阅读说明：本技术 一种太赫兹波光控调制器及其制备方法 (Terahertz wave light-operated modulator and preparation method thereof ) 是由 鲁远甫 佘荣斌 李光元 刘文权 张锐 于 2019-09-18 设计创作，主要内容包括：一种基于钝化工艺生长钝化膜的太赫兹波光控调制器及其制备方法,其中,在本征半导体材料上,利用原子层沉积系统、等离子体增强化学的气相沉积法或者低压力化学气相沉积法在半导体材料的太赫兹波入射面和太赫兹波出射面上都沉积钝化层,所述钝化层为氧化铝膜、氮化硅或者氧化硅。使用钝化工艺来改善本征半导体材料的表面缺陷,从而获得更高的载流子浓度,如此能够降低太赫兹波相关系统对照明的要求和成本,便于系统更加集成和用户的操作。此外,钝化层能隔绝半导体与空气的接触,防止氧化和污染,增强了太赫兹波光控调制器的稳定性,提高了调制器的使用寿命。(A terahertz wave light-operated modulator based on a passivation process to grow a passivation film and a preparation method thereof are disclosed, wherein passivation layers are deposited on a terahertz wave incident surface and a terahertz wave emergent surface of an intrinsic semiconductor material by utilizing an atomic layer deposition system, a plasma enhanced chemical vapor deposition method or a low-pressure chemical vapor deposition method, and the passivation layers are aluminum oxide films, silicon nitride or silicon oxide. The surface defects of the intrinsic semiconductor material are improved by using a passivation process, so that higher carrier concentration is obtained, the requirement and cost of a terahertz wave correlation system on illumination can be reduced, and the system is more integrated and is convenient for operation of a user. In addition, the passivation layer can isolate the contact of the semiconductor and air, prevent oxidation and pollution, enhance the stability of the terahertz wave light-operated modulator and prolong the service life of the modulator.)

1. A method for preparing a terahertz wave light-operated modulator selects an intrinsic semiconductor material, and is characterized by comprising the following steps of:

respectively depositing a passivation layer on a terahertz wave incident surface and a terahertz wave emergent surface of the intrinsic semiconductor material;

the deposition operation uses one of an atomic layer deposition method, a plasma enhanced chemical vapor deposition method, or a low pressure chemical vapor deposition method;

the passivation layer is made of aluminum oxide, silicon nitride or silicon oxide.

2. The method of claim 1, wherein the depositing is accomplished using an atomic layer deposition system, the depositing comprising:

s21, self-cleaning of the atomic layer deposition system;

s22, preheating the atomic layer deposition system, and placing a semiconductor material;

s23, setting system parameters, wherein the system parameters comprise the deposition cycle number;

s24, depositing a passivation layer on the terahertz wave incident surface or the terahertz wave emergent surface of the semiconductor material;

s25, taking out, turning over and repeating the steps S21-S24;

s26, placing the blank into an annealing furnace for rapid annealing;

wherein, in the step S22, before the semiconductor material is placed, a protection operation is further performed on the non-deposition surface of the semiconductor material.

3. The method of claim 2, wherein the protecting operation is adhering a non-deposition surface with a polyimide film.

4. The method of claim 2, wherein the protecting is accomplished by placing the non-deposition surface in close proximity to a surface of another semiconductor material.

5. The method according to claim 2, wherein the passivation layer is subjected to an antireflection treatment, the antireflection treatment including selecting an optimum thickness of the passivation layer according to an incident angle when the terahertz wave light control modulator is used; the optimal thickness is such that the reflectivity of the passivation layer is lowest.

6. The method of claim 5, wherein the number of deposition cycles in step S23 is determined according to the optimal thickness.

7. The method of claim 6, wherein the step S23 comprises setting the flow time of the aluminum source to 8S, the purge time of the nitrogen gas to 23S, the flow time of the water source to 8S, and setting the number of deposition cycles to 1230.

8. The method of claim 2, wherein: a cleaning process is also included before step S21; the cleaning process comprises the following steps:

s11, cleaning the semiconductor material by using acetone;

s12, washing with ultrapure water;

s13, etching by using hydrofluoric acid;

s14, taking out the etched semiconductor material, and adding ultrapure water for cleaning.

9. The method according to claim 2, wherein the step S26 is a rapid annealing at 400 ℃ for 5 minutes under a nitrogen atmosphere.

10. A terahertz wave light control modulator prepared by using the method of any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of terahertz wave sensing and imaging, in particular to a terahertz wave regulating and controlling device.

Background

Terahertz wave refers to (frequency)Rate 10¹¹Hz-10¹³Hz or wavelength 30 μm-3mm) between the microwave band and the optical band. It is in a particular position in the transition from electronics to photonics in the electromagnetic spectrum and therefore has unique properties. For example, many important biological molecules (e.g., proteins, DNA) and biological cells are characterized by low frequency vibrations (e.g., collective vibrations of the backbone of the molecule, rotation, and weak forces between molecules) in the terahertz spectrum (spectral fingerprinting). Based on terahertz spectrum analysis, relevant information such as spatial conformation, reaction kinetics, hydration, biological function and the like of biomolecules can be analyzed. In addition, terahertz wave can penetrate through various nonpolar materials (paper, plastic, ceramic and the like), and hidden target imaging is realized. Particularly, compared with the widely applied X-ray, the terahertz wave has lower photon energy (0.41-41meV), so that the terahertz wave has no damage to biological molecules and no ionization to biological cells, and can be used as an ideal biomedical nondestructive detection means. The sensing and imaging of terahertz waves are regarded as one of the most important application technologies of terahertz waves, and abundant physical and chemical information of a sample to be detected is obtained by analyzing the interaction between the terahertz waves and the sample to be detected, so that the terahertz waves are generally concerned by scientific research and the industry due to the intuition.

The terahertz wave modulator is an indispensable device for researching terahertz wave sensing and imaging, and the efficient and stable terahertz wave regulating and controlling device is the basis for researching terahertz science and technology. Since the start of the terahertz wave technology is late, an effective terahertz wave modulator device still needs to be developed. The modulation mechanism for regulating and controlling the terahertz waves comprises amplitude modulation, frequency modulation, phase modulation and polarization modulation. At present, the mature regulation and control mode of terahertz waves is amplitude modulation control, the realization means comprises electric control, light control, thermal control and nonlinear control, and the change of certain parameters of a modulator, such as refractive index, absorptivity and other parameters, is controlled through external change, so that the transmissivity or reflectivity of the terahertz waves is controlled.

Among the existing terahertz wave modulator devices, light-operated semiconductor (such as silicon, germanium, gallium arsenide, etc.) modulators are widely used in terahertz wave imaging and terahertz wave communication systems. The light control method is characterized in that pumping light is utilized to irradiate a semiconductor, and when photon energy exceeds the forbidden bandwidth of the semiconductor, carriers are generated, so that the conductivity of the semiconductor is changed, the transmittance of terahertz waves is influenced, and the function of controlling the terahertz waves by the pumping light is realized. The light control method has high control speed and high control accuracy, and is generally accepted by people. In general, the pump light can adjust the terahertz wave by irradiating the pump light onto the semiconductor to generate a temporary region with high reflectivity, and the terahertz wave is simultaneously incident on the region with high reflectivity, so that the terahertz wave is modulated by changing the on-off of the pump light. Shrekhamer et al irradiates intrinsic semiconductor silicon with a 980nm continuous laser at an output of 2W to realize a modulation depth of 67% for terahertz waves (modulation depth ═ terahertz wave transmittance without illumination-terahertz wave transmittance with illumination)/terahertz wave transmittance without illumination); busch et al achieved 94.8% modulation depth by irradiating intrinsic silicon with a 100fs laser; born et al use a 808nm continuous laser to output 2.28W of power to irradiate intrinsic silicon to realize 90% of modulation depth of terahertz waves. However, in order to realize that the modulation device effectively regulates and controls the terahertz waves and obtain higher photo-generated carrier concentration, such modulators often need to be equipped with a high-energy laser for illumination, such as a common amplified femtosecond laser, which substantially increases the cost and complexity of the whole system, is not beneficial to the integration of the system, cannot guarantee the safety in implementation, cannot recognize the operability, and cannot meet the integration requirements of terahertz wave imaging, sensing and communication.

In contrast, in the prior art, the efficiency of the terahertz wave light control modulator can be improved by utilizing the heterojunction effect of the two-dimensional material and the semiconductor, so that the requirement of the light control modulator on illumination is reduced. Weis and the like transplant single-layer graphene on intrinsic silicon, most of carriers excited by silicon flow to the graphene by utilizing the high electron mobility of two-dimensional graphene, and then the carrier concentration is sharply increased, so that the high-efficiency terahertz wave modulation is realized. On the same principle, the illiterate industry and the like transfer single-layer graphene on intrinsic germanium, and a 1550nm laser is used for illumination, so that the 94% modulation depth is realized; in addition, yangtong et al propose transfer of WS2 nanoplates on intrinsic silicon, achieving 56.7% terahertz wave modulation at 800nm continuous laser, 50mW illumination, 94.8% terahertz wave modulation at 470 mW. Even so, because the two-dimensional material is usually not stable enough, great problems will be brought about in the preservation and use of the device, and it is also very difficult to prepare the two-dimensional material on the device, and the cost of manufacture itself is high, which makes the terahertz light control modulator prepared with the two-dimensional material difficult to be moved out of a laboratory to meet practical applications.

Based on the current situation, in the field of terahertz wave sensing and imaging technology, a better technical scheme is obviously needed to solve the technical problems of high cost, high complexity, difficulty in storage and the like of the existing light-operated semiconductor modulator.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a terahertz wave efficient light control modulator based on a passivation process based on the attributes of semiconductor materials. Through the passivation technology, the service life of a current carrier of the semiconductor device is prolonged, the modulation depth of the semiconductor device is greatly improved, and meanwhile, the passivation layer has a protection effect on the device, so that the device is further far away from the influence of the external environment, and the whole semiconductor device has better stability.

Specifically, the application provides a method for preparing a terahertz wave light-operated modulator, which selects an intrinsic semiconductor material and is characterized in that passivation layers are respectively deposited on a terahertz wave incident surface and a terahertz wave emergent surface of the intrinsic semiconductor material; the deposition operation uses one of an atomic layer deposition method, a plasma enhanced chemical vapor deposition method, or a low pressure chemical vapor deposition method; the passivation layer is made of aluminum oxide, silicon nitride or silicon oxide.

In one embodiment, when the deposition operation is completed using an atomic layer deposition system, the deposition operation includes the steps of:

s21, self-cleaning of the atomic layer deposition system;

s22, preheating the atomic layer deposition system, and placing a semiconductor material;

s23, setting system parameters, wherein the system parameters comprise the deposition cycle number;

s24, depositing a passivation layer on the terahertz wave incident surface or the terahertz wave emergent surface of the semiconductor material;

s25, taking out, turning over and repeating the steps S21-S24;

s26, placing the blank into an annealing furnace for rapid annealing;

wherein, in the step S22, before the semiconductor material is placed, a protection operation is further performed on the non-deposition surface of the semiconductor material. The protective operation is preferably performed by adhering a polyimide film to the non-deposition surface. Alternatively, the protecting operation may be performed by placing the non-deposition surface in close proximity to a surface of another semiconductor material.

Further preferably, the passivation layer is subjected to antireflection treatment, and the antireflection treatment includes selecting an optimal thickness of the passivation layer according to an incident angle when the terahertz wave light-operated modulator is used; the optimal thickness is such that the reflectivity of the passivation layer is lowest. Further, the number of deposition cycles in the step S23 is determined according to the optimal thickness, so as to prepare a passivation layer with a proper thickness.

Specifically, when the passivation layer is aluminum oxide, the step S23 includes setting the aluminum source flowing time to be 8S, the nitrogen purging time to be 23S, the water source flowing time to be 8S, and setting the number of deposition cycles to be 1230.

A cleaning process may be further included before step S21 to clean the semiconductor material during transportation; the cleaning process comprises the following steps:

s11, cleaning the semiconductor material by using acetone;

s12, washing with ultrapure water;

s13, etching by using hydrofluoric acid;

s14, taking out the etched semiconductor material, and adding ultrapure water for cleaning.

Preferably, the step S26 is a rapid annealing at 400 ℃ for 5 minutes under a nitrogen atmosphere.

Correspondingly, the application also provides a terahertz wave light-operated modulator prepared by the preparation method.

Compared with the prior art, the invention adopts a brand new means, namely the terahertz wave light-operated modulator is prepared by using a passivation process, so that the surface of the modulator is provided with a passivation layer and can have higher photo-generated carrier concentration, thus realizing the high-efficiency modulation of the terahertz wave light control, reducing the requirements of the terahertz wave relation system on illumination and the cost of the system, being convenient for the system to be more integrated and being more convenient for the user to operate and use. In addition, the passivation layer can also isolate the contact of a semiconductor and air, and prevent oxidation and pollution, so that the stability of the terahertz wave light-operated modulator is enhanced due to the introduction of the passivation process, and the service life of the modulator is prolonged.

The foregoing description is only an overview of the technical solutions of the present application, and in order to make the technical solutions of the present application more clear and clear, and to implement the technical solutions according to the content of the description, the following detailed description is made with reference to the preferred embodiments of the present application and the accompanying drawings.

Drawings

FIG. 1 is a schematic view of the process for preparing an alumina film by the passivation process of the present invention;

FIG. 2 is a schematic view of a single layer antireflective film;

FIG. 3 is a graph showing the variation of reflectivity and minimum reflective film thickness with incident angle;

FIG. 4 is a schematic diagram of the selection of the optimal thickness of the film at a fixed incident angle;

FIG. 5 is a schematic diagram of an enhanced imaging experiment;

FIG. 6 is a flow chart of an imaging implementation method.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be described in detail and completely with reference to the following specific embodiments of the present application and the accompanying drawings. It should be apparent that the described embodiments are only some of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The basic working principle of the terahertz wave light-operated modulator is that pumping light is utilized to irradiate a semiconductor, when photon energy exceeds the forbidden bandwidth of the semiconductor, the semiconductor can generate photon-generated carriers, and the concentration of the carriers can change the conductivity of the semiconductor. Terahertz waves are electromagnetic waves to which semiconductor materials such as intrinsic silicon (or germanium) are transparent. However, if the concentration of photogenerated carriers increases, the conductivity of the semiconductor increases, thereby affecting the transmittance of the terahertz wave, which decreases as the concentration of carriers increases. According to the formula

Wherein n is the refractive index 3.418, the transmittance T and the conductivityIn inverse ratio, Z₀377 Ω, d semiconductor thickness, f frequency, m relative mass, ε₀Is the vacuum dielectric constant and e is the charge amount. Carrier concentration N proportional to conductivityTherefore, the larger the conductivity is, the larger the carrier concentration is, and the lower the transmittance of the terahertz wave is. The photogenerated carrier concentration also depends on temperature, light, semiconductor material, etc. Under the conditions that the device is not changed and the environment temperature is not changed, the carrier concentration can be directly changed by changing the illumination intensity according to a formula

Where a is the illumination area size, R is the reflectivity, h υ is the photon energy, d is the device thickness, and τ is the carrier lifetime (the average time from generation to recombination of photogenerated carriers). The carrier concentration N is proportional to the illumination intensity I, which is also the reason why the conventional photo-modulator uses high-power laser illumination to achieve high modulation depth. However, in addition to the illumination conditions, certain parameters of the semiconductor material itself may also determine the carrier concentration, such as carrier lifetime τ. The carrier concentration N and the lifetime τ are also in a proportional relationship. Carrier lifetimes include semiconductor body lifetimes, surface lifetimes and starvation lifetimes,

since low resistance attenuates terahertz waves in the terahertz wave band, a high-resistance intrinsic semiconductor is often used. For intrinsic semiconductor materials, however, since bulk defects are small, the lifetime of the charge carriers is very large, and the crystal lattice is relatively stable, and the lifetime of starvation is not considered, only the surface lifetime in formula (3) needs to be considered when considering the lifetime of the charge carriers in formula (2). In the case where the carrier lifetime of the modulator is mainly determined by the surface lifetime, the most significant factor affecting the carrier lifetime (i.e., affecting the surface lifetime) is also the surface defect, and the surface defect generally includes surface-attached impurities, a sacrificial oxide layer on the surface, and the like. Due to the presence of surface defects, defect levels are introduced, and the generated carriers are heavily recombined by the defects, resulting in a reduction in carrier lifetime. Therefore, if the surface defects can be improved, it will be possible to maintain the carrier lifetime at a large value, so that a higher carrier concentration can be obtained, which would be very advantageous for the terahertz wave modulator.

Passivation processes were first used on metals, with the activated metal being protected from corrosion by metal oxides. Subsequently, the process is also used for the preparation of a solar cell processing anti-conductive insulating layer and the packaging in the semiconductor field. In semiconductor devices such as silicon chips and the like, the passivation process can improve surface defects and protect the semiconductor from being oxidized by the outside, and the characteristics can help to improve the performance of the terahertz light-operated modulator. In the passivation process, an Atomic Layer Deposition (ALD) system, a Plasma Enhanced Chemical Vapor Deposition (PECVD) method or a Low Pressure Chemical Vapor Deposition (LPCVD) method may be used to deposit passivation on the semiconductor materialLayers, e.g. depositing aluminium oxide film (Al)₂O₃) Silicon nitride or silicon oxide. The deposited passivation layer has the characteristics of dense film and good uniformity, so that the passivation layer can be widely used for semiconductor materials. Based on the above characteristics of the passivation process, the present invention provides a terahertz wave light control modulator based on a passivation process to grow a passivation film, wherein a passivation layer, such as an aluminum oxide film (Al) is deposited on an intrinsic semiconductor material by using an atomic layer deposition system (ALD), a Plasma Enhanced Chemical Vapor Deposition (PECVD) or a Low Pressure Chemical Vapor Deposition (LPCVD) method₂O₃) And silicon nitride or silicon oxide, thereby improving the surface defects of the intrinsic semiconductor material, obtaining higher carrier concentration and reducing the requirement of the terahertz wave modulator on illumination.