阅读说明：本技术 一种调控锑化碲薄膜圆偏振光致电流的方法 (Method for regulating and controlling circularly polarized light induced current of tellurium antimonide film ) 是由 俞金玲 潘庆高 赵宜升 程树英 于 2019-10-18 设计创作，主要内容包括：本发明涉及一种调控锑化碲薄膜圆偏振光致电流的方法。该方法通过改变薄膜的厚度,来改变表面粗糙度,从而调控锑化碲薄膜中圆偏振光致电流；锑化碲薄膜中的圆偏振光致电流信号是由上表面态的信号和下表面态的信号叠加而成；由于上表面态和下表面态的自旋轨道耦合的方向是相反的；当薄膜厚度增加时,表面粗糙度增加,上表面态的贡献减小,上表面态和下表面态信号叠加以后下表面态的信号会占主导,从而使得圆偏振光致电流的大小甚至符号发生变化,起到调控锑化碲薄膜中圆偏振光致电流的作用。本发明调控效果显著,简单易行,成本低廉,有利于日后推广应用。(The invention relates to a method for regulating and controlling circularly polarized light induced current of a tellurium antimonide film. The method changes the surface roughness by changing the thickness of the film, thereby regulating and controlling the circular polarization photoinduced current in the tellurium antimonide film; the circularly polarized light current-generating signal in the tellurium antimonide film is formed by superposing a signal in an upper surface state and a signal in a lower surface state; the direction of spin-orbit coupling due to the upper and lower surface states is opposite; when the thickness of the film is increased, the surface roughness is increased, the contribution of the upper surface state is reduced, and the signal of the lower surface state can be dominant after the signals of the upper surface state and the lower surface state are superposed, so that the magnitude and even the sign of circularly polarized light induced current are changed, and the effect of regulating and controlling circularly polarized light induced current in the tellurium antimonide film is achieved. The invention has obvious regulation and control effect, is simple and easy to implement, has low cost and is beneficial to popularization and application in the future.)

1. A method for regulating and controlling circularly polarized light induced current of a tellurium antimonide film is characterized in that the surface roughness of the tellurium antimonide film is changed by changing the thickness of the tellurium antimonide film, and the regulation and control of circularly polarized light induced current in the tellurium antimonide film are realized.

2. The method for regulating and controlling the circularly polarized light induced current of the tellurium antimonide film as claimed in claim 1, wherein the tellurium antimonide film is grown on a (111) plane InP substrate by using a Molecular Beam Epitaxy (MBE) technique; before the growth starts, the vacuum degree of the chamber in the MBE system is pumped to 1.9 multiplied by 10^-19mbar, then the InP substrate is heated to 400 degrees and held at this temperature for half an hour; in the growth process of the tellurium antimonide film, the temperature of the InP substrate is kept at 200 ℃; sb sources and Te sources are used as raw materials for the growth of the outer edges of the molecular beams, and the purity of the Sb sources and the purity of the Te sources are both 99.9999 percent; the beam current ratio of Sb to Te is 6: 1; and annealing for half an hour after the growth of the tellurium antimonide film is finished, wherein the annealing temperature is 240 ℃.

3. The method for regulating and controlling the circularly polarized light induced current of the tellurium antimonide film as claimed in claim 2, wherein the tellurium antimonide film is of a single crystal structure; the tellurium antimonide film is p-type conductive, and the Fermi level enters a valence band; rashba spin splitting in the tellurium antimonide film is small, less than 0.05 eV.

4. The method for regulating and controlling the circularly polarized light induced current of the tellurium antimonide film as claimed in claim 2, wherein the temperature is room temperature.

5. The method for regulating and controlling the circularly polarized light induced current of the tellurium antimonide film as claimed in claim 1, wherein the tellurium antimonide film is excited by laser with a wavelength of 1064 nm.

6. The method for controlling the circularly polarized light induced current of the tellurium antimonide film as claimed in claim 1, wherein the thickness of the tellurium antimonide film is between 7 and 30 nm.

7. The method for controlling the circularly polarized light induced current of the tellurium antimonide film as claimed in claim 1, wherein the size of the tellurium antimonide film is 2 x 5mm²(ii) a The electrode on the tellurium antimonide film is a Ti/Au electrode, the thickness of Ti is 10 nanometers, and the thickness of gold is 100 nanometers; the diameter of the Ti/Au electrode is 0.5mm, and the electrode distance is 1 mm.

8. The method for regulating and controlling the circularly polarized light induced current of the tellurium antimonide film as claimed in claim 5, wherein the power of the excitation light with the wavelength of 1064nm is 30-250 mW; the power stability of the excitation light of 1064nm is that the power fluctuation within four hours is not more than 1%; wherein, the spot size of the excitation light with 1064nm hitting on the tellurium antimonide film is a circular spot with the diameter of 0.8mm, and the spot intensity is in Gaussian distribution.

Technical Field

The invention relates to the field of polarized light current regulation, in particular to a method for regulating and controlling circularly polarized light induced current of a tellurium antimonide film.

Background

The surface state of the three-dimensional topological insulator is locked by spin momentum because the surface state has strong spin orbit coupling effect and is protected by time reversal symmetry. Therefore, the method has good application prospect in the aspects of quantum computing and spintronics. The three-dimensional topological insulator tellurium antimonide has a simpler energy band structure, so that the three-dimensional topological insulator tellurium antimonide is widely concerned by people. However, the tellurium antimonide material which is usually grown is conductive in body state due to defects of the material and doping of the environment. Therefore, it is difficult to separate the signal of the surface state by the general transport measurement method. The circularly polarized light induced current requires a system with special symmetry, so that a surface state signal can be separated from a bulk state conductive tellurium antimonide film. Has a state of being D_3dA symmetric point group, so that no circularly polarized light is generated to generate current, and the surface state is C_3vThe symmetry point group can generate circularly polarized light induced current. Therefore, circularly polarized light induced current is a powerful tool for studying the surface state of tellurium antimonide of the three-dimensional topological insulator.

However, at present, no method for effectively regulating and controlling circularly polarized light induced current of three-dimensional topological insulator tellurium antimonide exists.

Disclosure of Invention

The invention aims to provide a method for regulating and controlling circularly polarized light induced current of a tellurium antimonide film, which has the advantages of obvious regulation and control effect, simplicity, practicability, low cost and contribution to popularization and application in the future.

In order to achieve the purpose, the technical scheme of the invention is as follows: the method for regulating and controlling circularly polarized light induced current of the tellurium antimonide film changes the surface roughness of the tellurium antimonide film by changing the thickness of the tellurium antimonide film, and realizes the regulation and control of circularly polarized light induced current in the tellurium antimonide film.

In an embodiment of the invention, the tellurium antimonide film is grown on a (111) plane InP substrate by using a molecular beam outer edge technique; before the growth begins, the vacuum degree of a chamber in the MBE system is pumpedTo 1.9X 10^-19mbar, then the InP substrate is heated to 400 degrees and held at this temperature for half an hour; in the growth process of the tellurium antimonide film, the temperature of the InP substrate is kept at 200 ℃; sb sources and Te sources are used as raw materials for the growth of the outer edges of the molecular beams, and the purity of the Sb sources and the purity of the Te sources are both 99.9999 percent; the beam current ratio of Sb to Te is 6: 1; and annealing for half an hour after the growth of the tellurium antimonide film is finished, wherein the annealing temperature is 240 ℃.

In an embodiment of the present invention, the tellurium antimonide thin film is of a single crystal structure; the tellurium antimonide film is p-type conductive, and the Fermi level enters a valence band; rashba spin splitting in the tellurium antimonide film is small, less than 0.05 eV.

In an embodiment of the present invention, the temperature is room temperature.

In one embodiment of the present invention, a laser with a wavelength of 1064nm is used to excite the tellurium antimonide thin film.

In an embodiment of the present invention, the thickness of the tellurium antimonide film is between 7 and 30 nanometers.

In an embodiment of the invention, the size of the tellurium antimonide film is 2 x 5mm²(ii) a The electrode on the tellurium antimonide film is a Ti/Au electrode, the thickness of Ti is 10 nanometers, and the thickness of gold is 100 nanometers; the diameter of the Ti/Au electrode is 0.5mm, and the electrode distance is 1 mm.

In one embodiment of the present invention, the power of the excitation light of 1064nm is 30-250 mW; the power stability of the excitation light of 1064nm is that the power fluctuation within four hours is not more than 1%; wherein, the spot size of the excitation light with 1064nm hitting on the tellurium antimonide film is a circular spot with the diameter of 0.8mm, and the spot intensity is in Gaussian distribution.

Compared with the prior art, the invention has the following beneficial effects:

1. the method for regulating and controlling the circularly polarized light induced current of the three-dimensional topological insulator tellurium antimonide film is quite simple and easy to implement, low in cost and beneficial to popularization and application in the future.

2. The method for regulating and controlling the circularly polarized light induced current of the three-dimensional topological insulator tellurium antimonide film has obvious regulation and control effect and larger regulation and control range.

Drawings

Fig. 1 is a schematic diagram of an experimental optical path according to an embodiment of the present invention.

FIG. 2 shows a curve of change of photocurrent with quarter-wave plate rotation angle, a formula fitting curve, and circularly polarized light induced Current (CPGE) and linearly polarized light induced current (L) obtained by fitting, which are generated by a Te antimonide thin film with a thickness of 7 nm and 30 nm under 1064nm laser excitation, according to an embodiment of the present invention₁And L₂) And background current (y)₀) (ii) a The incident angle was-30 degrees.

Fig. 3 is a graph showing the change of circularly polarized light induced current with incident angle under the excitation of 1064nm laser by using 7 nm, 20 nm and 30 nm thick tellurium antimonide films according to the embodiment of the present invention.

FIG. 4 is a surface atomic force microscopy topographic map of a tellurium antimonide film having a thickness of 7 nanometers (a), 20 nanometers (b), and 30 nanometers (c), respectively, as utilized in an embodiment of the present invention.

Fig. 5 is a schematic diagram of the optical paths of the laser used in the embodiment of the present invention for front incidence (a) and back incidence (b).

Fig. 6 shows the relationship between the circularly polarized light current and the incident angle in the case of laser back incidence, for the applied tellurium antimonide thin films with the thickness of 7 nm (a), 20 nm (b) and 30 nm (c), respectively.

Detailed Description

The technical scheme of the invention is specifically explained below with reference to the accompanying drawings.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

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 according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The embodiment provides a method for circularly polarizing photoinduced current in a tellurium antimonide film, and particularly changes the surface roughness of the tellurium antimonide film by changing the thickness of the tellurium antimonide film, so as to realize regulation and control of the circularly polarizing photoinduced current in the tellurium antimonide film.

In this embodiment, the tellurium antimonide film for measurement is grown on the InP substrate with (111) plane by using molecular beam outer edge technique; before the growth starts, the vacuum degree of the chamber in the MBE system is pumped to 1.9 multiplied by 10^-19mbar, then the substrate was heated to 400 degrees and held at this temperature for half an hour. During the growth of the sample, the substrate temperature was maintained at 200 degrees. Sb sources and Te sources are used as raw materials for the growth of the outer edges of the molecular beams, and the purity of the Sb sources and the purity of the Te sources are both 99.9999 percent; the beam current ratio of Sb to Te is 6: 1; and (4) annealing for half an hour after the growth of the film is finished, wherein the annealing temperature is 240 ℃. The adopted tellurium antimonide film sample is of a single crystal structure; the adopted tellurium antimonide film sample is p-type conductive, and the Fermi level enters the valence band. Rashba spin splitting in the tellurium antimonide film is small, less than 0.05 eV. The test temperature of the sample was room temperature.

In this example, a laser with a wavelength of 1064nm was used to excite the sample.

In this example, samples of different thicknesses were grown, the thickness of the samples being 7 nm, 20 nm and 30 nm, respectively.

In this example, the size of the Te antimonide film sample is 2X 5mm²(ii) a The electrode on the tellurium antimonide film sample is a Ti/Au electrode, the thickness of Ti is 10 nanometers, and the thickness of gold is 100 nanometers; the diameter of the Ti/Au electrode is 0.5mm, and the electrode distance is 1 mm.

In the embodiment, the power of the 1064nm excitation light is 30-250 mW; the power stability of the 1064-nanometer laser is that the power fluctuation within four hours is not more than 1%; wherein, the spot size of the 1064nm laser on the sample is a circular spot with a diameter of 0.8mm, and the spot intensity is Gaussian distributed.

Specifically, the following provides a specific implementation procedure of the present embodiment.

First, in this example, a molecular beam epitaxy apparatus was used to grow 7 nm, 20 nm and 30 nm thick tellurium antimonide films on a (111) plane InP substrate. The size of the tellurium antimonide film is 2 multiplied by 5mm². Before the growth starts, the vacuum degree of the chamber in the MBE system is pumped to 1.9 multiplied by 10^-19mbar, then the substrate was heated to 400 degrees and held at this temperature for half an hour. During the growth of the sample, the substrate temperature was maintained at 200 degrees. Sb sources and Te sources are used as raw materials for the growth of the outer edges of the molecular beams, and the purity of the Sb sources and the purity of the Te sources are both 99.9999 percent; the beam current ratio of Sb to Te is 6: 1; and (4) annealing for half an hour after the growth of the film is finished, wherein the annealing temperature is 240 ℃.

Then, a pair of Ti/Au electrodes with the size of a circular electrode with the diameter of 0.5mm and the electrode spacing of 1mm are grown on the tellurium antimonide film. The thickness of the Ti electrode was 10nm, and the thickness of the Au electrode was 100 nm. By adopting the test light path shown in fig. 1, laser from a laser passes through a chopper, a polarizer and a quarter wave plate in sequence and then strikes the midpoint of a connecting line of two electrodes on a sample. The diameter of the light spot is 0.8mm, and the intensity distribution of the light spot is Gaussian distribution. The incident angle of the laser is denoted as Θ₀。

Under the irradiation of the laser light, a photocurrent will be generated in the sample. This photocurrent was collected by two circular electrodes. And the current enters a preamplifier to be amplified and then enters a phase-locked amplifier. The reference frequency of the lock-in amplifier is the frequency of the chopper, and 231Hz is adopted in the embodiment. The photocurrent measurement temperature was room temperature.

In this example, 1064nm laser was used as the excitation light, and the power of the laser was 80 mW. The power stability of the laser is good, and the power fluctuation within four hours is not more than 1%. The embodiment changes the incident angle of light from 30 degrees to-30 degrees by 10 degrees. At each angle of incidence, the quarter wave plate is rotated from 0 degrees to 360 degrees in steps of 5 degrees. And recording the photocurrent of each quarter-wave plate at the rotation angle by a data acquisition card of a computer. Origin software was used to plot photocurrent against quarter wave plate rotation angle at a certain angle of incidence, as shown in fig. 2. Fig. 2 corresponds to an angle of incidence of-30 degrees. FIGS. 2(a) and (b) are graphs of photocurrent as a function of quarter-wave plate rotation angle for 30 and 7 nm thick Te antimonide films, respectively.

The data were fitted using equation (1) as follows:

J＝Csin(2α)+L₁sin(4α)+L₂cos(4α)+y₀formula (1)

Wherein C represents circularly polarized light induced Current (CPGE) generated by circularly polarized light excitation, and L₁And L₂Represents the linearly polarized current, y, generated by linearly polarized light excitation₀Representing background current due to photovoltaic effect, thermoelectric effect, etc. The fitted curve is shown as a solid line in fig. 2. The circularly polarized light induced current CPGE and the linearly polarized light induced current L can be obtained by fitting₁And L₂And background current y₀. This embodiment thus allows the measurement of circularly polarized light induced current when the angle of incidence is changed from 30 degrees to-30 degrees, as shown in fig. 3. The circularly polarized light induced current in fig. 3 and 2 has been normalized by the optical power, i.e. the circularly polarized light induced current divided by the optical power. The relationship between the circularly polarized light induced current in the tellurium antimonide film and the change of the incident angle is described by the following formula (2):

in the formula, theta₀For the angle of incidence, n is the refractive index of the topological insulator tellurium antimonide, and A is the fitting parameter. In this example, equation (2) is used to fit the change of circularly polarized light induced current in the tellurium antimonide film with the incident angle, and the fitting result is shown as the solid line in fig. 3. Therefore, the fitting result is better. As can be seen from fig. 3, when the incident angle is 30 degrees, the magnitude of the circularly polarized light current in the tellurium antimonide film changes from positive to negative as the film thickness increases.

Then, we measured the surface morphology of the three tellurium antimonide films with different thicknesses by using an atomic force microscope, and the surface roughness of the sample is obtained by analyzing the surface morphology. During measurement, different positions on a sample are selected for measurement, and finally, the surface roughness measured at different positions is averaged to obtain the surface roughness value of the sample. FIG. 4 is an image of typical surface topography measured by atomic force microscopy of a sample of tellurium antimonide thin film having thicknesses of 7 nm, 20 nm and 30 nm, respectively. By analytical measurements, we measured root mean square roughness of the surface of 7 nm, 20 nm and 30 nm thick tellurium antimonide films as 0.91, 1.27 and 1.71 nm, respectively. It can be seen that the surface roughness increases with increasing thickness.

By Hall measurement, we measured the carrier concentrations of the Te antimonide films of 7 nm, 20 nm and 30 nm in thickness to be 4.5X 10¹³、6.6×10¹³And 6.5X 10¹³cm^-2. From the value of the carrier concentration we can deduce that the fermi level at this point has entered the bulk valence band. The conductivity types of these three samples are known to be p-type conductivity by hall measurements. Based on theoretical calculations and angle-resolved photoelectron spectroscopy measurements, it is known that the band structure of a tellurium antimonide film hardly changes with thickness when the film thickness is greater than 7 nm. And from our hall measurement structure, there is also no great difference in fermi levels of thin films with thicknesses of 7 nm, 20 nm, and 30 nm. Such a slight difference in fermi levels does not cause circularly polarized light to have an opposite sign to the current. Therefore, the inversion phenomenon that the circularly polarized light induced current increases with the film thickness from 7 nm to 30 nm may be caused by the increase in the surface roughness with the increase in the thickness.

To verify our hypothesis, we measured circularly polarized light induced current at the back incidence of the laser, the measurement results are shown in fig. 6. Fig. 5(a) and (b) are experimental graphs of light paths of laser light incident from the front and back, respectively. Comparing fig. 4 and fig. 6, we found that, for a given incident angle (e.g., +30 degrees), when the laser is changed from front-side incidence to back-side incidence, the circularly polarized light current of the tellurium antimonide film with a thickness of 7 nm shows opposite sign, but the circularly polarized light current of the tellurium antimonide film with a thickness of 20 nm and 30 nm does not show opposite sign, and when the laser is incident on the back-side, the circularly polarized light current of the tellurium antimonide film with a thickness of 20 nm and 30 nm is much larger than that of the laser in the case of front-side incidence. According to the literature, this phenomenon indicates that the upper and lower surface states of a sample having a thickness of 7 nm are equally efficient in generating circularly polarized current. At this time, when the laser is incident from the front, the light intensity received by the upper surface state is stronger than that of the lower surface state, so that the circularly polarized light current of the upper surface state is dominant, and when the laser is incident from the back, the light intensity received by the lower surface state is stronger than that of the upper surface state, so that the lower surface state is dominant. When the laser light is changed from front incidence to back incidence, the sign of the circularly polarized light current of the 7 nm sample is reversed. For samples with thicknesses of 20 nm and 30 nm, when the laser light changes from front incidence to back incidence, no inversion phenomenon occurs in the circularly polarized light induced current, and the circularly polarized light induced current is larger when the laser light is incident on the back than when the laser light is incident on the front, which indicates that the lower surface state is dominant in both front incidence and back incidence. In combination with the surface roughness measured by atomic force microscopy, we can conclude that: as the thickness of the film increases, the surface roughness of the film increases, thereby increasing circularly polarized light induced current generated by the upper surface state; since the directions of the circularly polarized currents generated by the upper surface state and the lower surface state are opposite, the superposition of the circularly polarized currents generated by the upper surface state and the lower surface state changes from the upper surface dominance to the lower surface dominance with the increase of the thickness, so that the circularly polarized currents are opposite in sign with the increase of the thickness. Therefore, the surface roughness can be adjusted by adjusting the thickness of the sample, so that the circularly polarized light induced current of the three-dimensional topological insulator tellurium antimonide film can be effectively adjusted and controlled.

In conclusion, the method for regulating and controlling the circularly polarized light induced current of the three-dimensional topological insulator tellurium antimonide film provided by the embodiment is convenient to realize, low in cost and good in regulation and control effect.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.