Laser array with light emission through the substrate and method for producing the laser array

Abstract

A laser array with light emission through a substrate (12) of the laser array is described, comprising: a plurality of lasers (14) on the substrate, each formed as a vertical cavity surface emitter (VCSEL), the lasers (14) each having a semiconductor layer structure comprising a first Bragg mirror (18), a second Bragg mirror (20) and an active region (22) between the first and second Bragg mirrors (18, 20), the plurality of lasers (14) being grouped into one or more spaced-apart sub-arrays (24, 26, 28) of the laser array; at least one first metal layer (40) above the first Bragg mirror (18), which contacts the lasers (14) of the sub-array(s) (24, 26, 28) on a side of the active region (22) of the lasers (14) facing away from the substrate (12);at least one second metal layer (44) above the first Bragg mirror (18), which is galvanically isolated from the at least one first metal layer (40), and which contacts the lasers (14) of the sub-array(s) (24, 26, 28) through at least one opening (42) in the semiconductor layer structure on a side of the active layer (22) facing the substrate (12), wherein the at least one opening (42) extends as far as the substrate (12) or into the substrate (12) or as far as a layer between the substrate (12) and the active region (22); an insulation layer (48) above the at least one first and second metal layer (40, 44); a third metal layer (50) over the insulation layer (48), which contacts the at least one first metal layer (40) through first openings (51) in the insulation layer (48) and extends over regions of the at least one first metal layer (40) and over regions of the at least one second metal layer (44);and a fourth metal layer (52) over the insulation layer (48), which fourth metal layer (52) contacts the at least one second metal layer (44) through second openings (53) in the insulation layer (48), is galvanically isolated from the third metal layer (50), and extends over portions of the at least one first metal layer (40) and the at least one second metal layer (44). A method for manufacturing the laser array is also described.;

Description

The invention relates to a laser array with light emission through a substrate of the laser array. The invention further relates to a method for producing such a laser array.Vertical-cavity surface-emitting semiconductor lasers, referred to for short as VCSELs (vertical cavity surface emitting lasers), are used, for example, as radiation sources in sensor technology or in communication technology. VCSELs typically have a semiconductor layer structure in which semiconductor layers are epitaxially grown on a semiconductor substrate in a stacked arrangement. The semiconductor layer structure typically comprises a first Bragg mirror, an active region and a second Bragg mirror, which together form an optical resonator. A Bragg mirror is also referred to for short as a DBR (Distributed Bragg Reflector).VCSELs can be designed as so-called top emitters, in which the light emission takes place through a side of the semiconductor layer structure facing away from the substrate. In contrast, in the case of so-called bottom emitters, the light emission takes place through the substrate. VCSELs with light emission through the substrate offer some advantages over top emitters, for example because optics can be directly patterned into the surface of the substrate. Furthermore, bottom-emitting VCSELs are suitable for surface mounting technology, also referred to as SMT (surface-mounting technology) or SMD (surface-mounted device). The advantages of SMDs are miniaturization, smaller device dimensions, cost reduction, etc. The present invention relates specifically to an array of bottom emitting VCSELs.DE 10 2021 129 874 A1 discloses a bottom-emitting semiconductor laser component which is designed as an SMD. U.S. Pat. No. 10,826,278 B2 discloses a laser array with light emission through the substrate, which has a first metal layer, a second metal layer and an insulation layer between the first and second metal layers, wherein the second metal layer is contacted with the first metal layer by partial perforations in the insulation layer.It is an object of the present invention to provide a laser array or VCSEL array with light emission through the substrate, which can be produced cost-effectively and in a simple manner and which is suitable in particular for SMT.Another object of the present invention is to provide a method for manufacturing such a laser array.The object mentioned in the first place is achieved by a laser array with light emission through a substrate of the laser array according to claim 1.The laser array according to the invention with light emission through the substrate of the laser array has a plurality of lasers on the substrate. The lasers are each designed as VCSELs. The lasers each have a semiconductor layer structure comprising a first Bragg mirror, a second Bragg mirror and an active region between the first and second Bragg mirrors. The first Bragg mirror is arranged on the side of the active region facing away from the substrate. The plurality of lasers are grouped into one or more spaced sub-arrays of the laser array. The individual VCSELs may be defined, for example, by etching a plurality of mesas, each mesa defining a laser. After forming the mesas by etching, an oxidation may follow to define a current aperture. If the lasers are not defined as mesas, a current aperture may be defined by a proton implantation or a locally defined tunnel diode. The formation of the VCSELs on the substrate takes place in such a way that a plurality of lasers are each grouped into a sub-array. The lasers of a sub-array need not be formed as individual lasers or mesas, but a sub-array may be a connected region in which the lasers are connected to each other. The term "laser" is thus also generally understood in the present description as light emission position.The laser array according to the invention has one or more first metal layers which contact or contact the lasers of the sub-array or sub-arrays on a side of the active region of the lasers which is remote from the substrate. The at least one first metal layer commonly contacts the lasers of a sub-array. The individual lasers of a sub-array are thus addressed jointly. If there are a plurality of sub-arrays, each sub-array may be assigned a first metal layer, the first metal layers being separated from one another. The first metal layer serves for contacting the lasers of a sub-array according to a first polarity, for example a p-polarity.The laser array according to the invention has one or more second metal layers which is galvanically or electrically separated from the first metal layer or layers and which contacts the lasers of one or more, for example adjacent, sub-arrays through at least one aperture in the semiconductor layer structure on a side of the active layer facing the substrate, wherein the at least one aperture can extend as far as the substrate or into the substrate or as far as a layer between the substrate and the active region. The at least one second metal layer contacts the lasers of the sub-array jointly. The second metal layer contacts the lasers according to a polarity different from the polarity of the contacting of the lasers by the first metal layer. When the first metal layer contacts the lasers according to a p-polarity, the second metal layer contacts the lasers according to an n-polarity. When the first metal layer contacts the lasers according to an n-polarity, the second metal layer contacts the lasers according to a p-polarity. The at least one through-hole in the semiconductor layer structure can be realized in a simple manner by etching the semiconductor layer structure. Depending on the number of sub-arrays, multiple second metal layers may be distributed across the array.The at least one first metal layer is arranged above the first Bragg mirror, i.e. the Bragg mirror which is located on the side of the active region facing away from the substrate. The second metal layer is arranged partly at a level below the active layer of the lasers and partly, i.e. on the top, above the first Bragg mirror. Semiconductor layers may be located between the first Bragg mirror and the first and second metal layers. The at least one first and second metal layer can each be multilayer. The first and second metal layers may each include a first thin metal layer directly contacting the lasers and a second thick metal layer disposed on the first metal layer and in contact with or at least electrically connected to the first metal layer. The metal or metals of the first metal layer may be different from the metal or metals of the second metal layer.The laser array according to the invention further comprises an insulation layer over the at least one first and second metal layer. The insulation layer has perforations in defined regions, i.e. the at least one first and second metal layer are exposed in these perforations. Above the insulation layer is a third metal layer, which contacts the at least one first metal layer through first perforations in the insulation layer and extends over regions of the first metal layer(s) and over regions of the second metal layer(s). In the regions of the second metal layer(s), the third metal layer is galvanically separated from the second metal layer or layers via the insulation layer. A fourth metal layer is over the isolation layer contacting the second metal layer(s) through second apertures in the isolation layer, galvanically separated from the third metal layer, and extending over portions of the first metal layer(s) and the second metal layer(s). The fourth metal layer thus contacts the second or second metal layers, but does not contact the first or first metal layers, although it also extends over portions of the first metal layer(s).Hereinafter, when a plurality of sub-arrays and thus a plurality of first metal layers are present, these will be collectively referred to as a first metal layer. If a plurality of second metal layers are present, these are collectively referred to as a second metal layer.The advantage of the laser array according to the invention is that the third metal layer and the fourth metal layer can be formed over a large area and nevertheless sufficiently spaced apart from one another, so that the third and fourth metal layers are particularly well suited as solder pads for soldering on electronic components. The first metal layer and the second metal layer can have comparatively thick metal layers, in particular strip-shaped metal layers, on their side facing the third and fourth metal layers, as described above. The third and fourth metal layers can also be formed as thick metal layers. Overall, the laser array according to the invention can be produced easily and cost-effectively.The third metal layer serves to contact the lasers via the first metal layer according to a first polarity, for example a p-polarity, and the fourth metal layer serves to contact the lasers via the second metal layer according to a second polarity, for example an n-polarity. The third and the fourth metal layer can thus form anode and cathode of the laser array.The first metal layer extends over the lasers of a respective sub-array. The second metal layer, on the other hand, is preferably arranged in a region or regions outside the sub-array or sub-arrays.If the laser array comprises at least two sub-arrays spaced apart from each other, the second metal layer is preferably arranged in an intermediate region between the sub-arrays.In this configuration, the contacting of the lasers on the side of the active region facing the substrate is thus effected in the light emission-free regions of the array. In the case of strip-shaped rectangular sub-arrays, this has the advantage that the same current paths to the individual lasers result for the lasers of a sub-array.In addition or as an alternative to the aforementioned configuration, the second metal layer can surround the sub-array or the sub-arrays on an outer circumference of the sub-array or sub-arrays. It is advantageous here that the sub-arrays can be arranged at a smaller distance from one another, since the region between the sub-arrays is not required, or is required only to a lesser extent, for contacting the lasers via the second metal layer.Preferably, the at least one aperture in the semiconductor layer structure has an elongate shape in the direction parallel to the plane of the substrate with an aspect ratio of greater than 10, optionally greater than 20, further optionally greater than 40.The advantage here is that the apertures, due to their elongated shape, maximize the open area of the, for example n-doped, layer exposed during etching of the aperture, while the size of the aperture transverse to its longitudinal extension is small for example for the application of the second metal layer (substrate-side contacting) to the exposed semiconductor layer, so that the distance between the substrate-side contact to the lasers is advantageously short.The at least one aperture in the semiconductor layer structure may have an elongate shape in the direction parallel to the plane of the substrate with a short side length of less than 20 μm, optionally less than 15 μm, further optionally less than 10 μm.Since the at least one aperture in the semiconductor layer structure extends deeply into the semiconductor layer structure, a very small dimension of the at least one aperture transversely to its longitudinal extent is advantageous with respect to the deposition of the second metal layer which contacts the lasers on the substrate-side side of the active layer.Preferably, the sub-array or sub-arrays have the shape of a rectangle, wherein at least one side of the rectangle runs parallel to the at least one aperture in the semiconductor layer structure and preferably has substantially the same length as the at least one aperture. In this case, it is advantageous that the distance of each laser of the sub-array or of the sub-arrays from its closest substrate-side contact is substantially the same for all lasers. This results in current paths of substantially the same length from the substrate-side contacting to the individual lasers.In connection with the above-mentioned configuration in particular, according to which the second metal layer surrounds the sub-array or the sub-arrays on an outer circumference of the sub-array or sub-arrays, it is furthermore preferred if the at least one aperture in the semiconductor layer structure surrounds the sub-array or sub-arrays on an outer circumference of the sub-array or sub-arrays.Further preferably, the third and the fourth metal layer have an identical height level above the substrate on the top side. This is advantageous in particular for the suitability of the laser array as an SMD.Furthermore, it is preferred if the third and the fourth metal layer have the same shape and / or area dimension. This measure is also advantageous with regard to the suitability of the laser array as an SMD.It is likewise preferred if the first and the second metal layer have an identical height level above the substrate on the top side. This measure is advantageous in particular with regard to the production process of the laser array in order to simplify the application of the insulation layer, the perforations in the insulation layer and the application of the third and fourth metal layers.With regard to the suitability of the laser array according to the invention as an SMD, the third and fourth metal layers preferably have a distance of more than 100 μm, optionally more than 150 μm and less than 300 μm from one another.Further according to the invention there is provided a method of making a laser array with light emission through a substrate of the laser array according to claim 13. The advantages of the production method according to the invention result from the advantages of the laser array according to the invention. Preferred embodiments of the production method according to the invention also result from the preferred embodiments of the laser array according to the invention.In the production method, the at least one through hole is produced in the semiconductor layer structure by etching the semiconductor layer structure up to the substrate or into the substrate or up to a layer between the substrate and the active region.Further advantages and features will become apparent from the following description and the attached drawing.It is understood that the features mentioned above and still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the invention.Exemplary embodiments of the invention are illustrated in the drawings and are described in more detail below with reference to these. The following are shown: FIG. 1 shows a laser array in plan view at a first stage of its production; FIG. 1A is a cross-sectional view of a resonator region of a single laser of the array; FIG. 2 shows the laser array in FIG. 1 in plan view at a further stage of its production; FIG. 3 shows the laser array in FIG. 2 in plan view at a further stage of its production; FIG. 3A is a cross-sectional view of a portion of the laser array of FIG. 3; FIG. 4 shows the laser array in FIG. 3 in plan view at a further stage of its production; FIG. 4A is a cross-sectional view of a portion of the laser array of FIG. 4; FIG. 5 shows the laser array in FIG. 4 in plan view at a further stage of its production; FIG. 5A is a cross-sectional view of a portion of the laser array of FIG. 5; FIG. 6 shows the laser array in FIG. 5 in plan view at a further stage of its production; FIG. 7 shows the laser array in FIG. 6 in plan view at a final stage of its production; FIG. 8 is a modified plan view of a laser array at a stage of its manufacture; FIG. 9 shows the laser array in FIG. 8 in plan view at a further stage of its production; FIG. 10 shows the laser array in FIG. 9 in plan view at a further stage of its production; and FIG. 11 shows the laser array in FIG. 10 in plan view at a final stage of its production.Referring to Figs. 1 to 7, a first embodiment of a laser array 10 with light emission through a substrate 12 (Fig. 1A) of the laser array 10 will be described. Figures 1-7 show the construction and individual stages of the fabrication of the laser array 10.The laser array 10 includes a plurality of lasers 14, the positions of which are defined by, for example, etching a plurality of mesas. The mesas produced by the etching are correspondingly separated from each other by trenches 16. The individual lasers each have a semiconductor layer structure, which is shown schematically in FIG. 1A and has a first Bragg mirror 18, a second Bragg mirror 20 and an active region 22 between the first and second Bragg mirrors on the substrate 12. The first Bragg mirror 18 may be p-doped and the second Bragg mirror 20 may be n-doped, or vice versa. The light emission through the substrate 12 is indicated by an arrow 13. The plurality of lasers 14 are grouped into one or more spaced-apart sub-arrays 24, 26, and 28. In the example shown, the laser array 10 comprises three sub-arrays. However, more or less than three sub-arrays are possible.As shown, sub-arrays 24, 26 and 28 preferably have an elongated rectangular shape. A respective region 30 and 32 between the sub-arrays 24 and 26 and 26 and 28, respectively, likewise has an elongate rectangular shape. The regions 30 and 32 not occupied by lasers 14 serve as regions for contacting the lasers 14 on the side of the active region 22 facing the substrate, as will be described later. As a result, the current path starting from these contacts to the lasers 14 can be kept short and the same or at least similar for all lasers 14.If the lasers 14 are made from the semiconductor layer structure, which can be produced epitaxially, by etching mesas, the etching can be followed by an oxidation to produce a current aperture. However, a current aperture may also be defined by proton implantation or locally by tunnel junctions, etc. Three possible different configurations of the lasers 14 are shown in FIG. 1. In the sub-array 24, the lasers 14 are each formed as individual lasers 14 in total. The sub-array 26, on the other hand, is a connected region where the lasers are connected to each other at diagonal joints 34. Such a configuration has the advantage of a possible smaller distance of the lasers from one another and an increased mechanical stability of the array. In sub-array 28, junctions 34 are even extended into non-lasing outer perimeter 36 of array 10, and mechanical stability is thereby even further improved.It is understood that the sub-arrays 24, 26 and 28 of the laser array can be identical to one another, i.e. the laser array 10 can have either the configuration according to the sub-array 24, according to the sub-array 26 or according to the sub-array 28 in all sub-arrays 24, 26, 28.FIG. 1 furthermore shows, by way of example, a region 38 which can likewise serve for contacting the lasers on the side of the active region 22 facing the substrate 12 and is isolated from the lasing regions, for example by etching or proton implantation.Starting from FIG. 1, FIG. 2 shows a further stage of the laser array 10 during its production. At this stage, contacts 40A are formed on the lasers on the lasers 14, i.e. on the side of the active region 22 facing away from the substrate 12. Contacts 40A may be, for example, p-type contacts. However, this is not obligatory, but rather the contacts 40A can also be n-contacts. In the exemplary embodiment described further below, the contacts 40A are designed as p-contacts.The contacts 40A are a metal layer of a respective first metal layer 40 over the first Bragg mirror 18. Preferably, a passivation layer is applied around the mesas (laser 14) before or after metallization to produce the contacts 40A. Since the array 10 has three sub-arrays 24, 26, 28 in the example shown, three first metal layers 40 are present, one on each sub-array 24, 26, 28, respectively.Starting from FIG. 2, FIGS. 3 and 3A show the laser array 10 at a further stage of its production. At this stage, deep apertures 42 in the form of slits in the semiconductor layer structure are etched in the isolated regions 30 and 32, i.e., between sub-arrays 24, 26 and 28. The apertures 42 are elongated in shape and parallel to the long sides of the sub-arrays 24, 26, 28.The elongated apertures 42 are shown in cross-section in Fig. 3A. The perforations 42 can extend into the substrate 12 or a contact layer between the substrate 12 and the second Bragg mirror 20 or only into the second Bragg mirror 20. The apertures or holes 42 have an elongate shape in the exemplary embodiment, whereby the open region of the exposed (n-doped) contact layer is maximized, while the size of each aperture or hole 42 in a direction transverse to its longitudinal extent advantageously remains small for the subsequent two steps.Preferably, the apertures 42 in the semiconductor layer structure have an elongate shape in the direction parallel to the plane of the substrate 12 with an aspect ratio of greater than 10, optionally greater than 20, further optionally greater than 40. The perforations or holes 42 may have a length of their short side of less than 20 μm, optionally less than 15 μm, further optionally less than 10 μm.The perforations 42 are parallel to the long sides of the sub-arrays 24, 26 and 28, as shown in FIG. 3, and preferably have the same length as the sub-arrays 24, 26 and 28, as described above. This also creates essentially the same or at least very similar current paths from the substrate-side contacting to the lasers 14 on the side of the active region 22 facing the substrate 12.Starting from FIG. 3, FIG. 4 shows the laser array 10 at a further stage of its production. The illustration in FIG. 4 is rotated through 90° in relation to the illustration in FIG. 3. At this stage, on the areas 30 and 32 where the apertures 42 are present, a second metal layer 44 is deposited over the first Bragg mirror 18 which is galvanically or electrically separated from the first metal layer 40, i.e. the contacts 40A. The second metal layer 44 forms contacts 44A that contact the lasers 14 through the apertures 42 in the semiconductor layer structure on a side of the active layer 22 facing the substrate 12. The second metal layer 44 is deposited on the bottoms of the apertures 42 as shown in FIG. 4A. Since lithographic patterning in the deep and narrow apertures 42 is not possible or not simple, a defined region 46 is preferably also covered with the metal of the second metal layer 44 as shown in FIG. 4A. More preferably, the sidewalls of the deep apertures 42 are also metallized (not shown) to allow easier filling of the apertures 42 in the subsequent step. Corresponding to the number of three sub-arrays 24, 26, 28, in the exemplary embodiment shown there are two separated second metal layers 44. However, these are collectively referred to as second metal layer 44 in the present description.Starting from FIG. 4, FIGS. 5 and 5A show the laser array 10 at a further stage of its production. FIG. 5 has the same orientation as FIG. 4 At this stage, thick first metal layers 40B are deposited on sub-arrays 24, 26 and 28 containing lasers 14. More specifically, the metal layers 40B are applied to the contacts 40A and thus complete the first metal layer 40. the first metal layer 40 thus extends over all the lasers 14 of the respective sub-array 24, 26 and 28 and serves for contacting the lasers 14 on the side of the active region 22 facing away from the substrate 12. Preferably, the thick first and second metal layers 40B and 44B are deposited by electrodeless electroplating which allows thick metal layers. The thickness of the second metal layer 44B should be large enough to at least partially, preferably completely, fill the deep openings 42 with the metal, as shown in FIG. 5A, such that an electrical connection from the n-contact of the n-doped region is realized to the same extent as the p-contacting, as shown in FIG. 5A. The first and the second metal layer 40, 44 preferably have an identical height level above the substrate 12 on the top side. FIG. 5A further shows a passivation layer 47 on the Bragg mirror 18 and a barrier layer 49 on the thick metal layer 44B.Starting from FIG. 5, FIG. 6 shows the laser array 10 at a further stage of its production. FIG. 6 is rotated through 90° with respect to the illustration in FIG. 5, i.e. has the same orientation as FIG. 3. In this stage, an insulation layer or passivation layer 48 is applied to the first and second metal layers 40, 44, more precisely to the metal layers 40B and 44B, said insulation layer or passivation layer passivating the surface of the metal layers 40 and 44. Perforations or vias 51, 53 are introduced in the insulation layer 48, through which the metal layers 40 ( 40B) and 44 ( 44B) are partially exposed.Starting from FIG. 6, FIG. 7 shows a final stage of the laser array 10, FIG. 7 has the same orientation as FIG. 6, and a third metal layer 50 and a fourth metal layer 52 have been applied over the insulation layer 48 in this stage. The metal layers 50 and 52 are also formed as thick metal layers. The third metal layer 50 contacts the first metal layer 40 via the apertures 51 in the insulation layer 48. the third metal layer 50 extends over portions of the first metal layer 40 and over portions of the second metal layer 44, as can be seen from FIGS. 6 and 7, but is insulated from the second metal layer 44 via the insulation layer 48. The fourth metal layer 52 over the insulation layer 48 contacts the second metal layer 44 through second apertures 53 in the insulation layer 48. the fourth metal layer 52 is galvanically separated from the third metal layer 50 by the insulation layer 48. The fourth metal layer 42 also extends over portions of the first metal layer 40 and the second metal layer 44, as can be seen from FIGS. 6 and 7, but is insulated from the first metal layer 40 via the insulation layer 48.In the present exemplary embodiment, the third metal layer 50 serves as the anode and the fourth metal layer 52 as the cathode of the laser array 10.The third metal layer 50 thus contacts the lasers on the side of the active layer 22 facing away from the substrate 12, and the fourth metal layer 52 contacts the lasers 14 on the side of the active layer 22 facing the substrate 12.The thick metal layers 40 and 44 on the one hand, and the thick metal layers 50 and 52 on the other hand, as well as the insulation layer 48 between the metal layers 40, 44 on the one hand and the metal layers 50, 52 on the other hand, enable decoupling of the soldering connection side of the array 10 from the contact side of the anode and cathode contact of the lasers 14, The laser array 10 is easily suitable for reflow soldering with solder paste as used in the SMT, since the soldering areas, i.e. the upper sides of the metal layers 50 and 52, can be large and a sufficiently large distance, typically >100 μm, preferably >150 μm, is enabled between the soldering areas on the metal layers 50 and 52, while at the same time the arrangement of the lasers 14 and the substrate-side contacts can be optimized independently of one another. For the latter, a fine structure is given in the laser array 10 that minimizes the distance from the substrate-side contact to the lasers, and on the other hand, as much area of the chip is used for lasers as possible. At the same time, the lasers may be distributed over the majority of the chip area, resulting in better thermal management compared to a chip design in which the same set of lasers is clustered in a portion of the chip.In particular, the third and fourth metal layers 50 and 52 may have an identical height level above the substrate 12 on the top side, which is favored for the further processing of the laser array 10 as an SMD.In the exemplary embodiment shown, the third and fourth metal layers 50 and 52 have the same shape and / or area dimension, which is likewise advantageous.In particular, the first and second thick metal layers 40A, 40B and 44A, 44B for contacting the lasers on the anode and cathode sides result in fewer processing steps in the fabrication of the laser array. Because these thick metal layers additionally planarize the chip, a thin isolation layer 48 and the third and fourth metal layers 50 and 52 can be created with simple processing steps and used to implement large solder pads at the same height level, and both solder pads on the metal layers 50 and 52 can extend over both the first and second thick metal layers 40A, 40B and 44A, 44B.Referring to Figs. 8 to 11, a modified embodiment of a laser array 10' with light emission through the substrate 12 of the laser array 10' will be described. Only the differences of the laser array 10' from the laser array 10 will be described. Elements of the laser array 10' which are identical, similar or comparable to elements of the laser array 10 are provided with the same reference numerals, supplemented by an elevated line.Figure 8 shows the laser array 10' at a stage corresponding to the stage of the laser array 10 in Figure 3. The difference from the laser array 10 is that although the sub-arrays 24', 26' and 28' with the lasers 14' are again formed as rectangles, the intermediate regions 30' and 32' between the sub-arrays 24', 26' and 28' are narrower than the intermediate regions 30 and 32 of the laser array 10. In the intermediate regions 30' and 32', only one deep through hole 42' is located in each case in the semiconductor layer structure, while a further through hole 80' in the semiconductor layer structure for contacting the lasers surrounds the sub-arrays 24', 26', 28' annularly on their outer circumference on the side of the active layer 22 facing the substrate 12. The sub-arrays 24', 26' and 28' can thus be arranged at a smaller distance from one another, since the outer region around the sub-arrays is also used for the substrate-side contacting of the lasers 14'.Figure 9 shows a stage of the laser array 10' which corresponds to the stage of the laser array 10 in Figure 5. The first metal layer 40' again covers the lasers 14' here for contacting the lasers 14' on the side of the active region 22' facing away from the substrate 12'. The second metal layer 44' is located both between the sub-arrays 24', 26' and 28' and, in addition, corresponding to the aperture 80', surrounds the sub-arrays 24', 26' and 28' on their outer periphery and serves for contacting the lasers 14' on the substrate side.Figure 10 shows the laser array 10' at a stage of its manufacture corresponding to the stage of the laser array 10 in Figure 6. Here, apertures 51' and 53' are again present in the insulation or passivation layer 48', partially exposing the first and second metal layers 40', 44'.Fig. 11 shows the laser array 10' at a stage corresponding to the stage of the laser array 10 in Fig. 7. In FIG. 11, the third metal layer 50' and the fourth metal layer 52' are applied to the insulation layer 48', wherein here the third metal layer 50' forms the cathode and the fourth metal layer 52' forms the anode of the laser array 10' for contacting the lasers 14'.In this embodiment, the ring-shaped second metal layer 44' also forms a guard ring to protect the lasers 14' from moisture if the lasers 14' are not implemented by a complete trench or mesa etching, but if only apertures in the semiconductor layer structure are etched on four or more sides, so that although a plurality of lasers 14' are formed after the oxidation, the lasers 14' are connected to their neighbors via the complete semiconductor layer structure. In addition, ion implantation is used here to electrically separate the lasers 14' from the regions in which the substrate-side contact is formed in and around the deep apertures in the semiconductor layer structure.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 129 874 A1

[0004] U.S. Pat. No. 10,826,278 B2

[0004]

Claims

A laser array with light emission through a substrate (12) of the laser array, the laser array comprising: - a plurality of lasers (14) on the substrate, each configured as a vertical cavity surface emitter (VCSEL), the lasers (14) each having a semiconductor layer structure comprising a first Bragg mirror (18), a second Bragg mirror (20), and an active region (22) between the first and second Bragg mirrors (18, 20), the plurality of lasers (14) being grouped into one or more spaced-apart sub-arrays (24, 26, 28) of the laser array; at least one first metal layer (40) which contacts the lasers (14) of the sub-array or sub-arrays (24, 26, 28) on a side of the active region (22) of the lasers (14) facing away from the substrate (12); at least one second metal layer (44) which is galvanically separated from the at least one first metal layer (40) and which contacts the lasers (14) of the sub-array or sub-arrays (24, 26, 28) through at least one aperture (42) in the semiconductor layer structure on a side of the active layer (22) facing the substrate (12), wherein the at least one aperture (42) extends as far as the substrate (12) or into the substrate (12) or as far as a layer between the substrate (12) and the active region (22); an insulation layer (48) over the at least one first and second metal layer (40, 44); a third metal layer (50) over the insulation layer (48), which contacts the at least one first metal layer (40) through first perforations (51) in the insulation layer (48) and extends over regions of the at least one first metal layer (40) and over regions of the at least one second metal layer (44); and a fourth metal layer (52) over the insulation layer (48), which contacts the at least one second metal layer (44) through second perforations (53) in the insulation layer (48), is galvanically separated from the third metal layer (50) and extends over regions of the at least one first metal layer (40) and the at least one second metal layer (44).The laser array of claim 1, wherein the at least one second metal layer (44) is disposed in a region or regions outside the sub-array or sub-arrays (24, 26, 28).The laser array of claim 1 or 2, wherein the laser array comprises at least two sub-arrays (24, 26, 28), and wherein the at least one second metal layer (44) is disposed in an intermediate region between adjacent sub-arrays (24, 26, 28).The laser array according to any one of claims 1 to 3, wherein the at least one second metal layer (44) surrounds the sub-array or sub-arrays (24, 26, 28) on an outer periphery of the sub-array or sub-arrays (24, 26, 28).The laser array according to any one of claims 1 to 4, wherein the at least one first and the at least one second metal layer (40, 44) each comprise a thick metal layer (40B, 44B).The laser array according to any one of claims 1 to 5, wherein the at least one through hole (42) in the semiconductor layer structure in the direction parallel to the plane of the substrate (12) has an elongated shape with an aspect ratio of greater than 10, optionally greater than 20, further optionally greater than 40.The laser array according to any one of claims 1 to 6, wherein the at least one through hole (42) in the semiconductor layer structure in the direction parallel to the plane of the substrate (12) has an elongated shape with a short side length of less than 20 μm, optionally less than 15 μm, further optionally less than 10 μm.The laser array according to claim 6 or 7, wherein the sub-array or sub-arrays (24, 26, 28) have the shape of a rectangle, wherein at least one side of the rectangle runs parallel to the at least one aperture (42) in the semiconductor layer structure and preferably has substantially the same length as the at least one aperture (42).The laser array of any of claims 1 to 8, wherein the at least one aperture (42) in the semiconductor layer structure surrounds the sub-array or sub-arrays on an outer periphery of the sub-array or sub-arrays (24, 26, 28).The laser array of any of claims 1 to 9, wherein the third and fourth metal layers (50, 52) have a same height level above the substrate (12) at the top.The laser array of any of claims 1 to 10, wherein the third and fourth metal layers (50, 52) have a same shape and / or area dimension.The laser array of any of claims 1 to 11, wherein the first and second metal layers (40, 44) have a same height level above the substrate (12).The laser array according to any one of claims 1 to 12, wherein the third and fourth metal layers (50, 52) have a lateral distance of more than 100 μm, optionally more than 150 μm, and less than 300 μm from each other.A method of fabricating a laser array with light emission through a substrate (12) of the laser array, comprising the steps of: - fabricating a plurality of lasers (14) on the substrate (12), each configured as a vertical cavity surface emitter (VCSEL), the plurality of lasers (14) being grouped into one or more spaced-apart sub-arrays (24, 26, 28) of the laser array; wherein the lasers (14) each comprise a semiconductor layer structure comprising a first Bragg mirror (18), a second Bragg mirror (20), and an active region (22) between the first and second Bragg mirrors (18, 20); applying at least one first metal layer (40) over the first Bragg mirror (18), which first metal layer contacts the lasers (14) of the sub-array or sub-arrays (24, 26, 28) on a side of the active region (18) of the lasers (14) facing away from the substrate (12); applying at least one second metal layer (44) over the first Bragg mirror (18), which second metal layer is galvanically separated from the at least one first metal layer (40) and which second metal layer contacts the lasers (14) of the sub-array or sub-arrays (24, 26, 28) through at least one aperture (42) in the semiconductor layer structure on a side of the active layer (22) facing the substrate (12), wherein the at least one aperture (42) extends as far as the substrate (12) or into the substrate (12) or as far as a layer between the substrate (12) and the active region (22); - applying an insulation layer (48) over the at least one first and second metal layer (40, 44); - applying a third metal layer (50) over the insulation layer (48), which contacts the first metal layer (40) through first perforations (51) in the insulation layer (48) and extends over regions of the at least one first metal layer (40) and over regions of the at least one second metal layer (44); and - applying a fourth metal layer (52) over the insulation layer (48), which contacts the at least one second metal layer (44) through second perforations (53) in the insulation layer (48), is galvanically separated from the third metal layer (50) and extends over regions of the at least one first metal layer (40) and the at least one second metal layer (44).The method of claim 14, wherein the at least one aperture (42) in the semiconductor layer structure is created by etching the semiconductor layer structure up to the substrate (12) or into the substrate (12) or up to a layer between the substrate (12) and the active region (22).

Images