Ultrafast photoconductive material structure and terahertz photoconductive device

Abstract

The invention discloses an ultrafast photoconductive material structure which is characterized in that the ultrafast photoconductive material structure comprises a substrate layer and a rare earth doped In1-x-yGaxAlyAs semiconductor function layer, in the rare earth doped In1-x-yGaxAlyAs semiconductor function layer, rare earth materials are distributed in an island-shaped structure, and the rare earth materials are arranged in a multi-layer shape parallel to the substrate layer. A rare earth material is co-deposited into an In < 1-x-y > Ga < x > Al < y > As semiconductor, so that the material has excellent carrier mobility and dark resistivity while an ultrafast unbalanced carrier capturing process is realized. The invention further discloses a terahertz photoconductive device based on the structure, and terahertz emission and detection devices based on a photoconductive antenna can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of terahertz technology, specifically relating to an ultrafast photoconductive material structure, its preparation method, and the application of terahertz photoconductive devices. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies between 0.1 THz and 10 THz. Due to their low energy and long penetration distance, terahertz waves have wide applications in communications, spectroscopy, biomedicine, astronomy, security, and atmospheric remote sensing. The key to practical applications in the terahertz band lies in the radiation and detection of terahertz waves. Extensive research has been conducted for various application scenarios. There are many ways to generate terahertz waves, including photonic methods such as plasma, ferromagnetic and antiferromagnetic materials, nonlinear crystals, photoconductive antennas, and optical mixing; and electronic methods such as free-electron lasers, Schottky diodes, Gunn diodes, and single-carrier detectors. Among these, terahertz sources and detectors based on photoconductive antennas combine the advantages of room-temperature operation, fast response, wide radiation / detection frequency range, mature technology, relatively low cost, and high light-to-terahertz conversion efficiency, making them an important class of terahertz sources and detectors.

[0003] Terahertz photoconductive antennas utilize femtosecond lasers to pump ultrafast photoconductive materials into the antenna gaps. This generates photogenerated non-equilibrium carriers within the ultrafast photoconductive material. Under the influence of an applied voltage, these photogenerated non-equilibrium carriers produce transient currents, radiating terahertz waves—thus, a terahertz emission device based on a photoconductive antenna. The non-equilibrium carriers generated by the absorption of the ultrafast laser by the photoconductive material move towards two electrodes under the electric field of the terahertz electromagnetic wave. The transient currents are collected by the electrodes, achieving terahertz detection based on the photoconductive antenna. During the fabrication of terahertz photoconductive antennas, the material properties of the ultrafast photoconductor have a significant impact on terahertz radiation and detection performance. Currently, the most commonly used ultrafast photoconductive materials for terahertz photoconductive antennas are GaAs and InGaAs grown at low temperatures using molecular beam epitaxy, rare-earth-doped GaAs, and Fe or Rh-doped InGaAs. Based on the wavelength of the femtosecond laser used, they can be categorized into 800 nm and 1550 nm types. Traditional InGaAs-based semiconductor materials achieve picosecond-level carrier lifetimes through low-temperature growth or metal doping. However, due to the small band gap of InGaAs and the defects introduced by rare-earth elements and low-temperature growth, the electrical properties of the material system deteriorate, including reduced mobility and resistivity. Additional doping compensation is needed to optimize these electrical properties. Summary of the Invention

[0004] To overcome the shortcomings of the above-mentioned technologies, the present invention provides an ultrafast photoconductive material structure and a terahertz photoconductive device.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: An ultrafast photoconductive material structure comprising a substrate layer and rare-earth-doped In 1-x-y Ga x Al y As a semiconductor functional layer. Among them, rare-earth-doped In... 1-x-y Ga x Al y In the functional layer of As semiconductor, rare earth materials are distributed in an island-like structure and form a multilayer arrangement parallel to the substrate layer.

[0006] In a preferred embodiment of the present invention, the rare earth materials include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc.

[0007] In some embodiments of the present invention, the interlayer spacing of the multilayer arrangement is the same. In a preferred embodiment of the present invention, the interlayer spacing is 5-100 nanometers.

[0008] In some embodiments of the present invention, rare earth-doped In 1-x-y Ga x Al y The overall thickness of the As semiconductor functional layer is 0.1-2 micrometers.

[0009] In some embodiments of the present invention, the substrate layer is made of InP, GaAs, Si, or Ge.

[0010] In some embodiments of the present invention, the ultrafast photoconductive material structure further includes a buffer layer disposed between the substrate layer and rare-earth-doped In. 1-x-y Ga x Al y As between semiconductor functional layers.

[0011] In some embodiments of the present invention, rare earth-doped In 1-x-y Ga x Al y The doping method for the As semiconductor functional layer is either co-deposition of rare earth materials or periodic deposition on In. 1-x-y Ga x Al y In As semiconductors.

[0012] In some embodiments of the present invention, rare earth-doped In 1-x-y Ga x Al yThe As semiconductor functional layer is grown on the substrate layer via epitaxy. In a preferred embodiment of the present invention, rare-earth-doped In... 1-x-y Ga x Al y The As layer is grown at a temperature of 300-600°C to ensure that the In... 1-x-y Ga x Al y The crystal quality of the As layer, with a background vacuum of 1×10⁻⁶. -7 ~1×10 -10 The growth rate of torr is 0.1-1 μm / hr.

[0013] On the other hand, the present invention also provides a terahertz photoconductive device, comprising the above Narrative Ultrafast photoconductive material structure. Beneficial effects

[0014] This invention provides an In based on rare earth doping 1-x-y Ga x Al y Ultrafast photoconductive material structures based on In, and terahertz photoconductive devices. Molecular beam epitaxy allows for precise control of rare earth doping methods in semiconductors, including uniform or periodic doping of island-like rare earth materials. 1-x-y Ga x Al y As semiconductor layers absorb excitation light to generate non-equilibrium carriers. Island-shaped rare earth materials are used to capture these non-equilibrium carriers and reduce their lifetime. This is achieved by adjusting the integration of island-shaped rare earth materials into In. 1-x-y Ga x Al y The As approach can further reduce the non-equilibrium carrier lifetime to the sub-psa level, enabling its use in high-performance terahertz photoconductive devices. Meanwhile, due to In... 1-x-y Ga x Al y Since the bandgap of semiconductors can be adjusted over a wide range, the ultrafast photoconductive material structure provided by this invention can be applied to terahertz photoconductive materials and devices with multiple excitation wavelengths, especially terahertz devices excited by 1550 nm light in the optical communication band. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the ultrafast photoconductive material structure in this invention.

[0016] Figure 2 This is a cross-sectional transmission electron microscope image of Er periodically distributed in InAlAs in Example 1.

[0017] Figure 3In embodiment 2 of the present invention, InP substrates with different rare earth Er doping concentrations are used. 0.5 Al 0.5 Schematic diagram and XRD pattern of As.

[0018] Figure 4 In embodiment 2 of the present invention, InP substrates with different rare earth Er doping concentrations are used. 0.5 Al 0.5 Time-domain reflectance plot of As.

[0019] Figure 5 In Embodiment 3 of this invention, In-based Er-doped In on an InP substrate 0.50 Ga 0.05 Al 0.45 Schematic diagram and optical microscope image of a strip-shaped terahertz photoconductive antenna made of As ultrafast photoconductive material.

[0020] Figure 6 In Embodiment 3 of this invention, In-based Er-doped In on an InP substrate 0.50 Ga 0.05 Al 0.45 Test results of a terahertz photoconductive antenna made of As ultrafast photoconductive material. The device type is a strip antenna with an antenna spacing of 200 μm.

[0021] Figure 7 In Embodiment 3 of this invention, In-based Er-doped In on an InP substrate 0.50 Ga 0.05 Al 0.45 Test results of a terahertz photoconductive antenna made of As ultrafast photoconductive material. The device type is a strip antenna with an antenna spacing of 100 μm.

[0022] Figure 8 This refers to the Er-doped In on the InP substrate in Embodiment 4 of the present invention. 0.52 Al 0.48 Schematic diagram and optical microscope image of an H-type terahertz photoconductive antenna made of As ultrafast photoconductive material.

[0023] Figure 9 This refers to the Er-doped In on the InP substrate in Embodiment 4 of the present invention. 0.52 Al 0.48 Test results of terahertz photoconductive antenna made of ultrafast photoconductive material. The device type is H-type antenna with an antenna spacing of 100 / 25 μm.

[0024] Figure 10 This refers to the Er-doped In on the InP substrate in Embodiment 4 of the present invention. 0.52 Al 0.48Test results of terahertz photoconductive antenna devices made of As ultrafast photoconductive material with an excitation light of 1550 nm. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] like Figure 1 As shown, the present invention provides an ultrafast photoconductive material structure comprising a substrate layer 1 and rare-earth-doped In disposed thereon. 1-x-y Ga x Al y As semiconductor functional layer 2, rare earth-doped In 1-x-y Ga x Al y As a semiconductor functional layer 2, serving as a region for the generation and annihilation of non-equilibrium carriers, it enables ultrafast non-equilibrium carrier capture and can be used as a functional layer for non-equilibrium carrier generation and ultrafast carrier capture in photoconductive antenna devices. In rare-earth-doped In... 1-x-y Ga x Al y In the semiconductor functional layer 2, rare earth materials 21 are distributed in an island-like structure throughout the layer, and these rare earth materials 21 form a multilayered arrangement parallel to the substrate layer in this functional layer, such as... Figure 1 As shown. By adjusting the rare earth material 21 and incorporating it into In 1-x-y Ga x Al y By using the semiconductor functional layer 2, the non-equilibrium carrier lifetime of the material system can be reduced to the subpsa level while retaining high dark resistivity and mobility. In these multilayered arrangements, the distribution of rare-earth material 21 in the island structure within each layer is random, meaning that the doping concentration of rare-earth material 21 can be different in each layer. Rare-earth-doped In 1-x-y Ga x Al y In the As semiconductor functional layer 2, x and y can be selected between 0 and 1, and x+y can also be selected between 0 and 1. Rare-earth-doped In 1-x- y Ga x Al y The overall thickness of the As semiconductor functional layer 2 is preferably 0.1-2.0 micrometers.

[0027] In this invention, substrate layer 1 can be made of commonly used semiconductor substrate materials, such as InP, GaAs, Si, Ge, etc. By selecting a suitable semiconductor substrate material, the amount of InP can be reduced. 1-x-yGa x Al y The As layer is lattice mismatched with the substrate to improve the crystal quality of the material.

[0028] The present invention may further include a buffer layer disposed between the substrate layer 1 and the rare earth-doped In layer. 1-x-y Ga x Al y Between the As semiconductor functional layers 2, surface flatness can be further improved, dislocation density reduced, and crystal quality enhanced. The material of the buffer layer can be a wide-bandgap ternary alloy material that matches the crystal lattice of the substrate material. For example, if the substrate material is InP, the buffer layer material can be InAlAs, InGaAs, GaAs, AlAs, or a superlattice structure composed of two of the above materials.

[0029] In this invention, rare earth-doped In 1-x-y Ga x Al y The As semiconductor functional layer 2 is grown by co-deposition or periodic deposition, and the rare earth doping concentration is 1×10⁻⁶. 17 Up to 5×10 21 cm -3 The rare earth materials doped with include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc.

[0030] In this invention, the interlayer spacing of the multilayered arrangement is uniform, which improves the absorption and trapping performance of charge carriers. The interlayer spacing is preferably 5-100 nanometers, and the specific selection is based on the absorption coefficient of the excitation wavelength of the device to be used later.

[0031] In this invention, rare earth-doped In 1-x-y Ga x Al y The doping method for the As semiconductor functional layer 2 is either co-deposition of rare earth materials or periodic deposition on In. 1-x-y Ga x Al y In As semiconductors, the periodic deposition method involves alternating growth of rare earth material layers and In. 1-x-y Ga x Al y As a semiconductor layer, rare earth material co-deposition involves simultaneously depositing rare earth materials and In. 1-x-y Ga x Al y As semiconductor material. In this invention, rare earth-doped In... 1-x-y Ga x Al yThe As semiconductor functional layer 2 is preferably grown on the substrate layer via epitaxy, which allows for precise control over the rare earth doping method in the semiconductor, while simultaneously improving the quality of the semiconductor layer. Specifically, rare earth-doped In... 1-x-y Ga x Al y The growth temperature of the As semiconductor functional layer is 300-600°C to ensure that In... 1-x-y Ga x Al y The crystal quality of the As layer, with a background vacuum of 1×10⁻⁶. -7 ~1×10 -10 The growth rate of torr is 0.1-1 μm / hr.

[0032] The present invention also provides a terahertz photoconductive device comprising an ultrafast photoconductive material structure. This photoconductive device structure can be used as a femtosecond laser-excited terahertz source and terahertz detector, and in particular, it can be used as a terahertz device excited by 1550nm light in the optical communication band.

[0033] The technical solutions of this invention will be described below with reference to the embodiments thereof. These embodiments are only a part of the embodiments of this invention, not all of them. Furthermore, the embodiments yield ultrafast photoconductive materials with varying rare-earth doping concentrations, which are then microfabricated into different types of photoconductive antenna devices. All other implementations obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Example 1

[0034] Structure of InP-based rare earth Er-doped InAlAs ultrafast photoconductive material.

[0035] The InAlAs ternary random alloy is lattice-matched with the InP substrate, with an In composition of 0.52. During molecular beam epitaxy, the baffles of the rare earth Er, In, Al, and As source furnaces are simultaneously opened to achieve simultaneous growth, as detailed below: (1) The InP(001) substrate was deoxidized in an arsenic atmosphere for 15 minutes at a deoxidation temperature of 520-540°C. (2) Molecular beam epitaxy was used to epitaxially grow InAlAs and ErAs layers, repeated 10 times, ending with an InAlAs layer.

[0036] Figure 2This is a cross-sectional transmission electron microscope image showing the periodic distribution of Er within the InAlAs framework in this embodiment. The bonding of ErAs and InAlAs materials can be controllably achieved through molecular beam epitaxy. As can be seen from the image, the rare earth material Er is distributed in a multilayered structure within the functional layers, with essentially uniform layer spacing, and the doping concentration of the rare earth material varies in each layer. Example 2

[0037] InP-based rare earth Er uniformly doped InAlAs ultrafast photoconductive material structure.

[0038] In 0.5 Al 0.5 As ternary random alloys are lattice-matched with InP substrates. During molecular beam epitaxy, the baffles of the rare earth Er, In, Al, and As source furnaces are simultaneously opened to achieve simultaneous growth, as detailed below: (1) The InP(001) substrate was deoxidized in an arsenic atmosphere for 15 minutes at a deoxidation temperature of 520-540°C. (2) Er-doped InAlAs ultrafast photoconductive material was epitaxially grown using molecular beam epitaxy. Different concentrations of Er were incorporated by changing the temperature of the rare earth Er source furnace, and the growth thickness was 1 μm.

[0039] Figure 3 In different Er doping concentrations in Embodiment 2 of the present invention 0.5 Al 0.5 X-ray diffraction pattern and corresponding structural diagram of the ultrafast photoconductive material As. Figure 3 It is known that different concentrations of rare earth element Er cause the diffraction peaks of Er:InAlAs to shift towards larger diffraction angles. As the Er doping concentration increases, the diffraction angle becomes larger, and the corresponding lattice constant becomes smaller. Er-doped In 0.5 Al 0.5 As ultrafast photoconductive materials still possess good crystal quality.

[0040] Figure 4 In this embodiment, In with different Er doping concentrations 0.5 Al 0.5 The transient time-domain reflectometry spectrum of ultrafast photoconductor materials shows that the incorporation of rare-earth Er shortens the non-equilibrium carrier lifetime to about 1 ps. With increasing Er doping concentration, Er-doped In... 0.5 Al 0.5 The non-equilibrium carrier lifetime of ultrafast photoconductive materials is gradually increasing.

[0041] By incorporating rare earth Er with In that is compatible with InP 0.5 Al 0.5In As semiconductor materials, the preparation of ultrafast photoconductive materials has been achieved. Example 3

[0042] InP substrate based on uniform Er doping In 0.50 Ga 0.05 Al 0.45 The specific design of the strip-shaped terahertz photoconductive antenna using ultrafast photoconductive material is as follows: (1) The InP(001) substrate was deoxidized in an arsenic atmosphere for 15 min at a deoxidation temperature of 520-540°C. (2) Er-doped In was epitaxially grown using molecular beam epitaxy. 0.50 Ga 0.05 Al 0.45 As an ultrafast photoconductive material, different concentrations of Er were incorporated by changing the temperature of the rare earth Er source furnace, with a growth thickness of 1 μm. (3) The pattern of the strip antenna is prepared by using the common micro-machining photolithography process. Then, 20 nm Ti, 30 nm Pt and 100 nm Au metal are deposited sequentially by electron beam evaporation equipment. After that, the metal is stripped by immersion in acetone, leaving the shape of the metal antenna. (4) Metal Ohmic Contact Treatment: The processed antenna is annealed at 450°C for 30s in a rapid annealing furnace under nitrogen protection.

[0043] In this embodiment, a schematic diagram of the strip antenna and an optical microscope image of the fabricated strip antenna are shown below. Figure 5 As shown in the figure. Then, the terahertz antenna was assembled and placed in the terahertz transmitter based on the 800 nm excitation time-domain spectrum of ZnTe electro-optic sampling for subsequent device performance testing.

[0044] Figure 6 In this embodiment, it is based on Er-doped In. 0.50 Ga 0.05 Al 0.45 Test results of an As photoconductive antenna with a 200 μm spacing strip antenna transmitter. Test conditions included a 30 mW excitation power, an 800 nm femtosecond laser, and a repetition rate of 80 MHz. The voltage of the transmitting antenna was increased from 30 V to 65 V. Time-domain, terahertz, and frequency-domain signals under different bias voltages are shown below. Figure 6 As the bias voltage increases, the terahertz signal gradually strengthens.

[0045] Figure 7 In this embodiment, it is based on Er-doped In. 0.50 Ga 0.05 Al 0.45Test results of an As photoconductive antenna with a 100 μm spacing strip antenna transmitter. Test conditions included a 13 mW excitation power, an 800 nm femtosecond laser, and a repetition rate of 80 MHz. The voltage of the transmitting antenna was increased from 30 V to 100 V. Based on the time-domain and frequency-domain terahertz signals under different bias voltages, the terahertz signal gradually increased with increasing bias voltage, and the peak value of the time-domain signal showed a linear relationship with the voltage. Example 4

[0046] InP substrate based on uniform Er doping In 0.52 Al 0.48 The specific design of the H-type terahertz photoconductive antenna using ultrafast photoconductive material is as follows: (1) The InP(001) substrate was deoxidized in an arsenic atmosphere for 15 min at a deoxidation temperature of 520-540°C. (2) Er-doped InAlAs ultrafast photoconductive material was epitaxially grown using molecular beam epitaxy. Different concentrations of Er were incorporated by changing the temperature of the rare earth Er source furnace. The growth thickness was 1 μm. (3) The pattern of the H-type antenna is prepared by using the common micro-machining photolithography process. Then, 20 nm Ti, 30 nm Pt and 100 nm Au metal are deposited sequentially by electron beam evaporation equipment. After that, the metal is stripped by immersion in acetone, leaving the shape of the metal antenna. (4) Metal Ohmic Contact Treatment: The processed antenna is annealed at 450°C for 30s in a rapid annealing furnace under nitrogen protection.

[0047] In this embodiment, a schematic diagram of the H-type antenna and an optical microscope image of the fabricated strip antenna are shown below. Figure 8 As shown in the figure. Then, the terahertz antenna was assembled and placed in the terahertz time-domain spectrum excited by 800 nm based on ZnTe electro-optic sampling for subsequent device performance testing.

[0048] Figure 9 In this embodiment, it is based on Er-doped In. 0.52 Al 0.48 Test results of an H-type transmitter with a 100 / 25 μm spacing using an As photoconductive antenna. Test conditions included a 13 mW excitation power, an 800 nm femtosecond laser, and a repetition rate of 80 MHz. The voltage of the transmitting antenna was increased from 30 V to 50 V. Based on the time-domain and frequency-domain terahertz signals under different bias voltages, the terahertz signal gradually increased with increasing bias voltage.

[0049] Figure 10 In this embodiment, it is based on Er-doped In. 0.52 Al 0.48Test results of an As photoconductive antenna with a 100 / 25 μm spacing H-type detector. Test conditions included a 13 mW excitation power, a 1550 nm femtosecond laser excitation frequency of 80 MHz, and Er-doped In. 0.52 Al 0.48 As photoconductive materials respond to 1550 nm excitation light.

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A structure of ultrafast photoconductive material, characterized in that, a substrate layer and a rare earth-doped In 1-x-y Ga x Al y As semiconductor functional layer, wherein in the rare earth-doped In 1-x-y Ga x Al y As semiconductor functional layer, the rare earth material is distributed in an island-like structure, and the rare earth material forms a multi-layered arrangement parallel to the substrate layer.

2. The ultrafast photoconductive material structure of claim 1, wherein The rare earth material comprises La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc.

3. The ultrafast photoconductive material structure of claim 1, wherein The layers of the multilayer arrangement have the same layer spacing.

4. The ultrafast photoconductive material structure of claim 3, wherein, The layer spacing is between 5 and 100 nm.

5. The ultrafast photoconductive material structure of claim 1, wherein, The rare earth-doped In 1-x- y Ga x Al y The overall thickness of the As semiconductor functional layer is 0.1-2.0 microns.

6. The ultrafast photoconductive material structure of claim 1, wherein, The material of the substrate layer is InP, GaAs, Si or Ge.

7. The ultrafast photoconductive material structure of claim 1, wherein Further comprising a buffer layer disposed between the substrate layer and the rare earth doped In 1-x-y Ga x Al y As semiconductor functional layer.

8. The ultrafast photoconductive material structure of claim 1, wherein, The rare earth doped In 1-x- y Ga x Al y The doping of the As semiconductor functional layer is either co-deposition of the rare earth material or periodic deposition in the In 1-x-y Ga x Al y As semiconductor.

9. The ultrafast photoconductive material structure of claim 1, wherein, The rare earth-doped In 1-x- y Ga x Al y The As semiconductor functional layer is grown on the substrate layer by epitaxy.

10. A terahertz photoconductive device, characterized by, A structure comprising the ultrafast photoconductive material according to any one of claims 1 to 8.

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