阅读说明：本技术 一种控制范德瓦耳斯外延与远程外延生长模式的装置及方法 (Device and method for controlling van der Waals epitaxy and remote epitaxy growth modes ) 是由 余晨辉 秦嘉怡 沈倪明 陈红富 陆炎 成田恬 罗曼 于 2021-09-27 设计创作，主要内容包括：本发明公开了一种控制范德瓦耳斯外延与远程外延生长模式的装置及方法,利用氮化镓-石墨烯衬底,通过改变给石墨烯层外加的栅极偏压,来控制外延生长模式的选择。若在石墨烯层栅极上外加正向偏压,那么石墨烯中的主要载流子类型为电子,抑制氮化镓的极性,外延生长模式选择的是传统的范德瓦耳斯外延,在石墨烯上只能生长二维范德瓦耳斯氮化镓单晶之外的薄膜。反之,若不对石墨烯层栅极施加外电压或者外加反向偏压,那么就选择远程外延,在石墨烯上将生长出二维范德瓦耳斯氮化镓单晶薄膜。本发明避免了因两种外延模式所需石墨烯厚度不同,而在生产过程中需多次制造衬底的问题。不仅可以生产高质量的氮化镓材料,还显著的节省了时间与制造成本。(The invention discloses a device and a method for controlling van der Waals epitaxy and remote epitaxy growth modes. If a forward bias is applied to the graphene layer gate, the main carrier type in the graphene is electrons, the polarity of the gallium nitride is inhibited, the epitaxial growth mode is selected from the traditional van der waals epitaxy, and only a film except a two-dimensional van der waals gallium nitride single crystal can be grown on the graphene. On the contrary, if external voltage or reverse bias is not applied to the grid electrode of the graphene layer, remote epitaxy is selected, and a two-dimensional van der waals gallium nitride single crystal thin film is grown on the graphene. The method avoids the problem that the substrate needs to be manufactured for many times in the production process due to different thicknesses of the graphene required by the two epitaxial modes. Not only can produce high-quality gallium nitride materials, but also obviously saves time and manufacturing cost.)

1. An apparatus for controlling van der waals epitaxy and remote epitaxy growth modes, the apparatus comprising: the device comprises a gallium nitride substrate (1), a single-layer graphene layer (2), a grid (3), a source electrode (4), a drain electrode (5), an external grid bias voltage (6) and an external source drain voltage (7); the source electrode (4) is connected with one end of the single-layer graphene layer (2), and the drain electrode (5) is connected with the other end of the single-layer graphene layer (2); the graphene layer (2) is connected above the gallium nitride substrate (1), and the grid (3) is connected below the gallium nitride substrate (1); the applied grid bias voltage (6) is a voltage applied between the source (4) and the grid (3); the applied source-drain voltage (7) is a voltage applied between the source (4) and the drain (5).

2. A method of making the device of claim 1, comprising the steps of:

step 1, growing graphene by adopting a Chemical Vapor Deposition (CVD) method, and obtaining a graphene layer (2) on a gallium nitride substrate (1) by a roll-to-roll peeling transfer technology;

step 2, depositing metal contact on the bottom layer of the gallium nitride substrate (1) to form a grid (3);

step 3, depositing metal contacts on two sides of the single-layer graphene layer (2) to form a source electrode (4) and a drain electrode (5);

and 4, applying a source-drain voltage (7) between the source (4) and the drain (5), and applying a gate bias voltage (6) between the source (4) and the gate (3).

3. A method of controlling van der waals epitaxial and remote epitaxial growth modes based on the apparatus of claim 2, characterised in that the selection of van der waals epitaxial and remote epitaxial growth modes is achieved by varying the gate bias (6) applied to the graphene layer (2) on the same substrate (1).

4. The method according to claim 3, wherein in step 4, when the applied gate bias (6) is a forward bias, the mode of epitaxial growth is selected to be van der Waals epitaxy, in which case a two-dimensional van der Waals single crystal film (9) is epitaxially grown independent of the gallium nitride substrate (1); when the applied grid bias voltage (6) is zero or reverse bias voltage, the epitaxial growth mode is selected to be remote epitaxy, and a two-dimensional Van der Waals gallium nitride single crystal thin film (8) is epitaxially grown.

5. The method according to claim 3, wherein in step 4, when the gate bias voltage (6) and the source-drain voltage (7) are both zero, the epitaxial growth mode is selected to be remote epitaxy, and a two-dimensional Van der Waals gallium nitride single crystal thin film (8) is epitaxially grown.

Technical Field

The invention relates to the technical field of low-dimensional film single crystal semiconductor epitaxial growth, in particular to a device and a method for controlling van der Waals epitaxy and remote epitaxial growth modes.

Background

In recent years, semiconductors have penetrated into the aspects of our lives. Compared with the first and second generation semiconductor materials, the third generation wide bandgap semiconductor material gallium nitride (GaN) has the characteristics of high saturated electron drift velocity, high thermal conductivity, high critical breakdown voltage and the like, has superior performances of high frequency, high voltage resistance, high temperature resistance and the like, and is a preferred material for high-power devices in extreme environments. The novel high-power semiconductor device can better meet the requirements of the fields of 5G technology, new energy automobiles, military detection and the like, has wide market prospect in the fields of high-end photoelectron and power electronic devices, and has become the focus of global semiconductor technology and industrial competition.

However, the performance of the GaN-based uv electric devices is still not ideal at present, mainly because: most GaN-based devices are fabricated on foreign substrates (e.g., silicon carbide, sapphire, etc.). The lattice distortion of the epitaxial layer can be caused by the problems of lattice mismatch, thermal mismatch and the like between the GaN epitaxial layer and the substrate, so that higher dislocation density, a mosaic crystal structure, biaxial stress, wafer warpage and the like are formed, and the performance and the service life of a GaN-based device are seriously influenced. In order to reduce epitaxial defects and threading dislocations, various heteroepitaxy of highly mismatched materials have been developed, such as: low temperature buffer layers, metamorphic buffer layers, and the like. Despite these advances, it remains a challenge to obtain good crystal quality for highly lattice-mismatched heteroepitaxial layers as compared to homoepitaxial layers. The two growth modes (Van der Waals epitaxy and remote epitaxy) related by the invention are mainly used for the growth of Van der Waals layered materials, and can solve the key problems of thermal mismatch, lattice mismatch and the like caused by the traditional heterogeneous substrate growth method which seriously affect the performance of materials and devices.

Van der waals epitaxy, which was discovered by Atsushi Koma group of university of tokyo in the middle of the 80's 19 th century during the epitaxial growth of selenium (Se) on tellurium (Te) substrates, is a method of performing two-dimensional thin-film material epitaxy on a two-dimensional substrate material having passivated dangling bonds on the surface. Since the manufacturing process of graphene is now well understood, a graphene material is generally used as a two-dimensional substrate material. In the traditional epitaxial process, a dangling bond exists on the surface of the substrate, covalent chemical bonding occurs between the dangling bond and the adsorbed atomic layer, and the traditional two-dimensional thin film material grows. In van der waals epitaxy, adsorbed atomic layers are bonded to graphene surfaces by van der waals forces without transferring or sharing electrons. This van der waals bonding effect is different from ionic or covalent bonding, is not a chemical bond between two materials, but results from an interatomic dipolar interaction, and is very weak, so van der waals epitaxy can allow the growth of heteroepitaxial films with a lattice mismatch greater than 60%. Two-dimensional laminar epitaxial materials bonded by van der waals forces, which are grown on a substrate such as graphene by van der waals epitaxy, are called van der waals thin film materials.

Remote epitaxy, a special new van der waals epitaxy technique, occurs by first inserting a two-dimensional graphene layer between the van der waals epitaxial thin film layer to be grown and a conventional substrate. Because the thin graphene layer under the critical thickness is transparent to the coulomb interaction between the atoms of the epitaxial layer to be grown on the upper layer and the surface of the traditional substrate on the lower layer, the polarity of the substrate under the graphene layer can control the growth of the epitaxial layer on the upper layer through the graphene layer, and the growth of the two-dimensional van der Waals film with the same crystal structure and material properties as the substrate is realized. Previously, Kim, Y et al have demonstrated a remote nucleation effect from the substrate to graphene by growing a wafer-level (001) gallium arsenide (GaAs) single crystal film on a single graphene coated (001) gallium arsenide wafer. The remote epitaxy method is also proved to be used for growing two-dimensional Van der Waals GaN materials on a GaN substrate with a graphene coating, can eliminate the influence of lattice mismatch, is the basis of developing novel devices, and is the fundamental guarantee for realizing high-performance devices.

Both of these epitaxy approaches use graphene materials. The graphene has extremely high carrier mobility and bipolar electric field effect, and is a half-metal material with zero band gap. The bipolar electric field effect means that the type (electron or hole) and density of carriers in graphene can be controlled by an external electric field. In remote epitaxy, the graphene material must be thin to be "transparent" when the epitaxially grown van der waals layer behaves the same as the substrate under the graphene layer. In van der waals epitaxy, the graphene layer must be thick to suppress the polarity of the substrate, and the lattice structure of the epitaxially grown van der waals layered material is determined by the graphene layer, regardless of the nature of the substrate layer. In both of the above epitaxial growth methods, the weak van der waals bonding of the graphene material helps to exfoliate the epitaxially grown thin film from the substrate, resulting in a perfect van der waals layered material, which is then transferred to any substrate of interest to the user.

Recent research shows that the critical thickness of the epitaxial growth of the two-dimensional van der Waals GaN thin film material on the GaN-graphene substrate is the thickness of the double-layer graphene. When the thickness of the graphene layer on the GaN substrate is less than the critical thickness, the polarity of GaN can penetrate the potential field of graphene to affect the growth of the epitaxial layer, which is suitable for the selective remote epitaxy technology, and when the thickness is greater than the critical thickness, the polarity of GaN is not enough to penetrate the graphene layer, so that other van der waals thin films unrelated to the GaN substrate can be grown only by using the traditional van der waals epitaxy mode. Although both van der waals epitaxy and homoepitaxy techniques can be used to grow two-dimensional van der waals thin films, the crystal structure and material properties of the films grown by these two techniques are different, as is known from the difference in the role of graphene in them. In the conventional technology, if switching between the van der waals epitaxy and the remote epitaxy technologies is required, the thickness of the graphene layer on the GaN substrate needs to be changed, that is, different substrates need to be manufactured, and the process cost and time cost of the thin film material preparation are increased sharply.

Disclosure of Invention

The invention provides a device and a method for controlling van der Waals epitaxy and remote epitaxy growth modes. Currently, there is no method available to freely select either remote epitaxy or van der waals epitaxy techniques on the same substrate. The invention provides a method for selectively growing Van der Waals GaN-based epitaxial thin film layers with different crystal structures and properties by changing the polarity of a graphene layer through changing the bias voltage applied to the graphene layer.

The technical scheme adopted by the invention is as follows:

a device for controlling Van der Waals epitaxy and remote epitaxy growth modes comprises a gallium nitride substrate, a single-layer graphene layer, a grid, a source electrode, a drain electrode, an applied grid bias voltage and an applied source drain voltage; the source electrode is connected with one end of the single-layer graphene layer, and the drain electrode is connected with the other end of the single-layer graphene layer; the graphene layer is connected above the gallium nitride substrate, and the grid electrode is connected below the gallium nitride substrate; the applied grid bias voltage is a voltage applied between the source electrode and the grid electrode; the applied source-drain voltage is a voltage applied between the source and the drain.

A method for preparing a device for controlling Van der Waals epitaxy and remote epitaxy growth modes comprises the following steps:

step 1, growing graphene by adopting a Chemical Vapor Deposition (CVD) method, and obtaining a graphene layer on a gallium nitride substrate by a roll-to-roll peeling transfer technology;

step 2, depositing metal contact on the GaN substrate layer to form a grid electrode;

step 3, depositing metal contacts on two sides of the graphene layer to form a source electrode and a drain electrode;

and 4, externally applying source-drain voltage between the source electrode and the drain electrode, and externally applying grid bias voltage between the source electrode and the grid electrode.

A method for controlling Van der Waals epitaxy and remote epitaxy growth modes by using the device is characterized in that the Van der Waals epitaxy and remote epitaxy growth modes are selected on the same substrate through changing a gate bias voltage applied to a graphene layer.

Further, in the step 4, when the applied gate bias is a forward bias, the mode of epitaxial growth is selected to be van der waals epitaxy, and a two-dimensional van der waals single crystal thin film independent of the gallium nitride substrate is epitaxially grown at this time; when the applied grid bias voltage is zero or reverse bias voltage, the epitaxial growth mode is selected to be remote epitaxy, and a two-dimensional Van der Waals gallium nitride single crystal film is epitaxially grown at the moment.

Further, in step 4, when the gate bias voltage and the source-drain voltage are both zero, the epitaxial growth mode is selected to be remote epitaxy, and at this time, a more perfect two-dimensional van der waals gallium nitride single crystal film is epitaxially grown.

Further, the GaN substrate in step 1 may be replaced with other GaN-based single crystal materials such as aluminum gallium nitride (AlGaN), aluminum nitride (AlN), etc., and the properties of the two-dimensional van der waals thin film grown by the remote epitaxy technique after replacement are determined by the corresponding replacement substrate.

Further, the graphene layer in step 2 may be prepared by using a chemical vapor deposition method, or by sublimating Si atoms in a silicon carbide (SiC) wafer by using a self-limited graphitization process, or separating graphene by using pyrolytic graphite, or by using other preparation methods, without affecting the effectiveness of the method for controlling the growth mode of the two-dimensional van der waals thin film proposed in this application.

Further, in step 5, the source and the drain should be as far away from the center of the GaN substrate as possible because the temperature is higher at the center of the GaN growth. When the source electrode and the drain electrode are far away, protection measures are needed to be carried out on the source electrode and the drain electrode, and failure at high temperature is prevented.

By adopting the technical scheme, the invention has the following beneficial effects:

(1) the van der waals epitaxy and remote epitaxy growth modes can be freely selected on the same substrate to obtain epitaxial layers with different crystal structures and properties. When the GaN material and other two-dimensional materials are needed at the same time, the substrate is allowed to be reused, and the production cost is saved while the time is saved.

(2) Due to the extremely weak van der waals bonding of the two-dimensional material graphene, the epitaxial layers generated by van der waals epitaxy and remote epitaxy can be easily peeled off from the graphene layer by using a two-dimensional auxiliary layer transfer technology, the thickness of the peeled epitaxial layer can be accurately controlled, the peeling speed is high, and a pure substrate is left after peeling.

(3) In the GaN-graphene substrate, due to the fact that graphene has good heat dissipation performance, the temperature of the substrate can be reduced in the subsequent epitaxial growth process of the single-layer graphene transferred on the GaN substrate.

Drawings

Fig. 1 is a schematic structural diagram of an apparatus for controlling van der waals epitaxy and remote epitaxy growth modes according to the present invention.

FIG. 2 is a flow chart of a method for controlling Van der Waals epitaxy and remote epitaxy growth modes according to the present invention.

Fig. 3 is a schematic diagram of a selected remote epitaxial growth mode.

Fig. 4 is a schematic diagram of a selected van der waals epitaxial growth mode.

Detailed Description

In order that the present invention may be more readily and clearly understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings.

Example 1:

referring to fig. 1, the apparatus for controlling van der waals epitaxy and remote epitaxy growth modes of the present embodiment includes a self-supporting gallium nitride (GaN) substrate 1, a single graphene layer 2, a gate 3, a source 4, and a drain 5.

The single graphene layer 2 is on top of the free standing GaN substrate 1, forming a GaN-graphene substrate.

The source electrode 4 and the drain electrode 5 are respectively arranged at two sides of the single-layer graphene layer 2, and the grid electrode 3 is arranged at the bottom layer of the GaN substrate 1. A gate bias voltage 6 is applied between the gate 3 and the source 4, and a source-drain voltage 7 is applied between the source 4 and the drain 5. The source 4 and drain 5 are far from the center of the GaN substrate 1 because the growth temperature is high. Even if far away, protection measures against failure at high temperatures need to be taken against the 4, 5 power supplies.

The manufacturing method of the device for controlling the van der Waals epitaxy and remote epitaxy growth modes comprises the following steps:

step 1, commercial GaN products were purchased as a self-supporting GaN substrate 1 of the device of the present invention.

And 2, growing the graphene by adopting a chemical vapor deposition method, and selecting the copper foil with a catalytic growth effect as a substrate for growing the graphene. After the residual gas in the quartz tube was sufficiently evacuated, the flow rate was adjusted to 10sccm H₂And 100sccm Ar mixed gas is heated to 1000 ℃, the temperature rise time is 50min, and the copper foil is annealed for 30min at 1000 ℃ to improve the single crystal size of the copper foil, so that preparation is made for graphene growth. Then, 1sccm of CH was introduced₄Keeping the temperature for 10min to form graphene nucleation sites on the copper foil, and then introducing CH with the flow rate of 3sccm₄The graphene is grown for 40 min. The growth of graphene is terminated by a self-limiting process, resulting in a single-layer graphene film. Finally, the copper foil is rapidly cooled to room temperature. The single graphene layer 2 is transferred to the GaN substrate 1 by a "roll-to-roll" transfer method to obtain a GaN-graphene substrate.

And 3, depositing contact metal Ti/Au on two sides of the single-layer graphene layer 2 and the bottom of the GaN substrate 1 by adopting an electron beam evaporation method to obtain good ohmic contact, and forming a source electrode 4, a drain electrode 5 and a grid electrode 3 of the device.

Step 4, a source-drain voltage 7 is applied between the source electrode 4 and the drain electrode 5;

and 5, applying a gate bias 6 between the source 4 and the gate 3, and controlling the selection of the epitaxial mode by changing the positive and negative of the applied gate bias 6.

The free-standing GaN substrate 1 in step 1 was a 2-inch bulk single crystal 600nm thick.

The thermal release tape in step 2 is composed of a unique adhesive having relatively strong adhesive force at room temperature. While at 90-120 deg.C, the adhesive force is lost rapidly. By utilizing the characteristic, the roll-to-roll transfer method comprises the following steps: after the graphene grows on the copper foilThe copper foil and graphene are passed together over two rollers and a soft pressure (0.2 MPa) is applied between the two rollers, causing the graphene film grown on the copper foil to adhere to the heat release tape. After etching the copper foil in the copper etchant-containing vessel, the transferred graphene film on the tape was rinsed with deionized water to remove the remaining etchant, and then the graphene film on the thermal release tape was inserted between rollers together with the GaN substrate and the rollers were heated to about 90-120 deg.C at a transport rate of about 150-^-1And transferring the graphene film from the adhesive tape to a GaN substrate to form the GaN-graphene substrate.

Wherein the heat release tape is directly available for purchase.

Compared with the traditional transfer method of graphene requiring PMMA, the roll-to-roll transfer method used in the step 2 avoids the problem of reduction of the electrical property of graphene caused by the residue of heavy metal impurities and PMMA, and meanwhile, the roll-to-roll transfer method is simple in process, does not need to use a large amount of organic solvents, does not involve high-temperature treatment, and can obtain large-area graphene with high cleanliness and flatness.

In the steps 4 and 5, when the applied source-drain voltage 7 and the gate bias voltage 6 are both zero, the remote epitaxy mode is selected, and the grown two-dimensional van der Waals GaN single crystal film is the most perfect. When the applied source-drain voltage 7 is-1V, the influence of the thickness and the dielectric constant of the GaN substrate is considered, and when a 237V forward gate bias voltage 6 is applied, the epitaxial growth mode is selected to be Van der Waals epitaxy; if a reverse gate bias 6 of-237V is applied or no gate bias 6 is applied, then remote epitaxy is selected.

In step 5, although the applied gate voltage is as high as 237V, when the first layer of van der waals material is grown, the applied gate voltage is no longer needed, and the time is short, so that the substrate is not damaged. Furthermore, if the applied gate voltage is still perceived to be too high, the required gate voltage can be reduced by reducing the thickness of the GaN substrate.

Referring to fig. 2, the principle of the method for controlling van der waals epitaxy and remote epitaxy growth modes of the present embodiment is:

in the above apparatus for controlling the van der waals epitaxy and remote epitaxy growth mode selection method, when the applied gate bias 6 between the gate 3 and the source 4 is changed, the GaN substrate 1 is not conductive, so that a gate electric field is applied to the single graphene layer 2, and a loop is not formed. For the Ga-face GaN substrate 1, the uppermost layer is Ga ions, and the Ga ions at this time are cations. When a reverse gate bias is applied, the inversion layer of the graphene layer 2 is a hole, which enhances the polarity of the GaN substrate, the mode of epitaxial growth occurs is remote epitaxy (see fig. 3), and the resulting epitaxial layer is a two-dimensional van der waals gallium nitride single crystal film 8 with the same lattice structure as the GaN substrate. Meanwhile, if the applied gate bias 6 and the source-drain voltage 7 are both zero, because the critical thickness of the epitaxial growth of the two-dimensional van der waals GaN film material on the GaN-graphene substrate is the thickness of the double-layer graphene, and the thickness of the graphene layer used in the present invention is a single layer, if the gate bias is not applied to the graphene layer above the GaN substrate, the polarity of the GaN substrate below the graphene layer can control the growth of the upper epitaxial layer through the graphene layer, the selected remote epitaxy is still performed, and the effect of the remote epitaxial growth of the two-dimensional van der waals gallium nitride single crystal film 8 is the best at this time. When a forward gate bias is applied, an inversion layer of graphene becomes electrons, the polarity of graphene is enhanced, and a potential field of a substrate is shielded, and van der waals epitaxy (see fig. 4) is selected, and a lattice structure of a two-dimensional van der waals single crystal thin film 9 epitaxially grown irrespective of a gallium nitride substrate is determined by the graphene layer 2.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.