WO2018206443A1

WO2018206443A1 - Semiconductor laser

Info

Publication number: WO2018206443A1
Application number: PCT/EP2018/061552
Authority: WO
Inventors: Matthias Peter; Teresa WURM; Christoph Eichler
Original assignee: Osram Opto Semiconductors Gmbh
Priority date: 2017-05-08
Filing date: 2018-05-04
Publication date: 2018-11-15
Also published as: DE102017109804A1

Abstract

The invention relates to a semiconductor laser (10), comprising a substrate (1), a defect mobility reduction layer (2) arranged on the substrate (1), and a semiconductor layer sequence (9) arranged on the defect mobility reduction layer (2), which semiconductor layer sequence comprises an active layer (4), the active layer (4) containing a nitride compound semiconductor material containing indium. The defect mobility reduction layer (2) comprises silicon-doped InxAlyGa1- x-yN with 0 ≤ x ≤ 0.03 and 0 ≤y ≤ 0.03, the dopant concentration in the defect mobility reduction layer (2) being between 1 * 1019 cm-3 and 3 * 1019 cm-3. The defect mobility reduction layer (2) has a thickness of at least 500 nm.

Description

description

SEMICONDUCTOR LASER The invention relates to a semiconductor laser, in particular an indium-containing one

Nitride compound semiconductor material based

Semiconductor lasers. This patent application claims the priority of German Patent Application 10 2017 109 804.6, the disclosure of which is hereby incorporated by reference.

Indium-containing nitride compound semiconductor materials are used in particular for the production of semiconductor lasers which emit laser radiation in the blue or green spectral range, for example.

It has been found that the growth of indium-containing nitride compound semiconductor materials can give rise to defect clusters which act as absorption centers and can degrade the efficiency of the semiconductor laser.

One problem to be solved is therefore one

indicate improved semiconductor laser, which is characterized in particular by a reduced defect cluster density.

This object is achieved by a semiconductor laser according to the independent claim. advantageous

Embodiments and developments of the invention are

Subject of the dependent claims. In accordance with at least one embodiment, the semiconductor laser comprises a substrate, one on the substrate

arranged defect mobility reduction layer, and a semiconductor layer sequence. The substrate is in particular a growth substrate suitable for the epitaxial growth of the semiconductor layer sequence. Furthermore, the

Semiconductor laser disposed on the substrate

Defect mobility reduction layer, which preferably directly adjoins the substrate. The

Defect mobility reduction layer is in the

Semiconductor laser in particular designed to reduce the propagation of defects from the substrate and thus counteract formation of defect clusters. On the

Defect mobility reduction layer is one

Semiconductor layer sequence arranged, which in particular comprises the active layer of the semiconductor laser.

The active layer is intended to emit laser radiation. The active layer can be used, for example, as a pn junction, as a double heterostructure, as a single layer

Quantum well structure or multiple quantum well structure

be educated. The term quantum well structure encompasses any structure, in the case of the charge carriers

Confinement a quantization of their

Experience energy states. In particular, the

Name Quantum well structure no information about the

Dimensionality of quantization. It thus includes quantum wells, quantum wires and quantum dots and any combination of these structures.

The active layer preferably comprises at least one indium-containing nitride compound semiconductor material. The active layer or at least a sub-layer thereof For example, in _x AlyGa _] _- _x -yN with 0 <x <1, 0 <y <1 and x

+ y <1. In a preferred embodiment, the active layer is a multiple quantum well structure with alternating quantum well layers of In _x] _Ga _] __ _x] _N where 0 <xl <1 and

Barrier layers of In _x 2Ga _] _- _x 2N with 0 <x2 <1 and x2 <xl.

In the semiconductor laser, the defect mobility reducing layer is advantageously doped with silicon

In _x Al _y Gai _x - _y N with 0 <x <0.03 and 0 <y <0.03 on or consists of it. The dopant concentration in the

Defect mobility reduction layer is preferably at least 1 × 10 ¹⁹ cm ^-3 . Furthermore, the

Defect mobility reduction layer has a thickness of at least 100 nm. Preferably, the

Defect mobility reduction layer with silicon

doped In _x Al _y Gai _x _ _y N with 0 <x <0.01 and 0 <y <0.01 or consists thereof. Particularly preferably, the

Defect mobility reduction layer with silicon

doped GaN (corresponding to x = 0, y = 0) or consists thereof.

The inventors have recognized in particular that it is at

Growth of indium-containing III-N compound semiconductors (e.g., InGaN) to form V-shaped defects (V-pits) can occur at dislocations originating from the substrate (at

Homoepitaxy) or from buffer layers (in heteroepitaxy). The dislocation density of the substrate may be at

Use of a GaN substrate, for example, about

5 * 10 ⁴ cm ^-2 to 5 * 10 ⁶ cm ^-2 . In the V-shaped

Defects grows containing the indium

Nitridverbindungshalbleitermaterial in crystal orientations different from the c-axis and it forms an area with different thickness and indium content in Compared to areas in c-direction. The

Quantum efficiency is significantly reduced in the vicinity of such dislocations or defects. The defects are visible, for example, in a photoluminescence microscope or

Cathodoluminescence microscope and typically have a diameter of less than 1 ym.

Under typical growth conditions of InAlGaN, dislocations originating from the substrate can slip and cluster defects can form, which are noticeable in large areas where the quantum efficiency is significantly lower. These defect clusters are also visible in a photoluminescence microscope or cathodoluminescence microscope and have a diameter of more than 1 μm, typically 20 μm to 40 μm. It has been found that the formation of defect clusters in particular of the integral amount of indium in the

Deposited layers, depends on the growth temperature of the overlying layers and the defect density and the substrate or the buffer layers. The defect clusters can reduce the efficiency of the semiconductor laser and act as absorption centers. This allows the

Performance of the semiconductor laser are degraded. The defect mobility reduction layer described herein therefore aims to counteract the formation of defect clusters.

The semiconductor laser described here makes particular use of the fact that the mobility of

Displacements by the between the substrate and the

inserted functional semiconductor layer sequence

Agility defect reduction layer having a high dopant concentration of at least 1 * 10 ¹⁹ cm ^-3, and a large thickness of at least 100 nm can be reduced. In particular, the propagation of dislocations from the substrate into the semiconductor layer sequence is reduced by the defect mobility reduction layer. Thus, with the defect mobility reducing layer, it is possible to reduce the number of defect clusters as compared with a semiconductor laser of otherwise the same layer structure and growth conditions, particularly the same

Growth time and growth temperature, significantly too

reduce.

In an advantageous embodiment, the

Dotierststoffkonzentration the Defektbeweglichkeits- Reduzierungssschicht between 1 * 10 ¹⁹ cm ^-3 and 3 * 10 ¹⁹ cm ^-3 , preferably between 1 * 10 ¹⁹ cm ^-3 and 2 * 10 ¹⁹ cm ^-3 . A high

Dopant concentration of at least 1 × 10 ¹⁹ cm ^-3 is advantageous, as already mentioned, in order to minimize the defect mobility. On the other hand, the dopant concentration should not be too high, otherwise the morphology of the defect mobility reduction layer will be detrimental

can change. In this regard, it is advantageous if the dopant concentration is not more than 3 * 10 ¹⁹ cm ^-3, and preferably not more than 2 * 10 ¹⁹ cm ^-3 . The dopant concentration is particularly preferably

Deficiency mobility reduction layer between

1.1 * 10 ¹⁹ cm ^"3 and 1.5 * 10 ¹⁹ cm ^{" 3} .

The defect-reducing effect of the defect mobility reducing layer can be further improved by increasing the thickness. In an advantageous

Design is the defect mobility

Reduction layer at least 500 nm thick. Preferably, the Defect mobility reduction layer at least 1000 nm or more preferably even at least 1500 nm thick.

Furthermore, it is advantageous if the defect mobility reduction layer has as large a distance as possible from the active layer of the semiconductor laser. The distance

between the defect mobility reducing layer and the active layer is preferably at least 1000 nm, particularly preferably at least 1500 nm. In this case, absorption effects due to free charge carriers are advantageously very low due to the high dopant concentration in the defect mobility reducing layer. Furthermore, typical laser parameters such as the steepness of the laser characteristic at such a large distance from the active layer are not adversely affected by the defect mobility reducing layer.

According to an advantageous embodiment, the

Semiconductor laser on a GaN substrate. A GaN substrate is characterized in particular by a particularly low

Dislocation density off. By a reduced

Dislocation density of the substrate arise in the growth of the semiconductor layer sequence less defect clusters. When using a GaN substrate, particularly low defect cluster densities can be achieved.

The substrate is preferably an n-doped substrate, in particular an n-doped GaN substrate. In particular, the substrate is preferably electrically conductive. This has the advantage that a flow expansion can take place in the substrate. An electrical contact of the semiconductor laser can be arranged, for example, on a rear side of the substrate. With a sufficiently thick substrate that is electrically is conductive, can be advantageously dispensed with a StromaufWeitungsschicht in the semiconductor layer sequence and so the absorption in the semiconductor layer sequence can be reduced. The substrate may, for example, be at least 100 μm thick. Preferably, the thickness of the substrate is between 100 ym and 150 ym. The thickness of the substrate is to be understood here as meaning the thickness of the substrate in the finished semiconductor laser. The substrate may be used in the epitaxial deposition of

Semiconductor layers have a greater thickness, for example about 400 ym, and are subsequently thinned.

The semiconductor laser is advantageously characterized by a particularly low defect cluster density, which is achieved in particular by means of the defect mobility reduction layer. Defect clusters can in particular by means of a

Photoluminescence microscope can be detected. Defect clusters show up in the photoluminescence microscope as dark spots and have a diameter of more than 1 ym,

typically in the range of 20 ym to 40 ym, on.

The defect cluster density of the semiconductor laser is preferably less than 200 cm ^-2 , more preferably less than 100 cm ^-2 . In particular, a defect cluster density in the range of 30 cm ^-2 to 200 cm ^-2 can be achieved. Compared to a conventional semiconductor laser which does not have the defect mobility reducing layer having the characteristics described above, the defect cluster density can be reduced by a factor of about 30. For example, in a conventional semiconductor laser, the defect cluster density may be between 1000 cm ² and 5000 cm ^-2 . According to an advantageous embodiment, the semiconductor layer sequence has an n-side cladding layer, an n-side waveguide layer, the active layer, a p-side waveguide layer and a p-side cladding layer. The cladding layers have in particular

Semiconductor material that has a larger electronic

Band gap and a lower refractive index than the

Waveguide layers has. The cladding layers may, for example, comprise AlGaN and the waveguide layers InGaN. The defect mobility reducing layer of the semiconductor laser is advantageously arranged between the substrate and the n-side cladding layer.

The semiconductor layer sequence of the semiconductor laser can in particular be based on an indium

Based nitride compound semiconductor material. "Based on an indium-containing nitride compound semiconductor" in the present context means that the

Semiconductor layer sequence or at least one layer thereof comprises an indium-containing III-nitride compound semiconductor material, preferably In _x Al _y Gai- _x - _y N, where 0 <x <1, 0 <y <1 and x + y <1 this material does not necessarily have a mathematically exact composition according to the above formula. Rather, it can have one or more dopants and additional constituents. For the sake of simplicity, however, the above formula contains only the essential constituents of the crystal lattice (In, Al, Ga, N), even if these may be partially replaced by small amounts of other substances.

The invention will be described below with reference to

Embodiments explained in more detail in connection with Figures 1 to 3. Show it:

1 shows a schematic representation of a cross section through a semiconductor laser according to a

Embodiment,

FIG. 2 shows a schematic representation of the intensity of the optical wave in the case of a semiconductor laser emitting in the blue spectral range according to an embodiment, and

Figure 3 is a schematic representation of the intensity I of the spontaneous electroluminescence emission at a current of 400 mA as a function of the wavelength λ for various embodiments of the semiconductor laser with the Defektbeweglichkeits Reduzierungsschicht and Comparative Examples without the Defektbeweglichkeits Reduzierungsschicht.

Identical or equivalent elements are shown in the figures with the same reference numerals. The components shown and the size ratios of the components with each other are not to be considered as true to scale.

1 has a semiconductor layer sequence 9 that has an n-type semiconductor region 3, a p-type semiconductor region 5, and an n-type semiconductor region 3 and the p-type semiconductor region 5 arranged for emission of radiation suitable active

Layer 4 comprises. The n-type semiconductor region 3 and the p-type semiconductor region 5 may each consist of several Sub-layers 3A, 3B, 5A, 5B, 5C and not necessarily exclusively of n-doped

Layers or p-doped layers, but may for example also have one or more undoped layers.

The semiconductor layer sequence 9 has in particular

Nitride compound semiconductor materials. The on

Nitride compound semiconductor materials based

Semiconductor laser 10 can in particular for the emission of

Laser radiation in the blue or green spectral range

be provided.

For electrical contacting of the semiconductor laser 10, for example, a first connection layer 6 on a

Subregion of the top 8 of the semiconductor laser 7 and a second connection layer 7 may be provided on a back side of the substrate 1. The semiconductor laser 10 can be known in the art per se semiconductor laser embodiments such as reflective layers on the side facets, and / or structuring as a stripe laser. Such known details are not here for simplicity

shown. The intended for the emission of laser radiation active

Layer 4 of the semiconductor laser 10 is preferably as

Single or multiple quantum well structure formed having one or more barrier layers 4A and one or more quantum well layers 4B. The electronic band gap of the at least one quantum well layer 4B is smaller than the electronic band gap of the at least one

Barrier layer 4A. The number N of periods of

For example, quantum well structure is between including 1 and inclusive 5, preferably 1 or 2. Particularly preferably, the semiconductor laser has a single quantum well structure (single quantum well). The active layer 4 of the semiconductor laser 10 is based

advantageously on an indium-containing

Nitride compound semiconductor material. The active layer 4 may in particular comprise alternating quantum well layers 4B made of In _x iGai- _x iN with 0 <xl -S 1 and barrier layers 4A

In _X 2Gai- _X 2 with 0 ^ x2 <1 and x2 <xl have. Due to the lower indium content x2, the barrier layers 4A have a larger electronic band gap than the

Quantum well layers 4B on. The active layer 4 of the semiconductor laser is preferably arranged between an n-side waveguide layer 3A and a p-side waveguide layer 5A. The

Waveguide layers 3A, 5A may in particular comprise InGaN. The waveguide formed by the waveguide layers 3A, 5A is, for example, of an n-side

Sheath layer 3B and a p-side cladding layer 5B surrounded. The cladding layers 3B, 5B preferably have AlGaN. The waveguide layers 3A, 5A and / or the

Sheath layers 3B, 5B may each consist of several

Sublayers be composed, which are not shown here for simplicity. Between the p-side

Cladding layer 5B and the first terminal layer 6 is preferably arranged a p-contact layer 5C, the

For example, GaN may have.

The semiconductor layer sequence 3, 4, 5 is applied to a substrate 1, wherein between the substrate 1 and the

Semiconductor layer sequence 3, 4, 5 a defect mobility Reduction layer 2 is arranged. The

Defect mobility reduction layer 2 is a silicon doped GaN layer. The dopant concentration of silicon in the defect mobility reducing layer is advantageously at least 1 × 10 ¹⁹ cm ^-3 . Due to the comparatively high dopant concentration in the

Defect mobility reduction layer 2 becomes the

Propagation of defects emanating from the substrate 1, advantageously reduced. This effect is stronger the greater the thickness D of the defect mobility reducing layer 2. The thickness D of

Defect mobility reduction layer 2 should be at least 100 nm, but with larger layer thicknesses

are more advantageous. Advantageously, the thickness D of the defect mobility reduction layer 2 is at least 500 nm and preferably at least 1000 nm. A particularly good

Reduction of the defect density can be achieved when the thickness D of the defect mobility reducing layer 2 is at least 1500 nm.

The substrate 1 is in particular for epitaxial

Growing of nitride compound semiconductor materials

suitable growth substrate. Particularly preferably, the substrate 1 is an n-doped GaN substrate. A GaN substrate is advantageously characterized by a particular in

Very low defect density compared to sapphire substrates. The defect density may be, for example, between 5 * 10 ⁴ cm ^-2 and 5 * 10 ⁶ cm ^-2 . By the defect mobility reducing layer 2

In particular, the formation of defect clusters decreases. "Defective clusters" here are groups of To understand defects having a lateral extent of more than 1 ym, in particular in the range of 20 ym to 40 ym. Such defect clusters show up, for example, in a study of the semiconductor layer sequence 9 by means of photoluminescence microscopy as dark spots. By the defect mobility reducing layer 2 can be

in particular, that the defect cluster density is less than 200 cm ^-2 , preferably less than 100 cm ^-2 . To avoid absorption losses in the highly doped defect mobility reduction layer 2, the active layer 4 preferably has a large distance d from the

Defect mobility reduction layer 2 on. The distance d is preferably at least 1000 nm and especially

preferably at least 1500 nm.

FIG. 2 schematically shows the course of the optical wave in the case of a semiconductor laser emitting in the blue spectral region according to an exemplary embodiment. Shown is the intensity of the optical wave as a function of one of

Surface of the semiconductor layer sequence outgoing

Location coordinate z. A distance d between the active layer and the defect mobility reducing layer 2 is preferably more than 1.5 μm. In this case, the optical wave in the region of the defect mobility

Reduction layer 2 advantageously only such a low intensity that absorption losses are negligible. FIG. 3 shows a schematic representation of the intensity I of the spontaneous electroluminescence emission in a

Amperage of 400 mA as a function of the wavelength λ for various embodiments of the semiconductor laser with the defect mobility reducing layer (black dots) and comparative examples without the

Deficiency mobility reduction layer (white dots). It turns out that the embodiments with the

Defect mobility reduction layer (interpolation line 12) on average have higher spontaneous emission than the examples without the defect mobility reduction layer (interpolation line 13). The measured spontaneous emission is a measure of the quantum efficiency of the semiconductor laser. It turns out that the means of defect mobility

Reduction layer achieved lower density of defect clusters can lead to increased quantum efficiency. The bigger the effect, the more pronounced the effect

Emission wavelength is. The defect mobility reducing layer is therefore particularly advantageous in a semiconductor laser having one for a

Nitride compound semiconductor laser comparatively large

Emission wavelength has. There at

As nitride compound semiconductors increase the emission wavelength with increasing indium content in the active layer, the defect mobility reduction layer is particularly advantageously applicable to active layers having a comparatively high indium content. The invention is not limited by the description with reference to the embodiments. Rather, the includes

Invention every new feature as well as every combination of

Features, which includes in particular any combination of features in the claims, even if this feature or this combination itself is not explicitly in the

Claims or embodiments is given. Reference sign list

1 substrate

2 defect mobility reduction layer

3 n-type semiconductor region

3A n-side cladding layer

3B n-side waveguide layer

4 active layer

4A barrier layer

4B quantum well layer

5 p-type semiconductor region

5A p-side cladding layer

5B p-side waveguide layer

5C p-contact layer

6 first contact layer

7 second contact layer

8 surface

9 semiconductor layer sequence

10 semiconductor lasers

11 optical wave

12 interpolation line

13 interpolation line

Claims

claims

A semiconductor laser (10) comprising

a substrate (1),

- One on the substrate (1) arranged

Defect Mobility Reduction Layer (2), and

a semiconductor layer sequence (9) arranged on the defect mobility reduction layer (2) and comprising an active layer (4), wherein the active layer (4) comprises an active layer (4)

Layer (4) contains an indium

Contains nitride compound semiconductor material,

wherein the defect Agility reduction layer (2) doped with silicon, In _x Al _y Ga _x - _y N with 0 ≤ x <0.03 and

0 <y <0.03, a dopant concentration in the defect mobility reducing layer (2)

between 1 × 10 ¹⁹ cm ^-3 and 3 × 10 ¹⁹ cm ^-3 , and the defect mobility reducing layer (2) has a thickness of at least 500 nm.

2. A semiconductor laser according to claim 1,

wherein the defect mobility reducing layer (2) comprises silicon doped GaN.

3. A semiconductor laser according to one of the preceding claims, wherein the dopant concentration of

Defect Mobility Reduction Layer (2) between

1 * 10 ¹⁹ cm ^"3 and 2 * 10 ¹⁹ cm ^{" 3} .

4. The semiconductor laser according to one of the preceding claims, wherein the dopant concentration of

Defect Agility Reduzierungssschicht (2) is between 1.1 * 10 ¹⁹ cm ^"3 and 1.5 * 10 ¹⁹ ^{cm" 3.}

A semiconductor laser according to any one of the preceding claims, wherein the defect mobility reducing layer (2) is at least 1000 nm thick.

A semiconductor laser according to any one of the preceding claims, wherein the defect mobility reducing layer (2) is at least 1500 nm thick.

7. A semiconductor laser according to one of the preceding claims, wherein a distance of the defect mobility

Reduction layer (2) of the active layer (4) is at least 1000 nm.

8. A semiconductor laser according to one of the preceding claims, wherein a distance of the defect mobility

Reduction layer (2) of the active layer (4) is at least 1500 nm.

9. A semiconductor laser according to one of the preceding claims, wherein the substrate (1) is a GaN substrate.

10. A semiconductor laser according to one of the preceding claims, wherein the substrate (1) is n-doped.

11. A semiconductor laser according to one of the preceding claims, wherein a defect cluster density of

Semiconductor layer sequence (9) is less than 200 cm ^-2 .

12. The semiconductor laser according to claim 1, wherein the semiconductor layer sequence comprises an n-side cladding layer, an n-side waveguide layer, the active layer, a p-side Waveguide layer (5A) and a p-side cladding layer (5B), and wherein the

Defect mobility reduction layer (2) between the substrate (1) and the n-side cladding layer (3B) is arranged.

13. A semiconductor laser according to one of the preceding claims, wherein the semiconductor layer sequence (9) on an indium-containing nitride compound semiconductor material

based.