CN110095888B - Terahertz modulator based on silicon-based microstructure on SOI (silicon on insulator), system and method - Google Patents

Terahertz modulator based on silicon-based microstructure on SOI (silicon on insulator), system and method Download PDF

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CN110095888B
CN110095888B CN201910376814.8A CN201910376814A CN110095888B CN 110095888 B CN110095888 B CN 110095888B CN 201910376814 A CN201910376814 A CN 201910376814A CN 110095888 B CN110095888 B CN 110095888B
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terahertz
silicon
layer
modulator
microstructure
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CN110095888A (en
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文岐业
张豪
申朝阳
何雨莲
杨青慧
谭为
冯正
张怀武
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University of Electronic Science and Technology of China
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0102—Constructional details, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/13—Function characteristic involving THZ radiation

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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
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Abstract

The invention provides a terahertz modulator based on a silicon-based microstructure on SOI (silicon on insulator), a preparation method and a modulation system thereof, wherein the terahertz modulator sequentially comprises the following components from bottom to top: bottom layer of Al2O3Substrate, SiO2Spacer layer, silicon-based microstructure, Al2O3Passivation layer with silicon-based microstructure on SiO2The isolation layers are periodically arranged, each silicon-based microstructure comprises two layers of square Si base step structures, and the modulation system comprises: the terahertz wave detector has a reflectivity of below 22% for terahertz waves of 0.4-0.85 THz, reaches the lowest 18% at the position of 0.82THz, can remarkably reduce the reflectivity of the modulation device to the terahertz waves, and improves the utilization rate of the terahertz waves; reaching 64.5 percent of modulation depth under the irradiation of 808nm laser with the power of 1200 mw; compared with the traditional silicon-based terahertz modulator, the terahertz imaging diffusion region effectively improves the resolution in the imaging system by over 21.9%.

Description

Terahertz modulator based on silicon-based microstructure on SOI (silicon on insulator), system and method
Technical Field
The invention belongs to the field of terahertz technology and application, relates to a terahertz imaging system and a terahertz amplitude modulation device in the related field, and particularly relates to a terahertz modulator based on a silicon-based microstructure on an SOI (silicon on insulator), a preparation method thereof and a light-operated terahertz modulation system based on the silicon-based microstructure on the SOI.
Background
Terahertz refers to an electromagnetic wave having a frequency in the range of 0.1THz to 10THz and a wavelength in the range of 0.03mm to 3 mm. Compared with X-rays, the terahertz waves can well penetrate through a plurality of nonpolar materials and dielectric materials, and can be used for perspective imaging of opaque objects; the photon energy of terahertz radiation is only millielectron volt (meV) magnitude and is smaller than the bond energy of various chemical bonds, so that various harmful ionization reactions cannot be caused; meanwhile, the water has a strong absorption effect on the terahertz, so that the terahertz radiation cannot penetrate through the skin of a human body or other organisms, and a foundation is laid for supplementing and replacing the terahertz waves as X rays in the security inspection field.
For the light-operated terahertz modulator, a modulation signal of the light-operated terahertz modulator is derived from external excitation laser, when the photon energy of incident laser is larger than the forbidden bandwidth of silicon, ground state electrons in the silicon absorb the energy carried by photons and jump to an excited state to form carriers, namely photo-generated carriers, the process is called as photo-doping, the concentration of the non-equilibrium carriers in the device is increased due to the action, the conductivity of the device is changed before and after the laser is added, the conductivity is improved after the laser is added, the attenuation of terahertz waves during the passing process is enhanced, the amplitude of the terahertz waves transmitted through the device is reduced, and therefore the modulation effect is achieved.
The traditional light-operated terahertz modulator has three main problems, one is that the insertion loss of terahertz waves is too high, the reflection of the traditional high-resistance silicon terahertz modulator on the terahertz waves is as high as 30%, which is a great loss under the conditions that the power of the existing terahertz radiation source is generally low and the sensitivity of a terahertz detector is relatively low, in 2014, Yan Peng, XiaoFei Zang and the like prepare a terahertz perfect absorber based on a double-layer doped silicon grating structure, the air gap mode resonance is excited through a grating array, and through a series of parameter optimization, the absorption rate of 95% of the terahertz waves is finally achieved, namely the reflectivity of the terahertz waves is only 5%, so that the problem of the insertion loss in the terahertz wave transmission is effectively solved; secondly, the modulation depth problem is solved, the modulation depth of the current traditional silicon-based light-operated terahertz amplitude modulator is relatively low, and the requirements of the current terahertz imaging system are difficult to meet; thirdly, the problem of carrier diffusion is that when modulation laser of the light-operated terahertz modulator is incident on the surface of the modulator, generated photon-generated carriers can be diffused to the periphery of a modulation laser signal to generate a larger corresponding area, which is not beneficial to improving the terahertz imaging precision.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide a terahertz modulator based on a silicon-on-SOI microstructure, a method for manufacturing the same, and an optically controlled terahertz modulation system based on the silicon-on-SOI microstructure.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the utility model provides a terahertz modulator based on silicon-based micro-structure on SOI, from supreme down includes in proper order: bottom layer of Al2O3Substrate 12, SiO2Isolation layer 11, silicon-based microstructure 10, Al2O3The passivation layer 9 and the silicon-based microstructures 10 are periodically arranged on the SiO2 isolation layer 11, each silicon-based microstructure 10 comprises two layers of square Si base step structures which are an upper Si base step 101 and a lower Si base step 102 from top to bottom respectively, the centers of the upper Si base step 101 and the lower Si base step 102 are aligned, and the side length of the upper Si base step 101 is smaller than that of the lower Si base step 102.
Preferably, the two square Si-based step structures of the silicon-based microstructure 10 are Si layers, the resistivity of the Si layers is greater than 3000 Ω · cm, and the total thickness of the two square Si-based step structures is 90 μm. Only high-resistance silicon with the resistivity higher than 3000 omega cm can the device generate obvious conductivity change after being illuminated. The total thickness of 90 μm is the size at which the simulation results are optimal.
Preferably, the distance between the centers of two adjacent silicon-based microstructures 10 is 100 μm, the side length of the upper Si-based step 101 is 66 μm, and the height thereof is 45 μm, and the side length of the lower Si-based step 102 is 84 μm, and the height thereof is 45 μm. The size is the size at which the simulation results are optimal.
Preferably, the surface of the terahertz modulator 8 is coated with a layer of Al with a thickness of 20-30nm by Atomic Layer Deposition (ALD)2O3The film acts as a passivation layer.
Preferably, the reflectivity of the terahertz modulator 8 to the terahertz beam 7 is 22% or less, and reaches 18% at the lowest.
Preferably, the modulation depth of the terahertz modulator 8 on the terahertz beam 7 reaches 64.5% under 808nm laser irradiation of 1200 mw.
In order to achieve the above object, the present invention further provides a method for preparing the terahertz modulator based on the silicon-based microstructure on SOI, which comprises the following steps:
the method comprises the following steps: performing 3D modeling on the silicon-based microstructure by using electromagnetic simulation software, setting the total thickness of a model to be 500 mu m and the thickness of a Si layer to be 90 mu m, setting boundary conditions and a solver, and then scanning by setting the side length and the step height of two layers of square steps as variables to obtain the optimal simulation parameters, wherein the optimal parameters obtained by final optimization are the side length of the step of the upper Si base to be 66 mu m and the height to be 45 mu m; the side length of the step of the lower Si base is 84 μm, and the height is 45 μm;
step two: cleaning the SOI substrate: firstly, putting an SOI substrate into a beaker filled with acetone, ultrasonically cleaning for 10-15min, then ultrasonically cleaning for 10-15min by using alcohol, finally ultrasonically cleaning for 10-15min by using deionized water, blow-drying the cleaned SOI substrate by using nitrogen, and drying in an oven;
step three: after processing a mask plate according to the size of the silicon-based microstructure obtained by simulation calculation, firstly putting an SOI substrate into a thermal oxidation furnace, growing a silicon dioxide mask layer with the thickness of 3 microns by adopting a dry oxygen oxidation method, then carrying out deep processing on a Si substrate on the SOI substrate by utilizing a semiconductor photoetching process and an ICP (inductively coupled plasma) etching method, etching the Si layer firstly to leave a lower-layer Si-based step, and then etching to prepare an upper-layer Si-based step so as to form the periodic silicon-based microstructure with double-layer square steps.
Step four: plating a layer of 20-30nm Al on the surface of the modulation device by using an atomic layer deposition method2O3The film acts as a passivation layer.
In order to achieve the above object, the present invention further provides an optically controlled terahertz modulation system based on a silicon-based microstructure on SOI, including: the terahertz radiation source 1 and the terahertz detector 2 are positioned at the left side and the right side of the terahertz modulator, a terahertz wave beam 7 emitted by the terahertz radiation source 1 vertically penetrates through the terahertz modulator 8 and then is incident into the terahertz detector 2, the incident direction of the terahertz wave beam 7 is the side of the terahertz modulator 8 with the silicon-based microstructure 10, and the terahertz radiation source 1 and the terahertz detector 2 are aligned in the horizontal direction;
the terahertz modulator sequentially comprises from bottom to top: bottom layer of Al2O3Substrate 12, SiO2Isolation layer 11, silicon-based microstructure 10, Al2O3Passivation layer 9, silicon-based microstructure 10 on SiO2The isolation layers 11 are periodically arranged, each silicon-based microstructure 10 comprises two layers of square Si base step structures which are an upper Si base step 101 and a lower Si base step 102 from top to bottom, the centers of the upper Si base step 101 and the lower Si base step 102 are aligned, and the side length of the upper Si base step 101 is smaller than that of the lower Si base step 102.
Preferably, the output wavelength of the semiconductor laser 3 is 300nm to 1000nm, and the laser intensity is 300mW or more. The wavelength of 300 nm-1000 nm is a visible light-infrared light band, the Si material only has high absorption to visible light of the band, the Si material can be penetrated by high wavelength, the electromagnetic wave with short wavelength has poor penetrability in the Si material, and fewer photon-generated carriers are generated. The laser intensity is more than 300mW to have the modulation effect.
Preferably, the laser modulator modulates the intensity of the laser light output from the optical fiber to generate a modulation with a varying intensityPreparing laser, and modulating the peak intensity of the laser to 50mW/cm2Therefore, a larger modulation depth can be obtained, and if the laser intensity is not enough, the modulation depth of the device is not high, and the modulation performance is not obvious. The spot area of the modulated laser completely covers the area of the terahertz wave beam to be modulated.
Preferably, the optical fiber 4 is an optical fiber matched with the semiconductor laser 3 for coupling the semiconductor laser 3 and the laser modulator 5.
The invention provides a terahertz modulator based on a Silicon-on-Insulator (SOI) substrate Silicon-based microstructure. The structural core adopts Si-SiO2-Al2O3An SOI substrate composed of three structural layers is used as a substrate of the modulator and used for isolating the modulation part of the modulator so as to reduce the diffusion of photon-generated carriers; the Si layer in the SOI substrate is deeply processed by utilizing semiconductor photoetching and ICP etching technologies, the Si layer is etched into a periodic array structure with double-layer square steps, the transmission of terahertz waves can be enhanced, and the prepared substrate is plated with Al by utilizing an atomic layer deposition method2O3The passivation layer can isolate air, passivate the surface of Si and finally improve the modulation depth of the terahertz modulator; the structure carries out amplitude modulation on terahertz waves in a mode of additionally adding excitation laser, the modulation process has the advantages of low insertion loss, large working bandwidth, high spatial modulation resolution, large modulation depth and the like, and the terahertz wave modulation structure can be widely applied to the technical fields of terahertz wave imaging and the like.
In terms of working principle, the structure mainly has three functions: first, the substrate on which the structure is prepared is made of Si-SiO2-Al2O3SOI substrate comprising a three-layer structure layer, the silicon-based part of which for modulation is grown in SiO2On the insulating substrate, therefore, in the process of generating the photon-generated carriers by the modulator under the irradiation of the excitation laser, the generated photon-generated carriers cannot diffuse to the substrate insulating layer, and cannot laterally diffuse the carriers through the substrate insulating layer, so that the carrier diffusion is reduced, and meanwhile, the Si-SiO crystal is used as the material for the optical modulator2-Al2O3Compared with the traditional silicon-based modulator, the structure can effectively reduce the terahertz insertion loss; secondly, after a series of physical and chemical etching processes, a Si layer of the structure which has a modulation effect on terahertz is prepared into a silicon-based microstructure with a double-layer square step structure, the height of each layer of step of the step is the same, and the side length is different, so that the Si filling rate between the layers of the silicon-based microstructure has an interface with echelon change, and the filling rate of the echelon change is macroscopically represented as the echelon change of the equivalent refractive index of the terahertz wave between the layers of the surface of the microstructure, so that in the terahertz transmission process, the high reflectivity from a low-refractive-index medium to a high-refractive-index medium is reduced to be the low reflectivity sequentially transmitted in a plurality of layers of media with smaller refractive index difference, the terahertz reflectivity of the microstructure device is reduced, and the insertion loss of the microstructure; finally, after the silicon-based microstructure is prepared, a layer of Al is plated on the surface of the modulator2O3The passivation layer can isolate the silicon-based microstructure from contacting with air, so that defects on the silicon surface are reduced, the carrier recombination time is delayed, the carrier concentration is increased, and the effect of improving the modulation depth of the device on terahertz waves is achieved2O3The layer can also prevent the silicon surface from being oxidized naturally and the thermal oxidation process caused by the action of laser, and the service life of the terahertz modulator is greatly prolonged.
Compared with the traditional silicon-based terahertz light-operated modulator, the terahertz light-operated modulator has the following advantages:
(1) the terahertz modulator based on the silicon-based microstructure on the SOI has the reflectivity of below 22% for the terahertz waves of 0.4THz-0.85THz, reaches the lowest 18% at the position of 0.82THz, can remarkably reduce the reflectivity of the modulation device to the terahertz waves, and improves the utilization rate of the terahertz waves.
(2) The terahertz modulator based on the silicon-based microstructure on the SOI can obviously reduce the carrier diffusion effect in the spatial light modulation process, and compared with the traditional silicon-based terahertz modulator, the terahertz imaging diffusion area is reduced, so that the resolution in an imaging system is effectively improved by 21.9%.
(3) The terahertz modulator based on the silicon-based microstructure on the SOI provided by the invention has Si-SiO2-Al2O3The SOI substrate with the three-layer structure can effectively enhance the transmissivity of the terahertz waves in the modulation device and reduce the insertion loss of the device for modulating the terahertz waves.
(4) The invention provides Al adopted by a terahertz modulator based on a silicon-based microstructure on SOI2O3The passivation layer can play a role in passivating silicon of the silicon-based microstructure, can effectively improve the modulation depth of the terahertz modulator, and can also improve the service life of the terahertz modulator.
Drawings
Fig. 1 is a schematic overall structure diagram of an optically controlled terahertz modulation system based on a silicon-on-SOI microstructure according to embodiment 3 of the present invention;
FIG. 2 is a front view of a terahertz modulator based on a silicon-on-SOI microstructure according to embodiment 1 of the present invention;
FIG. 3 is a top view of a terahertz modulator based on a silicon-on-SOI microstructure according to embodiment 1 of the present invention;
fig. 4 is a schematic diagram of the silicon-based microstructure according to embodiment 1 of the present invention, which reduces carrier diffusion and improves terahertz photo-controlled imaging resolution.
Fig. 5 is a flowchart of the preparation of the terahertz modulator based on the silicon-on-SOI microstructure according to embodiment 1 of the present invention.
FIG. 6 is a Scanning Electron Microscope (SEM) image of a silicon-based microstructure in example 1 of the present invention.
Fig. 7 shows THZ transmittance of a conventional high-resistance Si terahertz modulator (HR-Si) and a silicon-based Microstructure terahertz modulator (microstrueture) on an SOI substrate of embodiment 1 of the present invention when no laser modulation signal is applied.
Fig. 8 is a modulation depth variation curve of the terahertz modulator based on the silicon-on-SOI microstructure in accordance with embodiment 1 of the present invention under different modulation laser signal power intensities.
Fig. 9 is a comparison graph of spatial light imaging effects of the conventional high-resistance Si terahertz modulator and the terahertz modulator based on the silicon-based microstructure on the SOI substrate of embodiment 1 of the present invention at the same modulation depth (40%). Fig. 9(1) shows a conventional high-resistance silicon terahertz modulator, and fig. 9(2) shows a terahertz modulator based on a silicon-based microstructure on an SOI substrate.
Wherein 1 is a terahertz radiation source, 2 is a terahertz detector, 3 is a semiconductor laser, 4 is an optical fiber, 5 is a laser modulator, 6 is a laser beam, 7 is a terahertz beam, 8 is a terahertz modulator, 9 is Al2O3A passivation layer, 10 is a silicon-based microstructure, 101 is an upper Si-based step, 102 is a lower Si-based step, and 11 is SiO2Barrier layer, 12 is Al2O3The substrate 13 is a photocarrier generation region.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Example 1
As shown in fig. 2 and fig. 3, a terahertz modulator based on a silicon-on-SOI microstructure sequentially includes, from bottom to top: bottom layer of Al2O3Substrate 12, SiO2Isolation layer 11, silicon-based microstructure 10, Al2O3The passivation layer 9 and the silicon-based microstructures 10 are periodically arranged on the SiO2 isolation layer 11, each silicon-based microstructure 10 comprises two layers of square Si base step structures which are an upper Si base step 101 and a lower Si base step 102 from top to bottom respectively, the centers of the upper Si base step 101 and the lower Si base step 102 are aligned, and the side length of the upper Si base step 101 is smaller than that of the lower Si base step 102.
In this embodiment, the two square Si base step structures of the silicon-based microstructure 10 are Si layers, the resistivity of the Si layers is greater than 3000 Ω · cm, and the total thickness of the two square Si base step structures is 90 μm.
The distance between the centers of two adjacent silicon-based microstructures 10 is 100 micrometers, the side length of the upper Si-based step 101 is 66 micrometers, the height of the upper Si-based step is 45 micrometers, and the side length of the lower Si-based step 102 is 84 micrometers, and the height of the lower Si-based step is 45 micrometers.
The surface of the terahertz modulator 8 is plated with a layer of Al with the thickness of 20-30nm by an atomic layer deposition method2O3Film as Al2O3 A passivation layer 9.
As shown in fig. 7, the reflection spectrum of the conventional high-resistance silicon-based terahertz amplitude modulator (HR-Si) and the terahertz modulator sample (Microstructure) based on the silicon-based Microstructure on the SOI prepared in this embodiment without laser modulation measured on the terahertz time-domain spectroscopy test system is shown, and it can be seen from the figure that the high-resistance silicon reflects terahertz waves within a range of 30% to 33% in a frequency range of 0.4THz to 0.85THz, whereas the reflection of terahertz waves by the silicon-based Microstructure on the SOI substrate in the embodiment of the present invention is below 22%, which is as low as 18%, and the reflectivity has an obvious reduction effect with respect to the high-resistance silicon.
Fig. 8 shows that the terahertz amplitude modulator based on the silicon-based microstructure on the SOI substrate modulates the depth curve under different laser intensities according to this embodiment. As can be seen from the figure, the modulator prepared in the invention has modulation depth of up to 64.5% under the laser intensity of 808nm wavelength of 1200 mw.
Fig. 9 shows the terahertz spatial light modulation imaging test by the terahertz modulator based on the silicon-based microstructure on the SOI substrate and the conventional high-resistance silicon modulator used in this embodiment. In the test, a sample and a laser source are fixed, a light spot is adjusted to be 2mm in diameter, a terahertz wave beam is concentrated to be within the range of 0.2mm in diameter, the point of the terahertz wave beam concentrated irradiation is controlled by moving a sample rack translation stage, the transmission amplitude of the terahertz wave by the sample is subjected to point-by-point scanning test, and a space spectrum of the terahertz transmission by the sample is formed, wherein fig. 9(1) is a traditional high-resistance silicon terahertz modulator, and fig. 9(2) is a terahertz modulator based on a silicon-based microstructure on an SOI substrate and used in the embodiment of the invention. It can be seen from the figure that, under the condition that the control variables are the same laser irradiation range and the same modulation depth, the diameter of the carrier diffusion range in the silicon-based microstructure is 2.46mm, which is reduced by about 21.9% compared with the diameter of the carrier diffusion range on the high-resistance silicon by 3.15mm, and the size of the formed imaging pattern is closer to that of the modulated laser spot, which shows that the silicon-based microstructure on the SOI substrate has the functions of reducing the carrier diffusion and improving the imaging precision.
In summary, the modulation depth of the terahertz wave by the terahertz modulator based on the silicon-on-SOI microstructure prepared by the embodiment can reach 64.5% under the irradiation of 808nm laser of 1200 mw; the terahertz is 22% below without laser in the frequency range of 0.4THz-0.85THz, the reflectivity of 18% at the lowest is obviously reduced compared with the reflectivity of 30% of high-resistance silicon, the imaging result in the spatial light modulation imaging is close to the range of excitation laser, and the imaging pixel point is reduced by 21.9% compared with the imaging pixel point of the traditional silicon-based modulator.
Example 2
As shown in fig. 5, the method for manufacturing the terahertz modulator based on the silicon-on-SOI microstructure in embodiment 1 includes the following steps:
the method comprises the following steps: 3D modeling is carried out on the silicon-based microstructure by utilizing CST Microwave Studio software, the total thickness of a model is 500 mu m, the thickness of a Si layer is 90 mu m, after boundary conditions and a solver are set, the side length and the step height of two layers of square steps are set as variables to carry out scanning so as to obtain the optimal simulation parameters, and the optimal parameters obtained by final optimization are 66 mu m of the side length and 45 mu m of the step height of an upper layer Si base; the side length of the step of the lower Si base is 84 μm, and the height is 45 μm;
step two: cleaning the SOI substrate: firstly, putting an SOI substrate into a beaker filled with acetone, ultrasonically cleaning for 10-15min, then ultrasonically cleaning for 10-15min by using alcohol, finally ultrasonically cleaning for 10-15min by using deionized water, blow-drying the cleaned SOI substrate by using nitrogen, and drying in an oven;
step three: after processing a mask plate according to the size of the silicon-based microstructure obtained by simulation calculation, firstly putting an SOI substrate into a thermal oxidation furnace, growing a silicon dioxide mask layer with the thickness of 3 microns by adopting a dry oxygen oxidation method, then carrying out deep processing on a Si substrate on the SOI substrate by utilizing a semiconductor photoetching process and an ICP (inductively coupled plasma) etching method, etching the Si layer firstly to leave a lower-layer Si-based step, and then etching to prepare an upper-layer Si-based step so as to form the periodic silicon-based microstructure with double-layer square steps.
Step four: plating a layer of 20-30nm Al on the surface of the modulation device by using an atomic layer deposition method2O3The film acts as a passivation layer.
Example 3
As shown in fig. 1, an optically controlled terahertz modulation system based on a silicon-based microstructure on SOI includes: the terahertz radiation source 1 and the terahertz detector 2 are positioned at the left side and the right side of the terahertz modulator, a terahertz wave beam 7 emitted by the terahertz radiation source 1 vertically penetrates through the terahertz modulator 8 and then is incident into the terahertz detector 2, the incident direction of the terahertz wave beam 7 is the side of the terahertz modulator 8 with the silicon-based microstructure 10, and the terahertz radiation source 1 and the terahertz detector 2 are aligned in the horizontal direction;
the terahertz modulator sequentially comprises from bottom to top: bottom layer of Al2O3Substrate 12, SiO2Isolation layer 11, silicon-based microstructure 10, Al2O3Passivation layer 9, silicon-based microstructure 10 on SiO2The isolation layers 11 are periodically arranged, each silicon-based microstructure 10 comprises two layers of square Si base step structures which are an upper Si base step 101 and a lower Si base step 102 from top to bottom, the centers of the upper Si base step 101 and the lower Si base step 102 are aligned, and the side length of the upper Si base step 101 is smaller than that of the lower Si base step 102.
When laser is incident to the surface of the silicon-based microstructure on the SOI substrate, the surface of the silicon-based microstructure excites a photon-generated carrier, and due to the existence of the insulating layer at the bottom layer of the silicon-based microstructure, the diffusion of the carrier at the bottom of the silicon-based microstructure is isolated, so that the diffusion of the carrier is inhibited.
In this embodiment, the output wavelength of the semiconductor laser 3 is 300nm to 1000nm, and the laser intensity is 300mW or more. The wavelength of 300 nm-1000 nm is a visible light-infrared light band, the Si material only has higher absorption to the visible light of the band, the Si material can be penetrated by the higher wavelength, the penetrability in the Si material is poor due to the shorter wavelength, and the generation of photon-generated carriers is less. The laser intensity is more than 300mW to have the modulation effect.
In this embodiment, the laser modulator 5 modulates the intensity of the laser output from the optical fiber to generate modulated laser with varying intensity, and the peak intensity of the modulated laser reaches 50mW/cm2Therefore, a larger modulation depth can be obtained, and if the laser intensity is not enough, the modulation depth of the device is not high, and the modulation discrimination is not high. The spot area of the modulated laser completely covers the area of the terahertz wave beam to be modulated.
In this embodiment, the optical fiber 4 is an optical fiber matched with the semiconductor laser 3, and is used for coupling the semiconductor laser 3 and the laser modulator 5.
The following describes the testing process of the modulation system in detail:
a transmission type terahertz time-domain spectroscopy system (THz-TDS) is adopted, terahertz waves are generated by a femtosecond laser pumping photoconductive antenna, the terahertz waves are perpendicular to the surface of a silicon-based microstructure and incident to the surface of a sample, and the transmission waves are received by the photoconductive antenna. The specific operation steps are as follows:
the method comprises the following steps: opening terahertz Time Domain Spectroscopy (TDS) testing equipment and operating software thereof, and waiting for the TDS peak value of the equipment to be stable;
step two: adjusting the position of a terahertz transmitter, aligning the terahertz transmitter with a sample rack prepared in advance, and storing TDS data (TDS spectrum of air) at the moment as reference data; placing a terahertz modulator to be tested on a sample rack, and storing TDS data of a sample;
step three: and obtaining a frequency domain spectrum and a terahertz wave reflection spectrum through Fourier transform, and drawing a test chart by utilizing data processing software such as Origin and the like.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims (3)

1. The utility model provides a terahertz modulator based on silicon-based micro-structure on SOI which characterized in that from down to up includes in proper order: bottom layer of Al2O3Substrate (12), SiO2An isolation layer (11), a silicon-based microstructure (10), Al2O3A passivation layer (9) and a silicon-based microstructure (10) in SiO2The isolation layers (11) are periodically arranged, each silicon-based microstructure (10) comprises two layers of square Si-based step structures which are respectively an upper Si-based step (101) and a lower Si-based step (102) from top to bottom, the centers of the upper Si-based step (101) and the lower Si-based step (102) are aligned, and the side length of the upper Si-based step (101) is smaller than that of the lower Si-based step (102);
the two layers of square Si base step structures of the silicon-based microstructure (10) are Si layers, the resistivity of the Si layers is more than 3000 omega-cm, and the total thickness of the two layers of square Si base step structures is 90 mu m;
the distance between the centers of two adjacent silicon-based microstructures (10) is 100 micrometers, the side length of an upper Si-based step (101) is 66 micrometers, the height of the upper Si-based step is 45 micrometers, and the side length of a lower Si-based step (102) is 84 micrometers, and the height of the lower Si-based step is 45 micrometers;
the reflectivity of the terahertz modulator to the terahertz wave beam (7) is below 22% and reaches 18% at the lowest.
2. The method for preparing the terahertz modulator based on the silicon-on-SOI microstructure as claimed in claim 1, characterized by comprising the following steps:
the method comprises the following steps: performing 3D modeling on the silicon-based microstructure by using electromagnetic simulation software, setting the total thickness of a model to be 500 mu m and the thickness of a Si layer to be 90 mu m, setting boundary conditions and a solver, and then scanning by setting the side length and the step height of two layers of square steps as variables to obtain the optimal simulation parameters, wherein the optimal parameters obtained by final optimization are the side length of the step of the upper Si base to be 66 mu m and the height to be 45 mu m; the side length of the step of the lower Si base is 84 μm, and the height is 45 μm;
step two: cleaning the SOI substrate: firstly, putting an SOI substrate into a beaker filled with acetone, ultrasonically cleaning for 10-15min, then ultrasonically cleaning for 10-15min by using alcohol, finally ultrasonically cleaning for 10-15min by using deionized water, blow-drying the cleaned SOI substrate by using nitrogen, and drying in an oven;
step three: after processing a mask plate according to the size of a silicon-based microstructure obtained by simulation calculation, firstly putting an SOI substrate into a thermal oxidation furnace, growing a silicon dioxide mask layer with the thickness of 3 microns by adopting a dry oxygen oxidation method, then carrying out deep processing on a Si substrate on the SOI substrate by utilizing a semiconductor photoetching process and an ICP (inductively coupled plasma) etching method, etching the Si layer to leave a lower-layer Si-based step, and then etching to prepare an upper-layer Si-based step so as to form a periodic silicon-based microstructure with double-layer square steps;
step four: plating a layer of 20-30nm Al on the surface of the modulation device by using an atomic layer deposition method2O3The film acts as a passivation layer.
3. A light-operated terahertz modulation system based on a silicon-based microstructure on an SOI (silicon on insulator) is characterized by comprising: the terahertz laser comprises a semiconductor laser (3), a laser modulator (5), a terahertz modulator (8), a terahertz radiation source (1) and a terahertz detector (2), wherein the semiconductor laser (3) is connected with the laser modulator (5) through an optical fiber (4), a laser beam (6) emitted by the laser modulator (5) is incident to the surface of the terahertz modulator (8) to be used as excitation laser, the terahertz radiation source (1) and the terahertz detector (2) are positioned on the left side and the right side of the terahertz modulator, a terahertz beam (7) emitted by the terahertz radiation source (1) vertically penetrates through the terahertz modulator (8) and then is incident to the terahertz detector (2), the incident direction of the terahertz wave beam (7) is the side of the terahertz modulator (8) with the silicon-based microstructure (10), and the terahertz radiation source (1) and the terahertz detector (2) are aligned in the horizontal direction;
the terahertz modulator sequentially comprises from bottom to top: bottom layer of Al2O3Substrate (12), SiO2An isolation layer (11), a silicon-based microstructure (10), Al2O3A passivation layer (9) and a silicon-based microstructure (10) in SiO2The isolating layers (11) are periodically arranged, and each silicon-based microstructure (10) comprises two layers of square Si-based step junctionsThe structure comprises an upper layer Si-based step (101) and a lower layer Si-based step (102) from top to bottom, wherein the centers of the upper layer Si-based step (101) and the lower layer Si-based step (102) are aligned, and the side length of the upper layer Si-based step (101) is smaller than that of the lower layer Si-based step (102);
the output wavelength of the semiconductor laser (3) is 300-1000 nm, and the laser intensity is more than 300 mW;
the laser modulator (5) modulates the intensity of the laser output by the optical fiber to generate modulated laser with variable intensity, and the peak intensity of the modulated laser reaches 50mW/cm2In the above, the spot area of the modulated laser completely covers the area of the terahertz wave beam to be modulated;
the optical fiber (4) is matched with the semiconductor laser (3) and is used for coupling the semiconductor laser (3) and the laser modulator (5).
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