VCSEL for emitting laser light

Abstract

A VCSEL (10) for emitting a laser beam, having a main element (12) having a mesa portion (14) including a stack of different layers (19) stacked in a stacking direction (18), a light emitting region (22) being formed on a top surface (24) of the mesa portion (14), laser light generated in an active layer (20) in the stack emerging from the light emitting region (22), and an electrical contact (26) for feeding electrical energy to the active layer (20) being provided on the main element (12), at least one side portion (28) of the electrical contact (26) being disposed on a side surface (30) of the main element (12), the side surface (30) being oriented transversely to the layer (19), a VCSEL (10) is disclosed. Also disclosed is a VCSEL array (46), and a method for producing the VCSEL (10).

Description

Technical Field

[0001] The present invention relates to a VCSEL for emitting a laser beam. Further, the present invention relates to a VCSEL array having such a VCSEL, and an electric circuit board having such a VCSEL and / or VCSEL array. The present invention further relates to a method for producing such a VCSEL.

Background Art

[0002] VCSELs having electrical contacts for feeding electrical energy are known. These electrical contacts are mounted on the upper side and / or the lower side of the VCSEL (Vertical Cavity Surface Emitting Laser). This makes it impossible to perform efficient soldering, for example, using a jet soldering process.

[0003] For example, U.S. Patent No. 6,678,292 (B2) shows a VCSEL having both a p-type contact and an n-type contact on the light emitting surface. These contacts are connected to an electric circuit board via wires. This makes it impossible to perform a soldering process suitable for mass production.

[0004] The problem to be solved by the present invention is to provide a VCSEL that can be mounted on an electric circuit board by a soldering process suitable for mass production.

Summary of the Invention

[0005] There is proposed a VCSEL for emitting a laser beam, comprising a main element having a mesa portion having a stack of different layers stacked in a stacking direction, a light emitting region being formed on the top surface of the mesa portion, from which laser light generated in the active layer in the stack appears, and electrical contacts for feeding electrical energy to the active layer being provided on the main element, at least one side portion of the electrical contacts being arranged on the side surface of the main element, the side surface being oriented in a direction transverse to the layers.

[0006] The main element is formed by layers stacked on top of each other. The mesa portion forms the portion of the main element that emits laser light, and a light-emitting region is disposed on its surface. This surface includes the top surface that forms the outer side portion of one of the pair of Bragg mirrors with the active layer disposed therebetween.

[0007] The electrical contact contains metal and preferably covers a part of the side surface of the main element.

[0008] Advantageous embodiments and further developments of the invention are made possible by the means described in the dependent claims.

[0009] Advantageously, the top surface is oriented perpendicular to the stacking direction. The side surface is also oriented substantially perpendicular to the top surface or can form an angle greater than 90° with the top surface.

[0010] It is particularly preferred to attach an insulating layer between the side portion of the electrical contact and the side surface. This insulating layer can also function as an adhesive layer to ensure that the electrical contact adheres to the side surface.

[0011] In a special development, the electrical contact extends from its side portion to the upper side portion of the main element. This electrical contact can cover a part of the top surface in the upper portion.

[0012] Preferably, the side portion of the electrical contact configured as a cathode or anode can preferably be attached on the common side surface of the mesa portion. Thereby, both the supply and discharge of electrical energy in the VCSEL can be realized via a connection portion on the side surface that can be installed, for example, on the electrical solder contact of a conductor track on an electrical circuit board. For this purpose, the VCSEL can be tilted so that the beam axis of the laser light is parallel to the extending plane of the electrical circuit board, and the electrical contact is preferably disposed between the electrical circuit board and the VCSEL.

[0013] Alternatively or additionally, the electrical contact can be attached on different sides of the VCSEL. The electrical contact of the cathode can be arranged on the side opposite to the side of the anode electrical contact.

[0014] To achieve a low-stress transition between the upper and side portions of the electrical contact on the top surface, a chamfered or rounded portion can be formed in the transition region between the side surface and the top surface, and the portion of the electrical contact is disposed on the transition region. The transition region can be created by an etching process, for example, a combination of an isotropic etching process and an anisotropic etching process.

[0015] The solder barrier may be formed on the upper portion of the electrical contact on the top surface of the main element to prevent solder from flowing from the side portion to the light-emitting region. The solder barrier can be attached on the upper portion of the electrical contact in an additional process after the electrical contact is applied.

[0016] In a further exemplary embodiment, at least one electrical contact is formed only on the side surface without extending to the top surface. Thereby, since the metallized portion of the electrical contact does not reach the top surface, solder is prevented from flowing on the surface of the main element.

[0017] Furthermore, a VCSEL array can be formed by VCSELs and has at least two main elements, and each of the main elements has at least one side portion of the electrical contact on its side surface. The side portions can be attached on the side surfaces facing in opposite directions. Alternatively, the side portions can be arranged on the side surfaces facing in the same direction.

[0018] Furthermore, an electrical circuit board having a VCSEL and / or a VCSEL array can be provided, and the VCSEL or the VCSEL array is placed on the side surface on the electrical circuit board so that its side portion can be soldered onto the solder contact of the electrical circuit board.

[0019] Furthermore, a method of generating a VCSEL is proposed, in which a main element is disposed on a wafer, a trench is formed adjacent to the main element, the trench creates a side surface over the main element, and the side surface is provided with a side portion of an electrical contact assigned to a mesa portion of the main element. For example, an insulating layer containing silicon can be applied first, and a metal adhesion layer containing titanium, for example, is applied to this insulating layer. An electrical contact, which can be made of gold, can be applied to the adhesion layer.

[0020] Advantageously, the trench can be formed between two main elements, the side surface thereof is coated, and the two main elements are separated from each other by performing a separation cut along the trench, and by the separation cut, the side portion remains on the side surface. Specifically, the trench is not completely filled.

[0021] In another embodiment, the trench can be completely filled with metal such that the side surface is also coated with metal. Alternatively, only one side surface in the trench can be coated.

[0022] Preferably, after filling the trench, a portion reaching the trench adjacent to the trench can be removed so as to expose the main element having a side surface coated with metal, and as a result, the metal forming the side portion can be contacted. As a result, the portion adjacent to the trench is removed and the side portion is exposed.

[0023] The present invention will be described in more detail below based on exemplary embodiments with reference to the related drawings. The direction indications in the following description should be understood according to the reading direction of the drawings. The indications of the upper and lower positions should be understood according to the drawings.

Brief Description of the Drawings

[0024]

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Embodiments for Carrying Out the Invention

[0025] Figure 1 shows a VCSEL (Vertical Cavity Surface Emitting Laser) 10 that emits laser light. The VCSEL 10 has a main element 12 with a mesa portion 14. The main element 12, and thus the mesa portion 14 as well, are made from a stack 16 of different layers 19 stacked in the stacking direction 18.

[0026] The layers 19 perform different functions. Thus, the mesa portion 14 has a pair of Bragg mirrors, and an active layer 20 is disposed between the Bragg mirrors. The active layer 20 generates photons that emerge as laser light from the emission region 22. The emission region 22 is on the surface of the mesa portion 14. This surface includes a top surface 24 on the upper side portion 25 of the VCSEL, which is the outer side portion of the upper Bragg mirror.

[0027] Electrical contacts 26 for feeding electrical energy to the active layer 20 are provided on the main element 12. The electrical contacts 26 are configured as an anode 33 and a cathode 29 and have a metal portion. Further, at least one of the electrical contacts 26 has a side portion 28 disposed on the side surface 30 of the main element 12. The side surface 30 is oriented to cross the top surface 24 on the main element 12. The side surface 30 is preferably oriented at a right angle to the top surface 24. Alternatively, at least a part of the side surface 30 may form an angle greater than 90° with the top surface 24.

[0028] The electrical contacts 26 preferably contain gold applied to a titanium-containing adhesive layer in any case. The electrical contacts 26 cover only a part of the side surface 30 of the main element 12 by at least one side portion 28. The side portion 28 can be strip-shaped. Only one side portion 28 can be provided for each main element 12. The titanium-containing adhesive layer is applied to the insulating layer 31.

[0029] The main element 12 of the VCSEL 10 has a substrate 32, and a laminate 16 is disposed on the substrate 32. As a mere example, the mesa portion 14 is separated from the remaining portion of the main element 12 by a groove portion 34. In a transition region 36 between a top surface 24 and a side surface 30 of an upper side portion 25 of the main element 12, a chamfered portion or a rounded portion is formed. The groove portion 34 is filled with a material forming an insulating layer 31. The insulating layer 31 under the titanium-containing adhesive layer is continuously connected to the material in the groove portion 34.

[0030] An upper portion 35 of the electrical contact 26 is disposed on the top surface 24. The electrical contact 26 extends from the top surface 24 to the side surface 30, and a portion of the electrical contact 26 is disposed on the transition region 36 such that the portion is disposed between the upper portion 35 and the side portion 28.

[0031] On the upper side portion 25, a solder barrier 38 is disposed on the electrical contact 26, and for example, prevents solder from flowing from the side portion 28 to the light emitting region 22 on the top surface 24 of the main element 12 due to the surface tension of the solder. The solder barrier 38 is deposited on the electrical contact 26 by an additional process.

[0032] The exemplary VCSEL 10 of FIG. 1 has a substrate 32 on which the laminate 16 is disposed. The laminate 16 does not cover the entire substrate 32, and thus a step is formed. The top surface 24 is formed on the higher side of the step. On the lower side of the step, an upper portion 35 of the cathode 29 is disposed, and an ohmic contact 37 is formed between the upper portion 35 of the cathode 29 and the substrate 32. The electrical contact 26 extends from the upper portion 35 to the side surface 30 on the main element 12, and a portion of the electrical contact 26 covers the transition region 36 formed on the substrate 32.

[0033] Preferably, the anode 33 is disposed as an electrical contact 26 on the side portion of the VCSEL 10 opposite to the cathode 29. The side portion 28 extends along a side surface 30 extending from the substrate 32 to the laminate 16. The transition region 36 is formed on the laminate 16. The upper portion 35 extends to the light emitting region 22. A shoulder 40 is formed on the lower side portion of the substrate 32. The shoulder 40 creates a corner between the side surface 30 and the surface of the shoulder 40. The side portion 28 reaches the corner.

[0034] FIG. 2 shows, as a mere example, a further exemplary embodiment in which the cathode 29 is mounted on the side surface 30 of the main element 12 such that it does not extend to the upper side portion 25 of the main element 12. The cathode 29 is formed by the side portion 28 and there is no upper portion. An ohmic contact 37 is disposed on the side surface 30 of the main element 12, and this ohmic contact 37 can be formed only on the substrate 32. Preferably, the side portion 28 does not extend to the laminate 16. The cathode 28 is configured according to the exemplary embodiment of FIG. 1.

[0035] FIG. 3 shows a plan view of the VCSEL 10 having side portions 28 on both sides 42. The side portions 28 are structured according to FIG. 1 or FIG. 2. The anode 33 and the cathode 29 extend from the upper side portion 25 to the side surface 30. An elongated solder barrier 38 is disposed on the upper portion 35. The solder barrier 38 may contain titanium oxide or silicon nitride. Further, a longitudinal notch may be provided along the longitudinal extension of the solder barrier 38. Preferably, the solder barrier 38 is disposed closer to the transition region 36 than the end portion 39 opposite to the upper portion 35. Further, a test contact surface 44 may be provided on the upper portion 35 so that after the VCSEL 10 is manufactured in the factory, a test of the function of the VCSEL 10 can be performed in the factory.

[0036] FIG. 4 shows a VCSEL array 46 having a plurality of light emitting regions 22. For each light emitting region 22, a mesa portion 14 or a separate main element 12 may be provided, which are disposed on the VCSEL array 46. Side portions 28 are formed on the side surfaces 30 of the individual main elements 12 or mesa portions 14. In this case, the anodes 33 are alternately disposed as side portions 28 on the opposite side surfaces 28. As a mere example, three main elements 12 disposed along the virtual line are disposed on the VCSEL array 46. The side portions 28 are disposed on the sides opposite to each other with respect to the virtual line. The side portions 28 of the two outer main elements 12 are disposed on the sides on the same side with respect to the virtual line 47. The central main element 12 has side portions 28 directed in the opposite direction. The cathode 29 of the VCSEL array 46 is disposed on both sides of the VCSEL array 46 not assigned to a single main element 12. As a mere example, the cathode 29 is disposed at the longitudinal ends of the VCSEL array 46.

[0037] FIGS. 5-9 show a first exemplary embodiment of a method for generating a VCSEL 10 or a VCSEL array 46.

[0038] FIG. 5 shows that main elements 12 separated by trenches 49 are formed on a wafer 48 in a lithography-etching process. The etching direction 50 is indicated by an arrow. Two main elements 12 are shown as an example. Ohmic contacts 37 on the upper side portions 25 of the anodes 33 and cathodes 29 are generated by metallization.

[0039] FIG. 6 shows a passivation process involving subsequent exposure of the anodes 33 and cathodes 29 by etching. Passivation is achieved, for example, by a silicon nitride coating. At the upper side portions 25, the metallized portions are exposed by the etching process.

[0040] In FIG. 7, the side surface 30 within the trench 49 is coated with a metal such as gold, forming the side portions 28 of the cathode 29 and the anode 33. The corresponding upper portion 35 is also formed. An adhesion layer for the metallized portion can be provided by creating a seed layer applied by sputter deposition or atomic layer deposition. The cathode 29 and the anode 33 can be formed by the metallized portion. The final shape of the electrical contact can be predetermined by a lithography mask.

[0041] In FIG. 8, a solder barrier 38 is additionally applied and disposed on the upper portion 35.

[0042] In FIG. 9, the trench 49 is further deepened by a plasma etching process using a lithography mask until the substrate 32 is separated by this separation process so that the main elements 12 are separated from each other.

[0043] A second exemplary embodiment of a method for generating the VCSEL 10 or the VCSEL array 46 is shown in FIGS. 10 - 15.

[0044] In FIG. 10, the main element 12 is defined by an etched trench 49 defined by a lithography mask. In addition to the trench 49, a portion 50 that will be sacrificed in a subsequent process is formed. This portion 50 reaches the trench 49.

[0045] In FIG. 11, passivation is applied according to FIG. 6, and the etching process exposes the previously made metal contacts.

[0046] According to FIG. 12, the trench 49 is completely filled with a metal such as gold.

[0047] As a result, the side surface 30 is covered with the metal.

[0048] After the trench 49 is completely filled with metal and the side surface 30 is coated, an isotropic etching process is performed along the axis of the stacking direction 18 according to FIG. 13, whereby an opening 52 perpendicular to the layers of the laminate is created within the portion 50.

[0049] Subsequently, as shown in FIG. 14, an anisotropic etching process for enlarging the opening 52 is performed. Gallium arsenide and silicon nitride can be anisotropically etched.

[0050] Finally, a separation process corresponding to the process of FIG. 9 is performed by plasma etching according to FIG. 15.

[0051] FIG. 16 shows a schematic diagram of an electric circuit board 54 on which two VCSELs 10 are arranged.

[0052] FIG. 16A shows a VCSEL 10 corresponding to an exemplary embodiment of the preceding figures. In this exemplary embodiment, the laser axis 60 along which laser light substantially propagates is oriented parallel to the axis of the stacking direction 18. In this case, the laser axis 60 is oriented at a right angle to the electrical circuit board 54. The light emitting region 22 is disposed on the side of the VCSEL 10 opposite the electrical circuit board 54. The side portions 28 of the electrical contacts 26 are positioned on the side surface 30 and are oriented at a right angle to the main extension direction of the electrical circuit board 54. The side portions 28 are positioned in the region of the electrical conductor tracks 56 to which they are soldered. The cathode 29 is soldered to the solder contact of the conductor track 56 assigned to the cathode 29. The anode 33 is soldered to the solder contact which is a part of the conductor track 56 assigned to the conductor track 56 assigned to the anode 33. The solder forms a meniscus-shaped solder joint 58 at the corner between the conductor track 56 and the side portion 28. The solder joint 58 can be concave in the form of a groove as in FIG. 16A or alternatively convex. The side portions 28 are disposed on both sides of the VCSEL 10 as a mere example. Alternatively, the side portions 28 can be disposed on the same side surface 30 of the VCSEL 10 or on side surfaces separated by a common corner.

[0053] In the exemplary embodiment of FIG. 16B, the VCSEL 10 is oriented such that the laser axis 60 is parallel to the major extent surface of the electrical circuit board 54. The electrical contact 26 is positioned between the conductor track 56 and the main element 12 of the VCSEL 10, and the solder preferably forms a flat solder joint 58. In accordance with the inclined position of the VCSEL 10 and the stacking direction 18, which here is oriented parallel to the major extent surface of the electrical circuit board 54, the laser light from the light emitting region 22 propagates substantially parallel to the electrical circuit board 54. In an alternative form of FIG. 16B, the side portion 28 can be mounted on the side surface 30 of the VCSEL 10 that is oriented at a right angle to the major extent surface of the electrical circuit board 54, whereby a concave or convex solder joint 58 can be created at the corner between the conductor track 56 and the side portion 28.

Claims

1. A VCSEL (10) for emitting a laser beam, comprising an element (12) having a mesa portion (14) with a stack of different layers (19) stacked in a stacking direction (18), a light emitting region (22) being formed on a top surface (24) of the mesa portion (14), the laser beam generated in an active layer (20) within the stack emerging from the light emitting region (22), and electrical contacts (26) for feeding electrical energy to the active layer (20) being provided on the element (12), at least one side portion (28) of the electrical contacts (26) being disposed on a side surface (30) of the element (12), the side surface (30) being oriented transversely to the layers (19).

2. The VCSEL (10) according to claim 1, characterized in that the top surface (24) is oriented at a right angle to the stacking direction (18).

3. The VCSEL (10) according to claim 1 or 2, characterized in that an insulating layer (31) is attached between the side portion (28) of the electrical contacts (26) and the side surface (30).

4. The VCSEL (10) according to any one of claims 1 to 3, characterized in that the electrical contacts (26) extend from their side portions (28) to upper side portions (25) of the element (12).

5. The VCSEL (10) according to any one of claims 1 to 4, characterized in that side portions (28) of the electrical contacts configured as cathodes (29) or anodes (33) are preferably attached on a common side surface (30) of the element (12).

6. The VCSEL (10) according to any one of claims 1 to 5, characterized in that a chamfered or rounded portion is formed at a transition portion (36) between the side surface (30) and the top surface (24), and a portion of the electrical contacts (26) is disposed on the transition portion (36).

7. The VCSEL (10) according to any one of claims 1 to 6, characterized in that a solder barrier (38) is formed on the electrical contacts (26) on the top surface (24) of the mesa portion (14) to prevent solder from flowing from the side portions (28) to the light emitting region (22).

8. The VCSEL (10) according to any one of claims 1 to 7, characterized in that the electrical contact (26) is formed only on the side surface (30) without extending to the top surface (24).

9. An VCSEL array (46) having at least two major elements (12), each of the major elements (12) having at least one side portion (28) of an electrical contact (26) on its side surface (30), preferably according to any one of claims 1 to 8.

10. An electrical circuit board (54) having the VCSEL (10) and / or the VCSEL array (46) according to any one of claims 1 to 9, wherein the side portion (28) of the VCSEL (10) is arranged within a region of a conductor track (56) of the electrical circuit board (54) such that the side portion (28) can be soldered onto a solder contact of the electrical circuit board (54).

11. The electrical circuit board (54) according to claim 10, characterized in that at least one side portion (28) of the solder joint (58) is oriented at a right angle to the conductor track (56) and / or is placed on the conductor track (56).

12. A method of generating the VCSEL (10) according to any one of claims 1 to 11, wherein a major element (12) having a mesa portion (14) is arranged on a wafer (48), a trench (49) is formed adjacent to the major element (12), the trench generates a side surface (30) on the major element (12), and a side portion (28) of an electrical contact (26) assigned to the mesa portion (14) is provided on the side surface (30).

13. The method according to claim 12, characterized in that the trench (49) is formed between two major elements (12), the side surface (30) is coated, the two major elements (12) are separated from each other by performing a separation cut along the trench (49), and the side portion (28) remains on the side surface (30) by the separation cut.

14. The method according to claim 12, characterized in that the trench (49) is completely filled with metal, whereby the side surface (30) is also coated with metal.

15. After the trench (49) is filled, a portion adjacent to the trench (49) that reaches the trench (49) is removed so that the mesa portion (14) having the side surface (30) coated with the metal is exposed, and as a result, the metal can come into contact. The method according to claim 14, characterized in that.

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