CN114038927B - Ferroelectric integrated graphene plasma terahertz detector with high response - Google Patents

Abstract

The invention belongs to the field of optoelectronic communication technology, and specifically relates to a highly responsive ferroelectric integrated graphene plasma terahertz detector. It solves the problem of difficult electromagnetic wave conduction between parallel graphene nanoribbons in traditional silicon-based devices. The main solution includes using strontium titanate as the base, lanthanum strontium manganese oxide as the bottom electrode, and using epitaxial method to grow a layer of iron on the bottom electrode. Bismuth ferrite BFO uses piezoelectric force microscopy or watermarking method to obtain two parallel rectangular localized polarization domains, and then covers a layer of intrinsic graphene on the bismuth ferrite BFO, and adjusts the structure by applying different gate voltages to the bottom electrode. The chemical potential of graphene covering the rectangular locally polarized electric domain adjusts the absorption band of the terahertz detector.

Description

A highly responsive ferroelectric integrated graphene plasma terahertz detector

Technical field

The invention belongs to the technical field of optoelectronic communication, and specifically relates to a terahertz photoelectric detector. In particular, it relates to the structural design of a graphene terahertz detector based on a ferroelectric substrate.

Background technique

Terahertz (THz) waves refer to electromagnetic waves with frequencies in the range of 0.1 to 10THz (wavelength 3000 to 30 μm). It is the transition zone from macroscopic classical theory to microscopic quantum theory, and also the transition zone from electronics to photonics. Due to the lack of highly sensitive detectors and relatively effective terahertz sources in the past, this band is also known as the "terahertz gap" of the electromagnetic spectrum. Due to the large available bandwidth of terahertz, ultra-high-speed wireless data transmission can be achieved, and it also has great application possibilities in the field of sensing. In recent years, research on terahertz band detection has continued to develop and innovate, and many different high-sensitivity Detectors and terahertz sources were proposed, providing meaningful reference for terahertz research.

In the infrared (IR) and terahertz (THz) range, when graphene interacts with incident light, surface plasmon polaritons (SPPs) and localized surface plasmon polaritons (LSPs) appear. SPPs are surface waves excited at material boundaries; the excitation of these charge waves is achieved by appropriately matching the free space and surface plasmon momentum of the system. LSPs, on the other hand, are subwavelength surface waves supported in materials with characteristic dimensions comparable to the excitation wavelength. The latter aids the absorption mechanism and leads to enhanced absorption. Graphene-based absorbers (GBA) have attracted much attention in the past few years. Ke et al., reported a cross-shaped graphene array absorber that achieved 20% absorption; Xiao et al., proposed a periodic graphene ring array and introduced good angular polarization tolerance, achieving 25% absorption; Fang et al., achieved 30% absorption by incorporating graphene nanodisk arrays into active devices. Although the maximum absorption capacity of a single layer of graphene is greatly improved compared to its predecessors, the maximum absorption capacity does not exceed 30%. Therefore, designing a graphene absorber with higher absorbance is an urgent problem to be solved.

Contents of the invention

The invention solves the problem of difficult electromagnetic wave conduction between parallel graphene nanoribbons in traditional silicon-based devices, and thereby realizes the coupling of plasmon effects excited by two high chemical potential graphene nanoribbons.

Aiming at the problems of low optical absorption of graphene and difficulty in detection in the far-infrared band, the present invention proposes two parallel high chemical potential graphene nanoribbons on a ferroelectric base as a terahertz absorption structure for the detection sensitive layer. The device operates at the resonant frequency It has ultra-high responsivity (23.21A/W) at 3.85THz. The surface unit cell structure of the device consists of two parallel and symmetrical high chemical potential graphene nanoribbons and the surrounding intrinsic graphene.

In order to solve the above technical problems, the present invention adopts the following technical means:

A highly responsive ferroelectric integrated graphene plasma terahertz detector, using strontium titanate (STO) as the base and lanthanum strontium manganese oxide (LSMO) as the bottom electrode, using an epitaxial method to grow a layer of iron on the bottom electrode For bismuth ferrite BFO, two parallel rectangular localized polarization domains are obtained using piezoelectric force microscopy (PFM) or watermarking method, and then a layer of intrinsic graphene is covered on the bismuth ferrite BFO, and different gate voltages are applied to the bottom electrode. , thereby adjusting the chemical potential of graphene covering the rectangular localized polarization domain, thereby adjusting the absorption band of the terahertz detector.

In the above technical solution, the length of two parallel rectangular locally polarized electric domains is 0.5um, the width is 0.1um, and the interval is 0.5um.

In the above technical solution, the side length of the intrinsic graphene covered on the bismuth ferrite is 1um.

In the above technical solution, the chemical potential of graphene covering the rectangular localized polarization domain is 0.4 eV.

In the above technical solution, the chemical potential of graphene not covering the rectangular localized polarization domain is 0.01eV.

The main advantages of the present invention include:

1. The present invention proves that double special strip graphene can exhibit high response characteristics to the far-infrared band under the influence of specific ferroelectric domains.

2. The method of the present invention is universal and is applicable to the effect of polarization of all ferroelectric materials on the light absorption of patterned graphene.

3. The present invention adopts the method of introducing two parallel high chemical potential graphene nanoribbons into intrinsic graphene, which solves the problem of difficult electromagnetic wave conduction between parallel graphene nanoribbons in traditional silicon-based devices, and thereby realizes two parallel graphene nanoribbons. Coupling of plasmon interactions excited by high chemical potential graphene nanoribbons.

4. The present invention uses two parallel high chemical potential graphene nanoribbons to solve the problem of difficult electromagnetic wave conduction between parallel graphene nanoribbons in traditional silicon-based devices, and realizes the excitation of two parallel high chemical potential graphene nanoribbons. Coupling of plasmon effects, thereby enhancing localized surface polaritons, increases light absorption in the terahertz band. Since the graphene of conventional devices is the substrate, electromagnetic wave conduction between two graphene nanoribbons requires the addition of a graphene pattern to connect, resulting in loss or production cost. The polarization control of ferroelectric substrates does not require conductive patterns. It only needs to add polarization in specific areas to obtain high chemical potential graphene areas.

5. Compared with the square-shaped two parallel high chemical potential graphene nanoribbons of the present invention, the plasmon action excited by the short edge of the rectangular shape will also produce coupling and mutual reinforcement, while the square-shaped side length is longer and the diagonal Plasmon interactions excited at are difficult to couple. Compared with the fan shape, the rectangular structure is simpler, the adjustable pattern parameters are basically the same, and there is no need to make a triangular pattern in the middle as a conductor. However, the accuracy of the triangular pattern lithography machine is very high, especially the vertex position.

Description of the drawings

Figure 1 is a structural diagram of the simulated device and a schematic diagram of the shape of the BFO domain.

Figures 2 to 5 show that under the conditions of fixing the shape and size of the ferroelectric domain and the chemical potential of graphene in the downward polarization region being 0.01eV, the electrochemical potentials of graphene in the upward polarization region are 0.4eV, 0.6eV, and The curves of light absorption in the terahertz band corresponding to 0.7eV and 0.8eV.

Figure 6-Figure 7 shows that the ferroelectric domain with the polarization direction upward is 0.5um long and 0.1um wide, with an interval of 0.5um. The electrochemical potential of graphene is 0.4eV, 0.8eV; and the ferroelectric domain edge with the polarization direction downward 1um long, different electric field distribution diagrams when the chemical potential of graphene is 0.01eV.

Detailed ways

In order to facilitate understanding, the present invention will be further described below in conjunction with the accompanying drawings. The described examples are part of the parameter examples of the invention. Based on the examples in the present invention, all other examples obtained by those of ordinary skill in the art without any creative work shall fall within the protection scope of the present invention.

The invention provides a photoelectric detector based on ferroelectric materials and graphene, which includes: using strontium titanate (STO) as a base, lanthanum strontium manganese oxide (LSMO) as a bottom electrode, and growing a layer of BFO by epitaxial method.

Bismuth ferrite BFO is a ferroelectric material. Two parallel rectangular locally polarized electric domains are obtained using piezoelectric force microscopy (PFM) or watermarking method.

A single graphene layer is transferred onto polarized bismuth ferrite BFO.

Use FDTD solution simulation software to design the device structure and patterning of graphene. By setting up the light source and placing the monitor, calculate the transmittance, reflectivity, absorptivity, and surface electric field intensity distribution of the entire designed device.

More specifically, in the model, the ferroelectric domain is expressed in the form of high and low changes in the electrochemical potential of graphene, while the change in the shape of the ferroelectric domain is reflected in the different shapes of graphene at different electrochemical potentials.

Figure 1 shows the structure diagram of the device and the shape diagram of the ferroelectric domain of the unit BFO. In the structure in the upper picture of Figure 1, they are STO, LSMO, and BFO from bottom to top, and the surface of the device is covered with a layer of graphene. The structural diagram of a single-cell ferroelectric domain can be seen in Figure 1, which consists of two parallel and symmetrical high chemical potential graphene nanoribbons and the surrounding intrinsic graphene. The white area is a high graphene chemical potential (polarization direction upward) area (two parallel and symmetrical high chemical potential graphene nanoribbons), and the black area is an intrinsic graphene (polarization direction downward) area. By using FDTD solution simulation software to change the chemical potential of graphene in different regions, the effects of different polarization directions are realized. Set the length of the white area to 0.5um, the width to 0.1um, the interval to 0.5um, the side length of the black area to 1um, and the materials are set to high chemical potential graphene and intrinsic chemical potential graphene respectively to achieve a structure in which black wraps the white area. . The length and width (X, Y directions) of the simulation area are both 1um, and the boundary conditions in the X and Y directions are periodic boundary conditions. In this way, a large-scale array coupling structure can be simulated by calculating only one unit area. The boundary condition in the Z direction is PML, which can absorb all electromagnetic waves.

Figure 2 shows the terahertz band absorption curves corresponding to different graphene chemical potentials when the above device structural parameters are fixed. From top to bottom are the terahertz band absorption diagrams corresponding to the graphene chemical potential of 0.4eV, 0.6eV, 0.7eV, and 0.8eV. The chemical potential of graphene in the downward polarization area (black area) is set to 0.01eV, and the chemical potential of graphene in the upward polarization area (white area) is set to 0.4eV, 0.6eV, 0.7eV, and 0.8eV respectively. It can be seen that by applying different gate voltages to the bottom electrode to adjust different graphene chemical potentials, the light absorption band area and intensity of the device can be controlled. Among them, as the chemical potential of graphene increases, the absorption peak shifts to the left, 0.4eV chemical Under the potential, the light absorption peak is the strongest.

Figure 3 shows the device surface electric field distribution diagram corresponding to different graphene chemical potentials when the above device structural parameters are fixed. From top to bottom are the electric field distribution diagrams corresponding to the chemical potential of graphene of 0.4eV and 0.8eV. It can be seen from the figure that the strongest electric field is at both ends of the intersection between the white strip and the black area, thus confirming that this structure can achieve localized surface plasmons, thus enhancing the light absorption ability of graphene. Different chemical potentials will not affect the action area of localized surface plasmons, but will only affect the intensity, thus not affecting the absorption mechanism, confirming the regulatory effect.

As can be seen from the above pictures, the selective absorption of light by the device can be changed by using different ferroelectric materials and applying different gate voltages. And the above device structure is used to enhance the light absorption intensity of the device.

Claims (4)

1. A high-response ferroelectric integrated graphene plasma terahertz detector is characterized in that strontium titanate is used as a substrate, lanthanum strontium manganese oxide is used as a bottom electrode, a layer of bismuth ferrite BFO is grown on the bottom electrode by an epitaxial method, two parallel rectangular local polarized electric domains are obtained by a piezoelectric power microscope or a watermarking method, a layer of intrinsic graphene is covered on the bismuth ferrite BFO to form a ferroelectric polarized substrate with adjustable and controllable functions, a pair of graphene nano-strip structures and an interval region, chemical potential of graphene is adjusted by utilizing the polarization of the ferroelectric substrate, and terahertz waves are detected by virtue of the graphene strip structures patterned by the ferroelectric domains, the high-conductivity intrinsic graphene interval region and the adjustable graphene plasmon coupling effect.

2. The highly responsive ferroelectric integrated graphene-plasma terahertz detector of claim 1, wherein the patterning consists of a pair of parallel symmetric graphene nanoribbons of high chemical potential and their surrounding intrinsic graphene.

3. A highly responsive ferroelectric integrated graphene-plasma terahertz detector as claimed in claim 2, wherein the graphene nanoribbons are 0.5 μm long by 0.1 μm wide and the graphene electrochemical potential is 0.4eV or 0.8eV.

4. The highly responsive ferroelectric integrated graphene plasma terahertz detector of claim 2, wherein the intrinsic graphene has a side length of 1 μm and the chemical potential of graphene is 0.01eV.