Broad-area diode laser comprising integrated p-n tunnel junction

Abstract

The present invention relates to a broad-area diode laser (BAL) comprising an integrated p-n tunnel junction. The present invention in particular relates to a high-performance broad-area diode laser in which, in order to improve the beam quality and to reduce the thermal resistance, a p-n tunnel junction, biased in the reverse direction, is integrated in the layer system of the diode laser.

A laser diode according to the invention comprises an active layer (20) formed between an n-doped semiconductor material (10, 12, 14) and a p-doped semiconductor material (30, 32, 34), the active layer (20) forming, along a longitudinal axis, an active zone for generating electromagnetic radiation; wherein at least one n-doped intermediate layer (50, 54) is arranged between an overlying p-side metal contact (52) and the p-doped semiconductor material (30, 32, 34), and, in the at least one n-doped intermediate layer (50, 54) in the region above the active zone, a p-n tunnel junction (40) being formed which is directly adjacent to the p-doped semiconductor material (30, 32, 34).

Claims

1. A laser diode, comprising: an active layer formed between an n-doped semiconductor material and a p-doped semiconductor material, the active layer forming, along a longitudinal axis, an active zone for generating electromagnetic radiation; wherein at least one n-doped intermediate layer is arranged between an overlying p-side metal contact and the p-doped semiconductor material, and, in the at least one n-doped intermediate layer in the region above the active zone, a p-n tunnel junction being formed which is directly adjacent to the p-doped semiconductor material.

2. The laser diode according to claim 1, wherein the p-n tunnel junction comprises a p.sup.+ tunnel layer arranged on the p-doped semiconductor material and an n.sup.+ tunnel layer arranged thereon.

3. The laser diode according to claim 1, wherein the p-n tunnel junction is arranged on a p-doped sub-contact layer of the p-doped semiconductor material.

4. The laser diode according to claim 1, wherein the p-n tunnel junction is arranged on a p-doped cover layer of the p-doped semiconductor material.

5. The laser diode according to claim 1, wherein an n-doped cover layer is arranged on the p-n tunnel junction.

6. The laser diode according to claim 1, wherein a stripe width of the diode laser is specified over a lateral width W of the p-n tunnel junction.

7. The laser diode according to claim 1, wherein the p-n tunnel junction is formed as a layer and a stripe width of the diode laser is specified over a lateral width W of an opening in an n-current shield introduced into the p-doped semiconductor material.

8. The laser diode according to claim 1, wherein the p-n tunnel junction is formed as a layer and a stripe width of the diode laser is specified over a lateral width W of a region between two adjacent deep implantation areas.

9. The laser diode according to claim 1, wherein the semiconductor material is based on GaAs.

10. The laser diode according to claim 1, wherein the minimum distance between the active layer and the p-n tunnel junction is less than 1.3 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is described below with reference to exemplary embodiments and on the basis of the associated drawings, in which:

[0026] FIG. 1 is an exemplary schematic view of a first embodiment of a laser diode according to the invention,

[0027] FIG. 2 is an exemplary schematic view of a second embodiment of a laser diode according to the invention,

[0028] FIG. 3 is an exemplary schematic view of a third embodiment of a laser diode according to the invention,

[0029] FIG. 4 is an exemplary schematic view of a fourth embodiment of a laser diode according to the invention,

[0030] FIG. 5 is an exemplary schematic view of a fifth embodiment of a laser diode according to the invention, and

[0031] FIG. 6 is an exemplary schematic view of a sixth embodiment of a laser diode according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is an exemplary schematic view of a first embodiment of a laser diode according to the invention. The laser diode shown comprises an active layer 20 formed between an n-doped semiconductor material (n-substrate 10, n-side n-cover layer 12, n-waveguide layer 14) and a p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32, p-sub-contact layer 34), the active layer 20 forming, along a longitudinal axis, an active zone for generating electromagnetic radiation; wherein an n-contact layer 50 is arranged between an overlying p-side metal contact 52 and the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32, p-sub-contact layer 34), and, in the n-contact layer 50 in the region above the active zone, a p-n tunnel junction 40 being formed which is directly adjacent to the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32, p-sub-contact layer 34). The p-n tunnel junction 40 shown comprises a p+tunnel layer 42 arranged on the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32, p-sub-contact layer 34) and an n+tunnel layer 44 arranged thereon. In this embodiment, the p-n tunnel junction 40 is arranged on a p-doped sub-contact layer 34 of the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32, p-sub-contact layer 34). A stripe width of the diode laser is specified over a lateral width W of the p-n tunnel junction 40. In this embodiment, the residual layer thickness d.sub.res is defined as the minimum distance between the active layer 20 and the p-n tunnel junction 40.

[0033] This embodiment of the invention can be provided by a two-stage epitaxy process having an etching step between these two stages. In a first growth step, the structure can be grown as far as the p-n tunnel junction 40. The tunnel junction layers (42, 44) can then be selectively etched away outside the stripe. Following subsequent epitaxial growth of the n-contact layer 50, a p-n junction is produced in the outer regions of the structure in the reverse direction, while the central p-n tunnel junction 40 facilitates the flow of current. This is a known method for current and optical limitation in surface-emitting lasers having vertical resonators (VCSELs).

[0034] FIG. 2 is an exemplary schematic view of a second embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in FIG. 1, and therefore the individual reference signs and what they are each assigned to applies accordingly. By contrast with the embodiment shown therein, however, in this case the p-n tunnel junction 40 can be formed as a layer and the stripe width of the diode laser is specified over a lateral width W of an opening in an n-current shield 60 introduced into the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32, p-sub-contact layer 34). In particular, in the example shown, the n-current shield 60 is arranged within the p-sub-contact layer 34. In this embodiment, the residual layer thickness d.sub.res is defined as the minimum distance between the active layer 20 and the current shield 60.

[0035] In this embodiment of the invention, the current confinement can likewise be achieved by a two-step epitaxy process having an etching step between these two steps. In this case, the power cut-off at the component edges is produced independently of the tunnel junction by the so-called (enhanced) self-aligned lateral structure. For this purpose, highly n-doped layers can be integrated in the vicinity of the underside of the p-side contact layer (i.e. the p-sub-contact layer 34), which results in a reverse-biased p-n junction. The first growth step ends after the growth of these layers. They can then be selectively etched away in the center in order to make a corresponding opening for the flow of current. The rest of the p-sub-contact layer 34 as well as the p-n tunnel junction 40 and the n-contact layer 50 can then be grown over the structured n-current shield 60.

[0036] FIG. 3 is an exemplary schematic view of a third embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in FIG. 2, and therefore the individual reference signs and what they are each assigned to applies accordingly. The p-n tunnel junction 40 is likewise formed as a layer here. By contrast with the embodiment shown therein, a stripe width of the diode laser is specified over a lateral width W of a region between two adjacent deep implantation areas 70. In particular, in the example shown, the two marginal deep implantation areas 70 reach from the metal contact 52 into the p-cover layer 32. Since an opening for the flow of current can likewise be made by the deep implantation areas 70, the additional integration of an n-current shield 60 is not required. In this embodiment, the residual layer thickness d.sub.res is defined as the minimum distance between the active layer 20 and the underside of the deep implantation areas 70.

[0037] By contrast with the above-described exemplary embodiments, this embodiment can be produced by single-stage epitaxial growth, which reduces the complexity and thus costs of the production process. The current limitation is for example carried out by high-energy deep ion implantation at the edges of the component. This can prevent the flow of current by increasing the intermediate resistance and introducing point defects, at which carriers rapidly recombine. Deep implantation through the active zone effectively prevents current spreading and LCA, as a result of which the beam quality could be considerably improved, but the power and efficiency are significantly impaired. Therefore, an implantation profile that is dimensioned such that it ends above the active zone (e.g. within the p-cover layer) with regard to the total power is preferred.

[0038] FIG. 4 is an exemplary schematic view of a fourth embodiment of a laser diode according to the invention. The laser diode shown comprises an active layer 20 formed between an n-doped semiconductor material (n-substrate 10, n-side n-cover layer 12, n-waveguide layer 14) and a p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32), the active layer 20 forming, along a longitudinal axis, an active zone for generating electromagnetic radiation; wherein an n-contact layer 50 and a p-side n-cover layer 54 are arranged between an overlying p-side metal contact 52 and the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32), and, in the p-side n-contact layer 54 in the region above the active zone, a p-n tunnel junction 40 being formed which is directly adjacent to the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32). The p-n tunnel junction 40 shown comprises a p.sup.+ tunnel layer 42 arranged on the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32) and an n.sup.+ tunnel layer 44 arranged thereon. In this embodiment, the p-n tunnel junction 40 is arranged on a p-doped cover layer 32 of the p-doped semiconductor material (p-waveguide layer 30, p-cover layer 32). In addition, an n-doped cover layer 54 is arranged on the p-n tunnel junction 40. A stripe width of the diode laser is specified over a lateral width W of the p-n tunnel junction 40. In this embodiment, the residual layer thickness d.sub.res is defined as the minimum distance between the active layer 20 and the p-n tunnel junction 40.

[0039] The substantial difference from the embodiment shown in FIG. 1 is therefore that the p-n tunnel junction 40 is arranged on the p-doped cover layer 32 and thus closer to the active zone. The integration of an additional p-sub-contact layer 34 can be omitted. By bringing the p-n tunnel junction 40 closer to the active zone, although the production is more technologically complex (in particular in the variants having two-step epitaxial growth), it can achieve considerable power advantages.

[0040] FIG. 5 is an exemplary schematic view of a fifth embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in FIG. 4, and therefore the individual reference signs and what they are each assigned to applies accordingly. The actual operating principle and a possible production method can be seen in FIG. 2, however. This embodiment differs from the embodiment shown in FIG. 2 merely on account of the position of the tunnel junction 40 and the lack of a p-sub-contact layer 34.

[0041] FIG. 6 is an exemplary schematic view of a sixth embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in FIG. 5, and therefore the individual reference signs and what they are each assigned to applies accordingly. The actual operating principle and a possible production method can be seen in FIG. 3, however. This embodiment likewise differs from the embodiment shown in FIG. 3 merely on account of the position of the tunnel junction 40 and the lack of a p-sub-contact layer 34.

LIST OF REFERENCE SIGNS

[0042] 10 n-substrate (e.g. GaAs) [0043] 12 n-cover layer (n-side, e.g. AlGaAs) [0044] 14 n-waveguide layer (e.g. AlGaAs) [0045] 20 active layer (comprises active zone) [0046] 30 p-waveguide layer (e.g. AlGaAs) [0047] 32 p-cover layer (e.g. AlGaAs) [0048] 34 p-sub-contact layer (e.g. GaAs) [0049] 40 p-n tunnel junction [0050] 42 p.sup.+ tunnel layer (e.g. p.sup.+ GaAs) [0051] 44 n.sup.+ tunnel layer (e.g. n.sup.+ GaAs) [0052] 50 n-(sub-)contact layer (p-side, e.g. GaAs) [0053] 52 metal contact (p-side) [0054] 54 n-cover layer (p-side, e.g. AlGaAs) [0055] 60 n-current shield [0056] 70 deep implantation area [0057] W lateral width [0058] d.sub.res residual layer thickness