Vcsel for emitting laser light

Abstract

Disclosed is a VCSEL (10) for emitting laser light, having a main element (12) which has a mesa portion (14) comprising a stack of different layers (19) stacked in a stacking direction (18), wherein an emission region (22) from which the laser light generated in an active layer (20) in the stack emerges is formed on the top surface (24) of the mesa portion (14), wherein electrical contacts (26) for feeding electrical energy into the active layer (20) are provided on the main element (12), wherein at least one side portion (28) of an electrical contact (26) is arranged on a side surface (30) of the main element (12), wherein the side surfaces (30) are oriented transversely with respect to the layers (19). Also disclosed are a VCSEL array (46) and a method for producing a VCSEL (10).

Description

[0001] VCSEL for emitting laser light

[0002] The present invention relates to a VCSEL for emitting laser light. Furthermore, the present invention relates to a VCSEL array comprising such VCSELs, as well as to an electronic circuit board comprising such a VCSEL and / or a VCSEL array. Furthermore, the invention relates to a method for manufacturing such a VCSEL.

[0003] State of the art

[0004] VCSELs are known that feature electrical contacts for supplying electrical energy. These electrical contacts are attached to the top and / or bottom of the VCSEL (vertical-cavity surface-emitting laser). This makes efficient soldering, for example, using a wave soldering process, impossible.

[0005] For example, US6678292B2 shows a VCSEL that has both p-type and n-type contacts on top of the emitting surface. The contacts are connected to an electrical board via wires. This makes a soldering process suitable for mass production impossible.

[0006] The object solved by the present invention is to provide a VCSEL which enables it to be mounted on an electrical circuit board by a soldering process suitable for mass production.

[0007] Disclosure of the invention

[0008] It is proposed to provide a VCSEL for emitting laser light with a base body which has a mesa section which has a stack of different layers stacked in a stacking direction, wherein an emission region is formed on the upper surface of the mesa section, from which emission region the laser light formed in an active layer in the stack emerges, wherein electrical contacts for feeding electrical energy into the active layer are provided on the base body, wherein at least one side section of an electrical contact is arranged on a side surface on the base body, wherein the side surfaces are aligned transversely to the layers.

[0009] The base body is formed by the stacked layers. The mesa section forms the laser-emitting part of the base body, on whose surface the emission region is arranged. The surface comprises the upper surface, which forms the outer side of one of a pair of Bragg mirrors, between which the active layer is arranged.

[0010] The electrical contacts comprise metal and preferably cover part of the side surface of the base body.

[0011] Advantageous embodiments and further developments of the invention are possible by the measures mentioned in the dependent claims.

[0012] Advantageously, the top surface is oriented perpendicular to the stacking direction. The side surfaces can also be approximately perpendicular or form an angle with the top surface that is greater than 90°.

[0013] It is particularly preferred to apply an insulating layer between the side portion of the electrical contact and the side surface. The insulating layer can simultaneously serve as an adhesive layer, ensuring that the electrical contact adheres to the side surface.

[0014] In a particular development, the electrical contact extends from its side section to the top side of the base body. The electrical contact can cover part of the top surface with an upper section. Preferably, the side sections of electrical contacts, which are designed as cathode or anode, can be attached to preferably a common side surface of the mesa section. This allows both the supply and the discharge of electrical energy in the VCSEL to be realized by connections on a side surface, which can be placed, for example, on an electrical solder contact of a conductor track on an electrical circuit board. For this purpose, the VCSEL can be tilted such that the beam axis of the laser light is aligned parallel to the extension plane of the electrical circuit board, wherein the electrical contacts are preferably arranged between the electrical circuit board and the VCSEL.

[0015] Alternatively or additionally, the electrical contacts can be mounted on different sides of the VCSEL. An electrical contact of the cathode can be arranged on an opposite side to the electrical contact of the anode.

[0016] To achieve a low-stress transition between an upper section of the electrical contact on the top surface and the side section, a chamfer or a rounding can be formed in a transition region between the side surface and the top surface, with a section of the electrical contact being arranged on the transition region. The transition region can be created by an etching step, for example, by a combination of an isotropic and an anisotropic etching step.

[0017] A solder barrier can be formed on the upper portion of the electrical contact on the top surface of the base body, preventing solder from flowing from the side portion to the emission region. The solder barrier can be applied in an additional step after the electrical contact has been applied to its upper portion.

[0018] In a further embodiment, at least one electrical contact is formed only on the side surface, without extending to the top surface. This prevents solder from flowing onto the surface of the base body because the metallization of the electrical contact does not extend to the top surface.

[0019] Furthermore, a VCSEL array can be formed using the VCSEL, which has at least two base bodies, each of which has at least one side section of an electrical contact on its side surfaces. Side sections can be attached to side surfaces that are oriented opposite each other. Alternatively, side sections can also be arranged on side surfaces that are oriented in the same direction. Furthermore, an electrical circuit board with a VCSEL and / or a VCSEL array can be provided, wherein the VCSEL or the VCSEL array rests on a side surface of the electrical circuit board, so that the side section can be soldered to a solder contact of the electrical circuit board.

[0020] Furthermore, a method for producing a VCSEL is proposed, wherein base bodies are arranged on a wafer. A trench is formed adjacent to a base body, creating a side surface on a base body. The side surfaces are provided with a side section of an electrical contact associated with a mesa section of the base body. An insulating layer, containing silicon, for example, can first be applied, onto which a metallic adhesion layer, containing titanium, for example, is applied. The electrical contact, consisting of gold, for example, can be applied to the adhesion layer.

[0021] Advantageously, the trench can be formed between two base bodies, the side surfaces being coated, and the two base bodies being separated from each other by making a separating cut along the trench, leaving the side sections on the side surfaces. In particular, the trench is not completely filled.

[0022] In an alternative embodiment, the trench can be completely filled with a metal, so that the side surface is also coated with a metal. Alternatively, only one side surface in the trench can be coated.

[0023] Preferably, after filling the trench, a section adjacent to the trench, extending to the trench, can be removed, exposing the base body with the metal-covered side surface, allowing contact to be made with the metal forming the side section. This removes the section adjacent to the trench and exposes the side section.

[0024] Brief description of the invention

[0025] The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings. Directional references in the following explanation are to be understood according to the reading direction of the drawings. The location references above and below are to be understood according to the meaning of the drawings. They show:

[0026] Fig. 1 a VCSEL with electrical contacts located on both a

[0027] side surface than on an upper surface of the base body,

[0028] Fig. 2 shows a VCSEL with electrical contacts, wherein at least one electrical contact is arranged only on one side surface of the base body,

[0029] Fig. 3 is a plan view of a VCSEL according to Fig. 1 or 2,

[0030] Fig. 4 is a plan view of a VCSEL array with VCSELs according to Fig. 1 or 2,

[0031] Fig. 5 to 9 show a first embodiment of a method for producing side sections on side surfaces of base bodies,

[0032] Fig. 10 to 15 a second embodiment of a method for producing

[0033] Side sections on side surfaces of basic bodies, and

[0034] Fig. 16 is a schematic representation of an electrical board with two different arrangement variants of the VCSEL.

[0035] Embodiments of the invention

[0036] Fig. 1 shows a VCSEL (vertical-cavity surface-emitting laser) 10 that emits laser light. The VCSEL 10 has a base body 12 with a mesa section 14. The base body 12 and thus also the mesa section 14 are constructed from a stack 16 of different layers 19 stacked in a stacking direction 18.

[0037] The layers 19 fulfill different functions, so that the mesa section 14 has a pair of Bragg mirrors between which an active layer 20 is arranged. The active layer 20 generates photons that emerge as laser light from an emission region 22. The emission region 22 is on the surface of the mesa section 14. The surface comprises a top surface 24 on the top side 25 of the VCSEL, which is the outside of the upper Bragg mirror. Electrical contacts 26 for feeding electrical energy into the active layer 20 are provided on the base body 12. The electrical contacts 26 are designed as an anode 33 and a cathode 29 and have metallic sections. Furthermore, at least one of the electrical contacts 26 has a side section 28 arranged on a side surface 30 of the base body 12. The side surface 30 is oriented on the base body 12 transversely to the top surface 24.The side surface 30 is preferably oriented perpendicular to the top surface 24. Alternatively, at least a portion of the side surface 30 may form an angle with the top surface 24 that is greater than 90°.

[0038] The electrical contacts 26 preferably comprise gold, each of which is applied to a titanium-containing adhesive layer. The electrical contacts 26 cover only a portion of the respective side surface 30 of the base body 12 by at least one side section 28. The respective side sections 28 can be strip-shaped. Only one side section 28 can be provided per base body 12. The titanium-containing adhesive layer is applied to an insulating layer 31.

[0039] The base body 12 of the VCSEL 10 has a substrate 32 on which the stack 16 is arranged. Purely by way of example, the mesa section 14 is separated from the remaining part of the base body 12 by slots 34. A chamfer or rounding is formed at a transition region 36 between the upper surface 24 on the upper side 25 of the base body 12 and the side surface 30. The slots 34 are filled with the material that forms the insulating layer 31. The insulating layer 31 below the titanium-containing adhesion layer is continuously connected to the material in the slots 34.

[0040] The upper portion 35 of the electrical contact 26 is arranged on the upper surface 24. The electrical contact 26 extends from the upper surface 24 to the side surface 30, with a portion of the electrical contact 26 being arranged on the transition region 36 such that the portion is located between the upper portion 35 and the side portion 28.

[0041] Solder barriers 38 are arranged on the top side 25 of the electrical contact 26. These barriers prevent solder from flowing from the side section 28 to the emission region 22 on the top surface 24 of the base body 12, for example, due to the surface tension of the solder. The solder barrier 38 is deposited on the electrical contact 26 in an additional step.

[0042] The exemplary VCSEL 10 in Fig. 1 has the substrate 32 on which the stack 16 is arranged. The stack 16 does not cover the entire substrate 32, so that a step is formed. The upper surface 24 is formed at the higher level of the step. At the lower level of the step, an upper section 35 of a cathode 29 is arranged, with an ohmic contact 37 formed between the upper section 35 of the cathode 29 and the substrate 32. The electrical contact 26 extends from the upper section 35 to a side surface 30 on the base body 12, with a section of the electrical contact 26 covering a transition region 36 formed on the substrate 32.

[0043] Preferably, an anode 33 is arranged as an electrical contact 26 on a side of the VCSEL 10 opposite the cathode 29. The side section 28 extends along a side surface 30 that extends from the substrate 32 to the stack 16. The transition region 36 is formed on the stack 16. The upper section 35 extends to the emission region 22. A shoulder 40 is formed on the underside of the substrate 32. The shoulder 40 creates a corner between the side surface 30 and a surface of the shoulder 40. The side section 28 extends to the corner.

[0044] Fig. 2 shows a further embodiment in which, purely by way of example, the cathode 29 is attached to the side surface 30 of the base body 12 in such a way that it does not extend to the top side 25 of the base body 12. The cathode 29 is formed by the side section 28, with no top section being present. An ohmic contact 37 is arranged on the side surface 30 of the base body 12, wherein the ohmic contact

[0045] 37 may be formed only on the substrate 32. Preferably, the side portion 28 does not extend to the stack 16. The cathode 28 is formed according to the embodiment of Fig. 1.

[0046] Fig. 3 shows a plan view of a VCSEL 10 having a side section 28 on respective opposite sides 42. The side sections 28 are structured according to Fig. 1 or Fig. 2. The anode 33 and the cathode 29 extend from the top side 25 to the side surfaces 30. In each case, an elongated solder barrier

[0047] 38 is arranged on the upper section 35. The solder barrier 38 can contain titanium oxide or silicon nitride. Furthermore, a longitudinal notch can be provided along the longitudinal extent of the solder barrier 38. Preferably, the solder barrier 38 is arranged closer to the transition region 36 than at an opposite end 39 of the upper section 35. Furthermore, test contact pads 44 can be provided on the upper section 35 so that, after the VCSEL 10 has been manufactured in a factory, a test for the functionality of the VCSEL 10 can be carried out in the factory.

[0048] Fig. 4 shows a VCSEL array 46 having a plurality of emission regions 22. A mesa section 14 or a separate base body 12 can be provided for each emission region 22, which are arranged on the VCSEL array 46. Side sections 28 are formed on the side surfaces 30 of the individual base bodies 12 or mesa sections 14. Anodes 33 are arranged as side sections 28 alternately on oppositely aligned side surfaces 28. Purely by way of example, three base bodies 12 are arranged on the VCSEL array 46, which are arranged along an imaginary line. The side sections 28 are arranged on opposite sides with respect to the imaginary line. The side sections 28 of the two outer base bodies 12 are arranged on the same side with respect to the imaginary line 47. The middle base body 12 has a side section

[0049] 28, which is oriented in the opposite direction. The cathodes 29 of the VCSEL array 46 are arranged on opposite sides of the VCSEL array 46, which are not assigned to a single base body 12. Purely by way of example, the cathodes 29 are arranged at the longitudinal ends of the VCSEL array 46.

[0050] Fig. 5 to Fig. 9 show a first embodiment of a method for manufacturing a VCSEL 10 or a VCSEL array 46.

[0051] Fig. 5 shows that on a wafer 48, base bodies 12 are formed by a lithography-etching step, which are separated by trenches 49. The etching direction 50 is indicated by arrows. Two base bodies 12 are shown as examples. The ohmic contacts 37 on the top side 25 for the anode 33 and the cathode

[0052] 29 manufactured by metallization.

[0053] Figure 6 shows a passivation step followed by etching of the anode 33 and the cathode 29. The passivation is achieved, for example, by a silicon nitride coating. On the top side 25, the metallizations are exposed by an etching step.

[0054] In Fig. 7, the side surfaces 30 in the trenches 49 are coated with a metal such as gold, forming the side sections 28 of the cathode 29 and anode 33. The corresponding top sections 35 are also formed in the process. By creating a seed layer, which is applied by sputtering or an atomic layer deposition method, an adhesion layer for metallization can be provided. The metallization can then create the cathode 29 and the anode 33. The final shape of the electrical contacts can be specified by a lithography mask.

[0055] In Fig. 8, the solder barrier 38 is additionally applied and arranged on the upper section 35. In Fig. 9, the respective trench 49 is further deepened by a plasma etching step using a lithography mask until the substrate 32 is severed by this separation step, so that the base bodies 12 are separated from each other.

[0056] A second embodiment of the method for manufacturing a VCSEL 10 or a VCSEL array 46 is shown in Figs. 10 to 15.

[0057] In Fig. 10, a base body 12 is delimited by etched trenches 49 defined by a lithography mask. A section 50 is formed next to the trenches 49, which is sacrificed in the subsequent steps. The section 50 extends to the trench 49.

[0058] In Fig. 11, a passivation is applied according to Fig. 6 and an etching step exposes metallic contacts that were previously applied.

[0059] According to Fig. 12, the trenches 49 are completely filled with a metal such as gold.

[0060] As a result, the side surfaces 30 are covered by the metal.

[0061] After the trenches 49 are completely filled with metal and the side surfaces 30 are covered, an isotropic etching step is carried out along the axis of the stacking direction 18 as shown in Fig. 13, so that openings 52 perpendicular to the layers of the stack are created in the section 50.

[0062] Subsequently, an anisotropic etching step is performed as shown in Fig. 14, which enlarges the openings 52. Gallium arsenide and silicon nitride can be etched anisotropically.

[0063] Finally, a separation step is carried out by a plasma etching according to Fig. 15, which corresponds to the step in Fig. 9.

[0064] Fig. 16 shows a schematic representation of an electrical board 54 on which two VCSELs 10 are arranged.

[0065] Fig. 16A shows a VCSEL 10 which corresponds to an exemplary embodiment of the preceding figures. In this exemplary embodiment, a laser axis 60, along which the laser light essentially propagates, is aligned parallel to the axis of the stacking direction 18. In the present case, the laser axis 60 is aligned perpendicular to the electrical circuit board 54. The emission region 22 is arranged on a side of the VCSEL 10 opposite the electrical circuit boards 54. The side sections 28 of the electrical contacts 26 are positioned on the side surfaces 30 and are accordingly aligned perpendicular to the main extension direction of the electrical circuit board 54. The side sections 28 are positioned in the region of electrical conductor tracks 56 to which they are soldered. A cathode 29 is soldered to a solder contact of a conductor track 56 assigned to the cathode 29.The anode 33 is soldered to a solder contact, which is part of a conductor track 56, which is assigned to a conductor track 56 associated with the anode 33. The solder forms a meniscus-like solder joint 58 in the corner between the conductor track 56 and the side section 28. The solder joint 58 can be concave in the form of a fillet, as in Fig. 16A, or alternatively convex. The side sections 28 are arranged purely by way of example on opposite sides of the VCSEL 10. Alternatively, they can be arranged on the same side surfaces 30 of the VCSEL 10 or on side surfaces separated by a common corner.

[0066] In the embodiment of Fig. 16B, the VCSEL 10 is aligned such that the laser axis 60 is parallel to the main extension plane of the electrical circuit board 54. The electrical contacts 26 are positioned between the conductor track 56 and the base body 12 of the VCSEL 10, with the solder preferably forming a flat solder joint 58. According to the tilted position of the VCSEL 10 and the stacking direction 18, which is now aligned parallel to the main extension plane of the electrical circuit board 54, the laser light from the emission region 22 propagates essentially parallel to the electrical circuit board 54. In an alternative of Fig. 16B, the side sections 28 can also be attached to side surfaces 30 of the VCSEL 10, which are aligned perpendicular to the main extension plane of the electrical circuit board 54, so that a concave or convex solder 58 can be created in the corner between a conductor track 56 and a side section 28.

Claims

Claims VCSEL (10) for emitting laser light with a base body (12) having a mesa section (14) comprising a stack of different layers (19) stacked in a stacking direction (18), wherein an emission region (22) is formed on the upper surface (24) of the mesa section (14) from which the laser light formed in an active layer (20) in the stack emerges, wherein electrical contacts (26) for supplying electrical energy to the active layer (20) are provided on the base body (12), wherein at least one side section (28) of an electrical contact (26) is arranged on a side surface (30) of the base body (12), the side surfaces (30) being oriented transversely to the layers (19). VCSEL (10) according to claim 1, characterized in that the upper surface (24) is oriented perpendicular to the stacking direction (18).A VCSEL (10) according to claims 1 and 2, characterized in that an insulating layer (31) is provided between the side section (28) of the electrical contact (26) and the side surface (30). A VCSEL (10) according to any one of the preceding claims, characterized in that the electrical contact (26) extends from its side section (28) to the top surface (25) of the base body (12). A VCSEL (10) according to any one of the preceding claims, characterized in that side sections (28) of electrical contacts, configured as cathode (29) and anode (33), respectively, are provided on preferably a common side surface (30) of the base body (12). VCSEL (10) according to one of the preceding claims, characterized in that a chamfer or a rounding is formed on a transition section (36) between the side surface (30) and the top surface (24), wherein a section of the electrical contact (26) is arranged on the transition section (36).A VCSEL (10) according to any one of the preceding claims, characterized in that a solder barrier (38) is formed on the electrical contact (26) on the upper surface (24) of the mesa section (14), which prevents a solder from flowing from the side section (28) to the emission area (22). A VCSEL (10) according to any one of the preceding claims, characterized in that an electrical contact (26) is formed only on the side surface (30), without extending to the upper surface (24). A VCSEL array (46), preferably according to any one of the preceding claims, comprising at least two base bodies (12), each of which has at least one side section (28) of an electrical contact (26) on its side surfaces (30).An electronic circuit board (54) comprising a VCSEL (10) and / or a VCSEL array (46) according to any of the preceding claims, wherein a side section (28) of the VCSEL (10) is arranged in the region of a conductor track (56) of the electronic circuit board (54) such that the side section (28) can be soldered to a solder contact of the electronic circuit board (54). An electronic circuit board (54) according to claim 10, characterized in that at least one side section (28) is oriented perpendicular to the conductor track (56) for soldering (58) and / or rests on the conductor track (56).A method for producing a VCSEL (10) according to one of the preceding claims, characterized in that base bodies (12) with a mesa section (14) are arranged on a wafer (48), wherein a groove (49) is formed next to a base body (12), which creates a side surface (30) on a base body (12), wherein the side surfaces (30) are provided with a side section (28) of an electrical contact (26) associated with a mesa section (14). A method according to claim 12, characterized in that the groove (49) is formed between two base bodies (12), wherein the side surfaces (30) are coated, and wherein the two base bodies (12) are separated from each other by making a separation cut along the groove (49), which leaves the side sections (28) attached to the side surfaces (30). The method of claim 12, characterized in that the trench (49) is completely filled with a metal, so that the side surface (30) is also covered with a metal. The method of claim 14, characterized in that after filling the trench (49), a section adjacent to the trench (49), extending to the trench (49), is removed, so that the mesa section (14) with the metal-covered side surface (30) is exposed, allowing contact with the metal.

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