阅读说明：本技术 用于注入自旋极化的电荷载流子并反射光的装置 (Device for injecting spin-polarized charge carriers and reflecting light ) 是由 M·林德曼 N·格哈特 M·霍夫曼 于 2019-02-28 设计创作，主要内容包括：本发明涉及一种用于注入自旋极化电子并反射光的装置(2),该装置(2)包括至少一个具有多个凹槽(4)的格子结构(3),其中该格子结构(3)被设计为用于反射光,并且其中在至少一些凹槽(4)中布置有用于注入自旋极化电子的相应注入触头(5、6)。(The invention relates to a device (2) for injecting spin-polarized electrons and reflecting light, the device (2) comprising at least one lattice structure (3) having a plurality of recesses (4), wherein the lattice structure (3) is designed for reflecting light, and wherein in at least some of the recesses (4) respective injection contacts (5, 6) for injecting spin-polarized electrons are arranged.)

1. An apparatus (2) for injecting spin-polarized electrons and reflecting the light, comprising: at least one lattice structure (3) with a plurality of grooves (4), wherein the lattice structure (3) is designed for reflecting light, and wherein in at least some of the grooves (4) respective injection contacts (5, 6) for injecting spin-polarized charge carriers are arranged.

2. Device (2) according to claim 1, characterized in that a first injection contact (5) and a second injection contact (6) are arranged in an alternating manner and wherein the first injection contact (5) is designed for injecting electrons having a first spin polarization and the second injection contact (6) is designed for injecting electrons having a second spin polarization different from the first spin polarization.

3. Device (2) according to any one of the preceding claims, characterized in that in some of the recesses (4) there are also provided metal contacts (13) for injecting spin-free polarized electrons.

4. Device (2) according to any of the preceding claims, characterized in that the length of the grooves (4) in the lattice structure (3) is smaller than the wavelength of the light to be reflected.

5. Device (2) according to any one of the preceding claims, characterized in that at least some of the injection contacts (5, 6) comprise respective ferromagnetic layers (8).

6. A device (2) according to claim 5, characterized in that said ferromagnetic layer (8) has a magnetization oriented perpendicular to said ferromagnetic layer (8).

7. Device (2) according to any one of the preceding claims, at least some of the injection contacts (5, 6) comprising respective tunnel barriers (9).

8. Arrangement (1), characterized by comprising an active area (12), a mirror (11) and a device (2) according to any of the preceding claims, wherein the mirror (11) and the device (2) are arranged for reflecting light into the active area (12).

9. Arrangement (1) according to claim 8, characterized in that at least some of the injection contacts (5, 6) of the device (2) are each designed as schottky contacts.

10. Method for operating an arrangement (1) according to claim 9, characterized in that spin-polarized electrons are injected into the active region (12) of the arrangement (1) through the injection contacts (5, 6), and wherein the polarization of the light generated by the arrangement (1) is influenced by the spin polarization of the electrons.

Drawings

The invention is explained in more detail below with reference to the drawings, in which:

fig. 1 is a schematic cross-sectional view of a first embodiment of a laser, having means for injecting spin-polarized electrons and for reflecting light,

FIG. 2 is a schematic plan view of the laser of FIG. 1, an

Fig. 3 is a schematic cross-sectional view of a second embodiment of a laser with means for injecting spin-polarized electrons and for reflecting the light.

Detailed Description

The described device may be used in a configuration, in particular in a laser, for injecting spin-polarized charge carriers such as electrons, holes, etc., and for reflection of light. The following are examples based on injection of spin-polarized holes.

Spin-polarized electrons can thus be injected into the active region of the laser, so that the electrons must travel uniformly over the entire active region, along particularly short paths, in order to recombine with the holes and thus produce light. The laser can therefore also be operated with particularly short spin relaxation lengths and therefore at relatively high temperatures and/or low external magnetic fields. It is even possible to omit the external magnetic field completely.

Fig. 1 is a schematic cross-sectional view of a first embodiment of a laser 1, which laser 1 has means 2 for injecting spin-polarized electrons and for reflecting the light. The laser 1 preferably uses semiconductor material, so that the laser 1 can also be referred to as a semiconductor laser and/or a laser diode. The laser 1 shown in fig. 1 is a preferred embodiment of an arrangement comprising said device. The configuration may typically be a light emitting component with a resonator. This may also be, for example, a resonant LED, in addition to a laser. In particular, this configuration may be referred to as a "device with a cavity".

Laser light can be generated by the laser 1 by recombining electrons and holes in the active region 12 of the laser 1. During recombination, photons are generated by the released energy. In particular, the active region 12 may be designed as a p-n junction. The laser light is generated at the junction between the p-type doped region and the n-type doped region. For example, p-GaA and n-GaA are considered as the material of the active region 12. The wavelength of the laser light generated by the laser 1 may be determined by the choice of material and/or doping of the material of the active region 12.

The photons generated in the active region 12 are reflected by a mirror 11 arranged below the active region 12 and by a device 2 arranged above the active region 12, which device serves in particular to reflect the light. According to the laser principle, such reflection of the generated photons leads to inductive emission of other photons. Thereby, laser light is generated in the active region 12. The arrangement of the device 2 above the active area 12 and the arrangement of the mirror 11 below the active area 12 are exemplary. Configuration 1 may be oriented as desired. In particular, the device 2 may also be arranged below the active region 12, and the mirror 11 may be arranged above the active region 12.

The mirror 11 is preferably designed as a bragg mirror. So-called Distributed Bragg Reflectors (DBRs) are particularly suitable. Preferably, the bragg mirror comprises a plurality of layers which collectively reflect the generated light. The layer is preferably formed of a semiconductor material. Preferably, the materials are selected so that the layers having the first and second refractive indices alternate. For example, GaA layers and AlGaA layers may be alternately arranged. The layer thickness is preferably equal to a quarter of the wavelength of the light to be reflected in all layers, so that the reflection of the light can take place in the manner of bragg reflection. Alternatively, the mirror can also be designed as a metal mirror.

The device 2 comprises at least one lattice structure 3 having a plurality of grooves 4. In the embodiment described here, it is arranged on the active region 12 and opposite the mirror 11, so that the lattice structure reflects photons generated in the active region at least partially back into the active region. The lattice structure thus forms a laser resonator in interaction with the opposite mirror, i.e. mirror 11. Fig. 1 shows four grooves 4 formed between the parts of the lattice structure 3. The lattice structure 3 is preferably composed of a semiconductor material and/or a metal.

As can be seen from the top view of the laser 1 of fig. 1 shown in fig. 2, in one embodiment the lattice structure 3 is rectangular. This means that the recesses 4 are rectangular and are arranged and aligned along straight lines, perpendicular lines or parallel lines. The grooves 4 preferably all have the same shape and/or extension. Preferably, the distances between adjacent grooves are all of the same size.

The smaller the grooves 4, the better the reflection of light on the lattice structure 3. Preferably, the length 14 of the grooves 4 in the lattice structure 3 is smaller than the wavelength of the reflected light, in particular smaller than half the wavelength of the reflected light. The length 14 of the grooves 4 is to be understood as the largest extension of the grooves 4 in a plane transverse to the lattice structure 3. This is the length shown in fig. 2. By means of such small grooves 4 in the lattice structure 3, light can be reflected particularly well.

The lattice structure may also differ from the design shown in the figures. In particular, the lattice structure is considered to be only one-dimensional. This means that the grooves are arranged in only one direction along parallel lines, whereas no grooves are provided in a direction transverse to this direction. Such an embodiment may also be described as the number of lattice periods in one direction being 1. The lattice structure may also be designed not as a right-angled structure but as a ring structure.

The active region 12, the mirror 11 and the device 2 are preferably designed as solids with respective lattice structures. The lattice structure will need to be distinguished from the lattice structure 3 described herein. The lattice structures of the active area 12, the mirror 11 and the device 2 may be different. In particular, in order to avoid tensions caused by such lattice mismatch, a respective matching layer 10 may be provided between the active area 12 and the mirror 11 and/or between the active area 12 and the device 2, as shown in the example of fig. 1. The matching layer 10 is preferably formed of a semiconductor material. The matching layer 10 may also be referred to as a "phase matching layer", among other things. If it is described that electrons are injected into the active region, this also means that electrons are injected into the active region 12 through the matching layer 10 if the matching layer 10 is present. Photons generated in the active region 12 pass through the matching layer 10 before being reflected by the mirror 11, are then reflected at the mirror 11, pass through the matching layer 10 again, so that the photons return into the active region 12.

The matching layer 10 forms together with the active region 12 a resonator of the laser and has a total optical thickness n x d, which preferably corresponds approximately to the emission wavelength. The location of the active region 12 need not be in the center of the resonator.

The matching layer 10 does not have to be clearly separated from the active area 12, the device 2 and/or the mirror 11. There may also be a smooth junction between the matching layer 10 and the device 2, the active region 12 and/or the mirror 11. The active region 12 may also smoothly flow into the device 2 and/or the mirror 11 if the matching layer 10 is not provided. For example, the mirror 11 may also have doping to assist in lasing.

Optionally, the matching layer 10 is preferably clearly separated from the active area 12, the device 2 and/or the mirror 11. If no matching layer 10 is provided, it is preferred that the active region 12 is clearly separated from the device 2 and/or the mirror 11.

The device 2 is further designed and arranged for injecting electrons into the active region 12. In particular, the electrons may be spin polarized. This means that the spin orientation of the injected electrons is not uniformly distributed between the two possible spin states "up" and "down", but one of the spin states is dominant. Therefore, the injected electrons are spin-polarized in this spin state as a whole. In the described laser 1, the spin polarization of the charge carrier system, i.e. the electrons, can be used to influence the polarization of the generated light and thus the properties of the light. The polarization of the light can be influenced in particular by creating and decomposing a spin polarization. For this purpose, it is possible to switch between, for example, rotation up and down or between the case of rotation polarization and non-polarization. Spin-polarized electrons may be injected into the active region 12 through the injection contacts 5, 6, and optionally via the matching layer 10. For this purpose, respective injection contacts 5, 6 are arranged at least in some of the grooves 4 of the lattice structure 3. As shown in the example of fig. 1, a respective injection contact 5, 6 is preferably arranged in each recess 4.

As shown in the example of fig. 1, the injection contacts 5, 6 may have respective metal layers 7. The metal layer 7 may be formed of, for example, gold, chromium and/or aluminum. The injection contacts 5, 6 may be contacted via a metal layer 7, for example via respective supply lines. All the injection contacts 5, 6 can be contacted together. Alternatively, individual injection contacts 5, 6 or groups of injection contacts 5, 6 may be contacted individually. The metal layer 7 may also serve to protect the underlying layers. Thus, the metal layer 7 may also be referred to as a "cap layer".

At least some of the injection contacts 5, 6 preferably comprise respective ferromagnetic layers 8. All injection contacts 5, 6 preferably comprise respective ferromagnetic layers 8. A layer structure composed of a plurality of sublayers may be used as the ferromagnetic layer 8. This layer structure is understood here as a ferromagnetic layer 8. For example, the ferromagnetic layer 8 can be designed as a multilayer sequence of Fe/Tb, Fe/Pt, Co/Pt and/or Co/Ni, or as an alloy with FeTb and/or CoFeB, for example. The ferromagnetic layer 8 may be formed of, for example, iron and/or terbium.

The electrons can be polarized by the ferromagnetic layer 8. If non-spin-polarized electrons are introduced into the ferromagnetic layer 8, the magnetization of the ferromagnetic layer 8 may preferably allow electrons of one spin orientation to pass through and retain electrons of the other spin orientation. In a simplified model, this can be described by the fact that: the ferromagnetic layer 8 has different ohmic resistances for the two spin-oriented electrons.

Preferably, the ferromagnetic layer 8 has a magnetization oriented perpendicular to the ferromagnetic layer 8. This magnetization may also be referred to as "out-of-plane" magnetization. In particular in the case of multilayer systems or hybrid systems composed of rare earths and transition metals, such a directional magnetization is very easy to set. For dimensionally appropriate layers, in particular in terms of layer thickness, an "out-of-plane" magnetization can occur spontaneously. The permanent external magnetic field is thus eliminated, which improves the practical usability of the laser 1.

More preferably, at least some of the injection contacts 5, 6 comprise respective tunnel barriers 9. All injection contacts 5, 6 preferably comprise a respective tunnel barrier 9. In particular, the tunnel barrier 9 may be formed of an oxide such as MgO or Al2O 3. Spin injection from the ferromagnetic layer 8 into the active region 12 of the laser 1 can result in considerable spin polarization loss, particularly at the interface between the ferromagnetic layer 8 and the adjacent semiconductor material. In particular, the semiconductor material may be part of the active region 12 or the matching layer 10. In particular, this loss of spin polarization may be due to a large difference between the electrical conductivities of the ferromagnetic and semiconductor materials. This loss of spin polarization can be reduced or avoided entirely by the tunnel barrier 9.

Instead of or in addition to the tunnel barrier 9, the intrinsic properties of the material used can also be used to form the barrier. Preferably, the injection contacts 5, 6 of at least some of the devices 2 are designed as respective schottky contacts. The formation of the injection contacts 5, 6 as schottky contacts may depend on the material properties of the adjacent semiconductor material (e.g., matching layer 10 or active region 12), in particular on its band structure. In this respect, when the device 2 is used for a particular laser 1, a schottky contact in said device 2 is formed.

All injection contacts 5, 6 are preferably designed as schottky contacts. Alternatively, all injection contacts 5, 6 preferably have a respective tunnel barrier 9. However, it is also possible that only some of the injection contacts 5, 6 have a tunnel barrier 9, that other injection contacts 5, 6 are designed as schottky contacts and/or that another part of the injection contacts 5, 6 is designed without a barrier.

Spin-polarized electrons can be injected into the active region 12 of the laser 1 through the injection contacts 5, 6. For example, holes may be injected into active region 12 through one or more mating contacts. The mating contacts are not shown in the figures. Metal electrodes are particularly suitable as mating contacts.

By injecting spin-polarized electrons into the active region 12, polarized light can be generated therein. In the described laser 1, the path between the injection contacts 5, 6 and the active region 12 can be particularly short, since the electrons are injected through one of the reflectors of the laser 1 and are therefore very close to the active region 12. In the embodiment described herein, spin-polarized electrons must pass through the thickness of the matching layer to reach the active region 12. Thus, the distance from the spin-polarized electrons to the active region is much shorter than in conventional configurations. The short path between injection and light generation may prevent electrons from losing spin polarization before reaching the active region 12. If the electrons lose spin polarization before reaching the active region 12, they will not produce polarized light. The path that an electron can travel at the loss of 50% of the original spin polarization is referred to herein as the spin relaxation length. The distance between the injection contacts 5, 6 and the active region 12 is preferably less than the spin relaxation length. In particular, the spin relaxation length may depend on the temperature and/or the magnetic field strength. Due to the small distance between the injection contacts 5, 6 and the active region 12, a higher laser operating temperature can be selected because the relatively small spin relaxation length is sufficient to transfer electrons into the active region while maintaining their spin polarization. Thus, the laser 1 can be used even at temperatures and magnetic field strengths that are more readily available than, for example, tens of mK at tesla. For example, the laser 1 may be used at room temperature and without an external magnetic field.

In particular, the laser 1 may be operated using a method in which spin-polarized electrons are injected into the active region 12 of the laser 1 via the injection contacts 5, 6, and the polarization of the laser light generated by the laser 1 is controlled by the spin polarization of the electrons. The laser light generated in this way can be used in particular for the transmission of information. This information may be encoded by the polarization of the electrons and, therefore, by the polarization of the light produced by the laser 1.

The specific polarization of the generated light can be obtained by injecting electrons with a specific spin polarization. The embodiment shown in fig. 1 comprises differently designed injection contacts 5, 6. The first injection contact 5 may have a first magnetic field direction and thus generate and inject electrons with spin-up. Then, the second injection contact 6 has a magnetic field direction opposite to that of the first injection contact, so that electrons having spin-down can be generated and injected. This allows the entire charge carrier system, i.e. the electrons, to be switched between up and down spins. This results in a cycle of light emission to the right or left. Alternatively, as shown in the example in fig. 3, the injection contact 5 or 6 and the metal contact 13 may be used. The spin-up or spin-down electrons are injected through the injection contacts 5 or 6, which causes a respective spin polarization in the charge carrier system. The same number of spin-up electrons and spin-down electrons can be injected through the metal contact 13, as a result of which the spin polarization in the charge carrier system is reduced. Further, for example, more than two different contact types may be used. The contents described for the first embodiment and the second embodiment can be applied to these embodiments.

In order to be able to change the spin polarization of the electrons, in the embodiment shown in fig. 1 the first injection contacts 5 and the second injection contacts 6 are arranged in an alternating manner. The first injection contact 5 is designed for injecting electrons having a first spin polarization and the second injection contact 6 is designed for injecting electrons having a second spin polarization different from the first spin polarization. In particular, all the first injection contacts 5 may be connected together to a first power supply line, and all the second injection contacts 6 may be connected to a second power supply line. The number of electrons injected through the injection contacts 5, 6 can be set by the intensity of the current applied to the respective power supply line. If current is applied to only the first lead, only electrons having the first spin polarization are injected, thereby generating light having the first polarization. If a current is applied only to the second lead, only the second spin-polarized electrons are injected, thereby generating light having the second polarization. If a current is applied to the first supply line at a first amperage and a current is applied to the second supply line at a second amperage, the polarization obtained can be adjusted by the ratio of the operating points of the two contacts. The alternating arrangement of the first injection contacts 5 and the second injection contacts 6 means that the second injection contacts 6 follow the first injection contacts 5 at least in one direction. The second injection contact 6 preferably follows the first injection contact 5 in each direction. This is the case in the example shown in fig. 2. This alternating arrangement allows electrons of different polarizations to be injected into the active region 12 in a uniformly distributed manner.

The first injection contact 5 and the second injection contact 6 are preferably designed to be different from each other so that the magnetization directions are opposite to each other, whereby the first spin polarization is opposite to the second spin polarization. This can be achieved in particular by magnetizing the ferromagnetic layers 8 of the injection contacts 5, 6 in the opposite direction.

To create the first injection contact 5 and the second injection contact 6, the ferromagnetic layer 8 is preferably formed in such a way that it has an out-of-plane magnetization. This can be achieved, for example, by a multilayer structure. After the ferromagnetic layer 8 is formed, the magnetic domains are oriented in the ferromagnetic layer 8, preferably by applying an external magnetic field to this step in the laser 1 fabrication process. After switching off the external magnetic field, the magnetic domains in the ferromagnetic layer 8 remain aligned in the respective directions. The magnetization of the ferromagnetic layer 8 can be adjusted according to the direction of the external magnetic field. It can be utilized that the magnetization characteristic is a hysteresis curve. It can be seen from the hysteresis curves that a minimum field-coercive field strength is required for the re-magnetization of the respective ferromagnetic layer 8.

In order for the first injection contact 5 and the second injection contact 6 to comprise ferromagnetic layers 8 with opposite magnetization, the ferromagnetic layers 8 preferably have different coercive field strengths in the two types of injection contacts 5, 6, preferably such that the hysteresis curves are of different widths. By applying, for example, an external positive field and then a negative field, differently oriented magnetizations or magnetization directions can be applied to the two types of injection contacts 5, 6. In this way, a higher magnetic field can first be applied in the first direction, so that the ferromagnetic layers 8 of both types of injection contacts 5, 6 are magnetized in the first direction. A magnetic field may then be applied in a second direction, opposite to the first direction, that magnetizes the ferromagnetic layer 8 of the injection contact 5 or 6 only with a narrow hysteresis curve, while the ferromagnetic layer 8 of the other injection contact 5 or 6 remains unchanged.

The width of the hysteresis curve depends, for example, on the spatial extension of the ferromagnetic layer 8, so that different hysteresis curves can be obtained by different dimensions of the injection contacts 5, 6. The embodiment in fig. 1 shows that the ferromagnetic layer 8 in the first injection contact 5 is thinner than the ferromagnetic layer 8 in the second injection contact 6, while the tunnel barrier 9 in the first injection contact 5 is thicker than the tunnel barrier 9 in the second injection contact 6. The different coercive field strengths can be obtained by different layer thicknesses of the ferromagnetic layer 8, so that the ferromagnetic layers 8 of the different injection contacts 5, 6 can be magnetized in opposite directions.

Alternatively or additionally, different material combinations may have different hysteresis curves, so that the two types of injection contacts 5, 6 can be produced by different materials.

Another possibility to have two types of injection contacts with the same material and the same dimensions produce different magnetizations is the photo-magnetic approach. Both types of injection contacts are initially magnetized. An opposing magnetic field with a weaker field strength is then applied in such a way that the hysteresis does not pass, but the material only re-magnetizes. Now, by means of a focused laser, it is possible to scan contact areas of only one contact type, so that the material is heated in these areas just briefly, while areas of the other contact type are not heated. As a result of the heating, the hysteresis curve of the material changes such that the applied external magnetic field is sufficient to magnetize, so that the magnetization directions of the heated contacts coincide, and the contacts then have a magnetization opposite to the first direction of magnetization. In particular, the device obtained by the photo-magnetic process may have injection contacts 5, 6, injection contacts 5, 6 being identical to each other except for the different magnetizations.

Fig. 3 is a schematic cross-sectional view of a second embodiment of a laser 1, which laser 1 has means 2 for injecting spin-polarized electrons and for reflecting the light. The second embodiment is the same as the first embodiment except for the differences described below.

In the second embodiment, only the first injection contacts 5 and the metal contacts 13 are arranged in the grooves 4, so that the injection contacts 5, 6 are not arranged in all grooves 4 of the lattice structure 3. The metal contact 13 is used to inject electrons without spin polarization. In this embodiment, electrons having a first spin polarization may be injected through the first injection contact 5, and electrons having no spin polarization may be injected through the metal contact 13. In contrast, in the first embodiment, electrons having the first spin polarization may be injected through the first injection contact 5, and electrons having the second spin polarization may be injected through the second injection contact 6. In one embodiment, zero spin polarization can be achieved with a simple metal contact 13 without magnetization. The metal contacts 13 do not require a tunnel barrier 9.

The manufacture of the second embodiment is simplified compared to the first embodiment, since only the injection contact 5, i.e. the contact, has to be magnetized, while the metal contact 13 does not require any post-processing.

In the described method for operating a device, in particular a laser, it is preferred that the resonance frequency of the arrangement of the polarization modulation system is formed by influencing, in particular maximizing, by means of birefringence. It is further preferred that the resonance frequency of the polarization modulation system, which is influenced, in particular maximized, is used for, for example, optical data transmission.

List of reference numerals

1 configuration

2 device

3 lattice structure

4 grooves

5 first injection contact

6 second injection contact

7 Metal layer

8 ferromagnetic layer

9 tunnel barrier

10 matching layer

11 mirror

12 active region

13 Metal contact

14 extension part