OPTOELECTRONIC SEMICONDUCTOR CHIP AND METHOD FOR PRODUCING AN OPTOELECTRONIC SEMICONDUCTOR CHIP

Abstract

In at least one embodiment, the optoelectronic semiconductor chip (100) comprises a semiconductor layer sequence (1) having an active layer (10), a doped current spreading layer (11) and an output coupling layer (12), which are arranged one above the other in this order. The active layer generates primary radiation during intended operation. The current spreading layer comprises a larger lateral electrical conductivity than the output coupling layer. The output coupling layer comprises output coupling structures (121) for coupling out radiation on an exit side (120) facing away from the active layer. The output coupling layer comprises a lower absorption coefficient for primary radiation than the current spreading layer.

Claims

1. An optoelectronic semiconductor chip (100) comprising: a semiconductor layer sequence (1) having an active layer (10), a doped current spreading layer (11) and an output coupling layer (12), which are arranged one above the other in this order, wherein the active layer (10) generates primary radiation in the intended operation, the current spreading layer (11) comprises a larger lateral electrical conductivity than the output coupling layer (12), the output coupling layer (12) comprises output coupling structures (121) for radiation output on an exit side (120) facing away from the active layer (10), the output coupling layer (12) comprises a lower absorption coefficient for the primary radiation than the current spreading layer (11).

2. The optoelectronic semiconductor chip (100) according to claim 1, wherein the exit side (120) of the output coupling layer (12) comprises a roughness of at least 200 nm.

3. The optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the output coupling layer (12) comprises a lower defect density than the current spreading layer (11) and/or the band gap of the output coupling layer (12) is larger than the energy of the primary radiation.

4. The optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the semiconductor layer sequence (1) is based on Al.sub.nIn.sub.1-n-mGa.sub.mP with 0≤n≤1, 0≤m≤1 and m+n≤1, the current spreading layer (11) comprises a larger Ga content than the output coupling layer (12).

5. The optoelectronic semiconductor chip (100) according to one of the preceding claims, further comprising a contact element (2) for injecting first charge carriers into the current spreading layer (11), wherein the contact element (2) comprises a bottom surface (20) adjacent to the semiconductor material of the semiconductor layer sequence (1).

6. The optoelectronic semiconductor chip (100) according to claim 5, wherein the semiconductor layer sequence (1) comprises a doped contact layer (13) which is thinner than the current spreading layer (11) and comprises a higher doping than the current spreading layer (11), the contact layer (13) is adjacent to the bottom surface (20) of the contact element (2).

7. The optoelectronic semiconductor chip (100) according to the preceding claim, wherein the contact layer (13) is arranged on the exit side (120) of the output coupling layer (12) and is adjacent to the exit side (120).

8. The optoelectronic semiconductor chip (100) according to claim 6 or 7, wherein, a lateral extent of the contact layer (13) substantially corresponds to the lateral extent of the bottom surface (20) of the contact element (2), the lateral extent of the bottom surface (20) is at most 25% of the lateral extent of the active layer (10).

9. The optoelectronic semiconductor chip (100) according to claim 6, wherein the contact layer (13) is disposed between the current spreading layer (11) and the exit side (120) and is adjacent to the current spreading layer (11).

10. The optoelectronic semiconductor chip (100) according to one of claims 5 to 9, wherein the bottom surface (20) of the contact element (2) is directly adjacent to the current spreading layer (11).

11. The optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the output coupling layer (12) comprises a lower doping than the current spreading layer (11).

12. The optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the output coupling layer (12) is nominally undoped.

13. A method for producing an optoelectronic semiconductor chip (100), comprising the steps of: A) providing a semiconductor layer sequence having a doped contact layer (13), a less heavily doped output coupling layer (12) and an active layer (10), which are arranged one above the other in this order, wherein the active layer (10) generates primary radiation in the intended operation; B) applying a photoresist layer (3) to the side of the contact layer (13) facing away from the active layer (10), wherein the photoresist layer (3) completely covers the contact layer (13) both in an output coupling section (122) and in a contact section (123) of the semiconductor layer sequence (1); C) patterning and partially removing the photoresist layer (3) in the output coupling section (122); D) carrying out an etching process with which etching completely through the contact layer (13) and into the output coupling layer (12) is carried out in the regions of the output coupling section (122) in which the photoresist layer (3) has been removed, thereby forming output coupling structures (121) in the output coupling layer (12); the contact layer (13) in the output coupling section (122) is removed, the photoresist layer (3) is not penetrated in the region of the contact section (123); E) removing the photoresist layer (3) in the region of the contact section (123); F) applying a contact element (2) to the contact layer (13) in the region of the contact section (123).

14. The method according to claim 13, wherein in step D) a first etchant is first used which attacks the material of the photoresist layer (3) and partially or completely removes the photoresist layer (3) in the output coupling section (122).

15. The method according to claim 14, wherein the first etchant attacks the contact layer (13), the first etchant is used until the contact layer (13) in the output coupling section (122) is completely removed.

16. The method according to claim 14, wherein in step D) a second etchant is used after the first etchant has partially or completely removed the photoresist layer (3) in the region of the output coupling section (122), wherein the second etchant attacks the contact layer (13), the second etchant is used until the contact layer (13) in the output coupling section (122) is removed.

17. The method according to one of the preceding claims, wherein the step F) is carried out before the step B) and in step B) the photoresist layer (3) is applied to the contact element (2) in the region of the contact section (123).

Description

[0086] Showing in:

[0087] FIG. 1 a modification of an optoelectronic semiconductor chip,

[0088] FIGS. 2 to 5 different exemplary embodiments of the optoelectronic semiconductor chip in cross-sectional view,

[0089] FIGS. 6A to 8D various positions in different exemplary embodiments of the method for producing an optoelectronic semiconductor chip,

[0090] FIG. 9A a photograph of an output coupling layer as produced by the method,

[0091] FIG. 9B a top view of an exemplary embodiment of the optoelectronic semiconductor chip.

[0092] FIG. 1 shows a modification of the optoelectronic semiconductor chip 100. The optoelectronic semiconductor chip 100 comprises a semiconductor layer sequence 1 with an active layer 10 for generating electromagnetic primary radiation, a current spreading layer 11, which in the present case is, for example, n-doped, and a p-doped semiconductor layer 14. The current spreading layer 11 also serves as an output coupling layer and is provided with output coupling structures 121 on an exit side 120 remote from the active layer 10. The semiconductor layer sequence 1 is based on AlInGaP, for example. The current spreading layer 11 comprises, for example, a doping concentration of at least 5.Math.10.sup.18 cm.sup.−3. The dopant in the current spreading layer 11 is, for example, Si or Te.

[0093] The semiconductor layer sequence 1 is divided in the lateral direction into a contact section 123 and one or more output coupling sections 122. In the contact section 123, the exit side 120 is planar within the manufacturing tolerance. The output coupling structures 121 are provided only in the output coupling section 122.

[0094] In the contact section 123, a contact element 2 is arranged on the exit side 120. The contact element 2 comprises a bottom surface 20 which is substantially parallel to the active layer 10, and is in direct contact with the semiconductor material of the semiconductor layer sequence 1. Electrons are injected into the current spreading layer 11 via the contact element 2, for example. The contact element 2 is metallic, for example.

[0095] To reduce the contact resistance between the contact element 2 and the current spreading layer 11, a contact layer 13 is provided between the contact element 2 and the current spreading layer 11. The contact layer 13 comprises, for example, at least twice as high a doping concentration as the current spreading layer 11, but is substantially thinner. The area of the contact layer 13 corresponds substantially to the area of the bottom surface 20 of the contact element 2.

[0096] In the intended operation of the semiconductor chip 100 of FIG. 1, primary radiation is generated in the active layer 10. The primary radiation is coupled out via the exit side 120 with the aid of the output coupling structures 121. In particular, due to the high doping of the current spreading layer 11 and the associated high doping in the output coupling structures 121, there is increased absorption of the primary radiation within the output coupling structures 121, which reduces the efficiency of the semiconductor chip 100.

[0097] FIG. 2 shows a first exemplary embodiment of the optoelectronic semiconductor chip 100. The structure of the semiconductor chip 100 is essentially the same as the structure of the semiconductor chip 100 of FIG. 1. However, unlike in FIG. 1, the current spreading layer 11 is now not structured. Rather, an output coupling layer 12 is provided on the side facing away from the active layer 10. The output coupling layer 12 now comprises the exit side 120 with the output coupling structures 121. The output coupling layer 12 is a semiconductor layer of the semiconductor layer sequence 1. However, the output coupling layer 12 is selected such that it comprises a lower absorption coefficient for the primary radiation of the active layer 10 than the current spreading layer 11. Thus, there is less absorption loss in the output coupling structures 121.

[0098] To ensure a lower absorption coefficient in the output coupling layer 12, the output coupling layer 12 can, for example, be less heavily doped than the current spreading layer 11. However, in the present case, a light doping, for example of at least 1.Math.10.sup.17 cm.sup.−3, is advantageous to enable transport of electrons from the contact element 2 to the current spreading layer 11 through the output coupling layer 12.

[0099] Furthermore, to achieve a low absorption coefficient in the output coupling layer 12, the output coupling layer 12 may be grown with a lower defect density than the current spreading layer 11. Also, it is possible that a composition whose band gap is larger than the energy of the primary radiation is chosen for the output coupling layer 12.

[0100] In FIG. 3, a second exemplary embodiment of the optoelectronic semiconductor chip 100 is shown. Unlike in FIG. 2, the contact element 2 is now not attached to the exit side 120, but penetrates the output coupling layer 12 starting from the exit side 120. The contact element 2 adjoins the contact layer 13 with its bottom surface 20. The contact layer 13 in turn adjoins the current spreading layer 11.

[0101] In the third exemplary embodiment of the optoelectronic semiconductor chip 100 shown in FIG. 4, unlike in FIG. 3, the contact layer 13 is not limited to the lateral extent of the contact element 2. Rather, the contact layer 13 extends over the entire lateral extent of the semiconductor chip.

[0102] In the fourth exemplary embodiment of FIG. 5, a contact layer 13 is omitted. The contact element 2 is directly adjacent to the current spreading layer 11.

[0103] In FIG. 6A, a first position in a first exemplary embodiment of the method for producing an optoelectronic semiconductor chip is shown. Here, a semiconductor layer sequence 1 comprising an active layer 10, an output coupling layer 12 and a contact layer 13 is provided. The contact layer 13 is highly doped. The output coupling layer 12 is less heavily doped. Other than shown, a current spreading layer may be disposed between the output coupling layer 12 and the active layer 10. The semiconductor layer sequence 1 is based on AlInGaP, for example.

[0104] A photoresist layer 3 is deposited on the contact layer 13. The photoresist layer 3 is patterned and partially removed in an output coupling section 122. As a result, islands 30 of photoresist are left standing. Between the islands 30, the contact layer 13 is exposed.

[0105] In contrast, in a contact section 123 arranged laterally adjacent to the output coupling section 122, the photoresist layer 3 extends without interruption.

[0106] In FIG. 6B, a second position of the method is shown in which a first etchant is used to etch through the contact layer 13 in regions where the photoresist layer 2 has been removed. The first etchant has also penetrated and etched into the output coupling layer 12. As a result, output coupling structures 121 have been formed in the output coupling layer 12. In the present case, these output coupling structures 121 have a truncated pyramid shape.

[0107] The first etchant is, for example, a chlorine-based dry chemical etchant. The first etchant etches anisotropically, for example.

[0108] Unlike shown in the figures, the output coupling layer 12 is preferably not etched through completely. That is, even after the etching process, the output coupling layer 12 is preferably simply connected.

[0109] In FIG. 6C, a third position of the method is shown. The first etchant has been used until the contact layer 13 and the photoresist layer 3 in the output coupling section 122 are completely removed. The remaining output coupling structures 121 consist exclusively of the output coupling layer 12.

[0110] In the contact section 123, however, the semiconductor layer sequence 1 is still completely covered by the photoresist layer 3. Accordingly, the contact layer 13 is also still present.

[0111] By removing the photoresist layer 3 in the contact section 123 and applying a contact element to the exposed contact layer 13, the semiconductor layer sequence 1 can be electrically contacted.

[0112] In FIG. 7A, a first position in a second exemplary embodiment of the method is shown. The position of the FIG. 7A corresponds to the position of the FIG. 6A.

[0113] In FIG. 7B, a second position is shown in which etching has been performed with a first etchant until the photoresist layer 3 in the output coupling section 122 is removed. Again, output coupling structures 121 have been formed due to the islands from the photoresist layer 3. In contrast, the photoresist layer 3 in the contact section 123 is not completely penetrated, which is partly due to the fact that the photoresist layer 3 in the contact section 123 has not been patterned.

[0114] In FIG. 7C, a third position of the method is shown. Using a second etchant different from the first etchant, the semiconductor layer sequence 1 was further etched. Thereby, the contact layer 13 in the output coupling section 122 was removed. What remains are again output coupling structures 121 consisting exclusively of the output coupling layer 12.

[0115] The second etchant may, for example, be an isotropic etchant.

[0116] FIGS. 8A to 8D show a third exemplary embodiment of the method. The positions shown in FIGS. 8A and 8B correspond to the positions shown in FIGS. 6A and 6B. Thus, again, output coupling structures 121 have been formed in the output coupling section 122 by means of a first etchant. With the first etchant, the photoresist layer 3 and the contact layer 13 in the output coupling section 122 have not been completely removed.

[0117] In FIG. 8C, a position is shown in which the photoresist layer 3 in the output coupling section 122 is completely removed with the help of, for example, an oxygen plasma. In the contact section 123, however, the photoresist layer 3 is not completely removed, which is again due to the smaller attack surface in the contact section 123.

[0118] In FIG. 8D, a position is shown in which the contact layer 13 in the output coupling section 122 is then also removed, for example by means of a second etchant different from the first etchant.

[0119] FIG. 9A shows a photograph of an output coupling layer 12 after it has been patterned by the method described herein. The resulting output coupling structures 121 are cone-shaped. The photoresist layer 3 is still present around the patterned region. In particular, a photograph of the method is shown here between steps D) and E).

[0120] In FIG. 9B, the completed semiconductor chip 100 is shown in a top view of the exit side 120. The patterned output coupling section 122 and the smaller contact section 123 with the contact element 2 can be seen.

[0121] This patent application claims priority of the German patent application 10 2018 119 622.9, the disclosure content of which is hereby incorporated by reference.

[0122] The invention is not limited by the exemplary embodiments based on the description thereof. Rather, the invention encompasses any new feature as well as any combination of features, which in particular includes any combination of features in the patent claims, even if these features or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

LIST OF REFERENCE SIGNS

[0123] 1 semiconductor layer sequence [0124] 2 contact element [0125] 3 photoresist layer [0126] 10 active layer [0127] 11 current spreading layer [0128] 12 output coupling layer [0129] 13 contact layer [0130] 14 semiconductor layer [0131] 20 bottom surface of contact element 2 [0132] 30 island of photoresist layer 3 [0133] 100 optoelectronic semiconductor chip [0134] 120 exit side [0135] 121 output coupling structures [0136] 122 output coupling section [0137] 123 contact section