SEMICONDUCTOR LASER DIODE AND METHOD FOR PRODUCING A SEMICONDUCTOR LASER DIODE

Abstract

The semiconductor laser diode includes a semiconductor layer sequence having an active zone. The semiconductor layer sequence has a shape of a generalized cylinder or a frustum, and a main axis of the semiconductor layer sequence is perpendicular to a main extension plane of the semiconductor layer sequence. The semiconductor layer sequence has a core region and an edge region directly adjacent to the core region. The main axis passes through the core region. The edge region borders the core region in directions perpendicular to the main axis. The semiconductor layer sequence has a larger refractive index in the core region than in the edge region.

Claims

1. A semiconductor laser diode comprising a semiconductor layer sequence with an active zone, wherein the semiconductor layer sequence comprises a shape of a generalized cylinder or a frustum, a main axis of the semiconductor layer sequence is perpendicular to a main extension plane of the semiconductor layer sequence, the semiconductor layer sequence comprises a core region and an edge region directly adjacent to the core region, the main axis passes through the core region, the edge region bounds the core region in directions perpendicular to the main axis, the semiconductor layer sequence comprises a larger refractive index in the core region than in the edge region, on a main surface of the semiconductor layer sequence a dielectric element is arranged, the dielectric element covers the core region in places, the edge region is free of the dielectric element, and the dielectric element causes mechanical strains in the semiconductor layer sequence, which changes the refractive index of the semiconductor layer sequence.

2. The semiconductor laser diode according to claim 1, wherein the core region and the edge region are based on the same semiconductor material system.

3. The semiconductor laser diode according to claim 1, wherein the semiconductor layer sequence comprises the shape of a straight circular cylinder.

4. The semiconductor laser diode according to claim 1, wherein the semiconductor layer sequence comprises the shape of a prism.

5. The semiconductor laser diode according to claim 1, wherein impurity atoms are introduced in the semiconductor layer sequence in the edge region.

6. The semiconductor laser diode according to claim 5, wherein the semiconductor layer sequence comprises a central zone which is at least partially located within the edge region, wherein the central zone comprises the active zone, a first waveguide layer and a second waveguide layer the active zone is arranged between the first and the second waveguide layers, and impurity atoms are introduced into regions of the central zone that are within the edge region.

7. (canceled)

8. The semiconductor laser diode according to claim 1, wherein a contact structure is arranged on a surface of the dielectric element facing away from the main surface (10), wherein the contact structure penetrates the dielectric element in places, and the contact structure is in direct contact with the semiconductor layer sequence in places.

9. The semiconductor laser diode according to claim 1, wherein the edge region comprises an output coupling structure, wherein the semiconductor layer sequence comprises a higher refractive index in the region of the output coupling structure than in the edge region surrounding the output coupling structure.

10. The semiconductor laser diode according to claim 9, wherein a main emission direction of radiation generated in operation is parallel to the main axis.

11. The semiconductor laser diode according to claim 9, wherein the semiconductor layer sequence (2) is in direct contact with a further dielectric element (14) in the region of the output coupling structure (13).

12. The semiconductor laser diode according to claim 1, wherein the semiconductor layer sequence is based on an Al.sub.nIn.sub.1-n-mGa.sub.mAs material system, an Al.sub.nIn.sub.1-n-mGa.sub.mN material system or an Al.sub.nIn.sub.1-n-mGa.sub.mP material system, wherein 0≤n≤1, 0≤m≤1 and m+n≤1, a refractive index difference between the semiconductor layer sequence in the core region and the edge region is at least 0.1% and at most 1%.

13. A method for producing a semiconductor laser diode comprising: providing a semiconductor layer sequence with an active zone; etching the semiconductor layer sequence so that the semiconductor layer sequence comprises a shape of a generalized cylinder or a frustum with a main axis perpendicular to a main extension plane of the semiconductor layer sequence; forming a core region and an edge region by changing a refractive index of the semiconductor layer sequence region by region, wherein the core region is bounded by the edge region in directions perpendicular to the main axis, wherein the refractive index of the semiconductor layer sequence in the core region is increased by applying a dielectric element in places to a main surface of the semiconductor layer sequence.

14. The method according to claim 13, wherein the refractive index of the semiconductor layer sequence in the edge region is reduced by introducing foreign atoms by means of diffusion.

15. (canceled)

16. The method according to claim 13, wherein a contact structure (12) is arranged on a surface of the dielectric element (11) facing away from the main surface (10) in such a way that the contact structure (12) penetrates the dielectric element (11) in places, and the contact structure (12) is in direct contact with the semiconductor layer sequence (2) in places.

17. The method according to claim 13, wherein an output coupling structure is formed in the edge region by increasing the refractive index of the semiconductor layer sequence in the region of the output coupling structure relative to the edge region surrounding the output coupling structure.

18. The method according to claim 17, wherein a further dielectric element is arranged on the semiconductor layer sequence in the region of the output coupling structure.

19. A semiconductor laser diode comprising a semiconductor layer sequence with an active zone, wherein the semiconductor layer sequence comprises a shape of a generalized cylinder or a frustum, a main axis of the semiconductor layer sequence is perpendicular to a main extension plane of the semiconductor layer sequence, the semiconductor layer sequence comprises a core region and an edge region directly adjacent to the core region, the main axis passes through the core region, the edge region bounds the core region in directions perpendicular to the main axis, the semiconductor layer sequence comprises a larger refractive index in the core region than in the edge region.

20. The semiconductor laser diode according to claim 19, wherein a main emission direction of radiation generated in operation is parallel to the main axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In the figures:

[0060] FIGS. 1 to 7 and 9 to 12 show exemplary embodiments of the semiconductor laser diode in various views.

[0061] FIGS. 8A to 8D show various process stages of a method for producing a semiconductor laser diode according to an exemplary embodiment.

DETAILED DESCRIPTION

[0062] FIG. 1 shows a semiconductor laser diode 1 according to a first exemplary embodiment in a plan view of a main surface 10 of the semiconductor layer sequence 2. The main surface 10 extends parallel to a main extension plane of the semiconductor layer sequence 2 and perpendicular to a main axis 4 of the semiconductor layer sequence 2, which comprises the shape of a straight circular cylinder. The main axis 4 is in particular a rotational symmetry axis of the semiconductor layer sequence 2.

[0063] The semiconductor layer sequence 2 comprises a core region 5 around the main axis 4 and, viewed from the main axis 4, an edge region 6 surrounding the core region 5. The edge region 6 and the core region 5 are directly adjacent to each other and comprise an interface with each other. In particular, the core region 5 is completely enclosed by the edge region 6 in directions perpendicular to the main axis 4. In a plan view of the main surface 10, the core region 5 comprises the shape of a circular disk. In the same view, the edge region 6 comprises the shape of a circular ring. In particular, the core region 5 and the edge region 6 each comprise an axis of rotational symmetry that coincides with the main axis 4 of the semiconductor layer sequence 2.

[0064] The semiconductor layer sequence 2 comprises a lower refractive index in the edge region 6 than in the core region 5. For example, a refractive index difference of the semiconductor layer sequence 2 between the edge region 6 and the core region 5 is 1×10.sup.−3. Due to the refractive index difference between the core region 5 and the edge region 6, electromagnetic radiation 15, indicated here and below as a dashed line for illustration, generated in the active zone 3 of the semiconductor layer sequence 2 propagates at the interface between the core region 5 and the edge region 6 in the semiconductor layer sequence 2. In particular, due to the refractive index difference, the electromagnetic radiation 15 is reflected at the interface by means of total internal internal reflection. Preferably, a ring mode of the electromagnetic radiation 15 is thus formed within the core region. Preferably, the core region 5 comprises, in plan view, a diameter of at least 1 μm and at most 200 μm, in particular of at least 5 μm and at most 50 μm, whereby in particular the condition for total reflection is fulfilled. The edge region 6 comprises a width, measured perpendicular to the main axis 4, which is between 100 nm and 10 μm inclusive. Preferably, the width is such that an evalescent wave formed in the edge region 6 due to total internal reflection at the interface between the core region 5 and the edge region 6 is not transmitted through the edge region 6.

[0065] In FIG. 2 the semiconductor laser diode of FIG. 1 is shown in a schematic sectional view. A sectional plane runs parallel to the main axis 4 and includes the main axis 4. The semiconductor layer sequence 2 comprises a first cover layer 16, a second cover layer 17 and a central zone 7, wherein the central zone 7 is arranged between the first 16 and the second 17 cover layer. The central zone 7 comprises a first waveguide layer 8, a second waveguide layer 9, and an active zone 3 arranged between the first waveguide layer 8 and the second waveguide layer 9. In the active zone 3, electromagnetic radiation 15 in the visible wavelength range or in the UV range or preferably in the IR range is generated during intended operation. In the present case, the semiconductor layer sequence 2 is based on an arsenide compound semiconductor material, such as InAlGaAs. In intended operation, electromagnetic radiation 15 with a peak wavelength of 910 nm, for example, is generated in the active zone 3. The peak wavelength is the wavelength at which the electromagnetic radiation generated in the active zone comprises its global intensity maximum. For example, the first cover layer 16 and the first waveguide layer 8 are n-doped. The second cover layer 17 and the second waveguide layer 9 are then p-doped. Alternatively, the doping can be the other way around. Preferably, the central zone 7 comprises a refractive index different from those of the first and second cover layers 16, 17. Preferably, electromagnetic radiation 15 generated in the active zone 3 propagates only in the central zone 7.

[0066] For example, the semiconductor layer sequence 2, in particular the central zone 7, comprises a refractive index of 3.5 in the core region 5. For example, the refractive index is an average refractive index. Preferably, the refractive index is specified for radiation 15 generated in the active zone 3. In particular, the refractive index is specified with reference to the peak wavelength. In the present case, therefore, for electromagnetic radiation 15 with a wavelength of 910 nm. The central zone 7 comprises a refractive index of 3.499 in the edge region 6. For example, the refractive index is an average refractive index.

[0067] In the present case, impurity atoms are introduced in the edge region 6 of the central zone 7. The impurity atoms are, for example, elements of group II, preferably aluminum. In particular, the impurity atoms change a band gap of the central zone 7 in the edge region 6. As a result, the refractive index of the central zone 7 in the edge region 6 is reduced. A concentration of impurity atoms in the edge region 6 of the central zone 7 is preferably between 1×10.sup.17 and 1×10.sup.20 cm.sup.−3.

[0068] The semiconductor laser diode 1 according to the exemplary embodiment of FIG. 3 shows essentially the same features as the semiconductor laser diode 1 according to FIG. 1. In contrast to the semiconductor laser diode of FIG. 1, here the core region 5 is covered by a contact structure 12 in plan view.

[0069] The semiconductor laser diode 1 of FIG. 3 is shown in FIG. 4 in a schematic sectional view. A sectional plane runs through the main axis 4. A dielectric element 11 is arranged on a main surface 10 of the semiconductor layer sequence 2. The dielectric element 11 covers the core region 5 of the semiconductor layer sequence 2 in places. In particular, the dielectric element 11 covers a major part of the main surface 10 in the core region 5. A contact structure 12 is arranged on a surface of the dielectric element 11 facing away from the main surface 10. The dielectric element 11 has been removed in places, so that the dielectric element 11 has a present two-part configuration. A first part of the optical element 11 comprises the shape of a circular disk in plan view. In particular, the main axis runs through this first part. The second part of the dielectric element 11 comprises the shape of a circular ring in plan view, which surrounds the first part of the dielectric element 11 in all directions perpendicular to the main axis 4. In regions formed between the first region and the second region of the dielectric element 11, the contact structure 12 penetrates the dielectric element 11. In these regions, the contact structure is in direct contact with the semiconductor layer sequence 2. Preferably, the contact structure 12 is in contact with the semiconductor layer sequence 2 exclusively in the core region 5.

[0070] For example, the dielectric element 11 was deposited on the main surface 10, in particular by means of vapor deposition, and subsequently structured in a lithographically defined etching process. Subsequently, for example, the contact structure 12 was sputtered onto the dielectric element 11.

[0071] The dielectric element 11 comprises, for example, an oxide, such as silicon dioxide (SiO2), or a nitride, such as silicon nitride (SiN). The contact structure 12 is formed, for example, from a metal, such as gold, platinum, or titanium, or is formed from a mixture of these metals.

[0072] Mechanical strains are induced in the semiconductor layer sequence 2 by the dielectric element 11. Preferably, the mechanical strains extend over the entire thickness of the semiconductor layer sequence 2 measured parallel to the main axis 4. Due to the mechanical strains, the refractive index of the semiconductor layer sequence 2 in the core region 5 is increased compared to the refractive index of the semiconductor layer sequence 2 in the edge region 6. For example, a refractive index difference of the semiconductor layer sequence 2 between the core region 5 and the edge region 6 is at least 1×10.sup.−3.

[0073] In intended operation, the semiconductor layer sequence 2 is supplied with current in particular by the contact structure 12. Preferably, the contact structure 12 is in direct contact with a semiconductor layer of the semiconductor layer sequence which is p-doped. Thus, the contact structure 12 is preferably a p-contact structure.

[0074] The semiconductor laser diode 1 of FIG. 5 shows essentially the same features as FIG. 1 with the difference that a contact structure 12 is arranged at the main surface 10. The contact structure 12 is preferably a p-contact structure 12 which comprises an axis of rotational symmetry which coincides with the main axis 4 of the semiconductor layer sequence 2. The p-contact structure 12 is only in direct contact with the semiconductor layer sequence 2 in the core region 5. In intended operation, the semiconductor layer sequence 2 is supplied with current via the contact structure 12. Due to the direct contact between the semiconductor layer sequence 2 and the contact structure exclusively in the core region 5, electromagnetic radiation is preferably generated exclusively in the core region 5.

[0075] The semiconductor laser diode 1 of FIG. 6 shows essentially all features of the semiconductor laser diode of FIG. 5 with the difference that an output coupling structure 13 is formed in the edge region 6. For example, in the region of the output coupling structure 13, diffusion of impurity atoms has been prevented. In particular, the semiconductor layer sequence 2 comprises the same refractive index in the region of the output coupling structure 13 as in the core region 5. Since there is thus no difference in refractive index between the core region 5 and the edge region 6 in the region of the output coupling structure 13, the condition for total internal reflection is not fulfilled here. Electromagnetic radiation 15 can therefore leave the semiconductor laser diode 1 in the region of the output coupling structure 13 perpendicular to the main axis 4.

[0076] The semiconductor laser diode 1 according to the exemplary embodiment of FIG. 7 comprises essentially the same features as the semiconductor laser diode of FIG. 6 with the difference that a further dielectric element 14 is arranged on the main surface 10 in the region of the output coupling structure 13. The further dielectric element 14 induces mechanical strains in the semiconductor layer sequence 2 in the region of the output coupling structure 13, whereby the refractive index in this region is increased compared to the surrounding edge region 6. For example, in the region of the output coupling structure 13, the refractive index of the semiconductor layer sequence 2 is increased above the value of the semiconductor layer sequence 2 in the core region 5. Therefore, the output of electromagnetic radiation 15 from the core region 5 is increased in the region of the output coupling structure 13.

[0077] In the method according to the exemplary embodiment of FIGS. 8A to 8D, a semiconductor layer sequence 2 is first provided on a substrate 18 (FIG. 8A). In particular, this method is used to produce a semiconductor laser diode 1 according to one of the exemplary embodiments explained above. The semiconductor layer sequence 2 comprises a first cover layer 16, a second cover layer 17 and a central zone 7 between these two layers. The central zone 7 comprises a first waveguide layer 8, a second waveguide layer 9, and an active zone 3 arranged therebetween. The substrate 18 is, for example, the growth substrate of the semiconductor layer sequence 2. In particular, the semiconductor layer sequence 2 has been grown on the substrate 18 in one piece.

[0078] In a next step, a mask 19 is applied to a surface of the semiconductor layer sequence 2 opposite to the substrate 18 (FIG. 8B). For example, the mask 19 is deposited on the semiconductor layer sequence 2. The mask 19 is, for example, a hard mask.

[0079] In a further step of the method, unmasked regions of the semiconductor layer sequence 2 are etched (FIG. 8C). In this process, semiconductor material of the semiconductor layer sequence 2 is removed in regions which are not covered by the hard mask 19. After etching, the semiconductor layer sequence 2 comprises a cylindrical shape. In particular, the semiconductor layer sequence 2 comprises a main axis 4. The main axis 4 runs perpendicular to the main extension plane of the semiconductor layer sequence 2, in particular perpendicular to the main extension plane of the active zone 3.

[0080] In a further method step, a core region 5 and an edge region 6 are formed (FIG. 8D). Previously, the hard mask 19 was removed. The edge region 6 is formed, for example, by introducing foreign atoms into the semiconductor layer sequence 2. For example, a refractive index of the semiconductor layer sequence 2 is reduced in the edge region. The impurity atoms are introduced into the semiconductor layer sequence 2 by diffusion, for example. For example, aluminum is diffused into the semiconductor layer sequence 2 based on a III-V compound semiconductor material. In particular, the impurity atoms change a band gap of the semiconductor layer sequence 2 in the edge region 6. As a result, the refractive index of the semiconductor layer sequence 2 is reduced in the edge region 6. In particular, by forming the core region 5 and the edge region 6, a finished semiconductor laser diode 1 is formed.

[0081] In contrast to the semiconductor laser diode 1 of FIG. 1, the semiconductor laser diode 1 according to the exemplary embodiment of FIG. 9 comprises an additional passivation layer 20. The passivation layer 20 is arranged on an outer surface of the semiconductor layer sequence 2, in particular of the edge region 6. The outer surface extends transversely, in particular perpendicularly, to the main surface 10 of the semiconductor layer sequence 2. The outer surface forms a lateral surface of the cylindrical semiconductor layer sequence 2. The passivation layer 20 completely covers the outer surface. The passivation layer 20 is formed, for example, with a II-VI compound semiconductor material, such as ZnSe. For example, the passivation layer 20 was applied after forming the edge region 6 and core region 5. For example, the passivation layer 20 was vapor deposited or deposited on the outer surface.

[0082] The exemplary embodiment of the semiconductor laser diode 1 according to FIG. 10 differs from the exemplary embodiment of FIG. 1 in that the semiconductor layer sequence 2 comprises the shape of a prism, in particular a straight prism. In the present plan view of the main surface 10, it can be seen that the prism comprises a base surface in the shape of a regular hexagon. For example, the semiconductor layer sequence 2 is based on GaN. In this case, advantageously, a semiconductor layer sequence 2 with the present geometrical shape can be produced particularly well.

[0083] The semiconductor laser diode 1 of FIG. 11 comprises essentially the same features as the semiconductor laser diode 1 of FIG. 10 with the difference that the base surface of the prism comprises the shape of a regular octagon.

[0084] The exemplary embodiment of the semiconductor laser diode 1 of FIGS. 12A and 12B differs from the exemplary embodiment of FIG. 1 inter alia in that the semiconductor layer sequence 2 comprises the shape of a frustum. FIG. 12A shows a plan view of the main surface 10 of the semiconductor layer sequence 2. FIG. 12B shows a section through the semiconductor layer sequence 2 according to FIG. 12A perpendicular to the drawing plane along the line A-A drawn therein.

[0085] The semiconductor laser diode 1 according to this exemplary embodiment comprises an output coupling structure 13 which essentially corresponds to the output coupling structure 13 explained in connection with FIG. 6. In particular, no total internal reflection of the radiation 15 occurs in the region of the output coupling structure 13 at the interface between the edge region 6 and the core region 5. Thus, radiation can penetrate into the edge region 6 in the region of the output coupling structure 13.

[0086] Side surfaces 22 of the semiconductor layer sequence 2 enclose an angle of, for example, 45° with the main surface 10 (see FIG. 12B). In the region of the output coupling structure 13, total internal reflection occurs at the side surface 22 of the semiconductor layer sequence 2 during operation. Due to the inclined side surface 22, the radiation 15 is reflected in the direction of the main surface 10 of the semiconductor layer sequence 2 during operation. In operation, the reflected radiation 15 exits the semiconductor layer sequence 2 through an output coupling surface 23. The output coupling surface 23 is a part of the main surface 10 (see FIG. 12A).

[0087] A main emission direction 21 of the radiation emitted from the semiconductor laser diode 1 in operation is parallel to the main axis 4.

[0088] The invention is not limited to the exemplary embodiments by the description thereof. Rather, the invention encompasses any new feature as well as any combination of features, which particularly includes any combination of features in the patent claims, even if that feature or combination itself is not explicitly specified in the patent claims or exemplary embodiments.