DE102008017268A1 - Surface-emitting semiconductor laser with monolithically integrated pump laser - Google Patents

Abstract

The invention relates to a surface emitting semiconductor laser comprising a semiconductor body (10) having an active zone (1) with a quantum well structure, the quantum well structure comprising a plurality of quantum wells (2) each formed of a quantum well layer (3) arranged between barrier layers (4) , and a pump laser (6) integrated monolithically into the semiconductor body (10) and emitting pump radiation for optically pumping the active zone (1). In this case, the pump radiation forms a mode profile (21) in the semiconductor body (10) and the quantum wells (2) are spaced apart such that they are each arranged in the region of a maximum (22) of the mode profile (21) of the pump radiation.

Description

The The invention relates to a surface-emitting semiconductor laser, in which a pump laser for optically pumping the active zone of the surface emitting semiconductor laser monolithic is integrated in the semiconductor body.

A surface Semiconductor lasers are also referred to as VCSELs (Vertical Cavity Surface Emitting Laser) or in the version with external resonator as VECSEL (Vertical External Cavity Surface Emitting Laser). Such surface emitting semiconductor lasers contain a vertical emitter region, typically through a quantum well structure is formed, wherein the vertical emitter region by optical Pumps or electric pumps for emitting laser radiation is stimulated.

From the pamphlets DE 10260183 A1 and DE 102004024611 A1 Optically pumped surface emitting semiconductor lasers are known in which the quantum well structure of the vertical emitter is optically pumped in each case with an external pump radiation source which is arranged outside the semiconductor chip and irradiates the pump radiation at an angle into the semiconductor body. In these embodiments of a surface-emitting semiconductor laser, it is known to arrange a reflector for the pump radiation on a rear side of the semiconductor body opposite the external pump radiation source, so that the semiconductor body forms a resonator for the pump radiation, in which a standing wave of the pump radiation is formed. By suitably adjusting the wavelength and the angle of incidence of the pump laser as well as the arrangement of the quantum well layers, it can be achieved that the quantum well layers are arranged in the maxima of the standing wave of the pump radiation field in order to achieve a high pumping efficiency of the quantum well layers.

From the pamphlets WO 01/93386 A1 and WO 2005/048424 A1 In each case, optically pumped surface-emitting semiconductor lasers are known in which the optical pumping of the quantum well structure of the vertical emitter is not effected by an external pump radiation source but by a pump laser monolithically integrated in the semiconductor body. In these embodiments, in each case an edge emitting pump laser is grown together with the vertical emitter on a common growth substrate, wherein the active layer of the vertical emitter and the pump laser can be arranged side by side, so that the pump radiation is irradiated directly in the lateral direction in the active zone, or be arranged one above the other can, wherein the pump radiation similar to the coupling of two waveguides in the active zone of the vertical emitter can couple.

Also in optically pumped surface emitting semiconductor lasers would be monolithically integrated pump radiation source It is desirable to have an optimal overlap between the pump radiation field and the quantum well layers of the vertical emitter to achieve. In contrast to the embodiments with External pump radiation source can be used in surface emitting semiconductor lasers with monolithic integrated pump radiation source not by a back reflector and a variation of the angle of incidence the pump radiation source, a pump resonator are generated, the Standing wave field to the arrangement of the quantum well layers in the Quantum well structure of the vertical emitter is adjusted. This is not possible because the emission of the pump radiation under a fixed angle of 90 ° to the emission direction of the vertical emitter takes place and thus in particular the parameter of the angle of incidence the pump radiation in the semiconductor body does not vary can be. Thus, that of surface emitting Semiconductor lasers with external pump radiation sources known optimization the overlap between the pump radiation field and the quantum well layers by means of a vertical pump resonator not readily on surface emitting Semiconductor laser with monolithically integrated pump radiation source transferred to.

Of the Invention is based on the object, a surface-emitting Semiconductor laser with monolithically integrated pump radiation source indicate that there is an improved overlap between the Pump radiation field and the quantum well layers of the surface emitting Semiconductor laser is achieved.

These The object is achieved by a surface-emitting semiconductor laser solved with the features of claim 1. advantageous Embodiments and developments of the invention are the subject the dependent claims.

One Surface emitting according to the invention Semiconductor laser includes a semiconductor body, the an active zone having a quantum well structure, wherein the quantum well structure contains several quantum well layers, each between barrier layers are arranged, and a monolithic in the semiconductor body integrated pump laser, the radiation for optical pumping of the active Zone emitted, wherein the pump radiation is a mode profile in the semiconductor body forms and the quantum well layers so spaced apart are that they are each within the range of a maximum of the fashion profile the pump radiation are arranged.

Under the arrangement of a quantum well layer in the region of a maximum the mode profile of the pump radiation is within the scope of the application Understand that the pump radiation is at the location of the quantum well layer at least 70% of the intensity of the maximum, preferably at least 90% of the intensity of the maximum.

The Invention makes use of the knowledge that at one Emission of the pump radiation perpendicular to the emission direction of the active zone of the surface emitting semiconductor laser by a monolithically integrated in the semiconductor body pump radiation source forms a mode profile of the pump radiation, the maxima in the range of active zone of the surface emitting semiconductor laser having. Under the mode profile of the pump radiation is doing the Intensity curve in the semiconductor body spreadable pump waves understood.

The Location of the maxima of the fashion profile may be due to a suitable design the layer structure of the semiconductor body influenced and in particular be chosen so that the position of the maxima with the positions of the quantum wells of the active zone of the surface emitting Semiconductor laser matches. This will be a high Pump efficiency and thus a high efficiency of the surface-emitting Achieved semiconductor laser.

Of the Distance of the maxima of forming in the semiconductor body Mode profile of the pump radiation depends in particular on the Wavelength of the pump radiation and of the layer thicknesses and refractive indices of those contained in the semiconductor body Semiconductor layers from. An arrangement in which the quantum wells each arranged in a maximum of the mode profile of the pump radiation are, by a simulation calculation under variation of this Parameters are found out.

The Quantum wells are each made up of a quantum well layer, formed between barrier layers are formed, wherein the barrier layers a larger electronic Have bandgaps than the quantum well layers. Prefers the quantum wells are spaced apart by spacer layers. The thickness of the spacer layers is dependent of the wavelength of the pump radiation and the layer thicknesses and refractive indices of the semiconductor layers in the semiconductor body optimized so that the quantum wells each in the area a maximum of the mode profile of the pump radiation are arranged. The distance between adjacent quantum wells is therefore preferably the same the distance between two maxima of the mode profile of the pump radiation or a multiple of it.

Advantageous forms that of the active zone of the surface emitting Laser laser emitted a standing wave in the semiconductor body, wherein the quantum wells are arranged such that they each in the range of a maximum the standing wave of the laser radiation are arranged. This is in doubt to understand that the laser radiation of the surface emitting Semiconductor laser at the location of the respective quantum well layer at least 70% of the intensity of the maximum, preferably at least 90% of the intensity of the maximum. The distance between adjacent quantum wells is therefore preferably equal to the distance between two maxima of the stationary Wave of laser radiation or a multiple of it. As a result of that the quantum wells each in a maximum of the standing Wave of the laser radiation are arranged, the laser radiation resonant due to the radiation emission of the quantum wells strengthened. The active zone of the surface-emitting Semiconductor laser thus provides a RPG structure (resonant periodic gain) represents.

at In a preferred embodiment, the quantum wells are arranged in several groups, the distances of the Quantum wells within the groups are lower than those Distances of neighboring groups. This execution based on the fact that the quantum wells usually a low compared to the period of the mode profile of the pump radiation Thickness, so that it is possible to use several quantum wells to be arranged in the region of a maximum of the mode profile of the pump radiation.

In order to each of the groups of quantum wells in the range of a maximum the mode profile of the pump radiation is arranged, is the distance adjacent groups preferably equal to the distance between two maxima the mode profile of the pump radiation or a multiple thereof.

Advantageous forms that of the active zone of the surface emitting Laser laser emitted a standing wave in the semiconductor body, wherein the groups of quantum wells are arranged such that they each in the range of a maximum the standing wave of laser radiation of the surface emitting Semiconductor laser are arranged. Because of the groups of Quantum wells each in a maximum of the standing wave the laser radiation are arranged, the laser radiation is through the radiation emission of the quantum wells resonantly amplified. The active zone of the surface emitting semiconductor laser thus represents a RPG structure (resonant periodic gain).

The spacing of adjacent groups of quantum wells is preferably equal to the distance between two maxima of the standing wave of the laser beam or a multiple thereof. In this way it can be achieved that the groups of quantum wells are arranged not only in the maxima of the pump radiation, but also in the maxima of the standing wave of the laser radiation.

The Number of quantum wells in the groups of quantum wells is preferably between 2 and including 4.

All in all is the number of quantum wells in the quantum well structure the active zone preferably between 5 inclusive and including 25.

The invention will be described below with reference to embodiments in connection with 1 to 6 explained in more detail.

It demonstrate:

1 FIG. 2 shows a schematic illustration of a cross section through a surface-emitting semiconductor laser according to a first exemplary embodiment of the invention, FIG.

2 a schematic representation of a cross section through the active zone of another embodiment of a surface emitting semiconductor laser according to the invention,

3 a schematic representation of the refractive index profile and the fundamental mode of the pump radiation in a semiconductor body which contains no active zone of a surface emitting semiconductor laser,

4 a schematic representation of the refractive index profile and the mode profile of the pump radiation in a semiconductor body of a surface emitting semiconductor laser according to the invention,

5 schematic representations of the active region of the surface emitting semiconductor laser, the intensity of the mode profile of the pump radiation in the active region of the surface emitting semiconductor laser and the absorption of the quantum wells in an embodiment of a surface emitting semiconductor laser according to the invention, and

6 schematic representations of the active surface of the surface emitting semiconductor laser, the intensity of the mode profile of the pump radiation in the active region of the surface emitting semiconductor laser and the absorption of the quantum wells in a conventional surface emitting semiconductor laser.

Same or equivalent components are in the figures each with provide the same reference numerals. The illustrated components as well as the size ratios of the components among themselves are not to be regarded as true to scale.

This in 1 illustrated embodiment of a surface emitting semiconductor laser includes a semiconductor body 10 , which is an active zone 1 of the surface emitting semiconductor laser and a pump laser 6 for optical pumping of the active zone 1 having. The pump laser 6 is monolithic in the semiconductor body 10 the surface emitting semiconductor laser integrated and in particular part of the Epitaxieschichtenfolge which the active zone 1 and the pump laser 6 includes.

The semiconductor body 10 has a substrate 11 which is preferably an electrically conductive substrate, in particular an n-doped substrate. For example, the substrate 11 an n-doped GaAs substrate.

On the substrate 11 can have one or more buffer layers 12 be applied, in particular to obtain a low defect density and / or a good lattice matching to the subsequently grown epitaxial layers.

The substrate 11 with the buffer layer applied thereon 12 follows a DBR mirror 13 after having a first resonator mirror for that of the active zone 1 of the surface emitting semiconductor laser emitted laser radiation 15 formed. The DBR mirror 13 is formed by a plurality of alternating layers which differ in their refractive index. The number of alternating layer pairs can be, for example, about 30 be. In this way, a high reflection for the laser radiation 15 achieved. The alternating layers of the DBR mirror 13 are preferably n-doped. For example, the DBR level 13 comprise alternating layers of n-doped AlGaAs layers and n-doped GaAs layers.

The second resonator mirror of the surface emitting semiconductor laser is outside the semiconductor body 10 arranged external resonator mirror 14 , The exemplary embodiment is therefore an external cavity surface emitting semiconductor laser (VECSEL).

Alternatively, the surface emitting semiconductor laser may be used in place of the external resonator mirror 14 also on the substrate 11 opposite surface of the semiconductor body 10 have applied second DBR mirror (not shown). Such an embodiment of an upper surface emitting semiconductor laser is referred to as VCSEL.

The DBR mirror 13 follows in the growth direction of the semiconductor body 10 the pump laser 6 to. The pump laser 6 has an active layer 7 on, in the lateral direction, ie perpendicular to the emission direction of the laser radiation 15 the active zone 1 of the surface emitting semiconductor laser. The active layer 7 of the pump laser 6 is between waveguide layers 8th arranged, respectively on shell layers 9 adjoin. In this way, a waveguide for the pump radiation is formed. At least part of the pump laser 6 emitted pump radiation, located in the waveguide of the pump laser 6 can be used for optical pumping of the surface emitting semiconductor laser in the active zone 1 overcouple. Transfer of radiation from the pump laser 6 into the active zone 1 takes place similar to the coupling of two waveguides. In this case, constructive and destructive interference of the modes of the pump radiation capable of propagating in the semiconductor body leads to a periodic energy transfer between the pump laser 6 and the active zone 1 of the surface emitting semiconductor laser. Between the pump laser 6 and the active zone 1 of the surface emitting semiconductor laser is preferably a coupling layer 16 arranged, whose thickness and refractive index is set such that in the waveguide of the pump laser 6 in the lateral direction propagating pump radiation in the active zone 1 of the surface emitting semiconductor laser can pass.

The pump laser 6 is electrically excited to emit pump radiation. A first electrical contact 17 for the pump laser 6 for example, on the of the active zone 1 remote from the back of the substrate 11 be arranged. To a p-contact 18 for the pump laser 6 to arrange, is the semiconductor body 10 preferably from the substrate 11 opposite surface to a region below the active zone 1 of the surface emitting semiconductor laser etched down. The p-contact 18 of the pump laser 6 For example, on the coupling layer 16 be upset. Preferably, the p-contact layer 18 around a layer of a transparent conductive oxide, for example around a ZnO layer.

The active zone 1 of the surface emitting semiconductor laser is in the semiconductor body 10 above the coupling layer 16 arranged. In particular, to protect against oxidation, the active zone 1 with a cover layer 19 be provided.

The active zone 1 of the surface emitting semiconductor laser has a quantum well structure comprising a plurality of quantum wells 2 contains. To simplify the illustration are in 1 only four quantum wells 2 shown. A preferred number of quantum wells is between 5 and 25 inclusive. The quantum wells 2 each through a quantum well layer 3 formed between barrier layers 4 is arranged, wherein the barrier layers 4 have a larger electronic bandgap than the quantum well layers 3 ,

The quantum wells 2 are each arranged in the region of a maximum of the mode profile of the pump radiation. The positions of the maxima of the mode profile of the pump radiation in the semiconductor body 10 depend in particular on the wavelength of the pump radiation, as well as on the refractive indices and layer thicknesses above the pump laser 6 arranged semiconductor layers. Optimal positioning of the quantum wells 2 such that they are each arranged in the region of a maximum of the mode profile of the pump radiation can be found on the basis of simulation calculations. The quantum wells 2 are advantageous by spacer layers 5 spaced apart, the thickness of the spacer layers 5 is chosen so that the positions of the quantum wells 2 coincide with the maxima of the mode profile of the pump radiation.

The laser radiation emitted by the surface emitting semiconductor laser 15 forms in the semiconductor body 10 advantageously a standing wave. The quantum wells 2 are preferably arranged such that they are in the maxima of the standing wave of the laser radiation 15 are arranged. The active zone 1 of the surface emitting semiconductor laser forms in this way an RPG (resonant periodic gain) structure. Furthermore, the quantum wells 2 advantageously arranged such that they are additionally in the maxima of the mode profile of the pump radiation. By this arrangement of quantum wells 2 This results in effective pumping of all quantum wells 2 ,

A preferred embodiment of the active zone 1 of the surface emitting semiconductor laser is in 2 shown. The active zone 1 contains a quantum well structure, where the quantum wells 2 in several groups 20 are arranged. Each of the groups 20 contains two quantum wells 2 , The distances of the quantum wells 2 within the groups 20 are smaller than the distances of the groups 20 of quantum wells 2 , The distances of the quantum wells 2 within the groups 20 and the distances of the groups 20 of quantum wells are preferably by spacer layers 5 set. The groups 20 of quantum wells 2 are advantageously arranged such that each group 20 in the region of a maximum of the mode profile of the pumping beam is positioned. It exploits the fact that the quantum wells 2 Compared to the period of the mode profile of the pump radiation have a comparatively small thickness, so that it is possible, several quantum wells 2 to be arranged in the region of the maximum of the mode profile of the pump radiation. The groups are advantageous 20 of quantum wells 2 arranged such that each group 20 is arranged both in a maximum of the mode profile of the pump radiation and in a maximum of the standing wave of the laser radiation. The distance of the groups 20 is therefore advantageously equal to the distance between two maxima of the mode profile of the pump radiation or a multiple thereof. Furthermore, the distance of the groups 20 preferably equal to the distance between two maxima of the standing wave of the laser radiation of the surface emitting semiconductor laser or a multiple thereof.

In 3 is schematically the course of the refractive index n (curve 23 ) and the intensity profile I _{p of} the pump radiation (curve 24 ) is shown along a vertically extending spatial coordinate z for a semiconductor body, in which no active zone of a surface emitting semiconductor laser on the pump laser 6 is arranged. It was assumed that the semiconductor body has a DBR mirror 16 and the pump laser 6 wherein, instead of an active zone of a surface emitting semiconductor laser, only a transparent contact layer 18 with low refractive index is applied to the pump laser. In this case, the pump radiation would be in its fundamental mode in the area of the pump laser 6 spread.

4 represents the course of the refractive index n (curve 25 ) and the propagating modes of the pump radiation (curves 26 . 27 ) along a vertical spatial coordinate z for a semiconductor body in an embodiment of a surface emitting semiconductor laser according to the invention, wherein an active zone 1 of the surface emitting semiconductor laser on the pump laser 6 is arranged. The energy of in 3 illustrated basic mode of the pump laser 2 becomes in the spreadable modes 26 . 27 transferred by mode coupling. Because the two fashions 26 . 27 have slightly different propagation constants, this leads to the propagation of the modes in the semiconductor body to a periodic constructive or destructive interference of the two modes 26 . 27 , The periodic constructive and destructive interference of the modes causes periodic energy transfer between the pump laser and the active region of the surface emitting semiconductor laser. The distance between the maxima of the mode profile 26 . 27 can be influenced by a suitable design of the layer structure.

In 5 is schematically an active zone on the left side 1 in one embodiment of the surface emitting semiconductor laser, in which the quantum well structure has five groups 20 of quantum wells 2 contains. Every group 20 contains two quantum wells 2 , In the middle part of the 5 is schematically the intensity I _{p of} the mode profile of the pump radiation in the active zone 1 of the surface emitting half-liter laser. The group of quantum wells 20 in the active zone 1 are arranged such that each group 20 in the range of a maximum 22 of the fashion profile 21 the pump radiation is arranged. The one on the right side of the 5 shown simulated absorption A _{p of} the quantum wells 2 clarifies that in all quantum wells 2 a uniformly high absorption of the pump radiation takes place. In this way, the surface-emitting semiconductor laser is pumped particularly efficiently.

In 6 is comparison to an active zone 1 of a conventional surface emitting semiconductor laser. The active zone 1 includes fourteen quantum wells 2 whose arrangement does not correspond to that in the middle part of the 6 illustrated intensity profile I _{p of} the mode profile 21 the pump radiation is adjusted. In particular, not all quantum wells are 2 in the range of a maximum 22 of the fashion profile 21 arranged.

The one on the right side of the 6 illustrated simulation of the absorption A _{p of} the pump radiation in the quantum wells 2 clarifies that the quantum wells 2 disadvantageously have an uneven absorption of the pump radiation. The efficiency of the optical pumping of the surface emitting semiconductor laser is thereby compared to that in 5 illustrated embodiment of a surface emitting semiconductor laser according to the invention is reduced.

The The invention is not by the description based on the embodiments limited. Rather, the invention includes every new feature as well any combination of features, especially any combination includes features in the claims, also if this feature or combination itself is not explicit specified in the patent claims or exemplary embodiments is.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 10260183 A1 [0003]
• DE 102004024611 A1 [0003]
• WO 01/93386 A1 [0004]
• WO 2005/048424 A1 [0004]

Claims (10)

Surface emitting semiconductor laser comprising - a semiconductor body ( 10 ), which is an active zone ( 1 ) having a quantum well structure, wherein the quantum well structure comprises a plurality of quantum wells ( 2 ), each consisting of one between barrier layers ( 4 ) arranged quantum well layer ( 3 ) are formed, and - a monolithic in the semiconductor body ( 10 ) integrated pump laser ( 6 ), the pump radiation for optically pumping the active zone ( 1 ), characterized in that the pump radiation has a mode profile ( 21 ) in the semiconductor body ( 10 ) and the quantum wells ( 2 ) are spaced apart so that they each in the range of a maximum ( 22 ) of the mode profile of the pump radiation are arranged. Surface emitting semiconductor laser according to claim 1, characterized in that the quantum wells ( 2 ) by spacer layers ( 5 ) are spaced from each other. Surface emitting semiconductor laser according to claim 1 or 2, characterized in that that of the active zone ( 1 ) emitted laser radiation ( 15 ) a standing wave in the semiconductor body ( 10 ), the quantum wells ( 2 ) are arranged such that they each in the region of a maximum of the standing wave of the laser radiation ( 15 ) are arranged. Surface emitting semiconductor laser according to claim 1 or 2, characterized in that the quantum wells ( 2 ) in several groups ( 20 ), the spacings of the quantum wells ( 2 ) within the groups ( 20 ) are smaller than the distances of neighboring groups ( 20 ). Surface emitting semiconductor laser according to claim 4, characterized in that the spacing of adjacent groups ( 20 ) equal to the distance between two maxima ( 22 ) of the fashion profile ( 21 ) of the pump radiation or a multiple thereof. Surface emitting semiconductor laser according to claim 4 or 5, characterized in that that of the active zone ( 1 ) emitted laser radiation ( 15 ) a standing wave in the semiconductor body ( 10 ), whereby the groups ( 20 ) of quantum wells ( 2 ) are arranged such that they each in the region of a maximum of the standing wave of the laser radiation ( 15 ) are arranged. Surface emitting semiconductor laser according to claim 6, characterized in that the spacing of adjacent groups ( 20 ) equal to the distance between two maxima of the standing wave of the laser radiation ( 15 ). Surface emitting semiconductor laser according to claim 7, characterized in that the spacing of adjacent groups ( 20 ) equal to a multiple of the distance between two maxima of the standing wave of the laser radiation ( 15 ). Surface-emitting semiconductor laser according to one of Claims 4 to 8, characterized in that the groups ( 20 ) two to four quantum wells ( 2 ). Surface emitting semiconductor laser according to one of the preceding claims, characterized in that the active zone ( 1 ) between 5 and 25 quantum wells inclusive ( 2 ) contains.