CN102593272B - The preparation method of epitaxial structure - Google Patents

Abstract

The invention relates to an epitaxial structure and a preparation method thereof. The epitaxial structure includes: a base with an epitaxial growth plane, and an epitaxial layer formed on the epitaxial growth plane of the base, wherein a carbon nanotube layer is further included between the epitaxial layer and the base. The preparation method of the epitaxial structure comprises the following steps: providing a substrate, the substrate has an epitaxial growth surface supporting the growth of the epitaxial layer; setting a carbon nanotube layer on the epitaxial growth surface of the substrate; and growing on the epitaxial growth surface of the substrate epitaxial layer.

Description

Fabrication method of epitaxial structure

technical field

The invention relates to an epitaxial structure and a preparation method thereof.

Background technique

Epitaxial structures, especially heteroepitaxial structures, are one of the main materials for making semiconductor devices. For example, in recent years, the preparation of gallium nitride epitaxial wafers for light-emitting diodes (LEDs) has become a research hotspot.

The gallium nitride epitaxial wafer means that under certain conditions, the molecules of gallium nitride material are regularly arranged and directional grown on the sapphire substrate. However, the preparation of high-quality GaN epitaxial wafers has always been a difficult research point. Due to the difference in lattice constant and thermal expansion coefficient between gallium nitride and sapphire substrates, there are many dislocation defects in the epitaxial layer of gallium nitride. Moreover, there is a large stress between the GaN epitaxial layer and the sapphire substrate, and the greater stress will cause the GaN epitaxial layer to crack. This heteroepitaxial structure generally has a lattice mismatch phenomenon, and is prone to form defects such as dislocations.

The prior art provides a method for improving the above-mentioned disadvantages, which uses a non-flat sapphire substrate to epitaxially grow gallium nitride. However, in the prior art, microelectronic processes such as photolithography are usually used to form grooves on the surface of the sapphire substrate to form a non-flat epitaxial growth surface. This method is not only complicated in process and high in cost, but also pollutes the epitaxial growth surface of the sapphire substrate, thereby affecting the quality of the epitaxial structure.

Contents of the invention

To sum up, it is indeed necessary to provide a method for preparing an epitaxial structure with simple process, low cost and no pollution to the substrate surface.

A method for preparing an epitaxial structure, which includes the following steps: providing a substrate, the substrate has an epitaxial growth surface supporting the growth of an epitaxial layer; providing a self-supporting carbon nanotube film, the carbon nanotube film is composed of a plurality of carbon A continuous overall structure of nanotubes, the axial directions of the plurality of carbon nanotubes extend along the same preferred orientation, and the adjacent carbon nanotubes whose axial directions extend along the same preferred orientation are connected end to end by van der Waals force, the There are micropores or gaps between adjacent carbon nanotubes in the carbon nanotube film to form openings; the self-supporting carbon nanotube film is directly laid on the epitaxial growth surface of the substrate, and the self-supporting carbon nanotube film A plurality of carbon nanotubes extend along a direction parallel to the epitaxial growth plane; and an epitaxial layer is grown on the epitaxial growth plane of the substrate by using the directly laid carbon nanotube film as a mask.

Compared with the prior art, the method for obtaining a patterned mask by arranging a carbon nanotube layer on the epitaxial growth surface of the substrate is simple in process and low in cost, which greatly reduces the preparation cost of the epitaxial structure, and at the same time reduces the need for pollution of the environment.

Description of drawings

FIG. 1 is a process flow chart of a method for preparing a heteroepitaxial structure provided by an embodiment of the present invention.

Fig. 2 is a scanning electron micrograph of the carbon nanotube film used in the embodiment of the present invention.

FIG. 3 is a schematic structural diagram of carbon nanotube segments in the carbon nanotube film in FIG. 2 .

Fig. 4 is a scanning electron micrograph of a carbon nanotube film with multiple layers intersected in an embodiment of the present invention.

Fig. 5 is a scanning electron micrograph of the non-twisted carbon nanotube wire used in the embodiment of the present invention.

Fig. 6 is a scanning electron micrograph of the twisted carbon nanotube wire used in the embodiment of the present invention.

FIG. 7 is a schematic diagram of the growth process of the heteroepitaxial layer in the embodiment of the present invention.

FIG. 8 is a scanning electron micrograph of the cross-section of the heteroepitaxial structure prepared in the first embodiment of the present invention.

FIG. 9 is a transmission electron micrograph at the interface of the heteroepitaxial structure prepared in the first embodiment of the present invention.

FIG. 10 is a schematic perspective view of the heteroepitaxial structure provided by the first embodiment of the present invention.

FIG. 11 is a schematic cross-sectional view of the heteroepitaxial structure shown in FIG. 10 along the line XI-XI.

FIG. 12 is a schematic perspective view of the heteroepitaxial structure provided by the second embodiment of the present invention.

FIG. 13 is a schematic perspective view of the heteroepitaxial structure provided by the third embodiment of the present invention.

Description of main component symbols

Heteroepitaxial structures 10, 20, 30

Base 100, 200, 300

Epitaxial Growth Surface 101

Carbon nanotube layers 102, 202, 302

Holes 103

Heteroepitaxial layers 104, 204, 304

opening 105

Heteroepitaxial grains 1042

Heteroepitaxial thin films 1044

Carbon Nanotube Fragments 143

Carbon nanotubes 145

detailed description

The epitaxial structure provided by the embodiments of the present invention and its preparation method will be described in detail below with reference to the accompanying drawings. In order to facilitate the understanding of the technical solution of the present invention, the present invention first introduces a method for preparing a heteroepitaxial structure.

Please refer to FIG. 1 , an embodiment of the present invention provides a method for preparing a heteroepitaxial structure 10, which specifically includes the following steps:

S10: providing a substrate 100, and the substrate 100 has an epitaxial growth surface 101 supporting the growth of the heteroepitaxial layer 104;

S20: disposing a carbon nanotube layer 102 on the epitaxial growth surface 101 of the substrate 100;

S30 : growing a heteroepitaxial layer 104 on the epitaxial growth surface 101 of the substrate 100 .

Please refer to FIG. 1 , an embodiment of the present invention provides a method for preparing a heteroepitaxial structure 10, which specifically includes the following steps:

S10: providing a substrate 100, and the substrate 100 has an epitaxial growth surface 101 supporting the growth of the heteroepitaxial layer 104;

S20: disposing a carbon nanotube layer 102 on the epitaxial growth surface 101 of the substrate 100;

S30 : growing a heteroepitaxial layer 104 on the epitaxial growth surface 101 of the substrate 100 .

In step S10 , the substrate 100 provides the epitaxial growth plane 101 of the heteroepitaxial layer 104 . The epitaxial growth surface 101 of the substrate 100 is a molecularly smooth surface, and impurities such as oxygen or carbon are removed. The substrate 100 can be a single-layer or multi-layer structure. When the substrate 100 is a single-layer structure, the substrate 100 may be a single crystal structure, and has a crystal plane as the epitaxial growth plane 101 of the heteroepitaxial layer 104 . The material of the single-layer structure substrate 100 may be GaAs, GaN, Si, SOI, AlN, SiC, MgO, ZnO, LiGaO ₂ , LiAlO ₂ or Al ₂ O ₃ . When the substrate 100 is a multilayer structure, it needs to include at least one layer of the above-mentioned single crystal structure, and the single crystal structure has a crystal plane as the epitaxial growth plane 101 of the heteroepitaxial layer 104 . The material of the substrate 100 can be selected according to the heteroepitaxial layer 104 to be grown. Preferably, the substrate 100 and the heteroepitaxial layer 104 have similar lattice constants and thermal expansion coefficients. The thickness, size and shape of the base 100 are not limited and can be selected according to actual needs. The substrate 100 is not limited to the materials listed above, as long as the substrate 100 has the epitaxial growth surface 101 supporting the growth of the heteroepitaxial layer 104, it falls within the protection scope of the present invention.

In step S20, the carbon nanotube layer 102 is a continuous integral structure including a plurality of carbon nanotubes. A plurality of carbon nanotubes in the carbon nanotube layer 102 extend along a direction substantially parallel to the surface of the carbon nanotube layer 102 . When the carbon nanotube layer 102 is disposed on the epitaxial growth plane 101 of the substrate 100 , the extending direction of the carbon nanotubes in the carbon nanotube layer 102 is substantially parallel to the epitaxial growth plane 101 of the substrate 100 . The thickness of the carbon nanotube layer is 1 nanometer to 100 micrometers, or 1 nanometer to 1 micrometer, or 1 nanometer to 200 nanometers, preferably 10 nanometers to 100 nanometers. The carbon nanotube layer 102 is a patterned carbon nanotube layer 102 . The "patterning" means that the carbon nanotube layer 102 has a plurality of openings 105 , and the plurality of openings 105 penetrate the carbon nanotube layer 102 from the thickness direction of the carbon nanotube layer 102 . When the carbon nanotube layer 102 is disposed covering the epitaxial growth surface 101 of the substrate 100 , the portion of the epitaxial growth surface 101 of the substrate 100 corresponding to the opening 105 is exposed to facilitate the growth of the heteroepitaxial layer 104 . The opening 105 can be a micropore or a gap. The size of the opening 105 is 10 nanometers to 500 microns, and the size refers to the diameter of the micropores or the spacing in the width direction of the gaps. The size of the opening 105 is 10 nanometers to 300 micrometers, or 10 nanometers to 120 micrometers, or 10 nanometers to 80 micrometers, or 10 nanometers to 10 micrometers. The smaller the size of the opening 105 is, it is beneficial to reduce the occurrence of dislocation defects during the growth of the epitaxial layer, so as to obtain a high-quality heteroepitaxial layer 104 . Preferably, the size of the opening 105 is 10 nanometers to 10 micrometers. Further, the duty ratio of the carbon nanotube layer 102 is 1:100-100:1, or 1:10-10:1, or 1:2-2:1, or 1:4-4:1. Preferably, the duty ratio is 1:4˜4:1. The so-called “duty ratio” refers to the area ratio of the portion of the epitaxial growth surface 101 occupied by the carbon nanotube layer 102 to the portion exposed through the opening 105 after the carbon nanotube layer 102 is disposed on the epitaxial growth surface 101 of the substrate 100 .

Further, the "patterning" means that the arrangement of the carbon nanotubes in the carbon nanotube layer 102 is orderly and regular. For example, the axial directions of the plurality of carbon nanotubes in the carbon nanotube layer 102 are substantially parallel to the epitaxial growth plane 101 of the substrate 100 and extend substantially in the same direction. Alternatively, the axial directions of the plurality of carbon nanotubes in the carbon nanotube layer 102 may regularly extend substantially along more than two directions. Alternatively, the axial direction of the plurality of carbon nanotubes in the carbon nanotube layer 102 extends along a crystal direction of the substrate 100 or extends at a certain angle with a crystal direction of the substrate 100 . Adjacent carbon nanotubes extending in the same direction in the carbon nanotube layer 102 are connected end to end by van der Waals force.

On the premise that the carbon nanotube layer 102 has the aforementioned openings 105 , a plurality of carbon nanotubes in the carbon nanotube layer 102 may also be arranged randomly or randomly.

Preferably, the carbon nanotube layer 102 is disposed on the entire epitaxial growth surface 101 of the substrate 100 . The carbon nanotubes in the carbon nanotube layer 102 can be one or more of single-walled carbon nanotubes, double-walled carbon nanotubes or multi-walled carbon nanotubes, and the length and diameter can be selected as required.

The carbon nanotube layer 102 is used as a mask for growing the heteroepitaxial layer 104 . The so-called "mask" means that the carbon nanotube layer 102 is used to block part of the epitaxial growth surface 101 of the substrate 100, and expose part of the epitaxial growth surface 101, so that the heteroepitaxial layer 104 can only be formed from the epitaxial growth surface 101 The exposed part grows. Since the carbon nanotube layer 102 has a plurality of openings 105, the carbon nanotube layer 102 forms a patterned mask. After the carbon nanotube layer 102 is disposed on the epitaxial growth plane 101 of the substrate 100 , the plurality of carbon nanotubes extend along a direction parallel to the epitaxial growth plane 101 . Since the carbon nanotube layer 102 forms a plurality of openings 105 on the epitaxial growth surface 101 of the substrate 100 , a patterned mask is provided on the epitaxial growth surface 101 of the substrate 100 . It can be understood that compared with microelectronic processes such as photolithography, the method of epitaxial growth by setting a carbon nanotube layer 102 mask has simple process, low cost, and is not easy to introduce pollution on the extended growth surface 101 of the substrate 100. It is also environmentally friendly and can be greatly improved. The manufacturing cost of the heteroepitaxial structure 10 is reduced.

It can be understood that the substrate 100 and the carbon nanotube layer 102 together constitute a substrate for growing a heteroepitaxial structure. The substrate can be used to grow hetero-epitaxial layers 104 of different materials, such as semiconductor epitaxial layers, metal epitaxial layers or alloy epitaxial layers. The substrate can also be used to grow a homoepitaxial layer, thereby obtaining a homoepitaxial structure.

The carbon nanotube layer 102 may be pre-formed and directly laid on the epitaxial growth surface 101 of the substrate 100 . The carbon nanotube layer 102 is a macroscopic structure, and the carbon nanotube layer 102 is a self-supporting structure. The so-called "self-supporting" means that the carbon nanotube layer 102 does not need a large-area carrier support, but as long as the supporting force is provided on both sides, it can be suspended as a whole and maintain its own state, that is, the carbon nanotube layer 102 is placed (or fixed) on ) on two supports arranged at a specific distance apart, the carbon nanotube layer 102 located between the two supports can be suspended and maintain its own state. Since the carbon nanotube layer 102 is a self-supporting structure, the carbon nanotube layer 102 does not need to be formed on the epitaxial growth surface 101 of the substrate 100 through complex chemical methods. Further preferably, the carbon nanotube layer 102 is a pure carbon nanotube structure composed of a plurality of carbon nanotubes. The so-called "pure carbon nanotube structure" means that the carbon nanotube layer does not need any chemical modification or acidification treatment during the whole preparation process, and does not contain any functional group modification such as carboxyl group.

The carbon nanotube layer 102 can also be a composite structure including a plurality of carbon nanotubes and additive materials. The additive material includes one or more of graphite, graphene, silicon carbide, boron nitride, silicon nitride, silicon dioxide, amorphous carbon and the like. The additive material may also include one or more of metal carbides, metal oxides, and metal nitrides. The additive material is coated on at least part of the surface of the carbon nanotubes in the carbon nanotube layer 102 or disposed in the opening 105 of the carbon nanotube layer 102 . Preferably, the additive material is coated on the surface of the carbon nanotubes. Because the added material coats the surface of the carbon nanotubes, the diameter of the carbon nanotubes becomes larger, thereby reducing the openings 105 between the carbon nanotubes. The additive material can be formed on the surface of the carbon nanotubes by chemical vapor deposition (CVD), physical vapor deposition (PVD), magnetron sputtering and other methods.

After laying the carbon nanotube layer 102 on the epitaxial growth surface 101 of the substrate 100 , a step of organic solvent treatment may be included to make the carbon nanotube layer 102 more closely bonded to the epitaxial growth surface 101 . The organic solvent can be selected from one or a combination of ethanol, methanol, acetone, dichloroethane and chloroform. The organic solvent in this embodiment adopts ethanol. The step of treating with an organic solvent can drop the organic solvent on the surface of the carbon nanotube layer 102 to soak the entire carbon nanotube layer 102 through a test tube, or immerse the substrate 100 and the entire carbon nanotube layer 102 together in a container filled with an organic solvent. .

The carbon nanotube layer 102 can also be directly grown on the epitaxial growth surface 101 of the substrate 100 by methods such as chemical vapor deposition (CVD) or first grown on the surface of the silicon substrate, and then transferred to the epitaxial growth surface of the substrate 100 101.

Specifically, the carbon nanotube layer 102 may include a carbon nanotube film or a carbon nanotube wire. The carbon nanotube layer 102 can be a single-layer carbon nanotube film or a plurality of stacked carbon nanotube films. The carbon nanotube layer 102 may include multiple carbon nanotube wires arranged in parallel or multiple carbon nanotube wires arranged crosswise. When the carbon nanotube layer 102 is a plurality of stacked carbon nanotube films, the number of carbon nanotube films should not be too many, preferably 2-100 layers. When the carbon nanotube layer 102 is a plurality of parallel carbon nanotube wires, the distance between two adjacent carbon nanotube wires is 0.1 micron to 200 micron, preferably, 10 micron to 100 micron. The space between the two adjacent carbon nanotube wires constitutes the opening 105 of the carbon nanotube layer 102 . The length of the gap between two adjacent carbon nanotube wires may be equal to the length of the carbon nanotube wires. The carbon nanotube film or carbon nanotube wire can be directly laid on the epitaxial growth surface 101 of the substrate 100 to form the carbon nanotube layer 102 . By controlling the number of carbon nanotube film layers or the distance between carbon nanotube wires, the size of the opening 105 in the carbon nanotube layer 102 can be controlled.

The carbon nanotube film is a self-supporting structure composed of several carbon nanotubes. The plurality of carbon nanotubes extend along the same preferred orientation. The preferred orientation means that the overall extension direction of most carbon nanotubes in the carbon nanotube film basically faces the same direction. Also, the overall extension direction of the majority of carbon nanotubes is substantially parallel to the surface of the carbon nanotube film. Further, most of the carbon nanotubes in the carbon nanotube film are connected end to end by van der Waals force. Specifically, each carbon nanotube in the majority of carbon nanotubes extending in the same direction in the carbon nanotube film is connected end-to-end with the adjacent carbon nanotubes in the extending direction through van der Waals force. Of course, there are a small number of randomly arranged carbon nanotubes in the carbon nanotube film, and these carbon nanotubes will not significantly affect the overall alignment of most carbon nanotubes in the carbon nanotube film. The self-supporting carbon nanotube film does not need a large-area carrier support, but as long as the supporting force is provided on the opposite sides, it can be suspended as a whole and maintain its own film state, that is, the carbon nanotube film is placed (or fixed) in the spacer. When the two supports are arranged at a specific distance, the carbon nanotube film located between the two supports can be suspended in the air and maintain its own film state. The self-support is mainly realized by the presence of continuous carbon nanotubes in the carbon nanotube film that are extended and arranged end to end through van der Waals force.

Specifically, most of the carbon nanotubes extending in the same direction in the carbon nanotube film are not absolutely straight and can be properly bent; or they are not completely arranged in the extending direction and can be appropriately deviated from the extending direction. Therefore, it cannot be ruled out that there may be partial contact between parallel carbon nanotubes among the plurality of carbon nanotubes extending substantially in the same direction in the carbon nanotube film.

Please refer to FIG. 2 and FIG. 3 , specifically, the carbon nanotube film includes a plurality of continuous and directionally extended carbon nanotube segments 143 . The plurality of carbon nanotube segments 143 are connected end to end by van der Waals force. Each carbon nanotube segment 143 includes a plurality of parallel carbon nanotubes 145, and the plurality of parallel carbon nanotubes 145 are closely combined by van der Waals force. The carbon nanotube segment 143 has any length, thickness, uniformity and shape. The carbon nanotube film can be obtained by directly drawing some carbon nanotubes from a carbon nanotube array. The thickness of the carbon nanotube film is 1 nanometer to 100 micrometers, the width is related to the size of the carbon nanotube array from which the carbon nanotube film is pulled out, and the length is not limited. There are micropores or gaps between adjacent carbon nanotubes in the carbon nanotube film to form openings 105 , and the size of the micropores or gaps is less than 10 microns. Preferably, the carbon nanotube film has a thickness of 100 nanometers to 10 micrometers. The carbon nanotubes 145 in the carbon nanotube film preferably extend in the same direction. For the carbon nanotube film and its preparation method, please refer to the Chinese Publication Patent No. CN101239712B "Carbon Nanotube Film Structure and Preparation Method" filed by the applicant on February 9, 2007 and announced on May 26, 2010. ". To save space, it is only cited here, but all the technical disclosures of the above applications should also be regarded as a part of the technical disclosures of the present application.

Please refer to Fig. 4, when the carbon nanotube layer comprises multi-layer carbon nanotube films stacked, the extension directions of the carbon nanotubes in the adjacent two layers of carbon nanotube films form a cross angle α, and α is greater than or equal to 0 degrees is less than or equal to 90 degrees (0°≤α≤90°).

In order to reduce the thickness of the carbon nanotube film, the carbon nanotube film can be further heat-treated. In order to avoid the destruction of the carbon nanotube film when heated, the method for heating the carbon nanotube film adopts a local heating method. It specifically includes the following steps: locally heating the carbon nanotube film to oxidize some carbon nanotubes in the local position of the carbon nanotube film; heating. Specifically, the carbon nanotube film may be divided into multiple small regions, and the carbon nanotube film may be heated region by region in a manner from local to global. There are many methods for locally heating the carbon nanotube film, such as laser heating, microwave heating and so on. In this embodiment, the carbon nanotube film is irradiated by scanning laser with a power density greater than 0.1×10 ⁴ watts/square meter, and the carbon nanotube film is heated from local to whole. The carbon nanotube film is irradiated by laser, and part of the carbon nanotubes in the thickness direction are oxidized, and at the same time, the carbon nanotube bundles with larger diameters in the carbon nanotube film are removed, so that the carbon nanotube film becomes thinner.

It can be understood that the method for scanning the carbon nanotube film with the laser is not limited, as long as the carbon nanotube film can be irradiated uniformly. Laser scanning can be performed row by row along the direction parallel to the arrangement of carbon nanotubes in the carbon nanotube film, or can be performed column by row along the direction perpendicular to the arrangement direction of carbon nanotubes in the carbon nanotube film. The smaller the speed at which the laser with fixed power and fixed wavelength scans the carbon nanotube film, the more heat absorbed by the carbon nanotube bundles in the carbon nanotube film, and the more correspondingly destroyed carbon nanotube bundles, the carbon nanotubes after laser treatment The thickness of the film becomes smaller. However, if the laser scanning speed is too small, the carbon nanotube film will absorb too much heat and be burned. In this embodiment, the power density of the laser is greater than 0.053×10 ¹² watts/square meter, the diameter of the laser spot is in the range of 1 mm to 5 mm, and the laser scanning irradiation time is less than 1.8 seconds. Preferably, the laser is a carbon dioxide laser with a power of 30 watts, a wavelength of 10.6 microns, and a spot diameter of 3 mm. The relative movement speed between the laser device 140 and the carbon nanotube film is less than 10 mm/s.

The carbon nanotube wires may be non-twisted carbon nanotube wires or twisted carbon nanotube wires. Both the non-twisted carbon nanotubes and the twisted carbon nanotubes are self-supporting structures. Specifically, referring to FIG. 5 , the non-twisted carbon nanotube wire includes a plurality of carbon nanotubes extending parallel to the length of the non-twisted carbon nanotube wire. Specifically, the non-twisted carbon nanotube wire includes a plurality of carbon nanotube segments, the plurality of carbon nanotube segments are connected end to end by van der Waals force, and each carbon nanotube segment includes a plurality of carbon nanotube segments that are parallel to each other and closely combined by van der Waals force. nanotube. The carbon nanotube segment has any length, thickness, uniformity and shape. The length of the non-twisted carbon nanotubes is not limited, and the diameter is 0.5 nanometers to 100 microns. The non-twisted carbon nanotube wire is obtained by treating the carbon nanotube film with an organic solvent. Specifically, the entire surface of the carbon nanotube film is infiltrated with an organic solvent, and under the action of the surface tension generated when the volatile organic solvent volatilizes, multiple carbon nanotubes in the carbon nanotube film that are parallel to each other are tightly bound together by van der Waals force. Combined, so that the carbon nanotube film shrinks into a non-twisted carbon nanotube wire. The organic solvent is a volatile organic solvent, such as ethanol, methanol, acetone, dichloroethane or chloroform, and ethanol is used in this embodiment. Compared with the carbon nanotube film without organic solvent treatment, the non-twisted carbon nanotube wire treated by organic solvent has a smaller specific surface area and lower viscosity.

The twisted carbon nanotube wire is obtained by using a mechanical force to twist the two ends of the carbon nanotube film in opposite directions. Please refer to FIG. 6 , the twisted carbon nanotube wire includes a plurality of carbon nanotubes extending helically around the twisted carbon nanotube wire axially. Specifically, the twisted carbon nanotube wire includes a plurality of carbon nanotube segments, the plurality of carbon nanotube segments are connected end to end by van der Waals force, and each carbon nanotube segment includes a plurality of carbon nanotubes that are parallel to each other and closely combined by van der Waals force. Tube. The carbon nanotube segment has any length, thickness, uniformity and shape. The length of the twisted carbon nanotubes is not limited, and the diameter is 0.5 nanometers to 100 microns. Further, the twisted carbon nanotubes can be treated with a volatile organic solvent. Under the action of the surface tension generated when the volatile organic solvent volatilizes, the adjacent carbon nanotubes in the treated twisted carbon nanotubes are closely combined by van der Waals force, so that the specific surface area of the twisted carbon nanotubes is reduced, and the density and Increased strength.

For the carbon nanotube wire and its preparation method, please refer to the Chinese publication patent No. CN100411979C "a carbon nanotube rope and its manufacturing method" filed by the applicant on September 16, 2002 and announced on August 20, 2008 , Applicants: Tsinghua University, Hongfujin Precision Industry (Shenzhen) Co., Ltd., and the Chinese announcement patent No. CN100500556C, which was applied on December 16, 2005 and announced on June 17, 2009, "carbon nanotube wire and Its production method", applicant: Tsinghua University, Hongfujin Precision Industry (Shenzhen) Co., Ltd.

In step S30, the heteroepitaxial layer 104 can be grown by molecular beam epitaxy (MBE), chemical beam epitaxy (CBE), decompression epitaxy, low temperature epitaxy, selective epitaxy, liquid phase deposition epitaxy One or more of (LPE), metal organic vapor phase epitaxy (MOVPE), ultra vacuum chemical vapor deposition (UHVCVD), hydride vapor phase epitaxy (HVPE), and metal organic chemical vapor deposition (MOCVD), etc. accomplish.

The heteroepitaxial layer 104 refers to a single crystal structure grown on the epitaxial growth plane 101 of the substrate 100 by epitaxy, and its material is different from that of the substrate 100 , so it is called the heteroepitaxial layer 104 . The growth thickness of the heteroepitaxial layer 104 can be prepared as required. Specifically, the growth thickness of the heteroepitaxial layer 104 may be 0.5 nanometers to 1 millimeter. For example, the growth thickness of the heteroepitaxial layer 104 may be 100 nanometers to 500 micrometers, or 200 nanometers to 200 micrometers, or 500 nanometers to 100 micrometers. The heteroepitaxial layer 104 can be a semiconductor epitaxial layer, and the material of the semiconductor epitaxial layer is GaMnAs, GaAlAs, GaInAs, GaAs, SiGe, InP, Si, AlN, GaN, GaInN, AlInN, GaAlN or AlGaInN. The heteroepitaxial layer 104 can be a metal epitaxial layer, and the material of the metal epitaxial layer is aluminum, platinum, copper or silver. The heteroepitaxial layer 104 can be an alloy epitaxial layer, and the material of the alloy epitaxial layer is MnGa, CoMnGa or Co ₂ MnGa.

Please refer to FIG. 7, specifically, the growth process of the heteroepitaxial layer 104 specifically includes the following steps:

S31: Nucleate and epitaxially grow along a direction substantially perpendicular to the epitaxial growth plane 101 of the substrate 100 to form a plurality of heteroepitaxial crystal grains 1042;

S32: The plurality of heteroepitaxial crystal grains 1042 are epitaxially grown along a direction substantially parallel to the epitaxial growth plane 101 of the substrate 100 to form a continuous heteroepitaxial thin film 1044;

S33 : The heteroepitaxial thin film 1044 is epitaxially grown along a direction substantially perpendicular to the epitaxial growth plane 101 of the substrate 100 to form a heteroepitaxial layer 104 .

In step S31, the plurality of heteroepitaxial crystal grains 1042 start to grow on the part of the epitaxial growth surface 101 of the substrate 100 exposed through the opening 105 of the carbon nanotube layer 102, and the growth direction thereof is substantially perpendicular to the substrate. The epitaxial growth surface 101 of 100, that is, a plurality of heteroepitaxial crystal grains 1042 undergo vertical epitaxial growth in this step.

In step S32, by controlling the growth conditions, the plurality of heteroepitaxial crystal grains 1042 grow homoepitaxially along a direction substantially parallel to the epitaxial growth plane 101 of the substrate 100 and integrate the carbon nanotube layer 102 covered. That is, in this step, the plurality of heteroepitaxial crystal grains 1042 undergo lateral epitaxial growth and directly close together, and finally form a plurality of holes 103 around the carbon nanotubes to surround the carbon nanotubes. Preferably, the carbon nanotubes are spaced apart from the heteroepitaxial layer 104 surrounding the carbon nanotubes. The shape of the hole is related to the arrangement direction of the carbon nanotubes in the carbon nanotube layer 102 . When the carbon nanotube layer 102 is a single-layer carbon nanotube film or a plurality of carbon nanotube wires arranged in parallel, the plurality of holes 103 are substantially parallel grooves. When the carbon nanotube layer 102 is a multi-layer intersecting carbon nanotube film or a plurality of intersecting carbon nanotube wires, the plurality of holes 103 is an intersecting trench network.

In step S33 , due to the presence of the carbon nanotube layer 102 , the lattice dislocations between the heteroepitaxial grains 1042 and the substrate 100 stop growing during the process of forming the continuous heteroepitaxial thin film 1044 . Therefore, the heteroepitaxial layer 104 in this step is equivalent to performing homoepitaxial growth on the surface of the defect-free heteroepitaxial film 1044 . The heteroepitaxial layer 104 has fewer defects. In the first embodiment of the present invention, the substrate 100 is a sapphire (Al ₂ O ₃ ) substrate, and the carbon nanotube layer 102 is a single-layer carbon nanotube film. This implementation adopts MOCVD process for epitaxial growth. Among them, high-purity ammonia (NH ₃ ) is used as the source gas of nitrogen, hydrogen (H ₂ ) is used as the carrier gas, trimethylgallium (TMGa) or triethylgallium (TEGa), trimethylindium (TMIn ), trimethylaluminum (TMAl) as Ga source, In source and Al source. Specifically include the following steps. Firstly, put the sapphire substrate 100 into the reaction chamber, heat it to 1100°C-1200°C, feed H ₂ , N ₂ or a mixture thereof as a carrier gas, and bake at high temperature for 200-1000 seconds. Next, continue to feed the carrier gas, and lower the temperature to 500°C to 650°C, pass in trimethylgallium or triethylgallium and ammonia gas, and grow a GaN low-temperature buffer layer with a thickness of 10nm to 50nm. Then, stop feeding trimethylgallium or triethylgallium, continue feeding ammonia gas and carrier gas, and simultaneously raise the temperature to 1100°C-1200°C, and keep it at a constant temperature for 30-300 seconds to perform annealing. Finally, keep the temperature of the substrate 100 at 1000° C. to 1100° C., continue to feed ammonia gas and carrier gas, and at the same time re-fuse trimethylgallium or triethylgallium to complete the lateral epitaxial growth process of GaN at high temperature. And grow high-quality GaN epitaxial layer. After the samples were grown, the samples were observed and tested with a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Please refer to FIG. 8 and FIG. 9 , in the heteroepitaxial structure prepared in this embodiment, the heteroepitaxial layer only grows from the epitaxial growth surface of the substrate where there is no carbon nanotube layer, and then connects together. A plurality of holes are formed on the surface of the heteroepitaxial layer in contact with the substrate, and the carbon nanotube layer is arranged in the holes and spaced apart from the heteroepitaxial layer. Specifically, it can be clearly seen from FIG. 8 that the interface between the GaN epitaxial layer and the sapphire substrate, wherein the dark part is the GaN epitaxial layer, and the light part is the sapphire substrate. The surface of the GaN epitaxial layer in contact with the sapphire substrate has a row of holes. It can be seen from FIG. 9 that carbon nanotubes are arranged in each hole. The carbon nanotubes in the holes are arranged on the surface of the sapphire substrate, and are spaced apart from the GaN epitaxial layer forming the holes.

Please refer to FIG. 10 and FIG. 11 , which illustrate a heteroepitaxial structure 10 prepared according to the first embodiment of the present invention, which includes: a substrate 100 , a carbon nanotube layer 102 and a heteroepitaxial layer 104 . The substrate 100 has an epitaxial growth surface 101 . The carbon nanotube layer 102 is disposed on the epitaxial growth surface 101 of the substrate 100, the carbon nanotube layer 102 has a plurality of openings 105, and the epitaxial growth surface 101 of the substrate 100 corresponds to the openings of the carbon nanotube layer 102 Partial exposure of 105. The heteroepitaxial layer 104 is disposed on the epitaxial growth surface 101 of the substrate 100 and covers the carbon nanotube layer 102 . The carbon nanotube layer 102 is disposed between the heteroepitaxial layer 104 and the substrate 100 .

The heteroepitaxial layer 104 covers the carbon nanotube layer 102, and penetrates a plurality of openings 105 of the carbon nanotube layer 102 to contact the epitaxial growth surface 101 of the substrate 100, that is, the carbon nanotube layer The heteroepitaxial layer 104 is penetrated into the plurality of openings 105 of the 102 . The heteroepitaxial layer 104 and the carbon nanotube layer 102 it covers are microscopically arranged at intervals, that is, a plurality of holes 103 are formed on the surface of the heteroepitaxial layer 104 in contact with the substrate 100, and the carbon nanotube layer 102 is arranged on In the holes 103 , specifically, the carbon nanotubes in the carbon nanotube layer 102 are respectively arranged in a plurality of holes 103 . The holes 103 are formed on the surface of the heteroepitaxial layer 104 in contact with the substrate 100 , and the holes 103 are all blind holes in the thickness direction of the heteroepitaxial layer 104 . In each hole 103 , carbon nanotubes are basically not in contact with the heteroepitaxial layer 104 .

The carbon nanotube layer 102 is a self-supporting structure. The carbon nanotube layer includes a carbon nanotube film or a carbon nanotube wire. In this embodiment, the carbon nanotube layer 102 is a single-layer carbon nanotube film, the carbon nanotube film includes a plurality of carbon nanotubes, and the axial direction of the plurality of carbon nanotubes extends along the same direction with preferred orientation, extending Adjacent carbon nanotubes with the same orientation are connected end to end by van der Waals force. Micropores or gaps are partially spaced between adjacent carbon nanotubes perpendicular to the extending direction, thereby constituting the opening 105 .

Please refer to FIG. 12 , which is a heteroepitaxial structure 20 prepared according to the second embodiment of the present invention, which includes: a substrate 200 , a carbon nanotube layer 202 and a heteroepitaxial layer 204 . The materials of the substrate 200 and the heteroepitaxial layer 204 of the heteroepitaxial structure 20 in the second embodiment of the present invention, and the positional relationship between the substrate 200, the carbon nanotube layer 202 and the heteroepitaxial layer 204 are different from those in the first embodiment. The meta-epitaxial structure 10 is basically the same, the difference is that the carbon nanotube layer 202 is a plurality of parallel and spaced carbon nanotube wires, and micropores are formed between adjacent carbon nanotube wires.

The carbon nanotube wires may be non-twisted carbon nanotube wires or twisted carbon nanotube wires. Specifically, the non-twisted carbon nanotube wire includes a plurality of carbon nanotubes extending along the length direction of the non-twisted carbon nanotube wire. The twisted carbon nanotube wire includes a plurality of carbon nanotubes extending helically around the twisted carbon nanotube wire axially.

In the second embodiment of the present invention, the substrate 100 is a silicon on insulator (SOI: silicon oninsulator) substrate, and the carbon nanotube layer 102 is a plurality of parallel and spaced carbon nanotube lines. This implementation adopts MOCVD process for epitaxial growth. Among them, trimethylgallium (TMGa) and trimethylaluminum (TMAl) are used as the source material of Ga and Al respectively, ammonia gas (NH ₃ ) is used as the source material of nitrogen, hydrogen gas (H ₂ ) is used as the carrier gas, and the horizontal Type horizontal reactor heating. Specifically, firstly, a plurality of parallel and spaced carbon nanotube wires are laid on the epitaxial growth surface 101 of the SOI substrate 100 . Then epitaxially grow a GaN epitaxial layer on the epitaxial growth surface 101 of the substrate 100, the growth temperature is 1070°C, and the growth time is 450 seconds, mainly for the vertical growth of GaN; then keep the reaction chamber pressure constant, raise the temperature to 1110°C, and decrease The Ga source flow rate was kept constant to promote lateral epitaxial growth, and the growth time was 4900 seconds; finally, the temperature was lowered to 1070°C, and the Ga source flow rate was increased to continue vertical growth for 10000 seconds.

Referring to FIG. 13 , the third embodiment of the present invention provides a heteroepitaxial structure 30 , which includes: a substrate 300 , a carbon nanotube layer 302 and a heteroepitaxial layer 304 . The materials of the substrate 300 and the heteroepitaxial layer 304 of the heteroepitaxial structure 30 in the third embodiment of the present invention, and the positional relationship between the substrate 300, the carbon nanotube layer 302 and the heteroepitaxial layer 304 are different from those of the second embodiment. The meta-epitaxial structure 20 is basically the same, the difference is that the carbon nanotube layer 302 is a plurality of intersecting and spaced carbon nanotube wires, and micropores are formed between the four intersecting and adjacent carbon nanotube wires. Specifically, the plurality of carbon nanotube wires are arranged parallel to the first direction and the second direction respectively, and the first direction and the second direction are arranged to intersect. An opening is formed between four intersecting and adjacent carbon nanotube wires. In this embodiment, two adjacent carbon nanotube wires are arranged in parallel, and two intersecting carbon nanotube wires are perpendicular to each other. It can be understood that the carbon nanotube wires can also be arranged in any crossing manner, as long as a plurality of openings are formed in the carbon nanotube layer 302 so as to partially expose the epitaxial growth surface of the substrate 300 .

The heteroepitaxial structure 30 of the third embodiment of the present invention can be prepared by the same method as that of the first embodiment or the second embodiment.

A fourth embodiment of the present invention provides a homoepitaxial structure, which includes: a substrate, a carbon nanotube layer and an epitaxial layer. The carbon nanotube layer in the fourth embodiment of the present invention can adopt the carbon nanotube layer of the above-mentioned first embodiment to the third embodiment, and the materials and positional relationship of the substrate, the carbon nanotube layer and the epitaxial layer are basically the same as those of the first embodiment. The difference is that the substrate and the epitaxial layer are made of the same material, thus forming a homogeneous epitaxial structure. Specifically, in this embodiment, the materials of the substrate and the epitaxial layer are both GaN.

The fourth embodiment of the present invention further provides a method for preparing a homoepitaxial structure, which specifically includes the following steps:

S100: providing a substrate, and the substrate has an epitaxial growth surface supporting growth of a homoepitaxial layer;

S200: disposing a carbon nanotube layer on the epitaxial growth surface of the substrate, where the substrate and the carbon nanotube layer together form a substrate; and

S300: growing a homoepitaxial layer on the epitaxial growth surface of the substrate.

The growth method of the homoepitaxial layer in the fourth embodiment of the present invention is basically the same as the growth method of the heteroepitaxial layer in the first embodiment, the difference is that the material of the substrate and the epitaxial layer is the same, thereby forming a homoepitaxial structure .

The present invention adopts a carbon nanotube layer as a mask to be arranged on the epitaxial growth surface of the substrate to grow the epitaxial layer, which has the following effects:

First, the carbon nanotube layer is a self-supporting structure, which can be directly laid on the epitaxial growth surface of the substrate. Compared with the prior art, the mask is formed by processes such as photolithography after deposition, and the present invention has simple process, low cost, and Good for mass production.

Second, the carbon nanotube layer is a patterned structure, its thickness and opening size can reach nanoscale, and the heteroepitaxial crystal grains formed when the substrate is used to grow the epitaxial layer have a smaller size, which is beneficial to Reduce the generation of dislocation defects to obtain high-quality heteroepitaxial layers.

Third, the opening size of the carbon nanotube layer is nanoscale, and the epitaxial layer grows from the exposed epitaxial growth surface corresponding to the nanoscale opening, so that the contact area between the grown epitaxial layer and the substrate is reduced, reducing The stress between the epitaxial layer and the substrate during the growth process is reduced, so that a thicker heteroepitaxial layer can be grown, and the quality of the heteroepitaxial layer can be further improved.

In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should be included in the scope of protection claimed by the present invention.

Claims (8)

1. a preparation method for epitaxial structure, it comprises the following steps:

Thering is provided a substrate, this substrate has the epitaxial growth plane of a support outer layer growth；

Thering is provided the carbon nano-tube film of a self-supporting, this carbon nano-tube film is the continuous print overall structure including multiple CNT, The preferred orientation the most in the same direction of the plurality of CNT extends, and described preferred orientation the most in the same direction extends Adjacent CNT is joined end to end by Van der Waals force, there is micropore between CNT adjacent in described carbon nano-tube film Or gap thus constitute opening；

The carbon nano-tube film of this self-supporting is laid immediately on the epitaxial growth plane of described substrate, the carbon nano-tube film of this self-supporting Multiple CNTs along be parallel to epitaxial growth plane direction extend；And

With this carbon nano-tube film directly laid for mask at the epitaxial growth plane grown epitaxial layer of substrate.

2. the preparation method of epitaxial structure as claimed in claim 1, it is characterised in that described epitaxial layer is a hetero-epitaxy Layer.

3. the preparation method of epitaxial structure as claimed in claim 2, it is characterised in that described substrate is a mono-crystalline structures body, And the material of described substrate is GaAs, GaN, Si, SOI, AlN, SiC, MgO, ZnO, LiGaO₂、LiAlO₂Or Al₂O₃。

4. the preparation method of epitaxial structure as claimed in claim 2, it is characterised in that described epitaxially deposited layer is from described substrate The some growth that exposed by this opening of epitaxial growth plane.

5. the preparation method of epitaxial structure as claimed in claim 2, it is characterised in that the growing method of described epitaxially deposited layer Specifically include following steps:

Along being basically perpendicular to the epitaxial growth plane direction nucleation of described substrate and being epitaxially-formed multiple hetero-epitaxy crystal grain；

The plurality of hetero-epitaxy crystal grain is epitaxially-formed one along the axis substantially parallel to the epitaxial growth plane direction of described substrate Continuous print hetero-epitaxy thin film；And

It is heterogeneous that described hetero-epitaxy thin film is epitaxially-formed one along the epitaxial growth plane direction being basically perpendicular to described substrate Epitaxial layer.

6. the preparation method of epitaxial structure as claimed in claim 2, it is characterised in that the growing method of described epitaxial layer includes Molecular beam epitaxy, chemical beam epitaxy method, reduced pressure epitaxy method, low temperature epitaxial method, selective epitaxy method, liquid deposition epitaxy, gold Belong to organic vapors epitaxy, ultravacuum chemical vapour deposition technique, hydride vapour phase epitaxy method and Metallo-Organic Chemical Vapor to sink One or more in area method.

7. the preparation method of epitaxial structure as claimed in claim 2, it is characterised in that described epitaxially deposited layer is received at described carbon Form multiple hole around mitron layer to be surrounded by the CNT in described carbon nanotube layer.

8. the preparation method of epitaxial structure as claimed in claim 1, it is characterised in that described epitaxial layer is a homoepitaxy Layer.