A diamond two-dimensional electron gas heterojunction structure based on nitrogen face polar boron aluminum nitrogen material and a preparation method thereof

Abstract

The application discloses a preparation method of a diamond two-dimensional electron gas heterojunction structure based on nitrogen face polarity boron aluminum nitrogen material, and comprises the following steps: obtaining a C face single crystal sapphire substrate; epitaxially growing boron aluminum nitrogen with a donor doped nitrogen face polarity wurtzite structure on the C face single crystal sapphire substrate to form a boron aluminum nitrogen epitaxial layer; in the process of growing the boron aluminum nitrogen, the component of boron and aluminum of the boron aluminum nitrogen epitaxial layer is controlled by regulating the ratio of a boron source and an aluminum source; and growing a diamond epitaxial layer on the boron aluminum nitrogen epitaxial layer to form a heterojunction. The application is based on the sapphire substrate material to prepare a diamond heterojunction device, the diamond layer required by the heterojunction is obtained by epitaxial growth, the size limitation of a high-quality diamond substrate is broken through, the heterojunction manufacturing cost is reduced, and an effective method for obtaining a large-size diamond heterojunction is provided.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor process technology, specifically relating to a diamond two-dimensional electron gas heterojunction structure based on nitrogen-faceted polar boron aluminum nitrogen material and its preparation method. Background Technology

[0002] Diamond is a new generation of ultra-wide bandgap semiconductor material, possessing advantages such as a large bandgap, high carrier mobility, and high thermal conductivity. It holds significant advantages and potential in next-generation high-voltage, high-power, high-temperature resistant, and radiation-resistant electronic devices. Simple fabrication processes and excellent p / n-type conductivity are crucial for realizing the application potential of diamond materials. Like most currently used semiconductor materials, diamond must be doped in some form to introduce a sufficiently high density of mobile carriers. However, while diamond's strong covalent bonds and close-packed crystal structure are the source of its excellent material properties, they also make room-temperature activation of bulk doping extremely difficult. Boron, as the most promising acceptor impurity in diamond p-type doping, still has an activation energy as high as 0.37 eV, resulting in a carrier concentration that can be ionized at room temperature being only a fraction of that at boron doping concentration. Furthermore, with increasing boron dopant concentration, the hole mobility of doped diamond decreases significantly, and heavy boron doping also negatively impacts diamond crystal quality, thus affecting device performance. For n-type doped diamond, phosphorus is the most commonly used donor impurity, with an activation energy as high as 0.6 eV and an even lower carrier ionization rate at room temperature. When the phosphorus doping concentration reaches 6.8 × 10⁻⁶... 16 cm -3 At that time, the concentration of activated electrons at room temperature was only 10. 11 cm -3 The difficulty in doping diamond semiconductors severely limits their development and application in the field of electronic devices.

[0003] In recent years, experiments have widely observed that hydrogen-terminated diamond surfaces exhibit p-type conductivity at room temperature. After treating diamond in hydrogen plasma to form a hydrogen-terminated diamond surface covered by CH bonds, exposure to air allows for the formation of a two-dimensional hole gas (2DHG) accumulation layer approximately 10 nm below the diamond surface due to transfer doping. The 2DHG concentration is around 10... 12 -10 14 cm -2 The order of magnitude, with mobility ranging from tens to 200 cm⁻¹ 2 / Vs. Field-effect transistors (FETs) based on hydrogen-terminated diamond p-type conductance have become the mainstream in diamond electronic device research, achieving a maximum output current density of 1.3A / mm, a cutoff frequency of 70GHz, a breakdown voltage of 2608V, and an output power density of 4.2W / mm at 2GHz.

[0004] Given the extreme difficulty in achieving n-type bulk doping ionization in diamond, yet the attainment of p-type surface conductance with high carrier concentration, realizing two-dimensional electron gas (2DEG) surface conductance using diamond-based heterojunction structures offers a new approach to diamond n-type conductance. In diamond-based heterojunctions, the two-dimensional electron gas is formed within the diamond, but its electrons are provided by donor impurities in the non-diamond barrier layer, or by principles similar to polar nitride heterojunctions, namely barrier layer polarization and surface state ionization. Diamond-based 2DEG heterojunctions can overcome the key challenges of extremely low ionization rates in diamond n-type bulk doping, making it difficult to achieve high conductance at room temperature, thus significantly increasing the current density of diamond n-type devices. First-principles studies have shown that by inducing channel charge through gate voltage, diamond / cubic boron nitride (c-BN) heterojunction interfaces can form high conductivity up to 5 × 10⁻⁶. 12 cm -2 Two-dimensional electron gas can be used to fabricate high-performance high-electron-mobility transistors (HEMTs).

[0005] However, some key issues still need to be addressed in forming diamond-based two-dimensional electron gas heterostructures. If an ultrawide bandgap (5.5 eV) diamond material is used as the channel layer to accommodate the two-dimensional electron gas, and another material is used as the barrier layer, then the bandgap of the barrier layer should be greater than the bandgap of diamond. Only ultrawide bandgap semiconductor materials such as aluminum nitride (AlN) and boron nitride (BN) meet this requirement.

[0006] The diamond and nitride barrier layer should also be able to form a band structure suitable for the two-dimensional electron gas of the diamond layer, that is, to form a potential well on the diamond side and a barrier on the barrier layer side; when the barrier layer is doped and ionized to provide electrons to form a two-dimensional electron gas, the height of the barrier should be greater than the ionization energy of the donor impurities in the barrier layer, so that the donor impurities can be ionized.

[0007] Aluminum nitride (ANT) belongs to the III-V group and is a wurtzite-structured compound semiconductor with a large bandgap (6.2 eV), high breakdown field (14 MV / cm), and strong polarization effect, making it well-suited as a barrier layer for polar semiconductor heterojunctions. However, its lattice constant differs somewhat from that of diamond, and direct growth of ANT on diamond can easily lead to crystal defects. Boron nitride (BN) is also an ultra-wide bandgap semiconductor with various crystal structures. Its lattice constant and polarization effect can be adjusted according to the crystal structure, making it advantageous as a barrier layer for diamond-based heterojunctions.

[0008] However, when fabricating diamond-based heterostructures by epitaxially growing boron nitride, aluminum nitride, or boron-aluminum-nitrogen alloy (BOA-NI) films on diamond, a significant challenge arises. Even if the heterojunction band structure and crystal growth ensure the formation of two-dimensional electron gas conductivity, fabricating gold-semiconductor contacts on the heterojunction material surface and establishing low-resistance ohmic contacts between the electrodes and the BOA-NI are difficult. This is because the electrodes and the BOA-NI are separated by an ultra-wide bandgap boron nitride, aluminum nitride, or BOA-NI top barrier layer. This makes the detection and characterization of the BOA-NI conductivity challenging. Summary of the Invention

[0009] To address the aforementioned problems in the prior art, this invention provides a diamond two-dimensional electron gas heterojunction structure based on nitrogen-faceted polar boron-aluminum-nitrogen material and its preparation method.

[0010] In a first aspect of the present invention, a method for preparing a diamond two-dimensional electron gas heterojunction based on a nitrogen-faceted polar boron aluminum nitrogen material is provided, comprising the following steps:

[0011] Obtain a C-plane single-crystal sapphire substrate;

[0012] Boron aluminum nitrogen with donor-doped nitrogen-faced polar fibrous wurtzite structure is epitaxially grown on the C-plane single-crystal sapphire substrate to form a boron aluminum nitrogen epitaxial layer; wherein, the boron and aluminum composition of the boron aluminum nitrogen epitaxial layer is controlled by adjusting the ratio of boron source to aluminum source during the boron aluminum nitrogen growth process.

[0013] A diamond epitaxial layer is grown on the boron-aluminum-nitrogen epitaxial layer to form a heterojunction.

[0014] A second aspect of the present invention provides a diamond two-dimensional electron gas heterojunction structure based on boron aluminum nitride material, which is prepared by the preparation method provided in the first aspect of the present invention, comprising: a C-plane single-crystal sapphire substrate, a boron aluminum nitride epitaxial layer with donor-doped nitrogen-faced polar fibrous wurtzite structure located on the C-plane single-crystal sapphire substrate, and a diamond epitaxial layer located on the boron aluminum nitride epitaxial layer.

[0015] The beneficial effects of this invention are:

[0016] 1. Diamond heterojunction devices are fabricated based on sapphire substrate material. The diamond layer required for the heterojunction is obtained by epitaxial growth, which breaks through the size limitation of high-quality diamond substrates and reduces the manufacturing cost of heterojunctions, providing an effective method for obtaining large-size diamond heterojunctions.

[0017] 2. By adjusting the ternary compound components boron, aluminum, and nitrogen, the lattice constant of the compound is controlled, reducing the lattice mismatch rate between the compound and diamond. This effectively alleviates the lattice distortion of diamond during epitaxy, reduces the surface states and dangling bonds at the heterojunction interface, and improves the heterojunction interface quality.

[0018] 3. A heterostructure is achieved by using the ternary compound boron-aluminum-nitrogen with variable composition. By changing the composition of the ternary compound, the band structure of the material is controlled, and the band level of the heterojunction interface is controlled to generate an electron potential well suitable for 2DEG transport.

[0019] 4. Using a diamond layer that accommodates the two-dimensional electron gas surface conductivity as the top layer of a heterojunction is beneficial for preparing low-resistance ohmic contacts from the upper surface of the heterojunction material, which facilitates the detection, analysis, and utilization of the two-dimensional electron gas surface conductivity.

[0020] 5. 2DEG can be formed at the diamond interface of the heterojunction through the polarization effect between the diamond layer and the boron aluminum nitrogen layer with nitrogen polarity. At the same time, 2DEG can be formed at the diamond interface of the heterojunction by utilizing the charge transfer effect between the n-type doped boron aluminum nitrogen epitaxial layer and the diamond. Furthermore, the band structure of the heterojunction interface can be controlled by combining the composition of boron aluminum nitrogen, thereby forming an electron potential well that is conducive to the transport of 2DEG.

[0021] 6. Boron-aluminum-nitrogen (BNA) alloys are expected to possess properties such as high breakdown field strength and high thermal conductivity. Combining BNA with diamond, which has even better properties, to form novel semiconductor heterojunction materials and devices will broaden the application fields and development prospects of semiconductor heterojunction devices.

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic flowchart of a method for preparing a diamond two-dimensional electron gas heterojunction based on nitrogen-faceted polar boron aluminum nitrogen material according to an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of a diamond two-dimensional electron gas heterojunction based on nitrogen-faceted polar boron aluminum nitrogen material provided in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram illustrating the preparation process of a diamond two-dimensional electron gas heterojunction based on nitrogen-faceted polar boron aluminum nitrogen material, as provided in an embodiment of the present invention.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1-C-plane single-crystal sapphire substrate, 2-boron aluminum nitride epitaxial layer, 3-diamond epitaxial layer Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0029] Example 1

[0030] like Figure 1 and Figure 3 As shown, a method for preparing a diamond two-dimensional electron gas heterojunction structure based on nitrogen-faceted polar boron aluminum nitrogen material includes the following steps:

[0031] Step 101: Obtain the C-plane single-crystal sapphire substrate 1.

[0032] Step 102: Epitaxially grow boron aluminum nitrogen with a donor-doped nitrogen-faced polar fibrous wurtzite structure on a C-plane single-crystal sapphire substrate 1 to form a boron aluminum nitrogen epitaxial layer 2.

[0033] Specifically, the MOVPE process was used at 1280℃ and 90 mBar, with trimethylaluminum, trimethylboron, and nitrogen as the aluminum, boron, and nitrogen sources, respectively. The ratio of trimethylaluminum to trimethylboron was determined based on the desired boron-aluminum-nitrogen alloy composition. To obtain a nitrogen-faceted polar fibrous wurtzite structure boron-aluminum-nitrogen epitaxial layer, a high nitrogen flow rate was controlled during the nucleation stage. Silicon, oxygen, or other suitable donor elements were added during the boron-aluminum-nitrogen growth process to achieve n-type doping. A 30 nm thick boron-aluminum-nitrogen epitaxial layer 2 was grown on the surface of a C-faceted single-crystal sapphire substrate 1.

[0034] Step 103: Epitaxially grow a diamond epitaxial layer 3 on the boron aluminum nitrogen epitaxial layer 2 to form a heterojunction.

[0035] Specifically, a diamond epitaxial layer 3 with a thickness of 50-100 μm was grown at a growth rate of 3 μm / h using MPCVD process under the conditions of substrate temperature of 915℃, microwave power of 3.9kW, pressure of 320mbar, hydrogen flow rate of 200sccm, and CH4 concentration of 6%, to form a heterojunction structure.

[0036] Specifically, such as Figure 2 As shown, a heterojunction structure is prepared through the above steps 101-103, including: a C-plane single-crystal sapphire substrate 1, a boron aluminum nitrogen epitaxial layer 2 with donor-doped nitrogen-faced polar fibrous wurtzite structure located on the C-plane single-crystal sapphire substrate 1, and a diamond epitaxial layer 3 located on the boron aluminum nitrogen epitaxial layer 2.

[0037] In this embodiment, the diamond epitaxial layer 3 is obtained by epitaxial growth, which breaks through the limitation of high-quality, large-size diamond substrates and provides an effective method for obtaining large-size, high-quality, low-cost diamond / boron aluminum nitride heterojunctions, which can promote the research progress and application of diamond heterojunction devices.

[0038] During the growth of boron aluminum nitrogen (BON), the composition of B and Al in the generated BON film is adjusted by regulating the ratio of B source to Al source, thereby controlling the lattice constant and band structure of BON, which reduces the lattice mismatch rate between BON and diamond and improves the quality of the heterojunction. At the same time, the control of the BON band structure can generate an electron potential well suitable for 2DEG transport at the heterojunction interface. By utilizing the polarization effect between the single-crystal diamond layer and the BON layer with nitrogen-polarized surface, or the transfer doping effect between the diamond layer and the donor-doped BON layer, 2DEG can be formed at the diamond interface of the heterojunction.

[0039] The heterostructure achieved in this embodiment differs from the traditional AlGaAs / GaAs heterostructure in several ways, and therefore the requirements for materials and processing conditions are also different:

[0040] First, the requirements for heterojunction materials differ. Traditional AlGaAs / GaAs heterostructures are purely single-crystal semiconductor heterojunctions, requiring both AlGaAs and GaAs materials to be single-crystal semiconductors. However, for the diamond heterojunction achieved in this invention, the diamond can be either single-crystal or polycrystalline.

[0041] Secondly, the formation mechanisms of 2DEGs differ. In traditional AlGaAs / GaAs heterostructures, doping the AlGaAs barrier layer causes the Fermi levels of the two materials to align. The doped AlGaAs barrier layer then has a higher Fermi level than the GaAs layer, leading to ionization of donor impurities, the emergence of charge carriers, and their entry into the channel layer, thus forming a 2DEG. However, in the diamond heterojunction involved in this invention, 2DEGs are formed on the diamond surface through the polarization effect or transfer doping of the epitaxial layer material.

[0042] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0044] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0046] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0047] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a diamond two-dimensional electron gas heterojunction structure based on nitrogen-faceted polar boron aluminum nitrogen material, characterized in that, Includes the following steps: Obtain a C-plane single-crystal sapphire substrate; Boron-aluminum-nitrogen (BAA) epitaxially grows a nitrogen-polar fibrous wurtzite structure with donor doping on the C-plane single-crystal sapphire substrate to form a BAA epitaxial layer. During the BAA growth process, the ratio of boron source to aluminum source is adjusted to control the boron and aluminum composition of the BAA epitaxial layer. Silicon source, oxygen source, or other donor elements are added during the BAA growth process to achieve n-type doping. In the nucleation layer stage, the nitrogen gas flow rate is controlled to ensure that the grown BAA epitaxial layer has nitrogen-polarity. A diamond epitaxial layer is grown on the boron-aluminum-nitrogen epitaxial layer to form a heterojunction. The heterojunction is formed on the diamond surface by the polarization effect or transfer doping of the epitaxial layer material.

2. A diamond two-dimensional electron gas heterojunction structure based on nitrogen-faceted polar boron aluminum nitrogen material, characterized in that, The material is prepared by the preparation method described in claim 1, comprising: a C-plane single-crystal sapphire substrate, a boron aluminum nitrogen epitaxial layer with a donor-doped nitrogen-faced polar fibrous wurtzite structure on the C-plane single-crystal sapphire substrate, and a diamond epitaxial layer on the boron aluminum nitrogen epitaxial layer. 2DEG can be formed at the heterojunction diamond interface by utilizing the polarization effect between the single-crystal diamond layer and the nitrogen-faced boron aluminum nitrogen layer, or by the transfer doping effect between the diamond layer and the donor-doped boron aluminum nitrogen layer.

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