WO2023125227A1 - 一种采用气相传输制备氮化铝晶体的方法 - Google Patents

一种采用气相传输制备氮化铝晶体的方法 Download PDF

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WO2023125227A1
WO2023125227A1 PCT/CN2022/141007 CN2022141007W WO2023125227A1 WO 2023125227 A1 WO2023125227 A1 WO 2023125227A1 CN 2022141007 W CN2022141007 W CN 2022141007W WO 2023125227 A1 WO2023125227 A1 WO 2023125227A1
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aluminum nitride
raw material
aluminum
nitrogen
temperature
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金雷
武红磊
覃佐燕
李文良
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深圳大学
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403—AIII-nitrides
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
    • C30B23/02—Epitaxial-layer growth
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • the invention belongs to the technical field of crystal growth, and specifically relates to a method for preparing aluminum nitride crystals by gas phase transport.
  • Deep ultraviolet optoelectronic devices such as light-emitting diodes (UVC-LED), deep ultraviolet lasers (UVC-LD), solar-blind ultraviolet detectors and other devices, are used in water disinfection, air purification, food safety, biomedicine, missile warning/early warning and other fields Has a wide range of applications.
  • As the functional layer material of the above-mentioned devices sapphire is currently used as the substrate material for the epitaxial growth of aluminum gallium nitride (AlGaN). Although sapphire has a high transmittance in the deep ultraviolet band, it suffers from lattice mismatch and thermal mismatch.
  • aluminum nitride has a bandgap width of 6.2eV and a refractive index of about 2.2. The rate can reach 78%, which meets the requirements of deep ultraviolet transparent substrate.
  • aluminum nitride and AlGaN have the most matching lattice constant and thermal expansion coefficient, especially the high aluminum component Al x Ga 1-x N (1 ⁇ x ⁇ 0.8) can only be prepared on aluminum nitride, and nitrogen
  • the dislocation density of AlGaN prepared on aluminum nitride single crystal substrate is more than 1000 times lower than that of AlGaN prepared on sapphire substrate, so aluminum nitride single crystal substrate is considered to be the most excellent substrate for AlGaN-based deep ultraviolet optoelectronic devices. Bottom material.
  • the physical vapor transport (PVT) method is the only way to prepare large-sized aluminum nitride crystals (size ⁇ 2 inches, thickness ⁇ 15 mm), and the crystal growth temperature in this method is as high as 2150 ° C to 2300 ° C.
  • the aluminum nitride crystal grown by PVT method still faces some problems as the substrate material of deep ultraviolet optoelectronic devices.
  • the most significant problem is that aluminum nitride has a strong absorption peak at 265nm (4.7eV). The peaks originate from point defects introduced by unintentional doping in the AlN crystal.
  • AlN raw materials contain carbon impurity elements. With the sublimation and transmission of AlN raw materials, carbon impurity elements are also transported to the growth surface of AlN crystals, and the defects of C N The form grows into the crystal, resulting in the absorption peak of aluminum nitride at 265nm in the deep ultraviolet band;
  • the atomic ratio of nitrogen and aluminum elements in aluminum nitride raw materials is less than 1:1, and the atomic ratio of nitrogen elements and aluminum elements in aluminum nitride vapor after blooming is also less than 1:1
  • the aluminum nitride crystal growth temperature is as high as 2150 °C ⁇ 2300 °C, the nitrogen elements in the aluminum nitride vapor at such a high temperature interact to form nitrogen gas, further reducing the nitrogen and aluminum elements in the vapor Therefore, the aluminum nitride crystal growth environment is an aluminum-rich environment (nitrogen-deficient environment), and a large amount of V N is produced in the crystal, which leads to the absorption peak of aluminum nitride V N at 265nm in the deep ultraviolet band.
  • aluminum nitride raw materials in view of the demand for high-purity nitrogen-rich aluminum nitride raw materials for aluminum nitride crystals with high transmittance in the deep ultraviolet band, that is, aluminum nitride raw materials contain extremely low impurity elements such as C and O on the one hand, and on the other hand
  • the atomic ratio of nitrogen element to aluminum element is greater than 1:1, and the present invention is suitable for physical vapor transport to prepare aluminum nitride crystals with high transmittance in the deep ultraviolet band.
  • the raw material is nitrogen-enriched aluminum nitride, and the atomic number ratio of nitrogen element to aluminum element is 1.05-1.30, purity ⁇ 99.99%, impurity elements carbon and oxygen content less than 2 ⁇ 1017cm-3, used for physical vapor transport method of aluminum nitride crystal growth.
  • a method for preparing aluminum nitride crystals by vapor transport comprising the following steps:
  • Step 1 Fixing the aluminum nitride raw material around the inner wall of the crucible to form a crystal growth chamber
  • Step 2 fixing the aluminum nitride seed crystal in the middle of the crystal growth chamber in the crucible;
  • Step 3 Put the crucible with the aluminum nitride raw material and aluminum nitride seed crystal assembled into the heating furnace, switch the growth atmosphere in the heating furnace to a pure nitrogen atmosphere, raise the temperature to the preset temperature in the crucible, and adjust to the desired temperature.
  • a small temperature gradient from high to low in the direction of the raw material to the seed crystal is formed around the seed crystal to grow aluminum nitride single crystal and keep it warm for a period of time; the small temperature gradient is axially and radially The temperature gradient is less than or equal to 10K/cm, and a low supersaturation of aluminum pressure is formed around the seed crystal;
  • Step 4 After the growth of the aluminum nitride single crystal is completed, the temperature is lowered to room temperature, and the crucible is opened to obtain the aluminum nitride crystal.
  • the raw material is nitrogen-rich aluminum nitride, the atomic number ratio of nitrogen element to aluminum element is 1.05-1.30, the purity is ⁇ 99.99%, and the content of impurity elements carbon, silicon, and oxygen is less than 2 ⁇ 10 17 cm -3 .
  • the aluminum nitride raw material is one or more of powder, sintered ceramic material, crystallized porous material or crystal bulk material.
  • the atomic number ratio of nitrogen to aluminum in the aluminum nitride crystal is 1.05-1.30, the purity is ⁇ 99.99%, and the impurity elements carbon, silicon and oxygen are all less than 2 ⁇ 10 17 cm -3 .
  • the aluminum nitride raw material is composed of single crystal or polycrystal of aluminum nitride, with a grain size of 0.5 mm to 5 mm.
  • the aluminum nitride raw material can be aluminum nitride powder with a purity ⁇ 97.5%, which is sintered at 2200-2300°C for 5-20 hours in a tungsten system high-temperature furnace to obtain aluminum nitride with a purity ⁇ 99.99%, and A nitrogen ion source is used to perform ion implantation on aluminum nitride to obtain aluminum nitride raw materials.
  • the aluminum nitride raw material can be prepared by an aluminum metal ammoniation method.
  • the aluminum nitride raw material can be prepared by a microwave-assisted aluminum metal nitriding method.
  • the ratio of the atomic number of the nitrogen element to the aluminum element of the nitrogen-enriched aluminum nitride raw material is 1.05-1.14; the growth temperature is 2200°C
  • the ratio of nitrogen to aluminum atoms in the nitrogen-enriched aluminum nitride raw material is 1.15-1.23;
  • the atomic number ratio is 1.24 to 1.30.
  • the environment for the growth of aluminum nitride by the PVT method is an aluminum-rich aluminum nitride vapor environment, that is, the ratio of nitrogen growth elements to aluminum growth elements is less than 1:1.
  • the absorption peak of AlN at 265nm in the deep ultraviolet band originates from point defects C N and point defects V N .
  • Figure 1 shows the theoretical calculation diagram of the formation energy of carbon defects in nitrogen-rich and aluminum-rich environments. It can be seen from the figure that the formation energies of CN 0 and CN -1 in aluminum-rich environments are 2eV and 1eV, respectively.
  • the formation energies of CN 0 and CN -1 in a nitrogen-rich environment are 5 eV and 4.1 eV, respectively, that is, under the same growth environment and C impurity element content, the formation energy of CN in an aluminum-rich environment is lower than that in a rich environment. Nitrogen environment is more likely to generate this type of defect.
  • Figure 2 shows the theoretical calculation diagram of the formation energy of intrinsic defects under nitrogen-rich and aluminum-rich growth conditions.
  • V N 0 , V N -1 , V N -2 in the aluminum-rich environment The lowest formation energies are 4.1eV, 0.5eV and -3eV, respectively, while the lowest formation energies of V N 0 , V N -1 , and V N -2 are 7.8eV, 4eV and 1eV in a nitrogen-enriched environment.
  • the formation energy of CN in the aluminum-rich environment is lower than that in the nitrogen-rich environment, and this type of defect is more likely to form.
  • the growth atmosphere of aluminum nitride crystals by PVT method
  • the adjustment of the environment that is, the use of nitrogen-rich aluminum nitride raw materials with low carbon content, combined with the crystal growth temperature during the actual growth process of aluminum nitride crystals, suppresses the content of CN and V N defects in aluminum nitride crystals, and achieves reduction or even
  • the advantage of the present invention is that the high-purity aluminum nitride raw material with high nitrogen composition is prepared by processing the aluminum nitride crystal growth raw material, and the aluminum nitride crystal is grown by using the raw material of the present invention, and the growth process adopts a conventional crystal growth process, and the obtained Aluminum nitride crystals have high transmittance in the deep ultraviolet band.
  • Figure 1 is a theoretical calculation diagram of the formation energy of carbon defects in nitrogen-rich and aluminum-rich environments
  • Figure 2 is a theoretical calculation diagram of the formation energy of intrinsic defects under nitrogen-rich and aluminum-rich growth conditions
  • 3 is a schematic diagram of the aluminum nitride crystal growth crucible device of the present invention, wherein 1 is a crucible cover, 2 is an aluminum nitride seed crystal, 3 is a gas transmission area, 4 is a crucible, and 5 is an aluminum nitride raw material.
  • Example 1 In this example, the raw material is aluminum-rich aluminum nitride raw material, the ratio of the atomic number of nitrogen element to aluminum element in the raw material is 0.95, and the content of impurity elements carbon and oxygen is about 2 ⁇ 10 18 cm -3 , and the crystal growth
  • the temperature is 2150°C, the growth atmosphere is 99.999% nitrogen, and the growth pressure is 600mbar.
  • the specific crystal growth crucible device is shown in Figure 3. After the crystal growth is completed, the crucible cooling rate is 20°C/h.
  • the AlN crystal grown in this example has a carbon impurity content of about 3 ⁇ 10 18 cm -3 , a ratio of nitrogen to aluminum content of about 0.87:1, a crystal color of amber, and an absorption cut-off edge of 300 nm.
  • the transmittance in the 230-280nm band is zero.
  • Embodiment 2 The difference between this embodiment and Embodiment 1 is that the content of impurity elements carbon and oxygen is about 2 ⁇ 10 17 cm -3 , and the rest of the process is the same.
  • the AlN crystal grown in this example has a carbon impurity content of about 4 ⁇ 10 17 cm -3 , a content ratio of nitrogen to aluminum of about 0.9:1, and the crystal color is light yellow.
  • the absorption cut-off edge is 210nm, and the transmittance in the 230-280nm band is 30%.
  • Example 3 The difference between this example and Example 1 is that the raw material first uses aluminum nitride powder with a purity ⁇ 97.5%, and sinters at a high temperature of 2250°C for 5 hours in a tungsten system high-temperature furnace to obtain a purity ⁇ 99.99%, a carbon impurity content of About 4 ⁇ 10 17 cm -3 of aluminum nitride, and then use nitrogen ion source to ion-implant the raw material to obtain the atomic number ratio of nitrogen and aluminum elements in the aluminum nitride raw material as 1.08:1, and the rest of the process same.
  • the AlN crystal grown in this example has a carbon impurity content of about 1 ⁇ 10 17 cm -3 , a ratio of nitrogen to aluminum content of about 1:1, and the crystal color is colorless , its absorption cut-off edge is 210nm, and the transmittance in the 230-280nm band is 69%.
  • Embodiment 4 The difference between this embodiment and Embodiment 3 is that the crystal growth temperature is 2230° C., and the rest of the processes are the same.
  • the AlN crystal grown in this example has a carbon impurity content of about 2 ⁇ 10 17 cm -3 , a nitrogen-aluminum content ratio of about 0.95:1, and a slightly yellowish crystal color.
  • the absorption cut-off edge is 210nm, and the transmittance in the 230-280nm band is 50%.
  • Embodiment 5 The difference between this embodiment and Embodiment 4 is that the atomic number ratio of nitrogen element to aluminum element in the aluminum nitride raw material is 1.21:1, and the rest of the process is the same.
  • the AlN crystal grown in this example has a carbon impurity content of about 0.9 ⁇ 10 17 cm -3 , a nitrogen-aluminum content ratio of about 1:1, and a colorless crystal color.
  • the absorption cut-off edge is 210nm, and the transmittance in the 230-280nm band is 66%.
  • Embodiment 6 The difference between this embodiment and Embodiment 5 is that the crystal growth temperature is 2290°C.
  • the AlN crystal grown in this example has a carbon impurity content of about 1.8 ⁇ 10 17 cm -3 , a nitrogen-aluminum content ratio of about 0.98:1, and a slightly yellowish crystal color.
  • the absorption cut-off edge is 210nm, and the transmittance in the 230-280nm band is 48%.
  • Embodiment 7 The difference between this embodiment and Embodiment 6 is that the atomic number ratio of nitrogen element to aluminum element in the aluminum nitride raw material is 1.28:1, and the rest of the process is the same.
  • the AlN crystal grown in this example has a carbon impurity content of about 0.8 ⁇ 10 17 cm -3 , a ratio of nitrogen to aluminum content of about 1:1, and a colorless crystal color.
  • the absorption cut-off edge is 210nm, and the transmittance in the 230-280nm band is 65%.
  • Embodiment 8 The difference between this embodiment and Embodiment 7 is that the raw material of aluminum nitride is prepared by the aluminum metal ammoniation method, and the rest of the process is the same.
  • Example 7 Compared with Example 7, there is no difference in the AlN crystal grown in this example.
  • Embodiment 9 The difference between this embodiment and Embodiment 8 is that the raw material of aluminum nitride is prepared by microwave-assisted nitriding of aluminum metal, and the rest of the process is the same.
  • Example 8 Compared with Example 8, there is no difference in the AlN crystal grown in this example.

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Abstract

一种采用气相传输制备氮化铝品体的方法，包括以下步骤：首先将氮化铝原料固定于坩埚内壁四周，使其围成一晶体生长腔，将氮化铝籽品固定于坩埚内晶体生长腔中间位置：将己装配好氮化铝原料和氮化铝籽品的坩埚放入加热炉中，切换加热炉中的生长气氛为纯氮气氛围，升温至坩埚内达到预设温度，并调节至所述籽品周围形成由所述原料至所述籽品方向温度由高到低的小温梯，进行氮化铝单晶晶体生长，并保温一段时间，降温至室温，打开坩埚，得到所述的氮化铝晶体。

Description

一种采用气相传输制备氮化铝晶体的方法 技术领域
本发明属于晶体生长技术领域，具体为一种采用气相传输制备氮化铝晶体的方法。
背景技术
深紫外光电子器件，如发光二极管(UVC-LED)、深紫外激光器(UVC-LD)、日盲紫外探测器等器件，在水消毒、空气净化、食品安全、生物医疗、导弹告警/预警等领域具有广泛的应用。作为上述器件的功能层材料，目前氮化铝镓(AlGaN)材料外延生长采用蓝宝石作为衬底材料，尽管蓝宝石在深紫外波段具有较高的透过率，但受到晶格失配和热失配的限制，很难实现高质量AlGaN外延层的生长，严重限制了深紫外光学器件的发展和性能的提升。作为重要的超宽禁带半导体材料材料之一，氮化铝的禁带宽度为6.2eV、折射系数约为2.2，理论上其透过截止边可达210nm，并且在210～800nm波段理论透过率可达78％，满足深紫外可透的衬底要求。此外，氮化铝与AlGaN具有最为匹配的晶格常数和热膨胀系数，尤其是高铝组分Al xGa 1-xN(1≥x≥0.8)只能在氮化铝上制备获得，并且氮化铝单晶衬底上制备的AlGaN位错密度比蓝宝石衬底上制备的AlGaN位错密度低1000倍以上，因此氮化铝单晶衬底被认为是AlGaN基深紫外光电子器件最为优异的衬底材料。
物理气相传输(PVT)法是制备大尺寸氮化铝晶体(尺寸≥2英寸，厚度≥15mm)唯一的方法，该方法中晶体生长温度高达2150℃～2300℃。目前，PVT法生长的氮化铝晶体在作为深紫外光电子器件的衬底材料仍面临着一些问题，其中，最为显著的问题为氮化铝在265nm(4.7eV)具有强烈的吸收峰，该吸收峰源于氮化铝晶体中非故意性掺杂而引入的点缺陷。Ramón Collazo等在《应用物理通讯》(Applied Physics Letters)的2012年第100期第191914页公开的《AlN大尺寸晶体中265nm吸收带的起源》(On the origin of the 265nm absorption band in AlN bulk crystals)一文中所述，当氮化铝晶体中碳/氧杂质浓度高于1018cm -3时，CN 0和CN -1之间的电子跃迁是265nm吸收峰的起源，即点缺陷CN导致了265nm吸收峰。此外，Lei Jin等在《材料快报》(Scripta Materialia)的2021年第190期第91-96页公开的《无色AlN大尺寸晶体的光学性质：本征缺陷诱导紫外吸收的研究》(Optical  property in colorless AlN bulk crystals:investigation of native defect-induced UV absorption)一文中所述，当氮化铝晶体中碳/氧杂质浓度为2～5×10 17cm -3时，氮空位(V N)是265nm吸收峰的起源，并随着氮空位浓度的降低，265nm吸收峰的吸收系数也降低。基于上述两文所述，氮化铝在深紫外波段265nm吸收峰源于两种点缺陷类型，分别为C N和V N，两种点缺陷产生的原因在于：
(1)点缺陷C N起源：氮化铝原料中含有碳杂质元素，随着氮化铝原料的升华与传输，碳杂质元素也输运到氮化铝晶体的生长表面，以C N的缺陷形式生长进入晶体中，导致氮化铝在深紫外波段265nm的吸收峰；
(2)点缺陷V N起源：一方面氮化铝原料中氮元素与铝元素的原子比小于1:1，生华后的氮化铝蒸气中氮基元与铝基元的原子比也小于1:1，另一方面氮化铝晶体生长温度高达2150℃～2300℃，如此高温度下的氮化铝蒸气中的氮基元相互作用生成氮气，进一步降低蒸气中氮基元与铝基元的原子比，因此氮化铝晶体生长环境为富铝环境(缺氮环境)，晶体中产生大量V N，这导致氮化铝V N在深紫外波段265nm的吸收峰。
技术问题
鉴于上述问题，针对深紫外波段高透过率氮化铝晶体对高纯的富氮氮化铝原料的需求，即氮化铝原料一方面含有极低的C、O等杂质元素，另一方面氮元素与铝元素的原子比大于1:1，本发明适用于物理气相传输制备深紫外波段高透过率氮化铝晶体的原料为富氮氮化铝，氮元素与铝元素的原子数量比值为1.05～1.30，纯度≥99.99％，杂质元素碳、氧的含量均小于2×1017cm-3，用于物理气相传输法氮化铝晶体生长。
技术解决方案
本发明的目的可通过以下技术方案实现：
一种采用气相传输制备氮化铝晶体的方法，包括以下步骤：
步骤一、将氮化铝原料固定于坩埚内壁四周，使其围成一晶体生长腔；
步骤二、将氮化铝籽晶固定于坩埚内晶体生长腔中间位置；
步骤三、将已装配好氮化铝原料和氮化铝籽晶的坩埚放入加热炉中，切换加热炉中的生长气氛为纯氮气氛围，升温至坩埚内达到预设温度，并调节至所述籽晶周围形成由所述原料至所述籽晶方向温度由高到低的小温梯，进行氮化铝单晶晶体生长，并保温一段时间；所述小温梯在轴向和径向上的温梯≤10K/cm,并在籽晶周围形成铝气压的低过饱和度；
步骤四、氮化铝单晶生长完毕，降温至室温，打开坩埚，得到所述的氮化铝晶体。
该原料为富氮氮化铝，氮元素与铝元素的原子数量比值为1.05～1.30，纯度≥99.99％，杂质元素碳、硅、氧的含量均小于2×10 17cm -3，用于物理气相传输法氮化铝晶体生长。
优选的，所述氮化铝原料为粉料、烧结陶瓷料、晶化态多孔料或晶体块状料中的一种或及多种。
优选的，所述氮化铝晶体中氮元素与铝元素的原子数量比值为1.05～1.30，纯度≥99.99％，且杂质元素碳、硅、氧的含量均小于2×10 17cm -3。
优选的，所述氮化铝原料由氮化铝单晶或多晶组成，粒径为0.5mm～5mm。
优选的，所述氮化铝原料可采用纯度≥97.5％的氮化铝粉，在钨系统高温炉中，通过2200～2300℃高温烧结5～20小时，获得纯度≥99.99％氮化铝，并采用氮离子源在对氮化铝进行离子注入，获得氮化铝原料。
优选的，所述氮化铝原料可通过铝金属氨化法制备获得。
优选的，所述氮化铝原料制备可通过微波辅助铝金属氮化法制备获得。
优选的，所述氮化铝晶体物理气相传输生长中，生长温度为2150～2200℃时，采用富氮氮化铝原料的氮元素与铝元素的原子数量比值为1.05～1.14；生长温度为2200～2260℃时，采用富氮氮化铝原料的氮元素与铝元素的原子数量比值为1.15～1.23；生长温度为2260～2300℃时，采用富氮氮化铝原料的氮元素与铝元素的原子数量比值为1.24～1.30。
有益效果
本发明的工作原理及有益效果：
目前，PVT法氮化铝生长的环境均为富铝的氮化铝蒸气环境，即氮生长基元与铝生长基元比小于1:1。氮化铝在深紫外波段265nm吸收峰源于点缺陷C N和点缺陷V N。如图1所示为富氮和富铝环境下碳缺陷的形成能理论计算图，从图中可以看出，在富铝环境下C N 0和C N -1形成能分别为2eV和1eV，而在富氮环境下C N 0和C N -1形成能分别为5eV和4.1eV，即在相同的生长环境和C杂质元素含量的情况下，富铝环境下C N的形成能低于富氮环境，更容易生成该类型缺陷。如图2所示为富氮和富铝生长条件下本征缺陷的形成能理论计算图，从图中可以看出，在富铝环境下V N 0、V N -1，V N -2的最低形成能分别为4.1eV、0.5eV和-3eV， 而在富氮环境下V N 0、V N -1，V N -2的最低形成能分别为7.8eV、4eV和1eV，即在相同的生长环境下，富铝环境下C N的形成能低于富氮环境，更容易生成该类型缺陷。基于上述分析，针对氮化铝晶体生长过程中由于点缺陷C N和点缺陷V N引入而导致的氮化铝在深紫外波段产生265nm吸收峰的问题，通过对PVT法氮化铝晶体生长气氛环境的调节，即采用低碳含量的富氮氮化铝原料，并结合实际氮化铝晶体生长过程中的晶体生长温度，抑制氮化铝晶体中的C N和V N缺陷含量，实现降低乃至消除氮化铝晶体在深紫外波段265nm的吸收峰的目的。
本发明的优点是通过对氮化铝晶体生长原料的处理，制备出高纯的高氮组分氮化铝原料，采用本发明原料生长氮化铝晶体，生长工艺采用常规晶体生长工艺，获得的氮化铝晶体在深紫外波段具有高透过率。
附图说明
图1为富氮和富铝环境下碳缺陷的形成能理论计算图；
图2为富氮和富铝生长条件下本征缺陷的形成能理论计算图；
图3为本发明氮化铝晶体生长坩埚装置示意图，其中1为坩埚盖、2为氮化铝籽晶、3为气体传输区、4为坩埚、5为氮化铝原料。
本发明的实施方式
实施例1：本实施例中原料为富铝氮化铝原料，原料的氮元素与铝元素的原子数量比值为0.95，杂质元素碳、氧的含量约为2×10 18cm -3，晶体生长温度为2150℃，生长气氛为99.999％氮气，生长气压为600mbar，具体晶体生长坩埚装置如图3所示，晶体生长完毕后，坩埚降温速率为20℃/h。
本实施例中生长的AlN晶体，其碳杂质含量约为3×10 18cm -3，氮元素与铝元素含量比约为0.87：1，晶体颜色为琥珀色，其吸收截止边为300nm，在230～280nm波段透过率为零。
实施例2：本实施例与实施例1不同的是杂质元素碳、氧的含量约为2×10 17cm -3，其余工艺相同。
与实施例1相比，本实施例中生长的AlN晶体，其碳杂质含量约为4×10 17cm -3，氮元素与铝元素含量比为约0.9：1，晶体颜色为浅黄色，其吸收截止边为210nm，在230～280nm波段透过率为30％。
实施例3：本实施例与实施例1不同的是原料首先采用纯度≥97.5％的氮化铝粉，在钨系统高温炉中通过2250℃高温烧结5小时，获得纯度≥99.99％、碳杂质含量约为4×10 17cm -3的氮化铝，之后采用氮离子源在对该原料中进行离子注入，获得氮化铝原料中氮元素与铝元素的原子数量比值为1.08:1，其余工艺相同。
与实施例1和2相比，本实施例中生长的AlN晶体，其碳杂质含量约为1×10 17cm -3，氮元素与铝元素含量比为约1：1，晶体颜色为无色，其吸收截止边为210nm，在230～280nm波段透过率为69％。
实施例4：本实施例与实施例3不同的是晶体生长温度为2230℃，其余工艺相同。
与实施例3相比，本实施例中生长的AlN晶体，其碳杂质含量约为2×10 17cm -3，氮元素与铝元素含量比为约0.95：1，晶体颜色为微黄色，其吸收截止边为210nm，在230～280nm波段透过率为50％。
实施例5：本实施例与实施例4不同的是氮化铝原料中氮元素与铝元素的原子数量比值为1.21:1，其余工艺相同。
与实施例4相比，本实施例中生长的AlN晶体，其碳杂质含量约为0.9×10 17cm -3，氮元素与铝元素含量比为约1：1，晶体颜色为无色，其吸收截止边为210nm，在230～280nm波段透过率为66％。
实施例6：本实施例与实施例5不同的是晶体生长温度为2290℃。
与实施例5相比，本实施例中生长的AlN晶体，其碳杂质含量约为1.8×10 17cm -3，氮元素与铝元素含量比为约0.98：1，晶体颜色为微黄色，其吸收截止边为210nm，在230～280nm波段透过率为48％。
实施例7：本实施例与实施例6不同的是氮化铝原料中氮元素与铝元素的原子数量比值为1.28:1，其余工艺相同。
与实施例6相比，本实施例中生长的AlN晶体，其碳杂质含量约为0.8×10 17cm -3，氮元素与铝元素含量比为约1：1，晶体颜色为无色，其吸收截止边为210nm，在230～280nm波段透过率为65％。
实施例8：本实施例与实施例7不同的是氮化铝原料通过铝金属氨化法制备获得，其余工艺相同。
与实施例7相比，本实施例中生长的AlN晶体无区别。
实施例9：本实施例与实施例8不同的是氮化铝原料通过微波辅助铝金属氮化法制备获得，其余工艺相同。
与实施例8相比，本实施例中生长的AlN晶体无区别。
以上所述仅是本发明的优选实施方式，应当理解本发明并非局限于本文所披露的形式，不应看作是对其他实施例的排除，而可用于各种其他组合、修改和环境，并能够在本文所述构想范围内，通过上述教导或相关领域的技术或知识进行改动。而本领域人员所进行的改动和变化不脱离本发明的精神和范围，则都应在本发明所附权利要求的保护范围内。

Claims (8)

  1. 一种采用气相传输制备氮化铝晶体的方法，其特征在于，包括以下步骤：
    步骤一、将氮化铝原料固定于坩埚内壁四周，使其围成一晶体生长腔；
    步骤二、将氮化铝籽晶固定于坩埚内晶体生长腔中间位置；
    步骤三、将已装配好氮化铝原料和氮化铝籽晶的坩埚放入加热炉中，切换加热炉中的生长气氛为纯氮气氛围，升温至坩埚内达到预设温度，并调节至所述籽晶周围形成由所述原料至所述籽晶方向温度由高到低的小温梯，进行氮化铝单晶晶体生长，并保温一段时间；所述小温梯在轴向和径向上的温梯≤10K/cm,并在籽晶周围形成Al气压的低过饱和度；
    步骤四、氮化铝单晶生长完毕，降温至室温，打开坩埚，得到所述的氮化铝晶体。
  2. 根据权力要求1所述的一种采用气相传输制备氮化铝晶体的方法，其特征在于，所述氮化铝原料为粉料、烧结陶瓷料、多晶化态多孔料或晶体块状料中的一种或及多种。
  3. 根据权力要求1所述的一种采用气相传输制备氮化铝晶体的方法，其特征在于，所述氮化铝晶体中氮元素与铝元素的原子数量比值为1.05～1.30，纯度≥99.99％，且杂质元素碳、硅、氧的含量均小于2×10 17cm -3。
  4. 根据权利要求1或2所述的一种采用气相传输制备氮化铝晶体的方法，其特征在于，所述氮化铝原料由氮化铝单晶或多晶组成，粒径为0.5mm～5mm。
  5. 根据权利要求1或2所述的一种采用气相传输制备氮化铝晶体的方法，其特征在于，所述氮化铝原料可采用纯度≥97.5％的氮化铝粉，在钨系统高温炉中，通过2200～2300℃高温烧结5～20小时，获得纯度≥99.99％的氮化铝，并采用氮离子源在对氮化铝进行离子注入，获得氮化铝原料。
  6. 根据权利要求1所述的一种采用气相传输制备氮化铝晶体的方法，其特征在于，所述氮化铝原料可通过铝金属氨化法制备获得。
  7. 根据权利要求1所述的一种采用气相传输制备氮化铝晶体的方法，其特征在于，所述氮化铝原料制备可通过微波辅助铝金属氮化法制备获得。
  8. 根据权利要求1所述的一种采用气相传输制备氮化铝晶体的方法，其特征在于，所述氮化铝晶体物理气相传输生长中，生长温度为2150～2200℃时，采用富氮氮化铝原料的氮元素与铝元素的原子数量比值为1.05～1.14；生长温度为 2200～2260℃时，采用富氮氮化铝原料的氮元素与铝元素的原子数量比值为1.15～1.23；生长温度为2260～2300℃时，采用富氮氮化铝原料的氮元素与铝元素的原子数量比值为1.24～1.30。
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