vcsel

Abstract

The invention relates to a VCSEL (100) comprising a laser emission region (102) which has a generally elongate rectangular shape by having a length (L) in the direction of a first dimension (X) from a first longitudinal end to a second longitudinal end of the laser emission region (102) which is greater than a width (B) of the laser emission region (102) in the direction of a second dimension (Y) perpendicular to the first dimension (X). The laser emission region (102) is surrounded at least in parts by one or more trenches (114). The VCSEL (100) has a first mirror (104 or 106), an outcoupling mirror (104 or 106), an active region (108) between the first mirror and the outcoupling mirror, and an oxide aperture (118) which has a non-oxidized inner region (120) and an oxidized outer region (122) peripherally surrounding the non-oxidized inner region (120). In a plane (XY) spanned by the first and second dimensions (X, Y), the oxidized outer region (122) has, in the region of the laser emission region (102), an oxidation width (OWy) in the direction of the second dimension (Y) proceeding from a lateral trench edge (124) which faces toward the laser emission region (102). To both sides of longitudinal ends (110, 112) of the non-oxidized region (122) in the direction of the first dimension (X), the oxidized outer region (122) has in each case one projection (150, 152), the extent (OWx) of which in the direction of the first dimension (X) proceeding from the respective first and second longitudinal ends (110, 112) of the non-oxidized region (120) is greater than the oxidation width (OWy).

Description

[0001] VCSEL

[0002] The invention relates to a VCSEL having a laser emission region of generally elongated rectangular shape.

[0003] Such a VCSEL is known from EP 4 131 676 A1.

[0004] According to the present invention, "oblong rectangular" is understood not only to mean a mathematically exact rectangular shape, but also deviations from it, as long as the basic shape of a rectangle is still recognizable. For example, the corners of the oblong rectangular shape can be rounded, or the longitudinal ends of the oblong rectangle can have a shape deviating from a straight line, e.g., the shape of a triangular angle, and / or the longitudinal edges of the rectangle can be slightly curved, etc.

[0005] In VCSELs with an elongated rectangular laser emission region, i.e., whose extension in a first dimension is larger, in particular many times larger, than its extension in a second perpendicular dimension, it has been observed that, in addition to the desired laser mode(s) the VCSEL is designed to emit, unwanted laser modes are also emitted by the VCSEL. Undesired laser modes are observed particularly when the VCSEL is optimized for high output power at high temperatures.

[0006] Typically, such VCSELs have a current confinement structure in the form of an oxide aperture. In the inner, non-oxidized region of the oxide aperture, the structures generating the laser light, typically one or more quantum wells, are electrically pumped to generate laser light, whereas in the outer, oxidized and therefore electrically non-conductive region of the oxide aperture they are not electrically pumped and do not generate light in this region. In general, the oxidation width of the oxidized region must be small. Laser modes generated within the non-oxidized region of the oxide aperture have a main propagation component in the direction perpendicular to the first and second dimensions, but also propagation components in the direction of the first and second dimensions. While the propagation components orWhile the wavevectors of the laser modes are small in the direction of the shorter second dimension, the propagation components or wavevectors of the laser modes in the direction of the long first dimension can be large due to the long extension of the non-oxidized region of the oxide aperture. In the direction of the first dimension, these laser mode components can penetrate into the oxidized region of the oxide aperture and be reflected back into the non-oxidized region by a reflective end face of the oxidized region, for example, due to a refractive index jump, where they are then amplified. The VCSEL then begins to lase with these modes.

[0007] Against this background, it is an object of the present invention to provide a VCSEL with a laser emission region of generally elongated rectangular shape, in which the emission of unwanted laser modes is at least reduced or even eliminated. Preferably, the oxidation width in the short second dimension should be kept small. Furthermore, the longitudinal ends of the non-oxidized region should preferably be perpendicular to the first dimension, but at least symmetrical in the second dimension.

[0008] According to the invention, the object is achieved by a VCSEL according to claim 1.

[0009] The VCSEL according to the invention has a laser emission region which has a generally elongated rectangular shape in that it has a length in the direction of a first dimension from a first longitudinal end to a second longitudinal end of the laser emission region which is greater than a width of the laser emission region in the direction of a second dimension perpendicular to the first dimension.

[0010] The laser emission region is surrounded at least in sections by one or more trenches. In this case, it can be provided that the laser emission region is completely surrounded by a continuous trench, so that the VCSEL is designed in the shape of a mesa. Alternatively, however, the laser emission region can only be surrounded in sections, i.e. partially, by individual trenches. For example, two trenches can extend along the long sides of the laser emission region in the direction of the first dimension. At the end faces of the laser emission region, short trenches can be present in the direction of the second dimension, which extend in the direction of the second dimension but are not continuous, and which do not necessarily merge into the trenches along the long sides of the laser emission region, although this is also possible. In the sense of the present invention, a "trench" is any opening orTo understand depression regardless of its shape or contour.

[0011] The VCSEL according to the invention comprises a first mirror, an output mirror, and an active region between the first mirror and the output mirror. The VCSEL can comprise a semiconductor layer structure comprising the mirrors and the active region. The mirrors can be Bragg mirrors. The active region can comprise one or more quantum wells. The VCSEL further comprises an oxide aperture having a non-oxidized inner region and an oxidized outer region circumferentially surrounding the non-oxidized inner region. The non-oxidized inner region can define the laser emission region.The oxidized outer region has, in a plane spanned by the first and second dimensions, an oxidation width in the direction of the second dimension in the region of the laser emission region, starting from a lateral trench edge facing the laser emission region, which extends laterally of the laser emission region in the first dimension. The oxidation width thus defined in the present disclosure is preferably small in the VCSEL according to the invention. The oxide aperture can be produced by oxidizing an oxidizable layer of the semiconductor layer structure of the VCSEL. The aforementioned trench or trenches serve as structures from which the oxidation starts.

[0012] According to the invention, the oxidized outer region has an extension in the direction of the first dimension on either side of the longitudinal ends of the laser emission region or the non-oxidized region, the extension of which, extending away from the respective first and second longitudinal ends of the non-oxidized region in the direction of the first dimension, is greater than the oxidation width. The longitudinal ends of the laser emission region can be the longitudinal ends of the non-oxidized region, although this is not mandatory.

[0013] By extending the oxidized region in the direction of the first dimension by a respective extension at the longitudinal ends of the laser emission region, wherein the extension of this extension away from the respective first and second longitudinal ends of the non-oxidized region in the direction of the first dimension is greater than the oxidation width, the propagation of unwanted modes is reduced or even prevented. In the region of the oxidized region extended in the first dimension, components of laser modes that propagate in the direction of the first (long) dimension can still penetrate. However, these are attenuated so strongly in the extensions that even if the oxidized outer region has end faces that give rise to reflection, these laser mode components do not reach the end faces or only in a greatly attenuated form and are therefore not reflected back into the active region with any appreciable intensity.In the direction of the second dimension, at the level of the laser emission region, the oxidation width can still be short. Furthermore, the frontal longitudinal ends of the non-oxidized region can be formed perpendicular to the first dimension, or at least symmetrically in the second dimension.

[0014] The extensions can be created by suitable trench structures which are oxidized during the oxidation to produce the oxide blend, as will be described later.

[0015] Preferred embodiments of the VCSEL according to the invention are specified in the dependent claims and / or are described below.

[0016] In one embodiment, the extension of the extension away from the respective first and second longitudinal ends of the non-oxidized region in the direction of the first dimension is greater than at least 1.5 times, at least 1.75 times, or at least 2 times the oxidation width.

[0017] The further the respective extension extends away from the non-oxidized region, which defines the laser emission region, toward the first dimension, the more laser modes penetrating the oxidized region are attenuated or even annihilated. Likewise, a front side of the oxidized region that causes reflections can be shifted further away from the non-oxidized region.

[0018] In one embodiment, at least one of the extensions may be aligned with the non-oxidized region.

[0019] This measure effectively dampens laser modes propagating in the first dimension and prevents back-reflection of such modes into the active region. One advantage of this measure is that the extension, at least in the area adjacent to the non-oxidized region, can be no wider or only slightly wider than the non-oxidized region in the second dimension.

[0020] In one embodiment, at least one of the extensions has the shape of a bar extending in the direction of the first dimension, the width of which in the second dimension is smaller than the sum of twice the oxidation width and the width of the non-oxidized region.

[0021] Such a configuration of one or both extensions can be achieved by etching one or more trenches into the semiconductor layer structure at the longitudinal ends during manufacture of the VCSEL prior to oxidation, which trenches extend in the direction of the second dimension but not across the entire width of the VCSEL, so that the bar(s) are formed in the semiconductor layer structure. During oxidation of the semiconductor layer structure, the bar is preferably completely oxidized in the plane spanned by the first and second dimensions, which is possible because the width of the bar(s) in the second dimension is smaller than the sum of twice the oxidation width and the width of the non-oxidized region.

[0022] In a further embodiment, at least one of the extensions has the shape of a T-bar having an inner section and an adjoining outer section, wherein the inner section has a width in the direction of the second dimension that is smaller than the sum of twice the oxidation width and width of the non-oxidized region, and the outer section has a width that is greater than the width of the inner section.

[0023] This embodiment represents a further development or modification of the above-mentioned configuration of at least one of the extensions as a bar, in that the narrow inner bar is followed by an outer bar that is wider in the direction of the second dimension. The advantage here is that the wider outer section of the T-bar is suitable as an area for making electrical contact with the VCSEL and / or for introducing vias. This is particularly advantageous with a short oxidation width. In contrast, with the known VCSEL there is only little space for making such a contact. Both the inner area and the outer area of ​​the T-bar are preferably fully oxidized in the plane spanned by the first and second dimensions.In a further embodiment, at least one of the extensions may have the shape of an L-beam having an inner portion which is arranged out of alignment with the laser emission region in the direction of the second dimension and has a width in the direction of the second dimension which is smaller than the sum of twice the oxidation width and width of the non-oxidized region, and an adjoining outer portion whose width in the direction of the second dimension is greater than that of the inner portion.

[0024] This embodiment is similar to the embodiment in which at least one of the extensions has the shape of a T-beam. In this embodiment too, the wider outer section of the L-beam can be used as a surface for applying a contact. A further advantage is that the electrical connection from the contact on the outer section to the long sides of the outer oxidation region can be established via the inner section of the L-beam. This allows the entire non-oxidized region to be electrically pumped homogeneously. However, this configuration is also possible in the other embodiments already described or still to be described. In this embodiment too, the L-beam is preferably completely oxidized in the plane spanned by the first and second dimensions.

[0025] Preferably in connection with the above-mentioned embodiment, it is further preferred if a notch between the inner section and the outer section has a concave curvature, viewed in the direction of the laser emission region, which is aligned with the laser emission region.

[0026] Due to the convex shape of the notch as seen from the non-oxidized region, back reflection of laser light is at least reduced, even if the notch is no further away from the adjacent longitudinal end of the non-oxidized region than the oxidation width. The advantage of this configuration is that the adjacent longitudinal end of the non-oxidized region runs perpendicular to the first dimension after oxidation. The notch can extend in the direction of the second dimension from a longitudinal side of the extension, but also in the direction of the first dimension from an end face of the extension. In a further embodiment, at least one of the extensions can have a continuous width in the second dimension in the direction of the first dimension that corresponds approximately to the sum of twice the oxidation width and the width of the non-oxidized region.

[0027] The advantage of this embodiment is that the extension(s) offer even more surface area for attaching contacts. In this embodiment, too, the respective extension of the oxidized region is preferably completely oxidized in the plane spanned by the first and second dimensions.

[0028] In a further embodiment, at least one of the extensions has one or more openings.

[0029] This configuration is particularly advantageous when, as in the aforementioned embodiment, the respective extension in the direction of the second dimension has a large width throughout the first dimension. Such openings, which can be introduced into the semiconductor layer structure by etching before oxidation, have the advantage that oxidation can additionally also take place starting from the openings, so that the extension or extensions can be completely oxidized in the first and second dimensions. By positioning the openings, a straight shape perpendicular to the first dimension or at least a shape of the longitudinal ends of the non-oxidized region that is symmetrical in the second dimension can be achieved.

[0030] In a further embodiment, the at least one or the plurality of openings may be arranged out of alignment with the non-oxidized region.

[0031] Since the edges of the openings can cause reflections of unwanted laser modes penetrating the extension, arranging the one or more openings out of alignment with the non-oxidized region prevents such backreflection into the non-oxidized region. The advantage is therefore that the openings can also be arranged at a distance from the adjacent longitudinal end of the non-oxidized region that is smaller than the oxidation width. The one or more openings can have any desired edge contour.

[0032] However, it is also possible for the at least one or at least one of the plurality of openings to be arranged in alignment with the non-oxidized region, wherein the opening aligned with the non-oxidized region then has a concave curvature, viewed in the direction of the laser emission region, at least on a side facing the non-oxidized region.

[0033] Here, too, the concave shape of the edge, viewed from the opening to the non-oxidized region, at least reduces the back reflection of unwanted laser modes into the active region. Due to the defocusing effect of the curvature, which can, for example, be partially circular, at most a small portion of the incident laser mode is reflected back into the non-oxidized region and thus into the active region. The opening aligned with the non-oxidized region can therefore be arranged at a distance from the adjacent longitudinal end of the non-oxidized region that is no greater than the oxidation width. This embodiment also enables a longitudinal end of the non-oxidized region that runs perpendicular to the first dimension.

[0034] In a further embodiment, at least one of the extensions has an outer end face which is inclined with respect to the second dimension.

[0035] The inclined design of the outer end face of at least one of the extensions can further reduce the potential for unwanted laser modes to be reflected back into the active region. This design is particularly advantageous when openings are present in one or both extensions, which serve as additional starting points for oxidation, with which the problem relating to the second dimension of asymmetric longitudinal ends of the non-oxidized region can be solved. As already mentioned above, the extension(s) of the oxidized region have the further advantage that their surfaces can be used for one or more contacts or for one or more vias for electrically contacting the VCSEL. Accordingly, in a further embodiment, at least one of the extensions has at least one contact and / or via for electrically contacting the VCSEL.

[0036] Likewise, in a further embodiment, it is provided that one or more contacts for electrically contacting the VCSEL are arranged along at least one longitudinal side of the VCSEL above the outer oxidized region.

[0037] The VCSEL according to the invention can be a bottom emitter or a top emitter, ie the laser emission can occur through the substrate side or through the opposite side of the VCSEL.

[0038] Further advantages and features can be found in the following description and the attached drawing.

[0039] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0040] Embodiments of the invention are illustrated in the drawings and will be described in more detail below with reference to them. They show:

[0041] Fig. 1 is a schematic sketch of a VCSEL according to the prior art in plan view, partly with oxidation fronts illustrated by way of example;

[0042] Fig. 2 shows the VCSEL in Fig. 1 in a schematic plan view after complete oxidation;

[0043] Fig. 3 shows a section through the VCSEL in Fig. 2 along the line III-III in Fig. 2; Fig. 4 shows the VCSEL in Fig. 2 with a laser mode propagating in the laser emission region;

[0044] Fig. 5 shows the VCSEL in Fig. 2 with a laser mode propagating into the outer oxidized region of the oxide aperture;

[0045] Fig. 6 shows another VCSEL according to the prior art in a modified form in a schematic plan view;

[0046] Fig. 7A shows an embodiment of a VCSEL in a schematic plan view before oxidation;

[0047] Fig. 7B shows the VCSEL in Fig. 7A in a schematic plan view, partially with illustrated oxidation fronts during oxidation;

[0048] Fig. 7C shows the VCSEL in Fig. 7A in a schematic plan view after complete oxidation;

[0049] Fig. 7D is a section through the VCSEL in Fig. 7C along the line VIII-VIII in Fig. 7C;

[0050] Fig. 8 shows another embodiment of a VCSEL in a schematic plan view after complete oxidation;

[0051] Fig. 9 shows another embodiment of a VCSEL in a schematic plan view after complete oxidation;

[0052] Fig. 10 shows a further embodiment of a VCSEL in a schematic plan view after complete oxidation; Fig. 11 shows a further embodiment of a VCSEL in a schematic plan view after complete oxidation;

[0053] Fig. 12 shows another embodiment of a VCSEL in a schematic plan view after complete oxidation; and

[0054] Fig. 13 shows another embodiment of a VCSEL in a schematic plan view after complete oxidation.

[0055] With reference to Figs. 1 to 5, a VCSEL 200 according to the prior art and the technical problem existing therein are first described.

[0056] The VCSEL 200 has a laser emission region 202. The laser emission region 202 is the region of the VCSEL 200 from which laser light emerges. In a VCSEL, the laser light typically emerges perpendicular to the semiconductor layer structure of the VCSEL 200. The laser emission direction here runs perpendicular to the plane of the drawing in Fig. 1 or 2, either into the plane of the drawing or out of the plane of the drawing, depending on whether the VCSEL 200 is a bottom emitter or a top emitter.

[0057] Fig. 1 shows a coordinate system with an X-axis and a Y-axis. Laser emission occurs in the direction of the Z-axis, which is perpendicular to the X- and Y-axes, either in the positive Z- or negative Z-direction. The X-axis is referred to below as the X-dimension, and the Y-axis as the Y-dimension. The Z-axis is shown in Fig. 3.

[0058] According to Fig. 3, the VCSEL 200 has a semiconductor layer structure. Generally, the VCSEL 200 includes a first mirror 204, a second mirror 206, and an active region 208 between the first mirror 204 and the second mirror. One of the two mirrors 204 and 206 is an output mirror for outputting the laser light from the VCSEL 200. The first mirror 204 and the second mirror 206 can be configured as Bragg mirrors, as is known in the VCSEL field. The active region 208 can include one or more quantum wells. Referring again to Figs. 1 and 2, the laser emission region 202 has a length L in the X-dimension from a first longitudinal end 210 to a second longitudinal end 212 of the laser emission region 202 that is greater than a width B of the laser emission region 202 in the Y-dimension. The aspect ratio, iethe ratio of length L to width B can be very large, for example greater than 5, or even greater than 10.

[0059] During the manufacture of the VCSEL 200, after the semiconductor layer structure has been produced, one or more trenches are etched into the semiconductor layer structure. In the VCSEL 200 according to Figs. 1 to 5, the trench in Fig. 1 is designated by reference numeral 214, with its outer edge 216 indicated by a dashed line. In the VCSEL 200, the trench 214 has been etched into the semiconductor layer structure as an elongated rectangular annular trench, so that the VCSEL 200 has the shape of a mesa in the XY plane within the trench 210.

[0060] According to Fig. 3, the VCSEL 200 has an oxide aperture 218 having a non-oxidized inner region 220 and an oxidized outer region 222 circumferentially surrounding the non-oxidized inner region 220. The oxide aperture 218 is typically created by oxidizing one or more layers, which typically have a high aluminum content, for example, close to the active region 208. The oxidized outer region 222 has an electrically insulating effect, so that during electrical pumping of the VCSEL 200, the current flows only through the non-oxidized region 220 of the oxide aperture 218, and accordingly, the laser light is generated in the active region 208, which lies below or above the non-oxidized region 220 in the Z direction. Since the oxidized outer region 222 is not electrically conductive, the quantum wells below or above the oxidized region 222 are not electrically pumped.However, since the oxidized material of the oxidized outer region 220 has a lower refractive index than the non-oxidized material in the non-oxidized region 220, the oxidized region 222 acts as a waveguide structure for the generated laser modes, as will be described below.

[0061] The oxidized outer region 222 has, in the XY plane in the region of the laser emission region 202, an oxidation width Owy in the Y direction, starting from a lateral trench edge 224 facing the laser emission region 202 and extending laterally of the laser emission region 202 in the X direction. For reasons of clarity, only individual oxidation fronts 226 are illustrated in Fig. 1 as semicircular areas. During the oxidation of the oxidizable layer(s) in the semiconductor layer structure, the oxidation fronts spread uniformly from the trench edge 224 into the oxidizable layer, as well as from the front edges 228 of the trench 214. Due to the trench structure of the VCSEL 200, the extension Owx (Fig. 2) of the oxidized region 222 at the longitudinal ends 210 and 212 in the X-dimension direction is equal to the oxidation width Owy in the Y-dimension direction.Since the goal is to keep the oxidation width Owy small in the Y direction so that the VCSEL 200 can be positioned close to an edge of the chip, Owx is also small. This leads, as described below, to the propagation of unwanted laser modes in the active region 208 of the VCSEL 200. This effect is described with reference to Figs. 4 and 5.

[0062] Typically, as mentioned above, a laser mode propagates primarily in the Z dimension. Nevertheless, a laser mode can also have components in the X and Y directions. In Fig. 4, an X component of a laser mode confined in the non-oxidized region 220 is illustrated by a double-headed arrow 230. In the Y direction, the width of the non-oxidized region 220 is typically very small, for example, 3 pm to 7 pm, so that only one or at most a few laser modes can occur in this direction, or the Y component of this laser mode or laser modes is small. The situation is different in the X dimension of the non-oxidized region 220, which can be comparatively large, for example, 30 pm to 60 pm and above, so that the X component of the wave vector of the laser modes can be comparatively large.If the X component is small enough and the refractive index jump at the longitudinal ends 210 and 212 of the laser emission region 202 and the non-oxidized region 220, respectively, is large enough, the laser mode is reflected back at the longitudinal ends 210 and 212, as indicated by arrows 232, so that the laser mode is confined to the non-oxidized region 220. In this case, no unwanted laser modes are amplified in the active region 208 and emitted by the VCSEL. However, if the refractive index jump from the non-oxidized region 220 to the oxidized region 222 is small and the X component of the laser mode is large, the laser mode is not completely reflected at the longitudinal ends 210, 212 of the non-oxidized region 220, but penetrates into the oxidized region 222 and is reflected back into the non-oxidized region 220 by the end faces 228 and 229 of the oxidized region 222, as indicated by arrows 234 in Fig. 5.As described above, the front ends 228 and 229 of the oxidized region 222 are defined by the trench structure of the trench 214. The refractive index jump at the longitudinal ends 228 and 229 is large compared to the refractive index jump from the non-oxidized region 220 to the oxidized region 222. For example, if one or more passivation layers with a refractive index of 2.0 are present in the trench 214, a refractive index jump of 3.5 occurs from, for example, GaAs to a refractive index of 2.0. If the trench 214 contains only air, this index jump is even larger. These modes, which penetrate into the oxidized region in the X-dimension direction and are reflected back from the longitudinal ends 228, 229 of the oxidized region, always exist.If the oxidation width Owy and thus the extension Owx, which is equal to Owy in the VCSEL 200, is small and the length L of the non-oxidized region 220 in the X-dimension is large, the ratio of the length of the path traveled by the light in the active region 208 in the non-oxidized region 220 to the length traveled by the light in the oxidized region 222 becomes very large. A mode penetrating the oxidized region 222 thus experiences significant amplification in the non-oxidized region 220 and only minor losses in the oxidized region 222. In particular, if the detuning of the laser cavity resonance to the maximum of the emission spectrum of the quantum wells is large at the same time, these higher-order laser modes can be amplified and begin to lase, in addition to the desired modes, or they can even assume the full emission power.In VCSELs operating at high power at high heat sink temperatures, the laser cavity resonance at room temperature can be deliberately detuned to such an extent that a good overlap of the cavity resonance with the emission spectrum of the quantum wells is ensured at higher temperatures. On the other hand, as already mentioned above, the oxidation width Owy should be kept small. As a result, with the VCSEL 200, unwanted higher-order laser modes cannot be confined by the oxide aperture 218 and thus escape from the VCSEL 200 as unwanted laser emission.

[0063] In the prior art, as shown in Fig. 6, attempts were made to eliminate the problem described above with beveled longitudinal ends 228, 229, which ensure that the laser modes penetrating the oxidized region 222 in the X-dimension direction are not reflected back into the active region or the non-oxidized region 220, but are deflected, as indicated by an arrow 240. The beveled front ends of the oxidized region 222 can be realized by a corresponding trench structure at the longitudinal ends of the VCSEL 200. However, after oxidation of the VCSEL 200, the longitudinal ends 210 and 212 of the non-oxidized region 220 also run obliquely to the X dimension, with the result that the desired laser modes confined to the non-oxidized region 220 (indicated by an arrow 242) are undesirably changed, as indicated by an arrow 244.However, when oxidizing the VCSEL 200, the longitudinal ends 210, 212 which are inclined with respect to the X and Y directions cannot be avoided due to the uniform propagation of the oxidation fronts.

[0064] With reference to Figs. 7 to 13, VCSELs 100 are described below according to several embodiments of the invention, in which the technical problem described above is solved. For elements, components, and parts of the VCSELs 100 that are identical, similar, or comparable to elements, components, and parts of the VCSELs 100, the same reference numerals as in Figs. 1 to 6, reduced by 100, are used. The following primarily describes the differences between the VCSELs 100 and the VCSEL 200, and unless otherwise stated, the description of the VCSEL 200 also applies to the VCSELs 100.

[0065] A first embodiment of a VCSEL 100 is described with reference to Figs. 7A-7D. The VCSEL 100 has, as shown in Fig. 7C, a laser emission region 102, from which laser light emerges, of a generally elongated rectangular shape. As shown in Fig. 7D, the VCSEL 100 has a semiconductor layer structure comprising a first mirror 104, a second mirror 106, and an active region 108 between the first mirror 104 and the second mirror 106. The first mirror 104 and the second mirror 106 can each be formed as Bragg mirrors from a plurality of layer pairs with alternating high and low refractive indices. The active region 108 can have one or more quantum wells.

[0066] The laser emission region 102 has a length L in the X direction from a first longitudinal end 110 to a second longitudinal end 112 of the laser emission region 102 that is greater, in particular several times greater, than a width B of the laser emission region 102 in the Y direction. The aspect ratio of length L to width B can be more than 5 or even more than 10.

[0067] During the manufacture of the VCSEL 100, after the semiconductor layer structure has been produced, one or more trenches 114 are etched into it, as indicated in Fig. 7A. The trench 114 can be a single trench that completely surrounds the laser emission region 102, so that the VCSEL 100 has the shape of a mesa. Alternatively, instead of a single trench 114 that completely surrounds the VCSEL 100, several individual trenches can be distributed around the circumference of the VCSEL 100, which then only surround the laser emission region 102 in sections, i.e., the trenches are each separated from one another, so that no mesa is created. In Fig. 7A, exemplary variants of trench structures are indicated at the left end of the VCSEL 100 with a dashed and a dash-dotted line. Furthermore, there may be no trench on end faces 115 and 117 of the VCSEL 100, as shown in Fig. 7A.In other words, in some embodiments, the VCSEL 100 may be formed as a mesa, in other embodiments, the VCSEL may be formed with ridge and trench structures.

[0068] According to Fig. 7D, the VCSEL 100 has an oxide aperture 118 having a non-oxidized inner region 120 defining the laser emission region 102, and an oxidized outer region 122 circumferentially surrounding the non-oxidized inner region 120. The oxide aperture 118 can be arranged, for example, in one of the mirrors 104, 106, near the active region 108, although this is not mandatory. The oxidized outer region 122, which is shown in Fig. 7C after complete oxidation, has an oxidation width Owy in the direction of the Y dimension in the region of the laser emission region 102, starting from a lateral trench edge 124 facing the laser emission region 102 and extending laterally of the laser emission region 102 in the X dimension.

[0069] Fig. 7A shows the VCSEL 100 before oxidizing the oxidizable layer of the semiconductor layer structure of the VCSEL 100, for example, a semiconductor layer with a high aluminum content. The oxidizable layer or layers can be located near the quantum wells of the active region 108, although this is not mandatory. The oxidation of the oxidizable layer or layers starts from the trench or trenches 124. In Fig. 7B, a few oxidation fronts 126 are shown by semicircles as examples. Fig. 7C shows the fully oxidized VCSEL 100.

[0070] In contrast to the VCSEL 200 in Figs. 1 to 5 and the VCSEL 200 in Fig. 6, the oxidized region 122 has an extension 150 and 152, respectively, in the X-dimension on both sides of the longitudinal ends 110 and 112 of the laser emission region 102. The extension 150 has an extension Owx away from the longitudinal end 110 of the non-oxidized region 120 in the X-dimension, which is greater than the oxidation width Owy. The same applies to the extension 152 at the opposite end of the VCSEL 100. The extensions 150 and 152 of the oxidized region 122 can be realized by appropriately structuring the trench 124 or trenches. For example, by means of a suitably designed mask used during etching of the trench or trenches 124, extensions 150' and 152' remain in the semiconductor layer structure according to Fig. 7A, which extensions are completely oxidized up to the oxidation width Owy during oxidation of the VCSEL 100, as shown in Fig. 7C.

[0071] The extension Owx of the respective extension 150 and 152 away from the respective longitudinal end 110 or 112 of the non-oxidized region 120 can be greater than at least 1.5 times, or at least 1.75 times, or at least twice the oxidation width Owy. This also applies to the exemplary embodiments described below. Due to the extensions 150 and 152 of the oxidized region 122, longitudinal ends 128 and 129 of the oxidized region 122, which can give rise to the back reflection of unwanted laser modes penetrating into the oxidized region 122, are located far enough away from the longitudinal ends 110, 112 of the non-oxidized region 120. The extensions 150 and 152 sufficiently attenuate unwanted laser modes penetrating these regions so that they cannot return to the active region 106, or at most, with negligible intensity. This effect is achieved, in particular, without increasing the oxidation width Owy.

[0072] In the embodiment according to Figs. 7A to 7D, the non-oxidized region 120 is not exactly rectangular, but the longitudinal ends 110 and 112 are symmetrical with respect to the Y dimension, so that the desired modes in the non-oxidized region 120 are not significantly changed.

[0073] The extensions 150 and 152 are aligned with the non-oxidized region 120 as shown in Fig. 7C. In the exemplary embodiment according to Figs. 7A to 7D, the extensions 150 and 152 are each formed as a bar extending in the X-dimension, the width of which in the Y-dimension is smaller than the sum of twice the oxidation width Owy and the width B of the non-oxidized region 120. This ensures that the extensions 150 and 152 are completely oxidized during the oxidation of the VCSEL 100, as shown in Fig. 7C. However, the width of the bar is equal to or greater than the width B of the non-oxidized region 120.

[0074] Fig. 8 shows a further embodiment of a VCSEL 100. Unless otherwise stated, the description of the VCSEL 100 in Figs. 7A to 7D also applies to the VCSEL 100 in Fig. 8. Furthermore, the same reference numerals are used for elements, components, and part names of the VCSEL 100 in Fig. 8 that are identical, comparable, or similar to elements, components, and part names of the VCSEL 100 in Fig. 8. Only the differences between the VCSEL 100 in Fig. 8 and the VCSEL 100 in Figs. 7A to 7D are described below. The VCSEL 100 in Fig. 8 has extensions 150 and 152 of the oxidized region 122, which are designed in the shape of a T-bar. The extension 150 has an inner portion 154 and an adjoining outer portion 156.The inner section 154 has a width in the Y dimension that is smaller than the sum of twice the oxidation width Owy and width B of the non-oxidized region 120, similar or the same as the extension 150 in Fig. 7C. The outer section 156 has a width in the Y dimension that is greater than the width of the inner section 154. The T-shape of the extensions 150 and 152 is achieved by a corresponding structure of the trench 114 (not shown). As with the VCSEL 100 in Figs. 7A to 7D, the extension Owx of the extensions 150 and 152, respectively, away from the longitudinal ends 110 and 112, respectively, of the non-oxidized region 120 is greater than the oxidation width Owy, with respect to the VCSEL 100 as described with respect to Figs. 7A to 7D.

[0075] The inner region 154 of the extensions 150 and 152 is aligned with the non-oxidized region 120. The outer region 156, which is wider in the Y dimension and is located above the extensions 150 and 152, can now be used, as shown in Fig. 8 for the extension 150, as a surface for contacting the VCSEL 100 for electrically pumping it. The outer region 156 offers sufficient space for this. For example, a p-contact 158 ​​and a p-via, i.e., an opening in the passivation layer that separates the p-contact directly on the semiconductor from the thicker overlying metal layer, could be arranged above the outer region 156. Due to the desired small oxidation width Owy, such a space is not available, for example, in the VCSEL 200 in Figs. 1 to 5, nor in the VCSEL 200 in Fig. 6.

[0076] The extensions 150 and 152 of the oxidized region 122 are completely oxidized in the XY plane, as shown in Fig. 8.

[0077] Fig. 9 shows a further embodiment of a VCSEL 100. Only the differences between the VCSEL 100 and the VCSELs in Figs. 7A to 7D and 8 are described below. Furthermore, the same reference numerals are used for elements, components and part names of the VCSEL 100 in Fig. 9 that are identical, comparable or similar to elements, components and part names of the VCSEL 100 in Fig. 7A to 7D and 8. The VCSEL 100 in Fig. 9 has a respective extension 150 and 152 of the oxidized region 122, which has a width in the Y dimension continuously over its extension Owx in the X dimension that corresponds approximately to the sum of twice the oxidation width Owy and width B of the non-oxidized region 120.To ensure complete oxidation of the extensions 150 and 152 of the oxidized region 122 in this configuration of the extensions 150 and 152, the extensions 150 and 152 have at least one, here a plurality of, openings 160 (illustrated as small circles), which also serve as starting positions for the oxidation of the oxidizable layer of the VCSEL 100. The advantage of this configuration is that even more space is available for contacts 158a and 158b. As for the previous embodiments in Figs. 7A to 7D and 8, the extension Owx of the extensions 150 and 152 from the longitudinal ends 110 and 112, respectively, of the non-oxidized region 120 is greater than the oxidation width Owy. In Fig. 8 and 9, the contacts 158 and 158a, 158b are shown only on the extension 150, but it is understood that further contacts can be provided on the extensions 152.

[0078] In the embodiment shown in Fig. 9, the openings 160 in the extensions 150 and 152 are not arranged in alignment with the non-oxidized region 120, so that the opening edges of the openings 160 are not exposed to X-components of unwanted laser modes and thus do not give rise to the reflection of such modes back into the active region.

[0079] Fig. 10 shows a modification of the VCSEL 100 in Fig. 9. The modification consists in that the extensions 150 and 152 have outer end faces 170, 172 that are inclined with respect to the Y dimension. In addition to the effect of the longer extension Owx in the X dimension compared to the oxidation width Owy, the inclined end faces 170 and 172 further reduce the amount of back-reflected light from the end faces 170 and 172. In contrast to the VCSEL 200 in Fig. 6, in which the non-oxidized region 120 is asymmetric with respect to the Y dimension, the non-oxidized region 120 of the VCSEL 100 in Fig. 10 is symmetric with respect to the Y dimension. This is achieved, as with the VCSEL 100 in Fig. 9, by the openings 160, which serve as starting positions for oxidation and are arranged symmetrically with respect to the Y dimension. The openings 160 ensure complete oxidation of the projections 150 and 152 in the XY plane.

[0080] Fig. 11 shows a modification of the VCSEL 100 of Fig. 8, in which the outer end face of the outer region 156 is inclined with respect to the Y dimension. As with the VCSEL 100 in Fig. 8, the symmetrical shape of the non-oxidized region 120 with respect to the Y dimension is achieved by the inner portion 154 of the extension 150, which is thinner in the Y dimension and bordered on both sides by openings or notches 153 in the Y dimension.

[0081] For reasons of clarity, no electrical contacts are shown above the extensions 150 and 152 in Fig. 10 and 11 as in Fig. 8 and 9, but they may also be present there.

[0082] Fig. 12 shows a further embodiment of a VCSEL 100, which is a modification of the VCSEL 100 in Fig. 9. As with the VCSEL 100 in Fig. 9, the extensions 150 and 152 each have a plurality of openings 160. An opening 160', as shown for the extension 150, is, in contrast to the VCSEL 100 in Fig. 9, aligned with the non-oxidized region 120. The distance of this opening 160' from the longitudinal end 110 of the non-oxidized region 120 is not greater than the oxidation width Owy.To prevent an unwanted laser mode 230 from being reflected back into the active region 108, the edge of the opening 160', which faces the non-oxidized region 120, is convexly curved as viewed from the non-oxidized region 120, so that, as indicated for the extension 152, laser light incident on this opening edge is scattered essentially in directions away from the X-direction, and at most a small portion is reflected back into the non-oxidized region 120. The edge of the opening 160' acts like a strongly defocusing mirror. While the openings 160 in the embodiment in Fig. 9 can also be rectangular, for example square, a round shape of the openings 160, in particular of the opening 160' aligned with the non-oxidized region 120, is preferred in the embodiment in Fig. 12. The advantage of the embodiment in Fig.12 is that due to the opening 160' being aligned with the non-oxidized region 120 at a distance of no more than the oxidation width Owy, it is achieved that the longitudinal ends 110, and the same applies to the longitudinal end 112, of the non-oxidized region 120, after the oxidation is complete, run at right angles to the X dimension and parallel to the Y dimension, respectively, similar to the VCSEL 200 in Figs. 1 to 5, but without the disadvantages associated with the VCSEL 200.

[0083] Fig. 13 shows a VCSEL 100 in which the extensions 150 and 152 have the shape of an L-bar having an inner section 180 and an outer section 182. Preferably, the extension 152 is arranged at the opposite end of the VCSEL 100, mirror-inverted with respect to the extension 150. The inner section 180 of the extensions 150, 152 is arranged out of alignment with the non-oxidized region 120 or the laser emission region 102 in the Y dimension and has a width in the Y dimension that is less than the sum of twice the oxidation width Owy and width B of the non-oxidized region 120. The outer section 282 has a width in the Y dimension that is greater than the width of the inner section 180 in the Y dimension.Between the inner section 180 and the outer section 182, an opening or notch 184 extends in the Y dimension, which can be realized by a corresponding structure of the trench or trenches 114. The notch 184 has a concavely curved edge 186, viewed in the direction of the non-oxidized region 120, which is aligned with the non-oxidized region 120 or the laser emission region 102. Although the edge 186 is spaced from the longitudinal end 110 of the non-oxidized region 120 by a distance smaller than the oxidation width Owy, as in the embodiment in Fig. 12, unwanted laser modes reflected at the edge 186 are primarily reflected in directions away from the X direction, so that back-reflection of unwanted laser modes from the edge 186 into the non-oxidized region 120 is at least greatly reduced.

[0084] The advantage of this embodiment, as with the embodiment in Fig. 12, is that longitudinal ends 110 and 112 of the non-oxidized region 120 run perpendicular to the X dimension.

[0085] In the embodiment in Fig. 13, furthermore, starting from the contacts 158 above the oxidized region 122 along the longitudinal sides 189, contacts 190 for electrically contacting the VCSEL 100 are arranged, which extend from the p-vias 158 along the non-oxidized region 120, so that the entire non-oxidized region 120 can be electrically pumped homogeneously.

[0086] Similar contact and via geometries extending along the long sides of the non-oxidized region 120 may also be present in the embodiments according to Figs. 7 to 12, but are not shown for reasons of simplified illustration.

[0087] While in Figs. 7 to 13 the extensions 150 are identical or mirror-imaged to the extensions 152, they can also be different. For example, in a VCSEL 100, an extension 152 of one of the described embodiments can be combined with an extension 150 of another of the described embodiments.

Claims

Claims 1. A VCSEL comprising a laser emission region (102) having a generally elongated rectangular shape, in that it has a length (L) in the direction of a first dimension (X) from a first longitudinal end (110) to a second longitudinal end (112) of the laser emission region (102) that is greater than a width (B) of the laser emission region (102) in the direction of a second dimension (Y) perpendicular to the first dimension (X), wherein the laser emission region (102) is surrounded at least in sections by one or more trenches (114), wherein the VCSEL (100) has a first mirror (104 or 106), an output mirror (104 or 106), and an active region (108) between the first mirror and the output mirror, and an oxide aperture (118) having a non-oxidized inner region (120) and a peripherally surrounding the non-oxidized inner region (120). oxidized outer region (122), wherein the oxidized outer region (122) in a plane (XY),which is spanned by the first and second dimensions (X, Y), has an oxidation width (Owy) in the direction of the second dimension (Y) in the region of the laser emission region (102) starting from a lateral trench edge (124) facing the laser emission region (102), wherein the oxidized outer region (122) has an extension (150, 152) on both sides of longitudinal ends (110, 112) of the non-oxidized region (122) in the direction of the first dimension (X), the extension (Owx) of which, away from the respective first and second longitudinal ends (110, 112) of the non-oxidized region (120) in the direction of the first dimension (X), is greater than the oxidation width (Owy).

2. VCSEL according to claim 1, wherein the extension (Owx) of the extension (150, 152) away from the respective first and second longitudinal ends (110, 112) of the non-oxidized region (120) in the direction of the first dimension (X) is greater than at least 1.5 times, at least 1.75 times, or at least 2 times the oxidation width (Owy).

3. VCSEL according to claim 1 or 2, wherein at least one of the extensions (15, 152) is aligned with the non-oxidized region (120).

4. VCSEL according to one of claims 1 to 3, wherein at least one of the extensions (150, 152) has the shape of a bar extending in the direction of the first dimension (X), the width of which bar in the second dimension (Y) is smaller than the sum of twice the oxidation width (Owy) and the width of the non-oxidized region.

5. VCSEL according to one of claims 1 to 4, wherein at least one of the extensions (150, 152) has the shape of a T-bar having an inner section (154) and an adjoining outer section (156), wherein the inner section (154) has a width in the direction of the second dimension (Y) that is less than the sum of twice the oxidation width (Owy) and the width of the non-oxidized region (120), and the outer section (156) has a width that is greater than the width of the inner section (154).

6. VCSEL according to one of claims 1 to 5, wherein at least one of the extensions (150, 152) has the shape of an L-beam having an inner section (180) which is arranged out of alignment with the non-oxidized region (120) in the direction of the second dimension (Y) and has a width in the direction of the second dimension (Y) which is less than the sum of twice the oxidation width (Owy) and the width of the non-oxidized region (120), and an adjoining outer section (182) whose width in the direction of the second dimension (Y) is greater than that of the inner section (180).

7. The VCSEL of claim 6, wherein a notch (184) between the inner portion (180) and the outer portion (182) has a concave curvature (186) viewed toward the non-oxidized region (120) and aligned with the non-oxidized region (120).

8. VCSEL according to one of claims 1 to 3, wherein at least one of the extensions (150, 152) has a width in the second dimension (Y) continuously in the direction of the first dimension (X) which corresponds approximately to the sum of twice the oxidation width (Owy) and width of the non-oxidized region (120).

9. VCSEL according to one of claims 1 to 8, wherein at least one of the extensions (150, 152) has an opening (160, 160').

10. VCSEL according to claim 9, wherein the at least one of the extensions (150, 152) has a plurality of openings (160, 160').

11. VCSEL according to claim 9 or 10, wherein the at least one or the plurality of openings (160) are arranged out of alignment with the non-oxidized region (120).

12. VCSEL according to one of claims 9 to 11, wherein the at least one or at least one of the plurality of openings (160') is arranged in alignment with the non-oxidized region (120), wherein the opening (160') has a concave curvature at least on a side facing the non-oxidized region as seen in the direction of the laser emission region.

13. VCSEL according to one of claims 1 to 12, wherein at least one of the extensions (150, 152) has an outer end face (170, 172) which is inclined with respect to the second dimension (Y).

14. VCSEL according to one of claims 1 to 13, wherein at least one of the extensions (150, 152) has at least one contact and / or via for electrically contacting the VCSEL (100).

15. VCSEL according to one of claims 1 to 14, wherein along at least one longitudinal side of the VCSEL (100) above the outer oxidized region (122) a or several contacts (190) are arranged for electrically contacting the VCSEL.

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