CN116316032A - Doped semiconductor saturable absorber mirror, preparation method thereof and laser - Google Patents

Abstract

The invention provides a doped semiconductor saturable absorber mirror, a preparation method thereof and a laser, wherein the doped semiconductor saturable absorber mirror comprises the following components: a distributed bragg reflector in a stacked arrangement and at least one period of a saturable absorber, wherein the one period of the saturable absorber comprises: the buffer layer, the saturable absorption layer and the first cover layer are arranged in a stacked mode, and the buffer layer is located between the distributed Bragg reflector and the saturable absorption layer; in the case where the semiconductor saturable absorber mirror includes a plurality of periods of the saturable absorber, it further includes: a spacing layer is arranged between any two adjacent period saturable absorbers; a P-type or N-type doped region a is present in the buffer layer or first cap layer or spacer. By applying the technical scheme of the invention, the problems of poor optical characteristics of the semiconductor saturable absorber mirror and poor performance and stability of an ultrafast laser formed based on components in the prior art can be effectively solved.

Description

Doped semiconductor saturable absorber mirror, preparation method thereof and laser

Technical Field

The invention relates to the field of ultrafast lasers, in particular to a doped semiconductor saturable absorption mirror, a preparation method thereof and a laser.

Background

The ultra-fast laser is laser with the pulse width in the picosecond or femtosecond level, and has wide application in the fields of material processing, medical treatment, laser radar, communication and the like along with the rapid development of laser technology. The semiconductor saturable absorber mirror (SESAM) is a Saturable Absorber Mirror (SAM) manufactured by adopting semiconductor materials and processes, is one of Saturable Absorbers (SA), and is an emerging two-dimensional material such as carbon nano tubes, graphene, transition metal sulfides and the like. However, the application is difficult to popularize because of the poor stability of the two-dimensional material. After decades of development, SESAM has relatively mature technology and stable output, has realized commercial production, and is widely used in solid lasers and fiber lasers. The improvement of the SESAM performance is therefore particularly important for the development of ultrafast laser systems.

Presently, SESAM faces a number of difficulties and challenges, the main problem being the low saturation flux and high modulation depth constraints. Compared with the three-dimensional bulk material, the two-dimensional quantum well material has more concentrated state density, so that the limitation of carriers in the semiconductor material is further improved, and the device performance of the quantum well material is better in theory. Following this idea, zero-dimensional quantum dot materials have been developed that are comparable in size to the de broglie wavelength of electrons in all three dimensions, and the carriers of quantum dots are subject to three-dimensional quantum confinement effects, giving them a separation energy level similar to that of atoms. The state density of the quantum dot material presents unique delta function distribution, and the distribution is more concentrated, so the quantum dot material has a plurality of new excellent characteristics.

The quantum dot semiconductor saturable absorber mirror (QD-SESAM) has a lower saturation flux than the quantum well material semiconductor saturable absorber mirror (QW-SESAM). However, lattice mismatch is introduced in the growth process of the quantum dot structure, so that more non-radiative recombination centers are generated, and the carrier non-radiative recombination process is enhanced. The optical quality of InAs/GaAs quantum dots is reduced, so that the QD-SESAM has weaker light absorption capacity and low modulation depth.

Disclosure of Invention

The invention mainly aims to provide a doped semiconductor saturable absorber mirror, a preparation method thereof and a laser, so as to solve the problem that the semiconductor saturable absorber mirror in the prior art is poor in optical characteristics.

In order to achieve the above object, according to one aspect of the present invention, there is provided a semiconductor saturable absorber mirror of a doping type, comprising: a distributed bragg reflector in a stacked arrangement and at least one period of a saturable absorber, wherein the one period of the saturable absorber comprises: the buffer layer, the saturable absorption layer and the first cover layer are arranged in a stacked mode, and the buffer layer is located between the distributed Bragg reflector and the saturable absorption layer; in the case where the doped semiconductor saturable absorber mirror includes a plurality of periods of the saturable absorber, the doped semiconductor saturable absorber mirror further includes: a spacer layer is arranged between any two adjacent period saturable absorbers, and a doped region A exists in a buffer layer or a first cover layer in any period of the saturable absorbers, or a doped region A exists in the spacer layer, and the doped region A is a P-type doped region or an N-type doped region.

In one embodiment, in the case where the doped region A is present in the buffer layer or the first cap layer, the distance between the doped region A and the saturable absorption layer is between 7 and 15nm, and the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm; in the case where the doped region A is present in the spacer layer, the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm.

In one embodiment, the doped semiconductor saturable absorber mirror further comprises: a substrate disposed on a side of the distributed Bragg reflector remote from the saturable absorber; and/or a second cover layer arranged on one side of the saturable absorber, which is far away from the distributed Bragg reflector.

In one embodiment, the substrate is a GaAs substrate and the second cap layer is a GaAs cap layer.

In one embodiment, the first cap layer is an InGaAs cap layer and the buffer layer is an InGaAs buffer layer or a GaAs buffer layer.

In one embodiment, the first cap layer has a thickness between 10-200nm and the buffer layer has a thickness between 10-100 nm.

According to another aspect of the present invention, there is provided a laser including: the semiconductor saturable absorber mirror is the doped semiconductor saturable absorber mirror.

According to a final aspect of the present invention, there is provided a method for manufacturing a doped semiconductor saturable absorber mirror, comprising: step S30: growing one or more cycles of a saturable absorber on a distributed bragg mirror, wherein the step of growing one cycle of the saturable absorber comprises: step S31: growing a buffer layer on the distributed Bragg reflector; step S32: after the buffer layer growth is completed, growing a saturable absorption layer on the surface of the buffer layer away from the distributed Bragg reflector; step S33: covering the first cover layer after the growth of the saturable absorption layer is completed; the step of growing a plurality of cycles of the saturable absorber comprises: step S34: after step S33, growing a spacer layer on the surface of the first cap layer remote from the saturable absorber layer, and then performing step S31 until the number of cycles of the grown saturable absorber reaches a preset value; the preparation method of the doped semiconductor saturable absorber mirror further comprises the following steps: during the growth of the buffer layer or the first cap layer, or during the growth of the spacer layer, a P-type doping element or an N-type doping element is introduced into the corresponding layer to form the doped region a.

In one embodiment, the distance between the doped region A in the buffer layer or the first cap layer and the saturable absorption layer is between 7-15nm, and the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm; the doping concentration of the doping element in the doping region A in the spacer layer is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm.

In one embodiment, prior to step S30, the preparation method further comprises: step S10: taking a substrate; step S20: growing a distributed Bragg reflector on the substrate; after step S30, the preparation method further includes: step S40: a second cap layer is grown on the surface of the saturable absorber remote from the distributed bragg mirror.

By applying the technical scheme of the invention, N or P doping is carried out on the buffer layer or the partial area of the first cover layer or the spacer layer, so that extra electrons or holes are provided, and the relaxation rate of carriers in the saturable absorption layer and the occupancy rate of holes in the valence band are improved. Therefore, the doped semiconductor saturable absorber mirror has the excellent optical characteristics of lower saturation flux and higher modulation depth, and solves the problem of poor optical characteristics of the semiconductor saturable absorber mirror in the prior art.

In addition to the objects, features and advantages described above, the present invention has other objects, features and advantages. The present invention will be described in further detail with reference to the drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:

FIG. 1 is a schematic diagram of a doped semiconductor saturable absorber mirror according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a doped semiconductor saturable absorber mirror according to a second embodiment of the present invention;

FIG. 3 is a schematic diagram of a doped semiconductor saturable absorber mirror according to a third embodiment of the present invention;

FIG. 4 is a schematic diagram of a doped semiconductor saturable absorber mirror according to a fourth embodiment of the present invention; and

fig. 5 is a schematic structural diagram of a fifth embodiment of a doped semiconductor saturable absorber mirror according to the present invention. Wherein the above figures include the following reference numerals:

10. a substrate; 20. a distributed Bragg reflector; 21. a first material layer; 22. a second material layer; 30. a saturable absorber; 31. a buffer layer; 32. a saturable absorber layer; 33. a first cap layer; 40. a second cap layer; 50. a spacer layer.

Detailed Description

It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.

In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other environments. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

As shown in fig. 1, a doped semiconductor saturable absorber mirror according to a first embodiment includes: adistributed bragg reflector 20 and asaturable absorber 30 arranged in a stacked manner, wherein thesaturable absorber 30 comprises: thebuffer layer 31, thesaturable absorber layer 32 and thefirst cap layer 33 are stacked, thebuffer layer 31 is located between thebragg reflector 20 and thesaturable absorber layer 32, and a doped region a is located in thefirst cap layer 33, and the doped region a is a P-type doped region or an N-type doped region.

By applying the technical solution of the first embodiment, N or P doping is performed on a partial area of thefirst cover layer 33 to provide additional electrons or holes, so as to increase the relaxation rate of carriers and the occupancy rate of holes in the valence band in thesaturable absorption layer 32. The doped semiconductor saturable absorber mirror has excellent optical characteristics of lower saturation flux and higher modulation depth.

It should be noted that doping actually introduces other substances, i.e. defects. The inventors have found in research that for a SESAM the light absorbing region is thesaturable absorber layer 32, i.e. the quality of thesaturable absorber layer 32 affects the overall SESAM optical properties. If thesaturable absorber layer 32 is doped, the optical properties of thesaturable absorber layer 32 may be severely affected. Therefore, the invention chooses to dope the buffer layer either P-type or N-type, and introducing doping into thefirst cap layer 33 will also provide electrons and holes to thesaturable absorber layer 32.

It should be noted that carriers provided by the P-type doping and the N-type doping are different, one being a hole and one being an electron. Hole scattering is lower than electron scattering efficiency because the change in hole wave vector required for energy conservation is large. Due to the doping, the relaxation of the carriers to the ground state is significantly enhanced, resulting in a multiplied reduction of the relaxation time, which is due to auger electron-hole scattering of the doped carriers. The final P-type doping and N-type doping may affect the optical characteristics of pulse width, saturation flux, etc. in the final effect.

Further, the inventors found in long-term studies that if the doped region a is located too far from thesaturable absorber layer 32, it is not beneficial to mitigate thermal runaway of carriers, affecting the SESAM temperature stability; too close may introduce too much non-radiative recombination centers. If the concentration of the doping element is too small to achieve the effect of hole compensation, too much can lead to larger non-radiative recombination, and the luminous efficiency is reduced. If the thickness of the doped region A is too thick, more composite centers can be introduced, and the performance of the saturable absorber is reduced; too thin a doped region will not effectively provide holes or electrons. Therefore, the precise control of the concentration of the doping element, the doping position and the thickness of the doped region can further achieve the aim of improving the optical characteristics of the SESAM, such as the characteristics of modulation depth, unsaturated loss, saturated flux, saturated light intensity, pulse width and the like.

In order to further improve the optical properties of the SESAM, in a first embodiment, the distance d between the doped region A and thesaturable absorber layer 32 is between 7 and 15nm, and the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness t of the doped region A is between 5 and 10 nm. In particular, there are two points in the difficulty of doping the buffer layer, the first point is the control of the doping sites, which are all on the order of nm, so it is clear that the growth rate of the material is known in order to introduce doping at the correct sites. The second point is the control of the doping concentration, where the MBE is doped by heating the dopant source material in a source furnace to form a molecular beam jet onto the substrate (this embodiment preferably uses a molecular beam epitaxy MBE apparatus for doping). The distance d refers to a distance between a surface of the doped region a near thesaturable absorption layer 32 and a surface of thesaturable absorption layer 32 near the doped region a.

The doping of a SESAM will be described in a specific exampleTable 1 shows the comparison of parameters of undoped SESAM and P-doped SESAM. Wherein the doping element of the P-doped SESAM is Be, and the doping concentration is 5 multiplied by 10¹⁸ /cm³ Thefirst cap layer 33 is doped at a distance of 10nm and the doped region a has a thickness t of 6 nm.

Table 1 parameter comparison of undoped SESAM and P-doped SESAM

，

From the above table, it can be seen that under the same SESAM structure, the P-doped SESAM has better performance than the super-fast laser obtained by undoped SESAM, and can obtain narrower pulse width.

Preferably, in other examples, the doping concentration of the doping element within the doping region a may be 3×10¹⁷ /cm³ 、5×10¹⁸ /cm³ 、1×10¹⁹ /cm³ 。

In the first embodiment, as shown in fig. 1, thesaturable absorption layer 32 is a quantum dot layer. Preferably, in this embodiment, the quantum dot layer is an InAs quantum dot layer. Of course, in other embodiments not shown in the figures, the saturable absorber layer may also be a quantum well layer.

As shown in fig. 1, in the first embodiment, the doped semiconductor saturable absorber mirror further includes:substrate 10 andsecond cap layer 40. Wherein thesubstrate 10 is arranged on the side of the distributedBragg reflector 20 remote from thesaturable absorber 30; thesecond cover layer 40 is arranged on the side of thesaturable absorber 30 remote from the distributedbragg mirror 20. Of course, in other embodiments not shown in the figures, the doped semiconductor saturable absorber mirror may also comprise one of a substrate and a cap layer.

In the first embodiment, the doping element in the P-type doped region includes one of Be, C, mg, zn, ge, cd. The doping element in the N-type doping region comprises one of Si, ge and Sn. Specifically, various impurities form different energy levels in GaAs, and group ii elements Be, mg, zn, cd, hg are shallow acceptors, which are P-type dopants of GaAs materials. The VI group elements S, se and Te are shallow donor impurities in GaAs and are N-type dopants. However, elements exist with amphoteric doping characteristics, such as Si, ge and Sn, which are elements of group IV. The presence of a group iv atom as a donor when on a group iii superlattice and an acceptor when on a group v superlattice ultimately appears to be a donor or acceptor depending entirely on the nature, concentration, and doping conditions of the material during preparation. Basically common to P or N type doping of GaAs are these elements, others may have some drawbacks.

In the first embodiment, thesubstrate 10 is a GaAs substrate, and thesecond cap layer 40 is a GaAs cap layer. Of course, in other embodiments, the material of the substrate may be InP, and the corresponding second cap layer material is typically InP.

In the first embodiment, thefirst cap layer 33 is an InGaAs cap layer, and thebuffer layer 31 is an InGaAs buffer layer. Of course, in other embodiments, thefirst cap layer 33 may also be an InGaP cap layer, a GaAsP cap layer, an AlGaAs cap layer, and an inagaas cap layer; the buffer layer may also be a GaAs buffer layer, an InGaAs buffer layer, a GaAsP buffer layer, or an inaias buffer layer.

In the first embodiment, the thickness of thebuffer layer 31 is between 10-100 nm. In the above structure, thebuffer layer 31 is designed to solve the problem of lattice mismatch (lattice mismatch) between materials, and thebuffer layer 31 is too thin to meet the requirements of the distance between the doped region a and thesaturable absorption layer 32 and the thickness of the doped region a; however, the buffer layer is too thick, which may have lattice mismatch problem, so that stress is generated, which may cause problems such as cracking or deformation of the film, and reduce the performance of the film.

In the first embodiment, the distributedbragg mirror 20 is a 31-period distributed bragg mirror, the 31-period distributedbragg mirror 20 includes thefirst material layer 21 and thesecond material layer 22 alternately stacked, and the refractive index of thefirst material layer 21 is different from the refractive index of thesecond material layer 22, the material of thefirst material layer 21 includes GaAs, and the material of thesecond material layer 22 includes AlGaAs. Specifically, the 31-period Distributed Bragg Reflector (DBR) is composed of two different refractive index materials of GaAs and AlGaAs, respectively, wherein GaAs refractive index n=3.3 and AlGaAs refractive index n=2.87 (different refractive indexes according to Al composition) at 1550nm band. The alternating λ/4n thicknesses of the two materials are satisfied here (i.e. the thickness of each layer of material in particular is obtained by substituting the wavelength λ and the refractive index n into the above formula).

In one embodiment, thesubstrate 10 is an undoped substrate (a semi-insulating region is present in the substrate) or an N-type Si doped substrate (an N-type region is present in the substrate). The N-type region and the semi-insulating region in the substrate are two different types of regions of semiconductor material, which differ primarily in resistivity and doping concentration:

n-type region: the N-type region refers to a region of N-type semiconductor material that is doped with a large number of donor atoms (e.g., silicon, selenium, carbon, etc.) in the substrate. These donor atoms provide excess free electrons and thus the N-type region has a higher electron concentration and a lower resistivity, also referred to as a "conductivity type" region.

Semi-insulating region: the semi-insulating region is a region between the N-type region and the P-type region, wherein the doping concentration is close to the intrinsic material concentration (Intrinsic Carrier Concentration). This means that the number of electrons and holes in the semi-insulating region is almost equal, there is no significant predominance of electrons or holes, the resistivity is very high, and the saturation behaviour is exhibited for the absorption and release of pump photons, hence the term "semi-insulating" region.

Because of the difference in electrical properties between the N-type region and the semi-insulating region, they can be used to fabricate different types of semiconductor devices. For example, in a laser, a semi-insulating type region is used as a mode field absorber instead of an N-type region as a portion through which an external pumping current passes, and the N-type region is used as a pumping region or a brillouin reflection feedback region.

When using substrates to make semiconductor saturable absorber mirrors (SESAMs), N-type GaAs materials are typically used as the best choice, rather than semi-insulating regions, for the following reasons:

increasing laser stability: the use of an N-type substrate may facilitate automatic mode locking because such a substrate may provide a bistable state in the laser and may facilitate a stable and reliable mode-locking saturation characteristic.

The pulse width is effectively controlled: the N-type substrate can better control the width of laser pulse, and the N-type semiconductor has high electron concentration and larger light absorption, so that saturated absorption is easier, and meanwhile, the substrate has good optical quality.

Realizing higher output efficiency: since the N-type substrate is excellent in conductivity, it is easier to inject current from the outside than the semi-insulating region, which achieves higher output efficiency.

The working principle of the SESAM is briefly described below:

the working principle of SESAM is based on the saturated absorber being in an absorbing state in weak light and in a "bleached" state in strong light. The working mechanism of the semiconductor saturable absorber is as follows: when the energy of the incident light is strong enough, the saturable absorber starts to absorb the light, so that carriers on the valence band are excited to the conduction band; along with the increase of light intensity, electrons on a conduction band are gradually increased, the light absorption of the saturable absorber is saturated, light pulses can pass through the saturable absorber without loss, the saturable absorber is in a bleaching state, and the formed ultrashort pulses can be applied to the fields of medical treatment, laser radar, laser cutting and the like.

The following briefly describes the beneficial effects of the embodiment:

annealing the active region during the growth of the saturable absorber layer, which is equivalent to the long-time growth of the upper cladding layer, forms Ga atomic vacancies In the process, and In-Ga intermixing of the QDs and surrounding materials occurs, resulting In blue shift of the luminescence peak. The introduction of the P type doping can improve the concentration of interstitial atoms and inhibit the generation and transfer of Ga vacancies, so that the In-Ga intermixing In the annealing process can be effectively inhibited, the blue shift of a luminescence peak is reduced, and the QD-SESAM optical characteristic is optimized.

The saturable absorption layer can generate In-Ga mixing effect In the growth process, and can also cause shallower limiting potential energy, so that the ground state gain is reduced. The P-type doping is introduced into the QD-SESAM to provide a large number of extra holes for the valence band, so that the occupation rate of the holes in the valence band is greatly improved, the ground state holes are difficult to thermally excite, the optical property, the absorption performance and the temperature stability of the quantum dot material are greatly improved, and the modulation depth and the damage threshold of the SESAM are further improved.

Very fast carrier kinetics in the saturable absorber layer were observed by quachi et al at room temperature, and Gundo ğ du et al reported a relaxation rate of 4.8 ps in undoped saturable absorber materials, and a fast relaxation time of 450 fs was achieved with P-doped structures with carrier relaxation times shortened to 1.4 ps after N-type doping was introduced. The introduction of doping elements can improve the carrier scattering probability in the saturable absorption layer, so that the doping can effectively improve the carrier relaxation rate, shorten the relaxation time of carriers in the saturable absorption material, and optimize the optical characteristics of the QD-SESAM.

Finally, parameters of doping type, doping position, doping concentration and doping width in the QD-SESAM are designed, so that the light absorption capacity of the QD-SESAM is increased, the carrier relaxation process is optimized, the modulation depth and optical characteristics of the QD-SESAM are improved, and the high-performance SESAM is prepared.

As shown in fig. 2, the doped semiconductor saturable absorber mirror of the second embodiment is different from the doped semiconductor saturable absorber mirror of the first embodiment only in that the doped region a is located in thebuffer layer 31.

By applying the technical solution of the second embodiment, N or P doping is performed in a partial region of thebuffer layer 31 to provide additional electrons or holes, so as to increase the relaxation rate of carriers and the occupancy rate of holes in the valence band in thesaturable absorption layer 32. The doped semiconductor saturable absorber mirror has excellent optical characteristics of lower saturation flux and higher modulation depth.

It should be noted that, introducing doping into thebuffer layer 31 also provides electrons and holes to the quantum dots. The difficulty in introducing doping into thebuffer layer 31 is the same as that in introducing doping into thefirst cap layer 33, and will not be described in detail here.

In the second embodiment, thefirst cap layer 33 is between 10-200nm and thebuffer layer 31 is between 10-100 nm. In the above structure, thefirst cap layer 33 is too thin to meet the requirements of the distance between the doped region a and thesaturable absorption layer 32 and the thickness of the doped region a, and if thefirst cap layer 33 is too thick, the performance of the heterojunction may be negatively affected, for example, the recombination rate of electrons and holes is increased, which reduces the electrical performance of the heterojunction.

As shown in fig. 3, the doped semiconductor saturable absorber mirror of the third embodiment is different from the doped semiconductor saturable absorber mirror of the first embodiment only in that the doped semiconductor saturable absorber mirror includes amulti-period saturable absorber 30. Thebuffer layer 31 of the first period of thesaturable absorber 30 is located between the 31 period of theDBR mirror 20 and thesaturable absorber layer 32 of the first period of thesaturable absorber 30, and thefirst cap layer 33 of the last period of thesaturable absorber 30 is located between thesaturable absorber layer 32 and thesecond cap layer 40. In the figure, B is the absorption zone formed by themulticycle saturable absorber 30. Aspacer layer 50 is disposed between any two adjacentperiodic saturable absorbers 30.

As shown in fig. 4, the semiconductor saturable absorber mirror of the fourth embodiment differs from the semiconductor saturable absorber mirror of the second embodiment only in that the semiconductor saturable absorber mirror of the doped type includes amulti-period saturable absorber 30. Thebuffer layer 31 of the first period of thesaturable absorber 30 is located between the 31 period of theDBR mirror 20 and thesaturable absorber layer 32 of the first period of thesaturable absorber 30, and thefirst cap layer 33 of the last period of thesaturable absorber 30 is located between thesaturable absorber layer 32 and thesecond cap layer 40. In the figure, B is the absorption zone formed by themulticycle saturable absorber 30. Aspacer layer 50 is disposed between any two adjacentperiodic saturable absorbers 30.

As shown in fig. 5, the semiconductor saturable absorber mirror of the doping type of the fifth embodiment differs from the semiconductor saturable absorbers of the doping type of the third and fourth embodiments only in that the location of the doped region a is located within thespacer layer 50. In the figure, C is the absorption zone formed by themulticycle saturable absorber 30. When the position of the doped region A is located in thespacer layer 50, the doping concentration of the doping element in the doped region A is only required to be ensured to be 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is 5-10 nm.

The present application also provides a laser, an embodiment of the laser according to the present application comprising: the semiconductor saturable absorber mirror is the doped semiconductor saturable absorber mirror. The semiconductor saturable absorber mirror of the doping type has the advantages because of the excellent optical characteristics of lower saturation flux and higher modulation depth. The semiconductor saturable absorber mirror is a passive mode-locking optical component for a laser. Is an important component for realizing ultra-short pulse output. Is widely applied to the fields of laser radar, precision measurement, biomedicine, industrial processing and the like.

The present application also provides a method for preparing a doped semiconductor saturable absorber mirror, and an embodiment one of the method for preparing a doped semiconductor saturable absorber mirror according to the present application includes: step S30: growing asaturable absorber 30 on the distributedbragg mirror 20, the step of thesaturable absorber 30 comprising: step S31: growing abuffer layer 31 on the distributedbragg mirror 20; step S32: after thebuffer layer 31 is grown, asaturable absorption layer 32 is grown on the surface of thebuffer layer 31 away from thebragg mirror 20; step S33: thefirst cover layer 33 is covered after the growth of thesaturable absorber layer 32 is completed; the growing step of thesaturable absorber 30 further includes: during the growth of thebuffer layer 31 or thefirst cap layer 33, a P-type doping element or an N-type doping element is introduced into the corresponding layer to form the doped region a. The doped semiconductor saturable absorber mirror prepared by the preparation method has the advantages of lower saturation flux, higher modulation depth and excellent optical characteristics.

In this embodiment, the saturable absorber layer is preferably epitaxially grown at a growth rate of 0.01 monolayer per second (0.01 ML/s).

In the present embodiment, the distance between the doped region A and thesaturable absorption layer 32 is between 7-15nm, and the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm. The doping type half of the doping type prepared by the preparation methodThe conductor saturable absorber mirror has more excellent optical characteristics.

In this embodiment, before step S30, the preparation method further includes: step S10: taking asubstrate 10; step S20: growing a distributedBragg reflector 20 on thesubstrate 10; after step S30, the preparation method further includes: step S40: asecond cap layer 40 is grown on the surface of thesaturable absorber 30 remote from the distributedbragg mirror 20.

The method for manufacturing the doped semiconductor saturable absorber mirror of the second embodiment is different from the method for manufacturing the doped semiconductor saturable absorber mirror of the first embodiment only in that: amulti-period saturable absorber 30 is grown on the distributedbragg mirror 20. Specifically, the step of growing thesaturable absorber 30 for a plurality of cycles includes: step S34: after step S33, aspacer layer 50 is grown on the surface of thefirst cap layer 33 remote from thesaturable absorber layer 32, and then step S31 is performed until the number of cycles of the grownsaturable absorber 30 reaches a preset value; the preparation method of the doped semiconductor saturable absorber mirror further comprises the following steps: during the growth of thebuffer layer 31 or thefirst cap layer 33, or during the growth of thespacer layer 50, a P-type doping element or an N-type doping element is introduced into the corresponding layer to form the doped region a. The doped semiconductor saturable absorber mirror prepared by the preparation method has the advantages of lower saturation flux, higher modulation depth and excellent optical characteristics.

In the present embodiment, when the doped region A is located in thebuffer layer 31 or thefirst cap layer 33, the distance between the doped region A and thesaturable absorption layer 32 is between 7-15nm, and the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm. When the doped region A is located in thespacer layer 50, the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm. The doped semiconductor saturable absorber mirror prepared by the preparation method has more excellent optical characteristics.

The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective parts shown in the drawings are not drawn in actual scale for convenience of description. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further discussion thereof is necessary in subsequent figures.

Spatially relative terms, such as "above … …," "above … …," "upper surface at … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial location relative to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or structures would then be oriented "below" or "beneath" the other devices or structures. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may also be positioned in other different ways (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

In the description of the present invention, it should be understood that the azimuth or positional relationships indicated by the azimuth terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal", and "top, bottom", etc., are generally based on the azimuth or positional relationships shown in the drawings, merely to facilitate description of the present invention and simplify the description, and these azimuth terms do not indicate and imply that the apparatus or elements referred to must have a specific azimuth or be constructed and operated in a specific azimuth, and thus should not be construed as limiting the scope of protection of the present invention; the orientation word "inner and outer" refers to inner and outer relative to the contour of the respective component itself.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A doped semiconductor saturable absorber mirror comprising:

a distributed bragg mirror (20) and at least one period of a saturable absorber (30) arranged in a stack, wherein the one period of the saturable absorber (30) comprises: a buffer layer (31), a saturable absorption layer (32) and a first cap layer (33) which are stacked, wherein the buffer layer (31) is positioned between the distributed Bragg reflector (20) and the saturable absorption layer (32);

in the case that the semiconductor saturable absorber mirror of the doping type comprises a plurality of periods of the saturable absorber (30), the semiconductor saturable absorber mirror of the doping type further comprises:

a spacer layer (50), said spacer layer (50) being arranged between said saturable absorbers (30) of any adjacent two cycles, characterized in that,

doped region a is present in either the buffer layer (31) or the first cap layer (33) within the saturable absorber (30) of any one cycle, or in the spacer layer (50), doped region a is present, which is either a P-type doped region or an N-type doped region.

2. The doped form of claim 1Semiconductor saturable absorber mirror, characterized in that the distance between the doped region a and the saturable absorber layer (32) is between 7-15nm in the presence of the doped region a within the buffer layer (31) or the first cap layer (33), the doping concentration of doping elements within the doped region a being 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm; in the case that the doped region A exists in the spacer layer (50), the doping concentration of the doping element in the doped region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm.

3. A doped semiconductor saturable absorber mirror according to claim 1, wherein said doped semiconductor saturable absorber mirror further comprises:

a substrate (10) disposed on a side of the distributed Bragg reflector (20) remote from the saturable absorber (30); and/or the number of the groups of groups,

a second cover layer (40) is arranged on the side of the saturable absorber (30) which is far away from the distributed Bragg reflector (20).

4. A doped semiconductor saturable absorber mirror according to claim 3, wherein the substrate (10) is a GaAs substrate and the second cap layer (40) is a GaAs cap layer.

5. A doped semiconductor saturable absorber mirror according to claim 1, wherein the first cap layer (33) is an InGaAs cap layer and the buffer layer (31) is an InGaAs buffer layer or a GaAs buffer layer.

6. A doped semiconductor saturable absorber mirror according to claim 1, wherein the thickness of the first cap layer (33) is between 10-200nm and the thickness of the buffer layer (31) is between 10-100 nm.

7. A laser, comprising: a semiconductor saturable absorber mirror, characterized in that it is a doped semiconductor saturable absorber mirror according to any one of claims 1 to 6.

8. A preparation method of a doped semiconductor saturable absorber mirror comprises the following steps:

step S30: growing a period or a plurality of periods of a saturable absorber (30) on a distributed bragg mirror (20), wherein the step of growing a period of the saturable absorber (30) comprises:

step S31: growing a buffer layer (31) on the distributed bragg mirror (20);

step S32: -after the buffer layer (31) growth is completed, growing a saturable absorber layer (32) on the surface of the buffer layer (31) remote from the bragg mirror (20);

step S33: covering the first cover layer (33) after the growth of the saturable absorption layer (32) is completed;

the step of growing a plurality of cycles of the saturable absorber (30) includes:

step S34: after said step S33, growing a spacer layer (50) on the surface of the first cap layer (33) remote from said saturable absorber layer (32), and then performing step S31 until the number of cycles of said saturable absorber (30) grown reaches a preset value; the preparation method of the doped semiconductor saturable absorber mirror is characterized by further comprising the following steps:

during the growth of the buffer layer (31) or the first cap layer (33), or during the growth of the spacer layer (50), a P-type doping element or an N-type doping element is introduced into the corresponding layer to form a doped region a.

9. The method of manufacturing a semiconductor saturable absorber mirror of claim 8, wherein the doped region a in the buffer layer (31) or the first cap layer (33) and the saturable regionAnd the absorption layer (32) is 7-15nm, the doping concentration of the doping element in the doping region A is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm; the doping concentration of the doping element in the doping region A in the spacer layer (50) is 10¹⁶ -10¹⁹ /cm³ The thickness of the doped region A is between 5 and 10 nm.

10. The method for manufacturing a doped semiconductor saturable absorber mirror according to claim 8 or 9, wherein prior to the step S30, the manufacturing method further comprises:

step S10: taking a substrate (10);

step S20: growing a distributed Bragg mirror (20) on the substrate (10); after the step S30, the preparation method further includes:

step S40: a second cap layer (40) is grown on a surface of the saturable absorber (30) remote from the distributed bragg mirror (20).

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