Semiconductor Emitter

Abstract

In an embodiment a semiconductor emitter includes a semiconductor layer sequence having a plurality of active zones, each active zone including at least one quantum well layer and at least two barrier layers between which the at least one quantum well layer is embedded, and at least one tunnel diode located along a growth direction of the semiconductor layer sequence between adjacent active zones, wherein a thickness of the at least one tunnel diode is at most 40 nm, and wherein a distance between adjacent barrier layers of adjacent active zones, facing the at least one tunnel diode, is at most 50 nm.

Claims

1-15. (canceled)

16. A semiconductor emitter comprising: a semiconductor layer sequence comprising: a plurality of active zones, each active zone including at least one quantum well layer and at least two barrier layers between which the at least one quantum well layer is embedded; and at least one tunnel diode located along a growth direction of the semiconductor layer sequence between adjacent active zones, wherein a thickness of the at least one tunnel diode is at most 40 nm, wherein, when in operation, a local intensity of a fundamental optical mode at the at least one tunnel diode is at least 50% of a maximum intensity, and wherein a distance between adjacent barrier layers of adjacent active zones, facing the at least one tunnel diode, is at most 50 nm.

17. The semiconductor emitter according to claim 16, wherein the active zones and the at least one tunnel diode are located in a common waveguide of the semiconductor layer sequence.

18. The semiconductor emitter according to claim 17, wherein a thickness of the common waveguide together with associated cladding layers is at most 4 ?m.

19. The semiconductor emitter according to claim 18, wherein at least one of the cladding layers comprises a stepped progression such that a refractive index of a respective cladding layer decreases in a direction away from the active zones with at least one step.

20. The semiconductor emitter according to claim 16, wherein a thickness of a space charge region is at least 30% of a total thickness of the at least one tunnel diode.

21. The semiconductor emitter according to claim 16, wherein a wavelength corresponding to a bandgap of the at least one tunnel diode is smaller by at least 30 nm than a wavelength of maximum intensity of a radiation generatable in the active zones.

22. The semiconductor emitter according to claim 16, wherein the at least one tunnel diode is formed of two oppositely highly doped layers, each having a thickness of at most 20 nm.

23. The semiconductor emitter according to claim 16, wherein the at least one tunnel diode is formed of two oppositely highly doped layers, each having a thickness of at most 15 nm, and of at least one intervening intermediate layer having a thickness of at most 15 nm.

24. The semiconductor emitter according to claim 16, wherein the semiconductor layer sequence further comprises at least one low-doped transition layer adjacent to the at least one tunnel diode, and wherein the at least one transition layer has a ramped refractive index profile with a refractive index increasing in a direction towards the at least one tunnel diode.

25. The semiconductor emitter according to claim 16, wherein the at least one tunnel diode comprises GaAs and/or InGaAs.

26. The semiconductor emitter according to claim 16, wherein the at least one tunnel diode comprises InP and InGaAs or InAsSb and GaSb.

27. The semiconductor emitter according to claim 16, wherein an average dopant concentration in the at least one tunnel diode is between 2?1019 cm-3 and 2?1020 cm-3, inclusive, and wherein a dopant concentration of layers of the semiconductor layer sequence adjacent to the at least one tunnel diode is smaller than the average dopant concentration in the at least one tunnel diode by at least a factor of three.

28. The semiconductor emitter according to claim 16, wherein an optical fundamental mode exhibits a plurality of local maxima and at least one local minimum, and wherein the active zones are located in the local maxima and the at least one tunnel diode is located in the at least one local minimum.

29. The semiconductor emitter according to claim 16, wherein at least two of the active zones is configured to generate radiation of different wavelengths.

30. The semiconductor emitter according to claim 16, wherein the semiconductor layer sequence comprises at least three of the active zones, wherein each of the active zones includes between two and ten, inclusive, of the quantum well layers, and wherein the semiconductor emitter is a semiconductor laser.

31. A semiconductor emitter comprising: a semiconductor layer sequence comprising: a plurality of active zones, each zone including at least one quantum well layer and at least two barrier layers between which the at least one quantum well layer is directly embedded; and at least one tunnel diode located along a growth direction of the semiconductor layer sequence between adjacent active zones, wherein a thickness of the at least one tunnel diode is at most 40 nm, wherein, when in operation, a fundamental optical mode at the at least one tunnel diode is at least 50% of a maximum intensity, wherein a distance between adjacent barrier layers of adjacent active zones, facing the at least one tunnel diode, is at most 50 nm, and wherein either the at least one tunnel diode consists of two oppositely highly doped layers, each having a thickness of at most 20 nm, or wherein the at least one tunnel diode consists of two oppositely highly doped layers, each having a thickness of at most 15 nm, and of at least one intervening intermediate layer having a thickness of at most 15 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In the following, a semiconductor emitter described here is explained in more detail with reference to the drawing on the basis of exemplary embodiments. Identical reference signs indicate identical elements in the individual figures. However, no references to scale are shown; rather, individual elements may be shown in exaggerated size for better understanding.

[0054] FIG. 1 shows a schematic sectional view of an embodiment of a semiconductor emitter described herein;

[0055] FIGS. 2 to 6 show schematic sectional views of semiconductor layer sequences for embodiments of semiconductor emitters described herein;

[0056] FIG. 7 shows a schematic refractive index curve and intensity curve of an example of a semiconductor emitter described here;

[0057] FIG. 8 shows a schematic representation of a refractive index curve of a semiconductor layer sequence for embodiments of semiconductor emitters described herein;

[0058] FIG. 9 shows a schematic sectional view of a tunnel diode for embodiments of semiconductor emitters described herein;

[0059] FIG. 10 shows a schematic representation of wavelength-dependent absorption losses; and

[0060] FIGS. 11 and 12 show schematic cross-sectional views of embodiments of semiconductor emitters described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0061] FIG. 1 shows an embodiment of a semiconductor emitter 1. The semiconductor emitter 1 comprises a semiconductor layer sequence 2 having a growth direction G and is, for example, a semiconductor laser diode. The semiconductor layer sequence 2 is located on a carrier 61. The carrier 61 may be a growth substrate of the semiconductor layer sequence 2 or a substitute carrier.

[0062] Optionally, a buffer layer 62 is located between the semiconductor layer sequence 2 and the carrier 61. The buffer layer 62 is, for example, a semiconductor layer or a bonding agent layer, such as a solder. On a side facing away from the carrier 61, the semiconductor layer sequence 2 may optionally have a contact layer 23 and/or a cap layer 25, for example, for making electrical contact with the semiconductor emitter 1. Electrical contacts or electrodes are not drawn to simplify the illustration.

[0063] Furthermore, the semiconductor layer sequence 2 comprises a waveguide 51 between two cladding layers 52. The cladding layers 52 have a lower average refractive index for radiation generated in the operation of the semiconductor emitter 1 than the waveguide 51. For example, a thickness of the cladding layers 52 is at least 1.5 times or twice a vacuum wavelength of maximum intensity of the radiation generated in the waveguide 51 divided by the average refractive index of the cladding layer 52 concerned.

[0064] Several active zones 31, 32 are present in the waveguide 51. A tunnel diode 41 is located between the active zones 31, 32. The waveguide 51 thus represents a common waveguide for all active zones 31, 32. For example, the waveguide 51 has a thickness of at least 0.3 times or 0.6 times and/or at most 1.8 times or 1.2 times or 0.9 times the vacuum wavelength of maximum intensity of the radiation generated in the waveguide 51 divided by the average or effective refractive index of the waveguide layer 51.

[0065] Various design options, in particular for the waveguide layer 51, are described below.

[0066] In the example of FIG. 2, the waveguide 51 comprises two of the active zones 31, 32, each of the active zones 31, 32 including at least two quantum well layers 22. The quantum well layers 22 are separated from each other by barrier layers 21.

[0067] A tunnel diode 41 is located between the active zones 31, 32. The tunnel diode 41 may be directly adjacent to the barrier layers 21 of the adjacent active zones 31, 32. A p-doped tunnel diode layer 26 and directly adjacent an n-doped tunnel diode layer 28 are located in the tunnel diode 41. The tunnel diode layers 26, 28 are highly doped and comparatively thin.

[0068] For example, the active zones 31, 32 are configured to generate laser radiation with a wavelength of maximum intensity in the near-infrared spectral range, that is, in particular from 0.7 ?m to 1.3 ?m. For example, the wavelength of maximum intensity is 940 nm. In this case, the n-doped tunnel diode layer 28 is formed, for example, from a 10 nm thick GaAs layer with a dopant concentration of 5?10.sup.19 cm.sup.?3, in particular of Te, alternatively also with Si and/or Ge. The p-doped tunnel diode layer 26 is, for example, a 10 nm thick GaAs layer with a dopant concentration of 1?10.sup.20 cm.sup.?3, in particular with C, alternatively also with Be, Mg and/or Zn.

[0069] Deviating from the illustration in FIG. 2, it is also possible that the tunnel diode layers 26, 28 are asymmetrically designed and have different thicknesses. For example, the n-doped tunnel diode layer 28 is thicker than the p-doped tunnel diode layer 26 by at least a factor of 1.2 or by at least a factor of 1.5, as is also possible in all other exemplary embodiments. For example, the n-doped tunnel diode layer 28 is 15 nm thick and made of GaAs:Te with a dopant concentration of 5?10.sup.19 cm.sup.?3 or higher, and the p-doped tunnel diode layer 26 is 10 nm thick and made of GaAs:C with a dopant concentration of 1?10.sup.20 cm.sup.?3 or higher, again, for example, for a laser with a maximum intensity emission wavelength of 940 nm.

[0070] Alternatively, for wavelengths of maximum intensity further in the infrared spectral range, the tunnel diode layers 26, 28 can also be made of p-doped InP and n-doped InGaAs or of p-conducting GaSb or InAs and n-conducting InAsSb. The above comments on the GaAs material system apply accordingly to the other material systems mentioned.

[0071] For example, the above thicknesses and dopant concentrations for the tunnel diode layers 26, 28 each apply with a tolerance of no more than a factor of 5 or no more than a factor of 2 or no more than a factor of 1.5.

[0072] In the example of FIG. 3, it is illustrated that the waveguide 51 has three active zones 31, 32, 33 and two tunnel diodes 41, 42. The tunnel diodes 41, 42, which are located alternately between the active zones 31, 32, 33, are designed in particular as described in connection with FIG. 2.

[0073] In addition, an intensity I of an optical fundamental mode in the waveguide 51 is drawn in FIG. 3. It can be seen that the tunnel diodes 41, 42 are not in zero crossings of the intensity I, but that local intensities IL at the tunnel diodes 41, 42 are almost as high as a maximum intensity IM of the fundamental mode. This arrangement of the tunnel diodes 41, 42 is made possible in particular by the fact that the tunnel diodes 41, 42 are thin and exhibit a low absorption coefficient with respect to the radiation generated in the active zones 31, 32, 33.

[0074] In FIG. 4 it is illustrated that the fundamental mode, unlike in FIG. 3, is not Gaussian-like, but shows a slightly modulated course in the region of maximum intensity in the waveguide 51. Here, the tunnel diodes 41, 42 are in or near local minima of the intensity I, but the local intensities IL at the tunnel diodes 41, 42 are nevertheless almost as high as the maximum intensity IM of the fundamental mode.

[0075] In all other respects, the comments on FIGS. 1 and 2 apply mutatis mutandis to FIGS. 3 and 4.

[0076] FIG. 5 shows another example of tunnel diodes 41, 42. In this case, an intermediate layer 27 is located between the highly doped tunnel diode layers 26, 28. The intermediate layer 27 can also be highly doped, corresponding to the tunnel diode layers 26, 28, namely n-doped or p-doped. A thickness of the intermediate layer 27 is, for example, at least 1 nm or at least 3 nm and/or at most 20 nm or at most 15 nm.

[0077] In the case of tunnel diode layers 26, 28 made of GaAs, the intermediate layer 27 is preferably made of InAs or InGaAs with, for example, an In content of at most 80% or at most 50% or at most 30% or at most 10%, although AlInGaAs layers with an Al content of, in particular, at most 30% or at most 10% or at most 1% and with an In content of at most 30% or of at most 10% are also possible.

[0078] Such tunnel diodes 41, 42 may also be used in all other embodiments.

[0079] In all other respects, the comments on FIGS. 1 to 4 apply accordingly to FIG. 5.

[0080] In the embodiment example of FIG. 6, at least one transition layer 24 is adjacent to the tunnel diode 41. If two transition layers 24 are present, the transition layer 24 at the n-doped tunnel diode layer 28 may be thicker than the p-side transition layer 24, for example, by a factor of at least 1.5 and/or by a factor of at most 4. A thickness of the thinner transition layer 24 is in particular at least 2 nm or at least 5 nm and/or at most 30 nm or at most 20 nm.

[0081] In the case of a GaAs-based tunnel diode 41, the transition layers 24 are preferably each made of AlGaAs, with an Al content towards the tunnel diode 41 preferably reducing steadily, in particular linearly. For example, an Al content on sides of the transition layers 24 facing away from the tunnel diode 24 is at least 5% and/or at most 30%, for example 14%, and on sides of the transition layers 24 facing the tunnel diode 24 the Al content is at most 20% or at most 5% or at most 0.5%, in particular 0%.

[0082] Such transition layers 24 may also be present in all other embodiments.

[0083] In FIG. 7 the intensity I of the fundamental mode in the semiconductor layer sequence 2 is illustrated, as well as the refractive index n. The semiconductor layer sequence 2 is based in particular on the material system AlInGaAs. In the waveguide 51, the active zones 31, 32, 33 and also the tunnel diodes 41, 42 have a relatively high refractive index. Thus, the tunnel diodes 41, 42 can contribute to waveguiding and increase the effective refractive index of the waveguide 51.

[0084] Furthermore, it can be seen in FIG. 7 that the fundamental mode is Gaussian-like. Thus, a high quality emission of the laser radiation is possible.

[0085] As an option, it is illustrated in FIG. 7 that one or both cladding layers 52 may have a decreasing refractive index in the direction away from the waveguide 51. For example, at least one step 53 is present in the refractive index curve, symbolized as a dash line. Alternatively, there may be a continuous refractive index decrease, not drawn.

[0086] As a further option, it is shown in FIG. 7 that the cladding layers 52 may also include at least one substructure 54, illustrated as a dash-dot line. The substructure 54 comprises, for example, a local refractive index increase optionally associated with an adjacent region of locally reduced refractive index.

[0087] In all other respects, the comments on FIGS. 1 to 6 apply accordingly to FIG. 7.

[0088] According to FIG. 8, the waveguide 51 is more structured with respect to the refractive index profile than in FIG. 7. Thus, the active zones 31, 32, 33 can each comprise weakly pronounced sub-waveguides of their own. A resulting effective refractive index is drawn as a dashed line.

[0089] With such a structure of the waveguide 51, intensity curves can be obtained which show a wavy course in the region of maximum intensity, as illustrated in FIG. 4.

[0090] In all other respects, the comments on FIGS. 1 to 7 apply mutatis mutandis to FIG. 8.

[0091] FIG. 9 illustrates an example of a space charge region 44 of the tunnel diode 41, 42. A thickness TR of the space charge region 44 is one third or more of a total thickness T of the tunnel diode 41, 42, that is, the space charge region 44 makes up a considerable portion of the tunnel diode 41, 42.

[0092] In this context, areas B1, B2 of the wavelength-dependent absorption A are schematically illustrated in FIG. 10. In region B1, absorption is predominantly due to fundamental absorption of the semiconductor material concerned. In contrast, absorption in region B2 is essentially based on the presence of free charge carriers.

[0093] Since in the tunnel diode 41, 42, as shown in particular in FIG. 9, the space charge region 44, which is essentially free of free charge carriers, accounts for a high proportion of the total thickness T of the tunnel diode 41, 42, the absorption due to free charge carriers can be minimized. In addition, absorption due to fundamental absorption can be virtually eliminated by the choice of material or by the choice of band gap for the tunnel diode 41, 42.

[0094] Thus, the tunnel diodes 41, 42 described herein have an overall low absorption coefficient for the generated radiation, so that the tunnel diodes 41, 42 can be placed in the common waveguide 51 in regions of high local intensity IL to improve the radiation pattern.

[0095] FIGS. 11 and 12 further illustrate embodiments of the semiconductor emitter 1. According to FIG. 11, the semiconductor layer sequence has a highly reflective resonator end mirror 71 on opposite facets as well as an outcoupling coating 72 with a reflectivity adapted to a required feedback back into the resonator. The facets are oriented parallel to the growth direction G.

[0096] In contrast, the facets according to FIG. 12 are oriented approximately at a 45? angle to the growth direction G. This allows the highly reflective resonator end mirror 71 and the outcoupling coating 72 to be applied to a surface of the semiconductor layer sequence 2. This design is also referred to as a horizontal cavity surface emitting laser, or HCSEL.

[0097] The semiconductor layer sequences 2 and in particular the tunnel diodes 41, 42 described in connection with FIGS. 1 to 10 can be used in all of the semiconductor emitters 1 according to FIGS. 11 and 12.

[0098] The invention described herein is not limited by the description based on the embodiments. 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 this feature or combination itself is not explicitly stated in the patent claims or embodiments.