the second Bragg mirror 142 and the active layer 16 .

[0051] Photodetector 20 detects light from standing wave 26 within resonant cavity 18. When laser light reflected from the outside re-enters resonant cavity 20, standing wave 26 is affected, and photodetector 20 identifies the resulting changes in standing wave 26. Photodetector 20 efficiently detects light re-entering resonant cavity 18 without requiring additional components. This makes VCSEL 10 extremely compact and highly integrated, while also providing high detection sensitivity.

[0052] The photodetector 20 has a layer sequence of differently doped layers and an absorption layer 21 having a thickness of 1 to 20 nanometers, preferably 10 nanometers, along the arrangement direction 1. The absorption layer 21 is composed of undoped aluminum gallium indium arsenide (AlGaInAs).

[0053] Furthermore, the composition of the absorption layer 21 is selected so that its energy absorption band matches the wavelength of light emitted by the laser. Furthermore, the energy absorption band is selected by the ratio of the base material elements to ensure that intrinsic absorption (fundamental frequency absorption) is always present over a wide temperature range. At the same time, the elemental ratios of the material must be selected so that laser amplification can still be achieved, thereby generating efficient laser light. Here, the ratio of aluminum to indium is selected so that the photodetector absorbs 0.1% to 0.3% of the light intensity. By way of example only, the absorption band edge of the photodetector can be approximately 100 nanometers below the laser wavelength to achieve maximum absorption efficiency.

[0054] The thickness of the entire photodetector 20 along the arrangement direction 1 is several tens of nanometers.

[0055] The photodetector 20 has a p-doped layer 212, which is located closer to the first Bragg reflector 141 in the alignment direction 1 than the n-doped layer 211 of the photodetector 20. These layers are primarily composed of doped indium phosphide (InP). An absorption layer 21 is arranged between the doped layers 211 and 212, which converts absorbed photons into electrical signals. For this purpose, an evaluation device is connected to the VCSEL 10.

[0056] Undoped or weakly doped indium phosphide (InP) regions of tens to 100 nanometers may be arranged near or in place of the doped layers 211 and 212. These buffer layers are used to prevent dopants from diffusing into the absorption layer and to avoid excessively high capacitance values.

[0057] The uppermost and lowermost layers (layers 36 and 34) of the third body portion 123 are n-type doped indium phosphide (InP) layers. A first Bragg reflector 141 is bonded to the uppermost layer 36, with a bonding layer 24 formed between the uppermost layer 36 and the Bragg reflector 141. A bonding layer 24 is provided between the second Bragg reflector 142 and the lowermost layer 34.

[0058] An embedded first tunnel junction 221 is formed between the uppermost layer 36 and the p-type doped layer 172 of the active layer 16. The first tunnel junction 221 is laterally structured by a photolithography and etching process, such that the first tunnel junction 221 is preferably formed centrally relative to the lateral extension of the active layer 16. The first tunnel junction 221 is conductive, confining the current injected into the active layer 16 via the electrode 38 and directing the current to a limited area of ​​the active layer 16.

[0059] The VCSEL 10 further includes a second tunnel junction 222 between the n-type doped layer 173 adjacent to the potential well and the p-type doped layer 212 of the photodetector 20. The second tunnel junction 222 can be structured in the same manner as the first tunnel junction 221. The second tunnel junction 222 prevents the formation of a pn junction interface between the n-type doped layer 173 adjacent to the potential well and the p-type doped layer 212 of the photodetector 20, thereby reducing the dissipation of the current passing through the VCSEL 10 and correspondingly reducing the heat generated by the VCSEL 10.

[0060] Steps 321, 322, and 323 are formed on the side of substrate 12 of VCSEL 10, exposing various layers of substrate 12. Steps 321, 322, and 323 can be formed in a single layer, or alternatively, a first layer can be laterally shorter than a subsequent layer. Steps 321, 322, and 323 have a first surface perpendicular to alignment direction 1 and a second surface parallel to alignment direction 1.

[0061] The first Bragg reflector 141 has a shorter extension in the lateral direction than the subsequent uppermost layer 36. Therefore, a first step 321 is formed between the first Bragg reflector 141 and the uppermost layer 36.

[0062] The second step 322 is formed in the n-type doping layer 173 .

[0063] The third step 323 is formed in the n-type doped layer 211 , or in a replacement buffer layer below the photodetector 20 .

[0064] At least one electrode 38 is provided on each of the steps 321, 322, and 323 formed on the substrate 12. The electrodes 38 are arranged on the surfaces of the corresponding steps 321, 322, and 323, which are oriented perpendicular to the arrangement direction 1. For example, the steps may extend 10 microns laterally and have a height of 0.2 microns. Alternatively, the electrodes 38 may be arranged on the surfaces of the steps 321, 322, and 323 oriented parallel to the arrangement direction 1. Typically, the electrodes 38 are annular in design and surround the axis of symmetry of the substrate 12. The electrodes 38 form an ohmic contact with the material of the substrate 12.

[0065] The electrode 38 on the first step 321 is the cathode or anode of the active layer 16. The second tunnel junction 222 arranged above the photodetector 20 causes polarity reversal, so that the electrode 38 on the second step 322 can be the anode or cathode of the active layer 16 and the cathode or anode of the photodetector 20 at the same time. The cathode or anode of the photodetector 20 is arranged on the third step 323.

[0066] In another embodiment, an alternative arrangement of the electrodes 38 and the polarity of the active layer 16 and the photodetector 20 is provided, wherein the electrode 38 on the second step 322 constitutes the anode or cathode of the active layer 16 and the photodetector 20, and the electrodes 38 on the first step 321 and the third step 323 are the cathode or anode of the active layer 16 and the photodetector 20, respectively.

[0067] In a next embodiment (not shown), another alternative to the electrode arrangement is provided: instead of three electrodes 38 , four electrodes 38 are provided, wherein the active layer 20 has two electrodes 38 and the photodetector 20 has two electrodes 38 independent therefrom.

[0068] exist Figure 2 A schematic diagram of the standing wave 26 is shown in FIG. 4 , where the x-axis 42 represents linear propagation in the resonator 18 and the y-axis 44 represents the field strength of the standing wave 26 .

[0069] The figure shows where along the x-axis 42 the tunnel junctions 221 , 222 , the active layer 16 , the absorption layer 21 and the electrode 38 are arranged.

[0070] Two electrodes 38 are positioned at the outer nodes 30 of the standing wave 26. Arranged between these outer nodes 30 is at least one further electrode 38, which is likewise arranged at a respective node 30.

[0071] Furthermore, tunnel contacts 221 , 222 are arranged at nodes 30 between external electrodes 38 .

[0072] Photodetector 20 is positioned between an antinode 28 of standing wave 26 and a node 30 directly adjacent to antinode 28 within resonant cavity 18. Therefore, photodetector 20 is protected from excessive light intensity and saturation. Furthermore, the photodetector must not extract excessive power from the laser. VCSELs are sensitive to losses in the 0.1% to 1% range. The photodetector's position allows adjustment for these losses, ensuring that the VCSEL can detect sufficient light.

[0073] Preferably, the photodetector 20 may be less than 102 nm to less than 141 nm, and in particular less than 108 nm, from the antinode.

[0074] In another approach, the photodetector 20 may be positioned at the antinode 28 of the standing wave 26 .

[0075] Furthermore, if the material composition of the photodetector 20 is chosen appropriately, it can also serve as an additional active layer. In this process, a forward current flows through the photodetector 20, thereby generating additional photons and enhancing the standing wave field, which results in additional so-called gain.

[0076] exist Figure 3 A through 3D illustrate a first approach to the basic process steps for manufacturing a VCSEL 10. In this process, VCSEL 10 is manufactured using first, second, and third body portions 121, 122, and 123. A first wafer includes first body portion 121 and a first substrate 521; a second wafer includes second body portion 122 and a second substrate 522; and a third wafer includes third body portion 123 and a third substrate 523.

[0077] The third substrate 523 contains indium phosphide (InP) because the third body portion 123 is based on indium phosphide. Therefore, the first and second substrates 521, 522 do not contain indium phosphide (InP) because the first and second body portions 121, 122 include Bragg reflectors 141, 142, which do not contain indium phosphide.

[0078] exist Figure 3 In Figure A, the first wafer is connected to the third wafer so that the first body portion 121 is bonded to the third body portion 123. As a result, the composite of the first and third body portions 121, 123 is disposed between the first and third substrates 521, 523.

[0079] exist Figure 3 B shows the process of removing the third substrate 523 from the composite of the first and third body parts 121, 123. The removal process can be completed by an etching process. After removal, the first substrate 121 and the stack including the first and third body parts 121, 123 disposed thereon remain.

[0080] according to Figure 3 C. Bonding the second body portion 122 to the third substrate 523. During this process, the second wafer is connected to the composite on the first substrate 521, such that the second body portion 122 is bonded to the third body portion 123. Finally, the first substrate 521 is removed from the stack consisting of the first, second, and third body portions 121, 122, and 123. The third body portion 123 is positioned between the first and second body portions 121 and 122.

[0081] exist Figure 3 D shows that the first substrate 521 is removed, for example by an etching process, so that only the second substrate 522 with the attached body parts 121, 122, 123 remains. Finally, the base body 12 can be structured and the electrodes 38 can be arranged.

[0082] Another approach to this process is Figure 4 A to 4D are shown.

[0083] according to Figure 4A, first connect the second wafer and the third wafer at this location, so that the second main body part 122 and the third main body part 123 are bonded together.

[0084] exist Figure 4 B shows the process of removing the third substrate 523 from the composite of the second and third wafers, so that the second substrate 522 and the stack with the second and third body parts 122, 123 arranged thereon remain.

[0085] exist Figure 4 In C, it is provided to connect the stack on the first wafer to the second substrate 522 so that the first body portion 121 is bonded to the third body portion 123 .

[0086] Finally, according to Figure 4 C, removing the first substrate 521 from the stack consisting of the first, second and third body parts 121 , 122 , 123 .

[0087] In each process solution, the substrate 12 of the VCSEL 10 can be structured by photolithography and etching processes. For example, steps 321 , 322 , and 323 can be formed. Then, an electrode 38 is applied to the surface of the substrate 12 .

[0088] This process can be used to manufacture a vertical cavity surface emitting laser (VCSEL) 10 having a basic structure, wherein the Bragg reflectors 142 of the second wafer, which include undoped GaAs / AlGaAs reflector pairs, are bonded to the third InP wafer via wafer bonding. The Bragg reflectors 142 of the second wafer have a high reflectivity (>99.9%), and 30 to 50 reflector pairs are provided.

[0089] A so-called bonding interface is formed between the second and third body parts 122 , 123 , since the surfaces of the two body parts 122 , 123 are connected to one another here and form a bonding layer 24 .

[0090] An outermost n-type doped contact layer 34 made of indium phosphide (InP) is provided on the Bragg reflector 142 .

[0091] In the region of the photodetector 20 , a lower n-doped indium phosphide (InP) layer 211 is arranged relative to the arrangement direction 1 , which layer has a low n-doping or is not n-doped.

[0092] The thickness of the undoped AlGaInAs forming the absorption layer 21 is, for example, 10 nanometers.

[0093] Additionally, an upper indium phosphide (InP) layer 212 is provided that has a lower p-type doping or is not p-type doped.

[0094] The second tunnel contact layer 222 is composed of a very thin (10 to 20 nanometers) layer of highly doped p++ and n++ materials (doping concentrations are both>>10 19 It should be noted that the tunnel contact layer 222 is positioned at a node of the standing wave field. In principle, the structure and position of the first tunnel contact layer 221 are the same as those of the second tunnel contact layer 222.

[0095] Furthermore, the intermediate n-type doped contact layer 173 disposed below the active layer 16 is composed of indium phosphide (InP).

[0096] The active layer 16 has an n-type doping concentration and a p-type doping concentration. In addition, 5 to 6 potential wells are provided in the active layer 16. The area around the potential wells in the active layer is undoped, so the potential wells are embedded in the undoped layer.

[0097] The potential well is positioned at the antinode 28 of the standing wave field. Regarding alignment direction 1, a first tunnel contact layer 221 is provided above the active layer 16. The upper outer n-doped contact layer 34 is also made of indium phosphide (InP). A further bonding interface with a bonding layer 24 is provided above this layer.

[0098] First, a stack of undoped GaAs / AlGaAs mirror pairs is applied as Bragg reflectors 141. This stack is connected to an InP wafer via wafer bonding. The reflectivity of the Bragg reflectors 141 on the light-exiting side is approximately 99%, requiring approximately 20 mirror pairs.

[0099] These layers can be applied to the substrate by metal chemical vapor deposition.

Claims

1. A VCSEL (10) for generating laser light, comprising a substrate (12), wherein: The substrate (12) has a first, a second and a third main body part (121, 122, 123) stacked in layers in sequence along an arrangement direction (1), wherein the main body parts (121, 122, 123) are connected to each other by a bonding process, wherein the first main body part (121) has a first Bragg reflector (141), the second main body part (122) has a second Bragg reflector (142), and the third main body part (123) has an active layer (16), wherein the first and second main body parts (12 1, 122) form a resonant cavity (18), in which the third body part (123) is arranged between the first and second body parts (121, 122), wherein the first and second body parts (121, 122) do not contain indium and the third body part (123) contains indium, wherein a photodetector (20), in particular in the form of a photodiode, is arranged in the resonant cavity (18), and the photodetector is preferably arranged between the second Bragg reflector (142) and the active layer (16).

2. The VCSEL (10) according to claim 1, characterized in that A first tunnel junction (221) is arranged between the first Bragg reflector (141) and the active layer (16), wherein the tunnel junction (221) is positioned within the third body portion (123).

3. The VCSEL (10) according to claim 1 or 2, characterized in that A second tunnel junction (222) is arranged between the photodetector (20) and the active layer (16), so that when the tunnel junction (222) is contacted externally with an electrode (38), the tunnel junction (222) serves as a current conductor for the photodetector (20) and the active layer (16), wherein the tunnel junction (222) can be directly contacted when the layers of the tunnel junction (222) have a thickness of 200 nm to 300 nm or have a sacrificial layer or an etch stop layer, which is removed after the layers of the tunnel junction are exposed.

4. The VCSEL (10) according to any one of the preceding claims, characterized in that A bonding layer (24) is formed between the third main body part (123) and the first and / or second main body part (121, 122), respectively.

5. The VCSEL (10) according to any one of claims 2 to 4, characterized in that The photodetector (20) is positioned between an antinode (28) of a standing wave (26) within the resonant cavity (18) and a node (30) immediately adjacent to the antinode (28).

6. The VCSEL (10) according to any one of claims 2 to 5, characterized in that The tunnel junction (221, 222) is positioned at a node (30) of a standing wave (26) within the resonant cavity (18).

7. The VCSEL (10) according to any one of claims 2 to 6, characterized in that The absorption layer (21) of the photodetector (20) has a thickness oriented along the arrangement direction (1) of 1 nm to 20 nm, preferably 10 nm.

8. The VCSEL (10) according to any one of claims 2 to 7, characterized in that The material of the photodetector (20) is preferably rich in indium and / or aluminum relative to the material of the remaining base body (12) such that the absorption of the laser light is enhanced.

9. The VCSEL (10) according to any one of the preceding claims, characterized in that The base body (12) has steps (321, 322, 323) which expose the layer of the base body (12), so that at least one electrode (38) is arranged on each step (321, 322, 323).

10. The VCSEL (10) according to any one of the preceding claims, characterized in that The Bragg reflectors (141, 142) are bonded to the n-type doped layers (34, 36) of the second body portion (122).

11. The VCSEL (10) according to any one of claims 3 to 10, characterized in that Three electrodes (38) are provided in total, wherein one electrode (38) is arranged between the active layer (16) and the photodetector (20), and is electrically connected to the active layer (16) and the photodetector (20).

12. The VCSEL (10) according to any one of claims 3 to 11, characterized in that An electrode (38) is arranged at each of two outer nodes (30) of a standing wave (26), wherein a further electrode (38) is arranged at a node (30) between the outer nodes (30).

13. The VCSEL (10) according to any one of the preceding claims, characterized in that The active layer (16) has 2 to 6, in particular 5 or 6, quantum mechanical potential wells.

14. The VCSEL (10) according to any one of the preceding claims, characterized in that The Bragg reflectors (141, 142) have layers which form a reflector pair within the respective Bragg reflectors (141, 142), wherein the reflectivity of the first Bragg reflector (141) is approximately 99% and the reflectivity of the second Bragg reflector (142) is approximately 99.9%.

15. The VCSEL (10) according to any one of the preceding claims, characterized in that A substrate is applied to the second Bragg reflector (142) on the side facing away from the resonant cavity (18).

16. The VCSEL (10) according to any one of the preceding claims, characterized in that The VCSEL (10) is configured to receive light and detect the light by means of a self-mixing interference effect.

17. The VCSEL (10) according to any one of claims 5 to 16, characterized in that At least one further electrode (38) is arranged between the nodes (30) of the standing wave (26), the at least one further electrode also being arranged at a node (30).

18. A method for manufacturing a VCSEL (10) having first, second and third body portions (121, 122, 123) according to any one of the preceding claims, wherein The first wafer has the first main body portion (121) and a first substrate (521), the second wafer has the second main body portion (122) and a second substrate (522), and the third wafer has the third main body portion (123) and a third substrate (523), characterized by the following steps: - connecting the first wafer and the third wafer so that the first main body portion (121) and the third main body portion (123) are bonded together, - removing the third substrate (523) from the composite of the first and third wafers, so that the first substrate (521) and the stack with the first and third body parts (121, 123) arranged thereon remain, - connecting the second wafer to the stack on the first substrate (521) such that the second body portion (122) is bonded to the third body portion (123), - removing the first substrate (521) from the stack of the first, second and third body parts (121, 122, 123) or - connecting the second wafer to the third wafer so that the second main body portion (122) and the third main body portion (123) are bonded together, - removing the third substrate (523) from the composite of the second and third wafers, so that the second substrate (522) and the stack with the second and third body parts (122, 123) arranged thereon remain, - connecting the first wafer to the stack on the second substrate (522) such that the first body portion (121) is bonded to the third body portion (123), - removing said first substrate (521) from the stack consisting of said first, said second and said third body portions (121, 122, 123).

19. The method according to claim 18, characterized in that The base body (12) of the VCSEL (10) is structured by a photolithographic etching process, and then the electrode (38) is applied on the surface of the base body (12).

20. A measurement method using a VCSEL (10) according to any one of the preceding claims, characterized in that The VCSEL (10) performs measurements based on the self-mixing interference effect.

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