WO2010017787A1

WO2010017787A1 - Optically pumped vcsel with a multiplicity of active areas for intensity reduction in the anti-resonant resonator

Info

Publication number: WO2010017787A1
Application number: PCT/DE2009/000861
Authority: WO
Inventors: Hans Lindberg; Stefan Illek
Original assignee: Osram Opto Semiconductors Gmbh
Priority date: 2008-08-13
Filing date: 2009-06-17
Publication date: 2010-02-18
Also published as: DE102008038961A1; DE102008038961B9; DE102008038961B4

Abstract

In at least one embodiment of the surface-emitting semiconducting laser chip (1), this embodiment comprises a first layer sequence (2) which has a reflective effect for primary radiation (P) at a primary wavelength. In addition, the semiconductor laser chip (1) has a layer stack (4) with at least one active area (5), wherein the layer stack (4) is applied to a main face of the first layer sequence (2) and is designed to emit the primary radiation (P). The thickness (D) of the layer stack (4) is designed such that it is non-resonant at the primary wavelength. Only slight optical losses occur within the semiconductor laser chip (1) within a surface-emitting semiconductor laser chip (1) such as this.

Description

description

OPTICALLY PUMPED VCSEL WITH A VARIETY OF ACTIVE AREAS FOR INTENSITY REDUCTION IN THE ANTI-RESONANT

RESONATOR

The invention relates to a surface-emitting semiconductor laser chip, to a laser arrangement having a surface-emitting semiconductor laser chip and to a method for producing such a semiconductor laser chip.

Semiconductor-based lasers offer great advantages in terms of efficiency, maintenance and size of the component compared to gas or solid state lasers with an optically pumped YAG or YLF crystal as the amplifier medium. One way to classify semiconductor lasers is to distinguish between edge emitting and surface emitting lasers. In edge-emitting semiconductor lasers, the light emitted by the semiconductor chip often has a line-like, asymmetrical cross-section of the beam profile. In the case of surface-emitting semiconductor lasers, the quality of the beam profile is usually more favorable since the beam profile is more symmetrical.

Surface emitting semiconductor lasers are also capable of producing higher intensity light than edge emitting semiconductor lasers. The optical power densities within the laser crystal can be several watts per cubic millimeter, for example in continuous wave mode. An object to be solved is to provide a surface emitting semiconductor laser chip with a high efficiency. Another object to be solved is to specify a laser arrangement with such a semiconductor laser chip. Furthermore, an object to be solved is to provide a method for producing such a surface-emitting semiconductor laser chip.

According to at least one embodiment of the surface-emitting semiconductor laser chip, this comprises a first layer sequence. The first layer sequence acts for a generated in operation of the semiconductor laser chip primary radiation with a primary wavelength λ _P reflective. The layer sequence can be formed from a single or, preferably, from several layers. It is possible that the layer sequence has a reflective metallic component. If the first layer sequence is designed as a Bragg mirror and has dielectric layers or semiconductor layers with alternately low and high refractive index, the layer sequence preferably comprises 20 to 40 pairs of layers with low and high refractive index. The thickness of the respective layers is preferably one quarter of the primary wavelength λ _P. Thickness here denotes the optical thickness, that is to say the integral over the product of geometric length and refractive index for the relevant wavelength.

The first layer sequence may alternatively or additionally also be reflective metal layers, reflective layers of a transparent conductive oxide, TCO for short, or a

Structure similar to a diffraction grating have. Preferably, all layers of the first layer sequence are configured just. However, it is equally possible that individual or all Layers have a curvature, so that about a focusing reflector is formed.

In the event that the first layer sequence is configured as a Bragg mirror, the primary radiation has a certain effective penetration depth into the Bragg mirror and thus into the reflective, first layer sequence. The effective penetration depth can be estimated as the primary wavelength λ _P divided by four times the refractive index difference between high and low refractive index layers. Is that the

Refractive index difference between the layers of high and low refractive index about 0.5, as is the effective depth of penetration therefore λ _P ₀ / (4 x 0.5), roughly .lambda.p, _0/2. In this estimation λ _{P (} o the

Vacuum wavelength of the primary radiation, so not like λ _P, the wavelength divided by the refractive index of the medium. The effective penetration depth is thus essentially a wavelength-dependent physical property of a Bragg mirror.

Surface emitting means that the semiconductor chip emits laser radiation in a planar manner on an outer surface of a semiconductor body. The surface over which the light radiation is emitted from the semiconductor laser chip has a two-dimensional character. In contrast to this, edge-emitting lasers whose light-emitting surface is linear and thus represents a substantially one-dimensional surface whose longitudinal extent is significantly larger than its transverse extent can be seen. Preferably, the surface over which the surface emitting semiconductor laser chip emits laser radiation has two major axes, each of the major axes has a greater length than an extension of a light-generating region of the semiconductor laser chip in a direction perpendicular to the light-emitting surface. Preferably, both major axes of the light-emitting surface are approximately the same size. "Approximately" means that the relative deviation is less than 25%, in particular less than 10% In other words, the light-emitting surface is, for example, ellipsoidal or, preferably, circular.

Semiconductor laser chip means that the chip is based essentially on semiconductor materials. In other words, the semiconductor laser chip has at least one active region, which is designed to generate the primary radiation, which is based on a semiconductor material. It is possible in principle that the semiconductor laser chip in addition

Semiconductor materials also other materials such as dielectric layers, passivation or electrically ohmic conductive layers, for example of a metal having. However, the generation of the laser radiation is based on at least one semiconductor material, such as GaAs, InGaAs, AlGaAs, GaP, InGaP, GaN, InGaN or InP. The semiconductor material may further include substances, for example in the form of dopants.

According to at least one embodiment of the surface-emitting semiconductor laser chip, the primary wavelength λ _P lies in the near-infrared spectral range, in particular between 1000 nm and 1100 nm. The primary wavelength λ _P can however also be at other wavelengths in the spectral range between 200 nm and 3500 nm.

According to at least one embodiment of the surface-emitting semiconductor laser chip has this a layer stack with at least one active area. The layers of the layer stack may be grown epitaxially and expand substantially parallel to the light-emitting surface. The at least one active area is configured to operate during operation of the

Semiconductor laser chips to generate the primary radiation with the primary wavelength λ _P. The primary wavelength λ _P may comprise one or more wavelength ranges. Preferably, the semiconductor laser chip has a plurality of active regions, in particular between five and 15 such regions. At least one active region is designed as a quantum dot, as a quantum wire or preferably as a quantum well.

The at least one active region may be optically or electrically pumped. The pumping of at least one active area can be direct or indirect. In direct pumping, for example, electron-hole pairs are generated in the active region itself. In the case of indirect pumping, for example, the layer stack

Barrier layers on which are generated by the pump electron-hole pairs, which then propagate into the active areas ^' or in at least one active area and there serve to generate the primary radiation.

In accordance with at least one embodiment of the surface-emitting semiconductor laser chip, the layer stack having the at least one active region is applied to a main side of the first layer sequence.

Preferably, first layer sequence and layer stacks are in direct contact with each other, but it is also possible for layers which serve, for example, an electrical contacting, be mounted between reflective first layer sequence and layer stack. A main side of the layer stack facing away from the first layer sequence is formed, at least in part, by a light exit surface.

In accordance with at least one embodiment of the surface-emitting semiconductor laser chip, the thickness of the layer stack is its optical thickness, that is to say the integral above the optical refractive index and a path along a running direction during operation of the

Semiconductor laser chips in the layer stack generated radiation. The layer stack is in particular limited by the light exit surface and the reflective first layer sequence. The light exit surface can be distinguished by the fact that a material having a significantly reduced refractive index, such as air or an antireflection layer, is present on the side of the layer stack facing away from the light exit surface. "Significantly reduced" means that the refractive index difference, starting from the

Light emitting surface-forming material, at least 20%, preferably at least 40%.

In accordance with at least one embodiment of the surface-emitting semiconductor laser chip, the thickness of the layer stack is designed such that it is non-resonant with respect to the primary wavelength λ _P. "Non-resonant" here means that with respect to nodes and antinodes within the semiconductor chip no electric light field is formed, as is the case in the resonant case, for example in a Fabry-Perot element. According to at least one embodiment of the surface-emitting semiconductor laser chip, the latter has a resonator. In this case, the resonator is preferably integrated in the semiconductor laser chip and formed by the light exit surface and by the reflective first layer sequence. The light exit surface has a non-vanishing reflectivity with respect to the primary wavelength λ _P. For example, the reflectivity is at least 2%, in the case of an anti-reflection coating on the side facing away from the light exit surface of the layer stack, or up to about 30%, in the case

Light exit surface is an interface between air and the layer stack.

According to at least one embodiment of the surface emitting semiconductor laser chip, this has an effective resonator length L. The effective resonator length L is formed from the sum of the thickness of the layer stack and the effective penetration depth of the primary radiation into the reflective first layer sequence. That is, the resonator length L is greater than or equal to the thickness of the layer stack. The respective thicknesses or lengths relate here to the optical lengths, that is to the integral over the product of path length and refractive index.

In at least one embodiment of the surface-emitting semiconductor laser chip, the latter comprises a first layer sequence which has a reflective effect for a primary radiation having a primary wavelength λ _P. In addition, the semiconductor laser chip comprises a layer stack having at least one active region, wherein the layer stack is applied to a main side of the first layer sequence and is designed to emit the primary radiation. The thickness of the layer stack is designed to be non-resonant with respect to the primary wavelength λ _P.

In other words, the semiconductor laser chip is designed with a non-resonant amplifier structure.

In such a surface emitting semiconductor laser chip, only small optical losses occur within the semiconductor laser chip. Therefore, such a semiconductor laser chip has a high efficiency.

The efficiency of a semiconductor laser chip results from the relation of gain achieved and optical losses occurring. Both gain and optical losses are approximately directly proportional to the optical intensity in the stack of layers having the at least one active region. That is, in the case where the gain is high, the optical losses are also high. This adversely affects the overall efficiency of the semiconductor laser chip.

The optical intensity in the semiconductor laser chip is highest, for example, when the thickness of the layer stack is designed such that the layer stack is resonant with respect to the primary wavelength λ _P. That is, in the resonant case forms within the

Semiconductor laser chips from a standing wave, which is analogous to a resonance in a Fabry-Perot element. In a non-resonant case, the optical intensity in the semiconductor laser chip is correspondingly reduced. At least three types of optical losses within the semiconductor laser chip can be reduced by non-resonant design of the thickness of the layer stack. Firstly, because of the reduced optical intensity in the semiconductor laser chip, the reabsorption of radiation within the semiconductor laser chip, for example through free carrier absorption, is also reduced. On the other hand, by reducing the absorption or reabsorption, the temperature, and in particular the temperature gradient, is within the second

Semiconductor laser chips reduced. Third, in the resonant case, as mentioned, the light exit surface and the reflective first layer sequence act as a Fabry-Perot resonator. In the case of resonance, a Fabry-Perot element has an increased transmission, which in the case of a

Semiconductor laser chips as optical power loss occurs.

One aspect of the operation of the semiconductor laser chip is therefore that can be reduced by the non-resonant structure disturbing effects by the formation of a thermal lens, for example by an optical pumping of the semiconductor laser chip. Since an effective penetration depth of the primary radiation and / or a pumping radiation into the semiconductor laser chip is reduced for a non-resonant structure of the semiconductor laser chip, in this case also the thermal lens and the associated losses are less pronounced.

It can therefore be reduced by reducing the optical intensity in the semiconductor laser chip, the optical losses and the efficiency or the efficiency of the semiconductor laser chip can be increased. This is possible if the gain in the stack is sufficiently high, so that the gain does not need to be optimized. In such a semiconductor laser chip so not the gain, English gain, but the efficiency is optimized or improved.

In accordance with at least one embodiment of the surface-emitting semiconductor laser chip, the effective resonator length L corresponds to the formula:

L = 0.5 N λ _P + 0.25 λ _P

N is a natural number. The tolerance for the effective resonator length L is in this case at most λ _P / 8.

In other words, the effective resonator length L corresponds to an integer multiple of half the primary wavelength λ _P , extended by λ _P / 4. That is, the effective resonator length L is thus 3λ _P / 4 or 5λ _P / 4 or 7λ _P / 4 and so on. Such an effective resonator length L reduces the Fabry-Perot effect and thus the transmission in the direction away from the layer stack through the reflective first layer sequence. The efficiency of the semiconductor laser chip is thereby increased.

Again, as below, that is considered effective

Resonator length L is the optical and not the geometric length to understand.

According to at least one embodiment of the surface-emitting semiconductor laser chip is the

Tolerance on the effective resonator length L at most λ _P / l6, in particular at most λ _P / 32. A reduced tolerance of the effective resonator length L leads to a more effective reduction of optical losses in the semiconductor laser chip and thus increases its efficiency.

In accordance with at least one embodiment of the surface emitting semiconductor laser chip, the thickness of the layer stack is designed such that the semiconductor laser chip is anti-resonant with respect to the primary wavelength λ _P. That is, the intensity of the electromagnetic field within the semiconductor laser chip corresponds to that of a Fabry-Perot element with minimal transmission. In the anti-resonant case, the optical intensity in the semiconductor laser chip is reduced. Such a choice of the thickness of the layer stack can also reduce the optical losses in the semiconductor laser chip.

In accordance with at least one embodiment of the surface-emitting semiconductor laser chip, no intensity maximum with respect to the optical intensity of the primary radiation is present at the light exit surface of the layer stack during operation of the semiconductor laser chip. Preferably, an intensity minimum is present at the light exit surface. The tolerance for this is at most λ _P / 16, in particular at most λ _P / 32. By minimizing the intensity at the light exit surface is also accompanied by a minimization of the optical intensity within the semiconductor chip. This also reduces the occurring optical losses in the half-fiber chips, whereby its efficiency is increased.

According to at least one embodiment of the surface emitting semiconductor laser chip, the latter comprises a plurality of active regions, wherein at least one distance between two adjacent active regions corresponds to a multiple of half of the primary wavelength λ _P and wherein at least one active region is in operation of the semiconductor laser chip in an intensity maximum of the primary radiation. Towards the reflective first layer sequence, the distances between adjacent active regions may preferably increase. If the active regions are arranged in groups with at least two active regions, wherein within a group the distances between adjacent active regions are approximately the same, the distances between the groups increase in the direction of the first layer sequence. Likewise, at least half of the active regions, in particular all active regions, are arranged in an intensity maximum of the primary radiation. Are active areas in the

Intensity maxima of the primary radiation placed so increases the gain of the semiconductor laser chip.

According to at least one embodiment of the surface-emitting semiconductor laser chip, the latter comprises at least one second layer which is connected to the

Light exit surface of the layer stack mounted and is partially reflective for the primary radiation. The second layer may be in direct physical contact with the light exit surface, this being the preferred case or separated by one or more functional layers from the layer stack. The at least one second layer is, for example, a layer which has a refractive index which lies between that of air and that of the layer stack forming material. About such a partially reflecting layer, the coupling-out efficiency can be increased from the semiconductor laser chip. In addition, the Reflectivity of the light exit surface of the layer stack can be selectively adjusted via such a second layer.

According to at least one embodiment of the semiconductor laser chip in which this comprises at least one second layer, the reflectance of the light exit surface of the layer stack with respect to the primary radiation due to the at least one second layer is between 2% and 20%, preferably between 7% and 13%. The reflectivity thus differs from that of an optimized, single-layer antireflection coating, with a reflectivity of less than 2%, and also of an interface air-light exit surface or air-semiconductor material, with a reflectivity of> 30%. Rather, a reflectivity is set, which has proven to be optimal in terms of avoiding losses in the semiconductor chip. A reflectivity of the light exit surface in said value range due to the second layer can be realized with comparatively little technical effort.

According to at least one embodiment of the

Semiconductor laser chips, the at least one second layer is a passivation. That is, the at least one second layer protects the layer stack at least in part from chemical or physical influences that are detrimental to the layer stack. Such a second layer increases the life of the semiconductor laser chip.

According to at least one embodiment of the surface emitting semiconductor laser chip, this is indirectly optically pumpable. Such pumping of the semiconductor laser chip is also called barrier pumping designated. That is, light having a pump wavelength λ _R is irradiated into the semiconductor laser chip. This pump light is absorbed in barrier layers in which electron-hole pairs are generated. These electron-hole pairs then propagate into the at least one active region and subsequently serve via recombination to generate the primary radiation. The barrier layers are preferably transparent to the primary radiation and designed to be absorbent for the pump radiation. Such a semiconductor laser chip has a high efficiency and a high beam quality.

According to at least one embodiment of the

Semiconductor laser chips is the at least one second layer designed as an antireflection layer with respect to the pump wavelength λ _R.

According to at least one embodiment of the surface emitting semiconductor laser chip, this is designed for a continuous wave operation. That is, the

Semiconductor laser chip is not operated pulsed. In particular, continuous wave operation means that a repetition rate is at most 10 Hz and a pulse duration is at least 0.1 s.

According to at least one embodiment of the surface emitting semiconductor laser chip, all active regions, within the manufacturing tolerances, are adapted to emit radiation of the same wavelength.

In accordance with at least one embodiment of the surface emitting semiconductor laser chip in which this is optically pumped, the pump radiation in the semiconductor chip is substantially parallel to the primary radiation. In other words, an angle between a beam axis of the primary radiation and a beam axis of the pump radiation is at most 30 °, in particular at most 20 °, preferably at most 10 °.

In addition, a laser arrangement with at least one surface-emitting semiconductor laser chip is specified. For example, the laser assembly may include a surface emitting semiconductor laser chip as described in connection with one or more of the above embodiments.

According to at least one embodiment of the laser arrangement, the latter comprises at least one surface emitting semiconductor laser chip and at least one pumping light source which is designed to pump the semiconductor laser chip.

In accordance with at least one embodiment of the laser arrangement, the latter comprises at least one external mirror which has a reflective effect for the primary radiation generated by the semiconductor laser chip. The external mirror is preferably a highly reflecting dielectric mirror or a metal mirror. The external mirror may have a curvature such that the external mirror, for example, has a focusing effect.

According to at least one embodiment of the laser arrangement is of the first layer sequence of the at least one

Semiconductor laser chips and formed by at least one external mirror, an external resonator of the laser array. In at least one embodiment of the laser arrangement, the latter comprises at least one surface-emitting semiconductor laser chip in accordance with one or more of the abovementioned embodiments. Furthermore, the laser arrangement comprises at least one pumping light source for pumping the semiconductor laser chip. In addition, the laser arrangement has at least one external mirror which has a reflective effect on the primary radiation, so that an external resonator of the laser arrangement is formed by the first layer sequence of the semiconductor laser chip and by the at least one external mirror.

Such a laser arrangement can have a compact design and permits a conversion of the radiation generated by the semiconductor laser chip into a secondary radiation having a secondary wavelength λ _s different from the primary radiation.

In accordance with at least one embodiment of the laser arrangement, the resonator of the laser arrangement comprises a wavelength-selective element. Optionally, the polarization of the primary and / or secondary radiation can also be defined via the wavelength-selective element; the spectral properties of the laser arrangement can be adjusted in a targeted manner via such a wavelength-selective element.

According to at least one embodiment of the laser arrangement, this comprises a wavelength-selective element in conjunction with a semiconductor chip, in which the light exit surface has a reflectivity in the range of 4% to 20%, in particular between 7% and 13%.

In accordance with at least one embodiment of the laser arrangement, the wavelength-selective element acts in one Wavelength range from 0.8 λ _P to 1.2 λ _P blocking for wavelengths λ _Res , which satisfy the condition with a wavelength tolerance of at most λ _P / 16 with respect to the effective resonator length L of the semiconductor laser chip:

λ _res = (2L) / N,

where N is a natural number. That is, the wavelengths λ _Res satisfy a resonance condition in the sense of a Fabry-Perot effect with respect to the effective resonator length L. For wavelengths λ _Res , with respect to which the resonator of the semiconductor laser chip is resonant, then the wavelength-selective element has a blocking effect. In this context, "blocking" may mean that the transmission for resonant wavelengths λ _Res is a few percent below the transmission for anti-resonant wavelengths λ _P. The wavelength range in which the element acts as a blocking element is preferably selected such that the entire gain range of the such a wavelength-selective element are suppressed layer stack such wavelengths λ _Res. prevents the semiconductor laser chip enters a resonant mode in which the optical intensity of the semiconductor laser chip is high and thus the optical loss is large. over such a wavelength-selective element may be a certain, In particular with respect to the effective resonator length of the semiconductor laser chip anti- resonant primary wavelength λ _{P are set} specifically.

In accordance with at least one embodiment of the laser arrangement, the wavelength-selective element is an etalon. Etalones can be very compact and beside the

Wavelength selectivity also have a polarization selectivity. About an etalon so both the spectral properties as well as the

Determine polarization properties of the laser array. A laser arrangement with an etalon is described, for example, in document WO 2008/028454 A1, the disclosure of which is hereby incorporated by reference.

In accordance with at least one embodiment of the laser arrangement, the resonator of the laser arrangement comprises at least one crystal for frequency doubling of the primary radiation

Frequency doubling, in particular near-infrared light with wavelengths in the range of 1 .mu.m, in particular between 0.95 .mu.m and 1.15 .mu.m, can be converted into green light with wavelengths, in particular in the range from 510 nm to 570 nm.

In accordance with at least one embodiment of the laser arrangement, during operation of the semiconductor laser chip, a thermal lens is formed in the latter, via which the primary radiation is focused into the crystal for frequency doubling. For a given pump power, a temperature gradient is formed in the semiconductor laser chip. This temperature gradient leads to a variation of the optical refractive index in a direction parallel to the light exit surface. This refractive index gradient has the effect of a lenticular element, in particular a condenser lens. Through this thermal lens, the primary radiation can be focused in the crystal. Such a thermal lens can eliminate an external lens outside the semiconductor laser chip and increase the doubling efficiency in the crystal.

There is also provided a method of manufacturing a surface emitting semiconductor laser chip. For example, by means of the method, a surface-emitting semiconductor laser chip can be produced, as described in conjunction with one or more of the abovementioned embodiments.

The method comprises the following steps according to at least one embodiment:

Providing a semiconductor laser chip having the first layer sequence and the layer stack, wherein the effective resonator length L of the semiconductor laser chip with a tolerance of at most λ _P / 16 corresponds to an integer multiple of half the primary wavelength λ _P , and

- Reduction of the effective resonator length L of the semiconductor laser chip with a tolerance of at most λ _P / 16 by a value of ((2 N - 1) λ _P ) / 4, where N is a natural number.

The provision of the semiconductor laser chip may include epitaxial growth of the first layer sequence and / or the layer stack on a growth substrate. The epitaxially grown layers can then be transferred from the growth substrate to a support or remain on the growth substrate. The fact that the effective resonator length L corresponds to a multiple of half the primary wavelength λ _P means that the semiconductor laser chip is resonant with respect to the primary wavelength λ _P.

The step of reducing the effective resonator length L follows the provision of

Semiconductor laser chips after. The effective resonator length L is in this case reduced by an odd multiple of the quarter-wavelength primary wavelength λ _P , that is, for example, by λ _P / 4, 3λp / 4, 5λp / 4 and so on. Such a reduction of the effective resonator length L means that the semiconductor laser chip previously resonant with respect to the primary wavelength λ _{P is} now non-resonant, in particular antiphonous.

The manufacturing tolerance in the individual method steps with respect to the respective optical thicknesses of the layers is, according to at least one embodiment, highest λ _P / 32.

By such a method, semiconductor laser chips having a non-resonant or antiresonant resonator effective length L, which are high in efficiency and high in efficiency, can be manufactured effectively and in high yield.

In other words, first a resonant semiconductor laser chip is produced in which the gain is optimized and thus the optical intensity in the layer stack is maximized. In this case, the primary wavelength λ _P lies in particular at the wavelength at which the optical amplification predetermined by the material of the at least one active region has a maximum during laser action. This maximum is in particular at approximately 1055 nm. Subsequently, the thickness of the layer stack is reduced, so that the semiconductor laser chip is, for example, anti-resonant at the primary wavelength λ _P. In particular, the primary wavelength λ _P does not change by reducing the thickness. However, the optical losses in the semiconductor laser chip decrease, since the intensity in the

Reduced semiconductor laser chip and the transmission is reduced by the reflective first layer sequence due to the Fabry-Perot effect. A difference between a resonant and an anti-resonant semiconductor laser chip thus lies in the effective resonator length L.

According to at least one embodiment of the method, before the step of reducing the effective resonator length L, the function of the semiconductor laser chip is tested at the primary wavelength λ _P in the resonant case. A resonantly constructed semiconductor laser chip can, regardless of the reflectivity of the light exit surface, show a laser action, in particular in the case of a light exit surface with a reflectivity> 30% in the case of an air-semiconductor material interface. In the case of a non-resonant or anti-resonant semiconductor laser chip, a light exit surface with a reflectivity of between 2% and 20%, in particular between 7% and 13%, may be required for this purpose. Thus, it is possible in the context of manufacturing early testing of the semiconductor laser chips.

In accordance with at least one embodiment of the method, the step of reducing the effective resonator length L is carried out with the aid of at least one etching stop layer. That is, preferably within the layer stack, there is an etch stop layer at such a position that the etching is automatically terminated at an effective resonator length L corresponding to an odd-numbered multiple of the quarter-wavelength primary wavelength λ _P. All active regions of the layer stack are preferably between the etch stop layer and the reflective first

Layer sequence. By using an etch stop layer, the effective resonator length L can be reduced particularly easily and accurately. In accordance with at least one embodiment of the method, the step of reducing the effective resonator length L is carried out by wet-chemical etching.

According to at least one alternative embodiment of the method, the semiconductor laser chip can also be produced directly, for example by epitaxial growth, as a non-resonant chip. In other words, the layer stack is thus grown such that its thickness is so large that an effective resonator length L results, so that the semiconductor laser chip is non-resonant or anti-resonant with respect to the primary wavelength λ _P. This eliminates the operation of reducing the effective resonator length L. However, testing of the component in production is difficult.

Some fields of application in which surface-emitting semiconductor laser chips or laser arrangements described here can be used are, for example, display devices, illumination devices for projection purposes, headlights, light emitters or else devices for general illumination.

Hereinafter, a surface emitting semiconductor laser chip described herein, a laser arrangement described herein, and a method described herein will be explained in more detail with reference to the drawings with reference to embodiments. The same reference numerals indicate the same elements in the individual figures. However, there are no scale relationships shown, but individual elements can be shown exaggerated for better understanding. Show it :

Figures 1 and 2 are schematic representations of resonant semiconductor laser chips (A) and schematic

Representations of the course of the optical intensity (B, C),

FIG. 3 a schematic representation of a semiconductor laser chip (A) described here, as well as a schematic representation of the intensity profile (B),

FIG. 4 shows a schematic representation of the structure of a semiconductor laser chip described here,

Figures 5 and 6 are schematic representations of the optical intensity profile and the

Refractive index profile for resonant and non-resonant semiconductor laser chips described herein,

Figure 7 is a schematic illustration of

Loss mechanisms with respect to the optical performance of a semiconductor laser chip,

FIG. 8 shows a schematic representation of a Fabry-Perot

Effects as well as amplification in the resonant (A, B) as well as in the anti-resonant case (C, D),

FIG. 9 shows a schematic illustration of a phase disturbance caused by a thermal lens for three different wavelengths (A) and position of the wavelengths with respect to the spectral position a resonance of an underlying semiconductor laser chip (B),

Figure 10 is a schematic representation of the expression of a thermal lens described here

Semiconductor laser chips in response to a maximum temperature in a pumping region for four different reflectivities of a

Light exit surface,

Figure 11 is a schematic representation of a

Embodiment of one described here

Laser arrangement,

Figure 12 is a schematic representation of the output power

(A), the emission wavelength (B) and the optical losses (C) of a semiconductor laser chip described here as a function of the reflectivity of the light exit surface,

13 shows schematic representations of the performance data of a semiconductor laser chip described here with an etalon and with an external resonator,

Figures 14 and 15 are schematic representations of a

Comparison between a resonant and an anti-resonant semiconductor laser chip described herein, and

Figure 16 is a schematic illustration of a

Manufacturing method for a semiconductor laser chip described here. FIG. 1A shows a surface-emitting semiconductor chip 1 which comprises a layer stack 4 with a thickness D. The thickness D is designed such that the semiconductor laser chip 1 is resonant with respect to a primary wavelength λ _{P of} a primary radiation P generated in the layer stack 4. The primary radiation P is symbolized by a thick, arrowed line.

The semiconductor laser chip 1 includes a reflective first layer sequence 2. This consists according to FIG IA in

Essentially from a reflective, metallic layer. A light exit surface 6 of the layer stack 4 is located on the side of the layer stack 4 opposite the layer sequence 2. The light exit surface 6, as well as the first layer sequence 2, at least partially reflectively acts via the refractive index jump between the air surrounding the layer stack 4 and the semiconductor material forming the layer stack 4 for the primary radiation P. As a result of the light exit surface 6 and of the first layer sequence 2, a resonator in the semiconductor laser chip

1 formed. Since the reflective first layer sequence 2 has a metallic design, and thus the primary radiation P has no significant penetration depth into the first layer sequence

2, the thickness D of the layer stack 4 is practically equal to an effective resonator length L of

Semiconductor laser chips 1.

FIG. 1B schematically shows the course of the optical intensity I in a direction x perpendicular to the light exit surface 6. Since the intensity I is proportional to the square of the electric field, the period length with respect to the intensity I is only half the period length of the electromagnetic field. The that is, two maxima with respect to the intensity I are not removed from each other by a whole primary wavelength λ _P , but only half a primary wavelength λ _P. All details of lengths or wavelengths refer in the following to the wavelength occurring in the corresponding medium, unless otherwise described. That is, the refractive index of the medium along the direction of extension of the light must be taken into account. The height of the intensity maxima is approximately the same within the entire layer stack 4.

The semiconductor laser chip 1 according to FIG. 1A is a resonant chip. That is, similar to a Fabry-Perot element are in the case of resonance at the ends of the resonator formed by the light exit surface 6 and first layer 2 thickness D maximum with respect to the optical intensity I. Since outside the layer stack 4, the refractive index is significantly lower as inside, the wavelength on the side facing away from the stack 4 layer of the light exit surface 6 is increased accordingly. The effective resonator length L in this case is equal to the thickness D of the layer stack 4 and is N λ _P / 2, where N is a natural number.

The semiconductor laser chip 1 according to FIG. 2A is likewise a resonant chip. The reflective first layer sequence 2 is here constructed by a sequence of layers with low refractive index 2a alternating with layers with high refractive index 2b. The first layer sequence 2 thus corresponds to a Bragg mirror which is suitable for the

Primary radiation P is highly reflective. The layer stack 4 is again in a resonator, which is formed by the light exit surface 6 and the first layer sequence 2 is. Since the first layer sequence 2 is composed of a plurality of dielectric or semiconducting layers, the primary radiation P has a certain effective penetration depth into the first layer sequence 2. This penetration depth can be estimated as the wavelength λ _P , _{0 of} the primary radiation in vacuum divided by four times the refractive index difference between low refractive index layers 2a and high refractive index layers 2b. When the refractive index of the layers 2a is about 3 and the refractive index of the layers 2b is about 3.5, the refractive index difference is about 0.5. The effective penetration depth is thus approximately 0.5 λ _P , ₀ . If the refractive index of the layer stack 4 is about 3.5, then the effective penetration depth is about 1.75 λ _P. The effective resonator length L corresponds to the sum of the thickness D of the layer stack 4 and the effective penetration depth into the first layer sequence 2. The resonator length L is thus greater than the thickness D of the layer stack 4 in the case of a Bragg mirror as reflective first layer sequence 2.

FIG. 2B shows the schematic curve of the optical intensity I. Along the x-axis, the intensity in the direction away from the layer stack 4 in the first layer sequence 2 decreases approximately exponentially, within the layer stack 4 the intensity I is evenly distributed on average.

FIG. 2C shows an alternative representation of the intensity profile. Here, the vertical dashed line denotes the effective penetration depth into the first layer sequence 2, the vertical dotted line the thickness D of the layer stack 4. Since it is a resonant Semiconductor laser chip 1 acts is located at the light exit surface 6 and at the fictitious point of the effective penetration into the first layer sequence 2, which have the distance L from each other, each a maximum of intensity I. To simplify the illustration, the effective

Penetration depth in the reflective first layer sequence 2 drawn shortened.

The layer stack 4 has three active regions 5. The active regions 5 are positioned at a distance T from one another which corresponds to half the primary wavelength λ _P. All active regions 5 are in regions of maximum intensity I.

FIG. 3A shows an exemplary embodiment of a non-resonant semiconductor laser chip 1. The layer stack 4 has a thickness D or the semiconductor laser chip 1 has an effective resonator length L, so that the semiconductor laser chip 1 is anti-resonant.

FIG. 3B again schematically shows the course of the intensity I along the x-axis. The effective resonator length L is again determined by the thickness D of the layer stack 4 and the effective penetration depth into the first layer sequence 2. The three active regions 5 in FIG

Layer stacks 4 are in maxima of intensity I and λ _P / 2 are spaced from each other. The effective resonator length L is selected so that a minimum of the optical intensity I is present at the light exit surface 6, an intensity maximum at the fictitious point of the effective penetration depth. The effective resonator length L thus corresponds to an odd-numbered, integer multiple of the quarter-wavelength primary wavelength λ _P. The point of effective Penetration depth in the first layer sequence 2 is indicated in Figure 3B by a vertical dashed line, the thickness D of the layer stack 4 by a vertical dotted line.

An embodiment of the surface-emitting, non-resonant semiconductor laser chip 1 is illustrated in FIG. Twenty-six pairs of low refractive index layers 2a and high refractive index layers 2b form the first reflecting layer sequence 2, which is designed as a Bragg mirror. On a main page of the first

Layer sequence 2, the layer stack 4 is applied. The layer stack 4 has barrier layers 16 and four active regions 5 which follow one another alternately. The barrier layers 16 are configured to absorb light of pump radiation R having a wavelength λ _R. About the pump radiation R 16 free electron-hole pairs are formed in the barrier layers. By means of energy relaxation these electron-hole pairs are captured in the active regions 5 designed as quantum wells. By recombination of the electron-hole pairs, the primary radiation P is finally generated. The layer stack 4 is delimited on the side facing away from the first layer sequence 2 by the light exit surface 6.

Optionally, the active areas 5 of

Be braced Verspannungskompensionsschichten 15. Via the strain compensation layers 15, the crystal lattice between barrier layers 16 and active regions 5 can be matched to one another. Likewise, at least one partially reflecting second layer 7 may be applied to the side of the light exit surface 6 facing away from the layer stack 4. The semiconductor laser chip 1 may be based on the gallium arsenide material system. Then, layers of high refractive index of the first layer sequence 2 are GaAs layers, and low refractive index layers 2a are AlAs or AlGaAs-95. AlGaAs-95 means that about 95% of the

Lattice sites of the gallium atoms, with respect to pure GaAs, are replaced by aluminum atoms. The layer thickness of the layers 2a, 2b is in each case one quarter of the primary wavelength λ _P. At an emission wavelength of about 1000 nm and a refractive index of about 4, the respective are

Layer thicknesses of the layers 2a, 2b in the order of 60 nm. The total thickness of the Bragg mirror or the first layer sequence 2 is then about 5 microns. The first layer sequence 2 may be grown on a non-subscribed GaAs substrate.

The barrier layers 16 of the layer stack 4 are made of GaAs and designed to absorb pump radiation R having a wavelength λ _R of approximately 808 nm. The quantum wells constituting the active regions 5 are made of InGaAs having a thickness in the range of 6 nm to 12 nm. The strain compensation layers 15 have a thickness in the range of 15 nm to 30 nm and are made of GaAsP, for example. The thickness of the individual barrier layers 16 in the exemplary embodiment according to FIG. 4 is approximately the same, wherein the layer thicknesses of the first and last barrier layer 16 seen from the first layer sequence 2 may have different thicknesses therefrom, in particular the barrier layer 16 located on the light exit surface 6 a thickness on, so that the

Semiconductor laser chip 1, as shown in Figure 3, anti-resonant and the active region 5 are each in maxima of the optical intensity I. The manufacturing tolerances with respect to individual layers are preferably below 10 nm, in particular at approximately 5 nm. This corresponds approximately to λ _P / 60.

Alternatively, the barrier layers 16 may have increasing thicknesses in the direction of the first layer sequence 2, so that the distances T between individual, adjacent active regions 5 in the direction of the first layer sequence 2 are likewise increased. The active regions 5 can also be arranged in groups. Within a group, the active regions 5 may have the same distances from one another. Toward the first layer sequence 2, the distances between individual, adjacent groups then increase preferentially. By increasing the distances between adjacent active regions 5 or groups in the direction of the first layer sequence 2, it can be compensated for that the pump radiation R is absorbed in the barrier layers 16 in the vicinity of the light exit surface 6, and the intensity of the pump radiation R in the direction toward first layer sequence 2 toward decreases approximately exponentially. To compensate for this effect and, therefore, in each of the

Barrier layers 16 each generates a roughly equal number of electron-hole pairs, the thickness of the barrier layers 16 grows exponentially towards the first layer sequence 2 towards. In order to ensure complete absorption of the pump radiation R, the entire

Layer stack 4 has a thickness D corresponding to a geometric thickness of the order of 2.5 μm.

Si ₃ N _{4 can} serve as the second layer 7. The thickness of the second layer 7, which is designed as an antireflection coating 17, is preferably at values around 100 nm. Since the refractive index of Si ₃ N _{4 is} in the range of 2.0, compared to a refractive index of approximately 3.5 Layer stack 4, a high Auskoppeleffizienz is ensured from the semiconductor laser chip 1.

FIGS. 5A, 5B schematically illustrate two resonant semiconductor laser chips 1. It's the

Refractive index n, see left ordinate axis, and the intensity I plotted, see right ordinate axis, each along a direction x perpendicular to the light exit surface 6. The horizontal arrows indicate which curve refers to which ordinate axis.

At the light exit surface 6, both have

Semiconductor laser chips 1 each have a maximum of the intensity I of the optical power in the operation of the semiconductor laser chip 1. Due to the resonant structure, the intensity I within the semiconductor laser chip 1, in particular within the layer stack 4, is comparatively high. In the direction away from the layer stack 4, the intensity I decreases exponentially within the first layer sequence 2 designed as a Bragg mirror.

According to FIG. 5A, the active regions 5, depicted as regions of increased refractive index, are located in maxima of the standing wave with respect to the intensity I. The active regions 5 thus represent a resonant periodic gain structure, also referred to as resonant periodic gain or RPG.

According to FIG. 5B, the distance between individual adjacent active regions 5 is close to

Light exit surface 6 first constant and then increases in the direction of the first layer sequence 2 out approximately exponentially. Furthermore, a second layer 7 in Form of AntireflexbeSayer 17 in the embodiment of Figure 5B available. The anti-reflection coating 17 has a refractive index of about 1.6.

In the figures 6A, 6B, 6C, the dependence of the intensity I within the stack of layers 4 is illustrated by the resonance condition, the manner of presentation follows 5A 5B _7. FIG. 6A shows a resonant semiconductor laser chip 1. According to FIG. 6B, the wavelength λ _{P of} the primary radiation P is shifted by 6 nm with respect to a resonance wavelength λ _Res . As a result, the intensity I of the light field within the semiconductor laser chip 1 decreases by a factor of approximately 2. With a further shift of the wavelength by 5 nm away from the resonance, ie a wavelength shift of 11 nm with respect to the resonance case, shown in FIG optical intensity I compared to Figure 6B. Compared to a resonant one

Semiconductor laser chip 1, the optical intensity I within the semiconductor laser chip 1 is thus significantly reduced in a non-resonant semiconductor chip 1.

The semiconductor layer stacks 4 illustrated in FIGS. 6A, 6B, 6C can optionally be designed in accordance with FIG. 5B.

Occurring optical losses and loss mechanisms are illustrated in FIG. Here, outside the operation of the semiconductor laser chip 1, its reflectance is measured. A radiation Pm having the wavelength λ _{P of} the primary radiation P is irradiated perpendicular to a semiconductor laser chip 1. Much of the light P _1n is reflected by the semiconductor laser chip 1. This reflected light is designated P _ref i. Part of the radiation P _1n , which in the Semiconductor laser chip 1 penetrates, is absorbed in the layer stack 4, referred to as Ε ^> m _3S . The absorption takes place, for example, at active regions 5, at impurities in the layer stack 4 or at disturbances of the crystal lattice. Part of the radiation is also transmitted through the Bragg mirror, which forms the reflective first layer sequence 2. This radiation _{component is} marked Pτ _ran.s. In particular, the radiation components Pτ _r ans and, at least partially, P s contribute to the optical power loss. If P _{1n is} known and P _Rβf i is measured, the sum of PAb ₃ and P _T r _a ns can be determined. The quotient P _Re fi / Pin is a reflectivity R of the semiconductor laser chip 1.

The losses due to the absorption in the layer stack 4 are approximately proportional to the optical intensity I in the layer stack 4. Therefore, these losses are reduced, in which the optical intensity I in the layer stack 4 is reduced, as is done by an anti-resonant structure of the semiconductor laser chip 1 ,

Another loss mechanism based on the Fabry-Perot effect and the transmitted light power P _Tr ans is illustrated in FIG. In FIG. 8A, the

Reflectance p of the semiconductor laser chip 1, with unpumped semiconductor laser chip 1, as a function of the wavelength λ applied. The reflectivity p has values of more than 98% in a spectral range from approximately 1010 nm to approximately 1090 nm. This spectral region corresponds to the spectral reflection width of the first layer sequence 2. At the center of this region at approximately 1050 nm, corresponding to the primary wavelength λ _P , there is a minimum at which the

Reflectance p drops well below 99%. This minimum is due to the Fabry-Perot effect in the resonant case in which the effective resonator length L is an integer multiple of λ _P / 2.

A corresponding representation in the case of an anti-resonant semiconductor laser chip 1 is illustrated in FIG. 8C. In order to ensure comparability, the optical losses due to absorption in the layer stack 4 are the same in each case in FIGS. 8A and 8C. In the range around 1050 nm there is a spectrally broad maximum of the reflectivity p. The reflectivity p here has values of well over 99% and is therefore significantly higher at this wavelength than in the case of a resonant semiconductor laser chip 1 according to FIG. 8A. That is, the optical losses due to the Fabry-Perot effect are reduced from about 1.2% in the resonant case to about 0.6% in the anti-resonant case. These optical losses are thus approximately halved.

FIG. 8B shows the reflectivity p with respect to the wavelength λ during operation of the semiconductor laser chip 1. In the area of the resonant wavelength λ _Res of 1050 nm, a clear maximum is shown. Due to the gain in the layer stack 4, the reflectivity p appears higher than 1 and is about 1.03 or 103%.

In the anti-resonant case, as can be seen in FIG. 8D, the maximum of the reflectivity p in the case of a gain is lower, at approximately 1.016, and significantly broader in spectrometry.

Thus, both the gain and the optical losses are reduced in the anti-resonant case. If the reduced gain in the anti-resonant case is sufficient for the operation of the semiconductor laser chip 1, then the anti-resonant Configuration more efficient due to the reduced optical losses. The parameter reflectivity p and thus the optical losses are particularly relevant in particular in laser arrangements or semiconductor laser chips 1, which have an external resonator in which only a low light output is coupled out per revolution. In other words, in such an external resonator, the light often passes through the external resonator, is often reflected on the semiconductor laser chip 1 and, in particular, the losses due to transmission through the first layer sequence 2 come to fruition. Such an external resonator with a low decoupling rate is used, for example, to frequency-double near-infrared radiation to ensure a high intensity within the external resonator and thus to increase the power of doubled light, since the doubling is an optically non-linear process.

Due to absorption of the primary radiation P in the layer stack 4 and due to absorption of the shorter wavelength pump radiation R, the semiconductor laser chip 1 is heated in the regions in which the pump radiation R is absorbed and the primary radiation P is generated. As a result, a temperature distribution is formed in the semiconductor laser chip 1. The temperature inside the pumped semiconductor region is highest here, in the edge regions the temperature decreases. Due to this temperature gradient, a thermal lens is formed, since the refractive index of the semiconductor material depends on the temperature. This means that in the center of the pumped area the refractive index is greater than at the edge areas. This corresponds to a condenser lens. Since the absorption of primary radiation P is approximately proportional to the optical Intensity I of the primary radiation P in the semiconductor laser chip 1, the thermal lens is more pronounced, the higher the optical intensity I in the semiconductor laser chip 1.

This is illustrated in Figure 9A. In FIG. 9A, the radial position r in micrometers is plotted against the phase disturbance q in radians. The thermal power deposited in the semiconductor laser chip 1 is assumed to be 1 W according to FIG. 9A, the diameter of the pumping beam R is approximately 100 μm. The curve marked M corresponds to a spherical mirror with a radius of curvature of 10 mm. This spherical mirror serves as a reference. In the case of a resonant wavelength at 1054 nm corresponds to the expression of the thermal lens at radial positions r up to about 50 microns in a good approximation of such a mirror. Spectrally distant from a resonant wavelength, for example, at 1060 nm and 1065 nm, the effect of the thermal lens, recognizable by the flatter course of the corresponding curves, decreases sharply.

In FIG. 9B, the reflectivity R is plotted against the wavelength λ. The wavelengths shown in FIG. 9A are symbolized by vertical arrows in FIG. 9B. The shape of the reflectivity curve is similar to that shown in FIG. 8B.

The expression of the thermal lens is also dependent on how strong the light exit surface has a reflective effect on the primary radiation P, as explained in more detail in FIG. In FIGS. 10A to 10D, the wavelength λ is plotted against a maximum temperature t occurring in a pumping region. Grayscale coded and marked with profile lines are the respective focal lengths entered the thermal lens. The smaller the value for the focal length, the stronger the thermal lens is pronounced. In all four sub-figures 10A to 10D it can be seen that the thermal lens is more pronounced at a certain wavelength λ with increasing temperature t.

According to FIG. 10A, the light exit surface 6 has no

Reflectivity, the reflectivity is thus exactly at 0%. Due to this, the expression of the thermal lens is almost independent of the wavelength λ, since the semiconductor laser chip 1 in the case of a vanishing reflectivity at the light exit surface 6 has no internal resonator, and thus no resonance or anti-resonance condition can be adjusted. For temperatures t in the range of 360 K, the focal length of the thermal lens is approximately 45 mm.

According to FIG. 10B, the light exit surface 6 has a reflectivity of 2%. This corresponds to one

Reflectivity, which has a semiconductor laser chip 1 with an optimized, single-layer antireflection coating 17. Since a resonator-like structure is formed via the finite reflectivity of the light exit surface 6 together with the first layer sequence 2, resonance and anti-resonance conditions are also fulfilled as a function of the wavelength λ. The resonance condition in which the effective resonator length L of the internal resonator of the semiconductor laser chip 1 formed by the light exit surface 6 and first layer sequence 2 is a multiple of half

Wavelength of the primary wavelength λ _P , the thickness of the thermal lens has a maximum. That is, at already a relatively low temperature t of about 340 K a focal length of 50 mm is achieved. In the anti-resonant case, at about 1030 nm and 1080 nra, this strength of the thermal lens is reached only at about 375 K.

The wavy curve of the thickness of the thermal lens substantially follows the intensity curve as a function of the wavelength λ in the semiconductor laser chip 1. This illustrates once again that the intensity I in the semiconductor laser chip 1 is highest in the resonant case and lowest in the anti-resonant case.

In FIG. 1C, the reflectivity of the light exit surface 6 is approximately 5%. The with respect to the wavelength λ oscillating expression of the thermal lens is therefore enhanced. Due to the higher reflectivity of the light exit surface 6, the intensity I in the semiconductor chip is reduced in the anti-resonant case and increased in the resonant case. Therefore, the effect of the thermal lens is also reduced at the anti-resonant wavelengths as compared to FIG. 10B.

According to FIG. 10D, the reflectivity of the light exit surface corresponds to 30%. This corresponds to a semiconductor laser chip 1 which has no second layer 7. Here the oscillating course of the effect of the thermal lens is most pronounced. In the anti-resonant case, the optical intensity I in the semiconductor laser chip 1 is further reduced with respect to lower reflectivities of the light exit surface 6. The shift of the sinusoidal wave-like structure towards a sawtooth-like structure is also due to a temperature effect. This shift with increasing temperature depends on the increasing Temperature also increasing refractive index together, causing the resonances and anti-resonances shift to larger wavelengths λ out.

FIG. 11 shows a laser arrangement 100 with a surface-emitting semiconductor laser chip 1. The semiconductor laser chip 1 is applied to a substrate 10. For example, a heat sink and a mechanically stable mounting surface can be realized via the substrate 10. The semiconductor laser chip 1 is optically pumped by a pump light source 13, which emits the pump radiation R, symbolized by a thin arrow line. The wavelength λ _{R of} the pump radiation is approximately 808 nm. The primary radiation P, symbolized by a thick arrow line, is emitted by the semiconductor laser chip 1. The emission of the primary radiation P is approximately perpendicular to the light exit surface 6 of the semiconductor laser chip 1, the coupling of the pump radiation R takes place at an angle of approximately 45 °. With regard to the primary radiation P, the semiconductor laser chip 1 and two mirrors 8a, 8b constitute an external resonator of the laser arrangement 100. Both mirrors 8a, 8b are highly reflective of the primary radiation P. The first mirror 8a transmits the primary radiation P in the direction of a doubling crystal 12 in the doubler crystal 12 partly in a secondary radiation S with a secondary wavelength λ _s «λ _P / 2, symbolized by an arrow-dashed line, converted. Subsequently, both converted S and primary radiation P strike the second mirror 8b and are reflected back towards the first mirror 8a. On the way back, another part of the primary radiation P is converted into the secondary radiation S. The first mirror 8a is transmissive to the Secondary radiation S, so that it is coupled out of the external resonator.

Optionally, the external resonator of the laser arrangement 100 may comprise a wavelength-selective element 11, which is designed, for example, as an etalon. Via the wavelength-selective element 11 it is also possible that the polarization of the primary radiation P is adjusted.

FIG. 12 shows the optical power of the primary radiation P, the emission wavelength λ _Em and the optical losses O _L in the semiconductor laser chip 1 as a function of the power of the pump radiation R for different reflectivities of the light exit surface 6. The respective curves, denoted by the respective reflectivity at the

Light exit surface 6 in%, are simulations for the case of a laser array 100, which in addition to the surface emitting semiconductor laser chip 1 has an external mirror 8, which has a reflectivity of 99% and corresponding to 1% of the primary radiation P from the laser array

100 decoupled. The simulated laser array 100 has no doubling crystal and no wavelength-selective element. The semiconductor laser chip 1 is an anti-resonant chip. The individual curves are each marked with the percentage of the reflectivity of the light exit surface 6.

According to FIG. 12A, compared to the power of the pump radiation R, the power of the primary radiation P decoupled from the laser arrangement 100 is plotted. At a high reflectivity of the light exit surface 6, the laser threshold is exceeded only at higher powers of the pump radiation R, so that the individual curves with increasing reflectivity of the Light exit surface 6 only begin at higher pump powers. The slope of the curves, up to a critical maximum value of the power of the pump radiation R, a maximum value at a reflectivity of the light exit surface 6 of about 10%. Thus, at least for pump powers in the range greater than about 0.8 W, a reflectivity of about 10% is a preferred value.

In FIG. 12B, the emission wavelength λ _{Em is} plotted relative to the power of the pump radiation R. The respective curves vary by a few nanometers. With a reflectivity of the light exit surface 6 of 30%, the emission wavelength λ _Em deviates significantly.

In FIG. 12C, in percent, the optical losses O _L in the semiconductor laser chip 1 are plotted against the power of the pump radiation R. With a reflectivity of the light exit surface 6 of approximately 10%, the optical losses are the lowest. A reflectivity of

Light emission surface of about 10% is also a preferred value with respect to this aspect.

With a reflectivity in the range of approximately 10%, therefore, there is an efficient coordination between the optical losses and the optical intensity in the semiconductor laser chip 1, and thus the gain.

If the reflectivity of the light exit surface 6 is relatively high, for example 30%, there is the possibility that the semiconductor laser chip 6, without additional measures, independently changes from an anti-resonant wavelength to a resonant wavelength, see FIG. 12B. These Possibility is given in particular, since the gain bandwidth of the gain medium or the active regions 5 and the spectral width of the reflectivity of the first layer sequence 2 can be up to 80 nm. In this approximately 80 nm wide

Spectral range is therefore in principle possible laser action.

If, for example, the effective resonator length L is 10.25 λ _P in the anti-resonant case, this could correspond, for example, to 10 λ _{Res of} the resonant wavelength λ _Res . The wavelength difference between λ _P and λ _Res would then, at a wavelength λ _P of approximately 1050 nm, be only approximately 30 nm. In other words, both the anti-resonant wavelength λ _P and the resonant wavelength λ _Res in the gain range are related to the laser action , The jumping from an anti-resonant to a resonant wavelength is favored, in particular, by the fact that the amplification is higher in the resonant case than in the anti-resonant case.

In order to prevent such a jumping of the wavelength at which the laser action takes place, as shown in FIG. 11, a wavelength-selective element 11 may be incorporated in the external resonator of the laser arrangement 100. This wavelength-selective element 11 can be transmissive for an anti-resonant wavelength λ _P , and at the same time for resonant wavelengths λ _{Res /} which lie in the gain region of the layer stack 4, have a blocking effect. "Blocking" here means that the transmission is for resonant

Wavelength λ _Res is a few percent below the transmission for anti-resonant wavelengths λ _P. For example, the transmission with respect to the wavelength λ _{P is} more as 99.9%, and the transmission with respect to the wavelength λ _Res less than 96%. Such an arrangement effectively suppresses jumping from an anti-resonant wavelength λ _P to a resonant wavelength λ _Res .

The effect of a wavelength-selective element 11 is illustrated in FIG. FIG. 13A shows the pumping power of the pump radiation R with respect to the power of the primary radiation P of a laser arrangement 100, for example as shown in FIG. In the case of a free-running laser of an anti-resonant arrangement, the semiconductor laser chip 1 automatically falls during operation to a resonant wavelength λ _Res of about 1032 nm, see FIG. 13B. As a result, the efficiency is significantly reduced, see Figure 13A. In the case of a wavelength-selective element 11 located in the external resonator of the laser arrangement 100, shown in the curve marked E, this effect does not occur and the power of the primary radiation P is clear at powers of the pump radiation R above approximately 0.5 W. higher.

FIG. 13B shows the wavelength-stabilizing property of the wavelength-selective element 11. The primary wavelength λ _P remains the same over the entire range of the pump power of the pump radiation R.

As a result, as shown in FIG. 13C, the optical losses O _L given in percent are also markedly reduced compared to a free-running operation without a wavelength-selective element 11.

In Figure 14, in percent, the optical losses O _{L of} a resonant semiconductor laser chip and an anti-resonant Semiconductor laser chips 1 compared to each other. The curve with respect to the resonant semiconductor laser chip is labeled "Res." Both semiconductor laser chips 1 have a resonant periodic amplifier structure, RPG for short, with six quantum wells. 3%, only 0.16% in the case of the anti-resonant semiconductor laser chip 1. The optical losses O _L are therefore almost halved due to the anti-resonant design of the semiconductor laser chip 1, the efficiency of which is significantly increased.

In Fig. 15, simulated performance data shown in Fig. 15B is compared with measured data shown in Fig. 15A. Simulation and calculation are in good agreement. Compared to a resonant semiconductor laser chip, the anti-resonant semiconductor chip 1 has an approximately 25 to 30% improved performance of the primary radiation P at a pump power of approximately 1.4 W. The measured values were determined using an external resonator with a length of 25 mm and an external mirror 8 with a reflectivity of 99.7%.

Due to the reduced intensity in the semiconductor laser chip 1 and because of the avoidance of the Fabry-Perot losses in the antiresonant case, therefore, the efficiency of an anti-resonant semiconductor laser chip 1 compared to a resonant semiconductor laser chip is significantly increased.

FIG. 16 schematically shows a production method for a non-resonant, surface-emitting

Semiconductor laser chip 1 shown. According to FIG. 16A, the layer stack 4 comprises three active regions 5 as well as an etching stop layer 18. The effective resonator length L corresponds an integer multiple of half the primary wavelength

FIG. 16B shows that the irradiation of the pump radiation R of the semiconductor laser chip 1 is tested. This test allows to determine at an early stage in the manufacturing process whether the

Semiconductor laser chip 1 is a functional device. This reduces rejects in later process steps and reduces manufacturing costs.

In the method step according to FIG. 16C, the effective resonator length L is reduced by an etching process up to an etch stop layer 18 until it is an anti-resonant semiconductor laser chip. The thickness by which the layer stack 4 is reduced in this case is an odd multiple of λ _P / 4.

According to FIG. 16D, a second layer 7 in the form of an antireflection layer 17 can optionally subsequently be applied, via which the reflectivity of the light exit surface 6 of the layer stack 4 can be adjusted in a targeted manner.

The invention described here is not by the

Description limited to the embodiments. Rather, the invention encompasses any novel 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 the exemplary embodiments. This patent application claims the priority of German Patent Application 10 2008 038 961.7, the disclosure of which is hereby incorporated by reference.

Claims

claims

1. Surface emitting semiconductor laser chip (1) with

a first layer sequence (2) which is reflective for a primary radiation (P) with a primary wavelength λ _P , and

a layer stack (4) having at least one active region (5), wherein the layer stack (4) is applied to a main side of the first layer sequence (2) and configured to emit the primary radiation (P), wherein a thickness (D) the layer stack (4) is designed so that this non-resonant with respect to

Primary wavelength λ _P is.

2. A surface emitting semiconductor laser chip (1) according to claim 1, which has an effective resonator length L, so that for the effective resonator length L with a tolerance of at most λ _P / 8:

where N is a natural number.

3. The surface emitting semiconductor laser chip (1) according to claim 2, wherein the tolerance for the effective resonator length L is at most λ _P / 16.

4. The surface emitting semiconductor laser chip (1) according to claim 1, wherein the thickness (D) of the layer stack (4) is so is configured such that the layer stack (4) is anti-resonant with respect to the primary wavelength λ _P.

5. Surface emitting semiconductor laser chip (1) according to one of the preceding claims, wherein at a light exit surface (6) of the layer stack (4) facing away from the first layer sequence (2), during operation of the semiconductor laser chip (1) no intensity maximum of the primary radiation (P ) is present.

6. Surface-emitting semiconductor laser chip (1) according to one of the preceding claims, wherein at least one distance (T) between two adjacent active regions (5) is a multiple of

Half of the primary wavelength λ _P and wherein at least one active region (5) is in operation of the semiconductor laser chip (1) in an intensity maximum of the primary radiation (P), and in at least one case, the distances (T) between adjacent active regions (5) increase towards the first layer sequence (2).

7. Surface emitting semiconductor laser chip (1) according to any one of the preceding claims, comprising at least one second layer (7) which is attached to the light exit surface (6) of the layer stack (4) and for the primary radiation (P) is partially reflecting.

8. Surface emitting semiconductor laser chip (1) according to claim 7, wherein the reflectance of the at least one second Layer (7) for the primary radiation (P) is between 2% and 20%.

9. laser arrangement (100) with - at least one surface emitting

Semiconductor laser chip (1) according to one of the preceding claims,

- at least one pumping light source (13) for pumping the semiconductor laser chip (1), and - with at least one external, for the primary radiation (P) reflective acting mirror (8), so that of the first layer sequence (2) and the at least one mirror (8 ) a resonator (9) is formed.

10. Laser arrangement (100) according to claim 9 with a surface-emitting semiconductor laser chip (1) according to

Claim 8, wherein the resonator (9) is a wavelength selective

Comprises element (11).

11. Laser arrangement (100) according to claim 10, wherein the wavelength-selective element (11) in one

Wavelength range from 0.8 λ _P to 1.2 λ _P blocking acts for wavelengths λ _Res , for which applies with a wavelength tolerance of at most λ _P / l6 with respect to the effective resonator length L of the semiconductor laser chip (1):

λ _res = (2 L) / N,

where N is a natural number.

12. A method for producing a surface emitting semiconductor laser chip (1) according to any one of claims 1 to 9, comprising the steps of:

- Providing a semiconductor laser chip (1) with the first layer sequence (2) and the layer stack (4), wherein the effective resonator length L of the semiconductor laser chip (1) with a tolerance of at most λ _P / l6 an integer multiple of half the primary wavelength λ _P corresponds , and - reducing the effective resonator length (L) of the semiconductor laser chip (1) with a tolerance of at most λ _P / 16 by a value of ((2 N-1) λ _P ) / 4, where N is a natural number.

13. The method of claim 12, wherein before the step of reducing the effective resonator length L, the function of the semiconductor laser chip (1) at the primary wavelength λ _{P is} tested.

14. The method of claim 12 or 13, wherein the step of reducing the effective resonator length L by means of at least one Ätzstoppschicht takes place.

15. The method of claim 12, wherein the step of reducing the effective resonator length L is via wet chemical etching.