CN202394003U - TeraHertz high-speed modulator - Google Patents

Abstract

The utility model discloses a terahertz wave high-speed modulator, which comprises a substrate layer, a buffer layer is grown on the substrate layer, a strained quantum well structure is grown on the buffer layer, and the strained quantum well structure is prepared on the upper surface of the strained quantum well structure. A metal metamaterial structure consisting of a periodic array of metal resonant units; the buffer layer is made of the same material as the substrate layer, the energy band gap of the potential well layer is smaller than that of the barrier layer, and the lattice constant of the barrier layer and the substrate layer The same or within 0.5% of the difference. The strained quantum well structure of the utility model has a very strong piezoelectric field generated by strain, which can significantly prolong the recombination life and concentration of photogenerated carriers, thereby greatly reducing the requirements for modulating laser power; by changing the InGaAs/GaAs strain The In composition in the quantum well and the width of the quantum well can flexibly adjust the size of the internal piezoelectric field and the degree of space separation of charges, and then conveniently adjust the modulation rate of the utility model.

Description

A high-speed terahertz wave modulator

technical field

The utility model belongs to the field of terahertz wave communication, in particular to a terahertz wave modulator.

Background technique

The contradiction between the limited spectrum resources of wireless communication and the rapidly growing high-speed business demands forces people to develop new spectrum bands. Terahertz waves refer to electromagnetic waves with a frequency ranging from 0.1 THz to 10 THz (1 THz = 10 ¹² Hz), with a wavelength of 0.03 mm to 3 mm, and have a large bandwidth. Therefore, the development of THz wireless communication technology has important practical application value . Among them, the terahertz wave modulator is one of the essential devices in the terahertz communication system, but the performance of the terahertz modulator is mainly limited by the selection and preparation of materials. The organic combination of new semiconductor substrate materials and electromagnetic meta-materials is expected to achieve breakthroughs in some key technologies of terahertz, especially terahertz modulation technology.

The THz wave modulators reported in recent years have a method of modulating THz waves by using semiconductor bulk materials. Based on ultra-high resistivity silicon (Si) wafers, Li Jiusheng from the China Jiliang Institute used 808 nm laser irradiation to generate photogenerated carriers to modulate THz waves. Due to the long recombination lifetime of carriers in ultra-high resistivity Si wafers, the modulation rate is only 0.2k bps. Gallium arsenide GaAs has a short lifetime of carriers, and it may become a substrate material for the preparation of high-speed terahertz modulators. L. Fekete et al. of the Czech Republic adopted the method of embedding a layer of GaAs defect layer in the alternately stacked SiO ₂ and MgO periodic structure to form a one-dimensional photonic crystal, using the concentration of photogenerated carriers generated by GaAs under 810 nm laser irradiation Changes to modulate the transmission characteristics of photonic crystals, so as to achieve the purpose of high-speed modulation of THz waves. However, due to the short lifetime of carriers in GaAs, the response time can reach the order of 130 ps, so although the modulation rate of the THz wave can reach the order of GHz in theory, in order to obtain a higher concentration of photogenerated carriers and a higher Large modulation depth, the luminous flux of the 810 nm modulated laser needs to reach a very high level of 0.8 μJ/cm ² , and the corresponding continuous wave output laser power needs to reach more than 10 ⁵ W, which makes it greatly restricted in practical applications limit.

Utility model content

Purpose of the utility model: Aiming at the above-mentioned existing problems and deficiencies, the utility model provides a terahertz wave modulator, so as to overcome the problem that the recombination lifetime of the carriers in the existing gallium arsenide substrate is too short so that superpower is required The defect of the modulated laser realizes the high-speed modulation of the terahertz wave under the excitation condition of the low-power modulated laser.

Technical solution: In order to achieve the purpose of the above utility model, the utility model adopts the following technical solution: a high-speed terahertz wave modulator, including a substrate layer, a buffer layer is grown on the substrate layer, and strained quantum wells are grown on the buffer layer structure, a metal metamaterial structure composed of a periodic array of metal resonant units prepared on the upper surface of the strained quantum well structure; the strained quantum well structure includes more than two potential barrier layers and at least one potential well layer, and the potential The well layer is in the middle of the two barrier layers, and the uppermost layer and the lowermost layer of the strained quantum well structure are both barrier layers; the substrate layer is <111> plane orientation, and the buffer layer is made of the same material as the substrate layer. The energy bandgap of the potential well layer is smaller than that of the barrier layer, and the lattice constants of the barrier layer and the substrate layer are the same or differ by no more than 0.5%.

When the terahertz wave passes through the metal metamaterial structure, the strained quantum well structure, the buffer layer, and finally exits from the lower surface of the substrate layer, another beam of modulated laser light with a wavelength of 810nm enters the quantum well to excite photogenerated carriers. Due to the lattice mismatch between the barrier layer and the potential well layer in the strained quantum well structure, a strong piezoelectric electric field can effectively separate electrons and holes in photogenerated carriers, thereby significantly increasing the concentration and recombination of photogenerated carriers lifetime, greatly reducing the power of the externally modulated laser required.

Preferably, the material of the substrate layer, the buffer layer and the barrier layer is gallium arsenide, and the material of the potential well layer is indium gallium arsenide. Or the substrate layer and the buffer layer are gallium arsenide, the barrier layer material is aluminum gallium arsenide, and the potential well layer material is gallium arsenide phosphide.

Preferably, both the barrier layer and the potential well layer in the strained quantum well structure have a <111> plane orientation, the barrier layer has a thickness of 10-300 nm, and the potential well layer has a thickness of 1-30 nm.

Preferably, the thickness of the buffer layer is 20-300 nm.

Preferably, the metal resonant unit in the metal metamaterial structure has a thickness of 0.2-5 microns and a period of 20-80 microns.

Another object of the present utility model is to provide a method for manufacturing the above-mentioned terahertz wave high-speed modulator, which specifically includes the following steps:

a. A buffer layer is grown on the <111> plane-oriented substrate layer by metal-organic chemical vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE);

b. Then continue to grow the <111> plane-oriented barrier layer, potential well layer and potential barrier layer on the buffer layer in sequence, thereby forming a <111> plane-oriented strained single quantum well layer, wherein the material selected for the potential well layer The energy bandgap of the barrier layer is smaller than that of the barrier layer, and the lattice constant of the barrier layer and the substrate layer is the same or the difference is within 0.5%;

c. Prepare a metal metamaterial structure consisting of a layer of periodically arranged metal resonant units on the upper surface of the strained quantum well structure by means of evaporation and etching.

Preferably, the substrate layer, the buffer layer and the barrier layer are all made of gallium arsenide, and the potential well layer is made of indium gallium arsenide.

Beneficial effects: Compared with the prior art, the utility model has the following advantages: by growing a <111>-oriented strained quantum well structure on a <111>-oriented substrate, an extremely strong piezoelectric field is obtained inside the quantum well; The piezoelectric field can effectively separate the electrons and holes in the photogenerated carriers, significantly prolong the recombination lifetime of the photogenerated carriers and increase the carrier concentration, thereby greatly reducing the requirements for externally modulated laser power; and At the same time, by changing the composition of In and the width of the quantum well in the <111>-oriented InGaAs/GaAs strained quantum well, the size of the internal piezoelectric field and the degree of charge space separation can be flexibly adjusted. Adjust the modulation rate of the terahertz wave modulator, and the modulation rate can reach more than 10Mbps.

Description of drawings

Fig. 1 is the structural representation of the utility model;

Fig. 2 is the energy band structure change diagram of the strained quantum well structure described in the utility model under the effect of the built-in piezoelectric field;

Fig. 3 is the relationship curve between the intensity of the piezoelectric field in the strained quantum well structure and the content of the indium (In) component in the potential well layer in the embodiment of the utility model;

Fig. 4 is a curve of the transmittance of the terahertz wave modulated by the modulator of the present invention as a function of the external excitation light intensity.

Among them, substrate layer 1 , buffer layer 2 , metal metamaterial structure 3 , barrier layer 4 , and potential well layer 5 .

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, further illustrate the utility model. It should be understood that these embodiments are only used to illustrate the utility model and are not intended to limit the scope of the utility model. After reading the utility model, those skilled in the art all fall within the scope of the present application to the modifications of various equivalent forms of the utility model The scope defined by the appended claims.

As shown in Figure 1, a high-speed terahertz wave modulator includes a <111>-oriented semi-insulating gallium arsenide (GaAs) substrate layer 1. First, a GaAs buffer layer is grown on the substrate by MOCVD metal organic chemical vapor phase epitaxy technology. layer 2, the thickness of the gallium arsenide buffer layer 2 is controlled at 20 to 300 nanometers, so that the lattice constant between the indium gallium arsenide potential well layer 5 and the gallium arsenide substrate layer 1 in the subsequent strained quantum well structure can be The larger difference is overcome, and finally a high-quality <111> plane-oriented strained quantum well structure is obtained.

Then, on the buffer layer 2, a gallium arsenide barrier layer 4 with a <111> plane orientation, an indium gallium arsenide potential well layer 5 and a gallium arsenide barrier layer 4 are sequentially grown to form a <111> plane orientation InGaAs/ GaAs strained quantum well structure, wherein the gallium arsenide barrier layer 4 has a thickness of 10 to 300 nanometers, and the indium gallium arsenide potential well layer 5 has a thickness of 1 to 30 nanometers; finally, light passes through the uppermost GaAs surface A layer of metal metamaterial structure 3 composed of a periodic array of metal resonant units is prepared by engraving, vapor deposition and etching. The metal metamaterial has a thickness of 0.2-5 microns and a period of 20-80 microns. Any shape of the electromagnetic resonator unit can be used.

The strong piezoelectric field generated by the lattice mismatch in the above-mentioned <111>-oriented InGaAs/GaAs quantum well can effectively separate the electrons and holes in the photo-generated carriers, thereby significantly increasing the concentration and recombination of the photo-generated carriers. lifetime, greatly reducing the power of the externally modulated laser required;

The barrier layer of the above-mentioned <111>-oriented InGaAs/GaAs quantum well can be made of aluminum gallium arsenide (AlGaAs) material that matches the lattice of the gallium arsenide substrate layer or has a difference within 0.5%, while the potential well can be made of gallium arsenide phosphide (GaAsP ) or other compound semiconductor materials whose energy band gap is lower than the barrier material and whose lattice mismatch with the substrate material is replaced.

The modulated terahertz wave passes through the metal metamaterial structure 3, the strained quantum well structure, and the buffer layer 2 in sequence, and finally emits from the lower surface of the GaAs(111) substrate layer 1, and is received and detected by a terahertz time-domain spectrometer (TDS). At the same time, another beam of modulated laser light with a wavelength of 810 nm is irradiated on the <111>-oriented InGaAs/GaAs strained quantum well structure to excite photogenerated carriers, whose concentration and recombination lifetime can be adjusted by the parameters of the strained quantum well structure. The concentration of photogenerated carriers varies with the intensity of the modulated light and is proportional to the recombination lifetime of the carriers, so changing the intensity of the modulated laser can affect the resonant frequency and resonant intensity of the metamaterial structure. The transmission spectrum of the terahertz wave detected by TDS reflects the modulated terahertz wave whose intensity changes at the same rate as the modulated light.

The introduction of the <111> oriented strained quantum well structure is the core innovation point of the utility model, and it is also the key technology to realize the high-speed modulation of the terahertz wave by the ordinary power laser. Since the lattice constants of the two semiconductor materials constituting the <111>-oriented strained quantum well are different, a piezoelectric field perpendicular to the direction of the quantum well will be generated by the piezoelectric effect in the quantum well. As shown in Figure 2, the generated strong piezoelectric field (~10 ⁵ V/cm) tilts the energy band structure of the quantum well, which leads to the effective separation of electrons and holes in the photogenerated carriers in space, so it can significantly Increase the concentration and recombination lifetime of photogenerated carriers. It is estimated that the lifetime of photogenerated carriers can be extended from tens of picoseconds in ordinary GaAs bulk materials to tens of nanoseconds in the <111>-oriented InGaAs/GaAs quantum well structure of the present invention. The carrier recombination lifetime of this order can not only meet the requirements of 10 Mbps or even higher modulation rate, but also can greatly reduce the power of the required modulation laser, even with a common 100 mW commercial semiconductor laser.

Fig. 3 is a calculated variation curve of the _{piezoelectric} field strength with the In composition x in the <111> orientation _InGaAs /GaAs quantum well. It can be clearly seen that by changing the In composition in the strained quantum well, the intensity of the piezoelectric field in the quantum well can be adjusted, thereby controlling the recombination lifetime of the photogenerated carriers.

Fig. 4 is a curve of the transmittance of the terahertz wave passing through the modulator of the present invention as a function of the external excitation light intensity. It can be seen that the maximum modulation depth at the frequency of 0.66 THz can reach 59%, and the modulation rate is 10 Mbps.

Claims (6)

1. THz wave high-speed modulator; It is characterized in that: comprise substrate layer (1); Go up growth at this substrate layer (1) one cushion (2) is arranged; In this cushion (2) growth the strained quantum well structure is arranged, at the metal metamaterial structure of forming by metal resonant element periodic array (3) of the upper surface preparation of this strained quantum well structure; Said strained quantum well structure comprises plural barrier layer (4) and at least one potential well layer (5), and said potential well layer (5) is in the middle of two barrier layers (4), and the said strained quantum well structure the superiors and orlop all are barrier layers; Said substrate layer (1) is＜111＞planar orientation; Said cushion (2) is identical with substrate layer (1) material; The band gap of said potential well layer (5) is less than barrier layer (4), and the grating constant of said barrier layer (4) and substrate layer (1) is identical or differ and be no more than 0.5%.

2. according to the said THz wave high-speed modulator of claim 1, it is characterized in that: said substrate layer (1), cushion (2) and barrier layer (4) material are gallium arsenide, and said potential well layer (5) material is an indium gallium arsenic.

3. according to the said THz wave high-speed modulator of claim 1, it is characterized in that: said substrate layer (1) and cushion (2) are gallium arsenide, and said barrier layer (4) material is a gallium aluminium arsenic, and said potential well layer (5) material is a gallium arsenic phosphide.

4. according to the said THz wave high-speed modulator of claim 2; It is characterized in that: barrier layer (4) and potential well layer (5) all are＜111＞planar orientation in the said strained quantum well structure; Said barrier layer (4) thickness is 10～300nm, and said potential well layer (5) thickness is 1～30nm.

5. according to the said THz wave high-speed modulator of claim 2, it is characterized in that: said cushion (2) thickness is 20～300nm.

6. according to the said THz wave high-speed modulator of claim 1, it is characterized in that: the thickness of metal resonant element is 0.2～5 micron in the said metal metamaterial structure (3), and the cycle is 20～80 microns.

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