WO2021012496A1 - 一种控制GaN纳米线结构与形貌的分子束外延生长方法 - Google Patents

一种控制GaN纳米线结构与形貌的分子束外延生长方法 Download PDF

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WO2021012496A1
WO2021012496A1 PCT/CN2019/116983 CN2019116983W WO2021012496A1 WO 2021012496 A1 WO2021012496 A1 WO 2021012496A1 CN 2019116983 W CN2019116983 W CN 2019116983W WO 2021012496 A1 WO2021012496 A1 WO 2021012496A1
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substrate
single crystal
gan nanowires
mbe
metal
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刘斌
吴耀政
张�荣
王科
陶涛
谢自力
修向前
陈敦军
郑有炓
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南京大学
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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
    • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
    • C30B23/02—Epitaxial-layer growth
    • 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
    • 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
    • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
    • C30B29/62—Whiskers or needles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02538—Group 13/15 materials
    • H01L21/0254—Nitrides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02587—Structure
    • H01L21/0259—Microstructure
    • H01L21/02603—Nanowires

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  • the invention relates to a method for preparing high-quality single crystal GaN nanowires by using PA-MBE, and belongs to the technical field of wide band gap semiconductor materials.
  • the III-nitride direct band gap material has a wider band gap, and its band gap covers the near-infrared band to the ultraviolet-visible band. It is an ideal material for solid-state lighting devices and ultraviolet optoelectronic devices; at the same time, Its high electron mobility and thermal conductivity make it widely studied in high-frequency and high-power power electronic devices.
  • GaN nanowires have received widespread attention in scientific research due to their large specific surface area, one-dimensional characteristics, and low dislocations. Nano-column LEDs, photodetectors, nanogenerators, photocatalytic water splitting, optically pumped lasers and other micro-nano structure devices prepared based on GaN nanowires have also been reported internationally.
  • Si-based GaN nanowires have great advantages and broad market prospects in optoelectronic integration.
  • the growth of high-quality GaN nanowire materials is a prerequisite for research, development and promotion of GaN nanowire-based devices.
  • One of the main reasons for the slow development of early GaN nanowires is the lack of suitable nucleation layer technology.
  • the morphological size, uniformity along the diameter, directionality, degree of merging of GaN nanowires directly grown on heterogeneous substrates, and nucleation layer control have always been important directions for relevant scientific researchers to actively explore.
  • GaN nanowire-based materials have advanced by leaps and bounds.
  • the domestic research progress on GaN nanowires is a little later than abroad, the research on GaN nanowire-based semiconductor materials and devices has also attracted enough attention from many universities and research institutes, and has achieved fruitful results.
  • research in the field of GaN nanowires is mainly focused on improving the quality of crystal growth, basic research on materials and device applications, and the tendency of device production to become practical and industrialized.
  • the technologies widely used in the preparation of high-quality single crystal GaN nanowires mainly include: metal organic chemical vapor deposition (MOCVD) technology and molecular beam epitaxy (MBE) technology.
  • MOCVD metal organic chemical vapor deposition
  • MBE molecular beam epitaxy
  • MOCVD epitaxy technology its good control of the vertical and lateral growth rates and high growth rate make it a great advantage to prepare GaN nanowires with high aspect ratios in batches.
  • MOCVD epitaxy technology metal organic chemical vapor deposition
  • MBE molecular beam epitaxy
  • MOCVD epitaxy technology its good control of the vertical and lateral growth rates and high growth rate make it a great advantage to prepare GaN nanowires with high aspect ratios in batches.
  • this technology also has certain drawbacks in device growth.
  • metal organic compounds are used as metal sources, which can easily introduce a large amount of deep-level impurities; the inter-diffusion is relatively serious and it is difficult to achieve precise interface control.
  • MBE molecular beam epitaxy
  • the use of molecular beam epitaxy (MBE) technology has the following characteristics: the substrate temperature is low, the growth rate is slow, the beam intensity is easy to accurately control, and the composition and doping concentration can be adjusted quickly as the source changes.
  • This technology can achieve atomic level growth to precisely control the thickness, structure and composition and form steep heterostructures.
  • PA-MBE on Si(111) surface substrates
  • the introduction of annealing and nitridation processes to prepare and change the distribution and morphology of island-shaped AlN nucleation points, and epitaxial growth of single crystal GaN nanowires has not yet Find relevant patent documents.
  • the purpose of the present invention is to provide a PA-MBE growth technology of high-quality GaN single crystal nanowires, by introducing annealing and nitriding processes to prepare and change the growth, distribution, and morphology of island-shaped AlN nucleation points, so that the preparation The distribution of island-shaped AlN crystallites tends to be independent and uniform.
  • a method of using PA-MBE Molecular Beam Epitaxy to prepare high-quality single crystal GaN nanowires.
  • Long island-shaped AlN nucleation points are grown on a Si substrate, and then GaN nanowires are grown on the island-shaped AlN nucleation points.
  • the steps include:
  • the Si substrate placed in the growth chamber is heated to any temperature in the range of 850°C-1000°C, and the baking reconstruction time is not less than 0.5h;
  • the metal source baffle is quickly closed, and the substrate is cooled from the growth temperature to 100-250°C, and then the film is taken.
  • the Si substrate is placed in a BOE (buffered oxidation etching solution) or HF (hydrofluoric acid) solution for cleaning for 5-10 minutes.
  • BOE buffered oxidation etching solution
  • HF hydrofluoric acid
  • the vacuum degree is below 1 ⁇ 10 -6 Torr, and the substrate is heated to 500-600°C.
  • the heating rate in step 3) is 15°C/min to 25°C/min.
  • the temperature drop rate in step 4) is 15° C./min to 25° C./min, and the time for depositing metal Al is 0.5 min-2.5 min.
  • step 5 in a heating rate of 10 °C / min to 20 °C / min, the flow rate introduced into the high purity N 2 to a plasma generator is 2-4sccm, N 2 99.99999% purity, when the N 2 flow rate of drop N To 0.6-1.0sccm, the nitration time is controlled at 1.0min-3.0min.
  • the heating/cooling rate in step 6) is 8°C/min to 15°C/min
  • the beam current of the metal Ga source is controlled between 1 ⁇ 10 -8 Torr to 1 ⁇ 10 -7 Torr
  • the growth time is 1.0 -8.0h.
  • the temperature drop rate in step 7) is 50°C/min to 100°C/min.
  • the thickness of the ultra-thin metal Al film is controlled within 1-4 nm.
  • Annealing steps, nitriding process parameter control and ultra-thin Al film thickness are the keys to preparing island-shaped AlN nucleation points in the present invention.
  • Ga atoms preferentially nucleate at the lowest point of potential energy.
  • Ga atoms exist more stably on AlN, so GaN nanowires are more inclined to grow on AlN.
  • the surface potential energy difference of the AlN film is small, and they can all become the nucleation points of GaN nanowires.
  • the high-quality GaN single crystal nanowires prepared by the invention can be repeatedly realized, and can be extended to PA-MBE epitaxial InGaN, AlGaN nanowire alloys and related quantum structures on a (111) plane single crystal Si substrate.
  • FIG. 1 is a schematic diagram of the epitaxial structure of high-quality single crystal GaN nanowires in Embodiment 1;
  • Example 2 is a scanning electron microscope (SEM) top view, a bird's eye view at a depression angle of 20 degrees, and a cross-sectional view of the high-quality GaN single crystal nanowires prepared in Example 1;
  • SEM scanning electron microscope
  • Figure 3 shows the diameter distribution and statistics of the high-quality GaN single crystal nanowires prepared in Examples 1-4;
  • SEM scanning electron microscope
  • SEM scanning electron microscope
  • Example 6 is a scanning electron microscope (SEM) top view, a bird's eye view at a depression angle of 20 degrees, and a cross-sectional view of the high-quality GaN single crystal nanowires prepared in Example 4;
  • FIG. 7 is an SEM topography diagram of a single nanowire transferred from a high-quality GaN single crystal nanowire made in Example 5 to a Si substrate;
  • Example 10 is a room temperature PL diagram of the high-quality GaN nanowires prepared in Example 5 at room temperature 300K;
  • 1 represents (111) plane Si substrate; second generation AlN nucleation layer; 3 represents epitaxially grown high-quality single crystal GaN nanowires.
  • the specific steps of the method for preparing high-quality single crystal GaN nanowires by using PA-MBE include:
  • the beam detector to analyze the metal source beam on the surface of the substrate, and control the metal Ga source beam to 1 ⁇ 10 -7 Torr by controlling the temperature of the top and bottom of the metal crucible in the MBE;
  • the Si substrate placed in the growth chamber is heated to 950°C at a heating rate of 20°C/min, and the baking reconstruction time is 0.5h;
  • the scanning electron microscope (SEM) top view, the bird's eye view at a depression angle of 20 degrees, and the cross-sectional view of the grown high-quality single crystal GaN nanowires are shown in Figure 2; the diameter distribution and statistics of the GaN nanowires are shown in Figure 3.
  • SEM scanning electron microscope
  • Figure 1 GaN nanowires are prepared from island-shaped AlN nucleation points. It can be seen from Figure 2 that the discrete GaN nanowires prepared at the annealing and nitriding temperature of 830°C have good directivity.
  • Figure 4 Surface annealing and nitriding temperature have a significant impact on the diameter of GaN nanowires.
  • step 1 the Si substrate is cleaned in HF solution for 10 minutes, and in preparation step 5, the substrate is heated to 730°C for nitridation, and the preparation step 6 is maintained The growth temperature was unchanged at 760°C.
  • FIG. 3 The diameter distribution and statistics of the manufactured high-quality GaN single crystal nanowires are shown in Fig. 3, and the top view of the SEM, the bird’s eye view of a depression angle of 20 degrees and the cross-sectional view are shown in Fig. 4.
  • Figure 4 shows the morphology of the GaN nanowires prepared at an annealing and nitriding temperature of 730°C. The bottom GaN merged layer is more obvious.
  • the steps in this embodiment are basically the same as those in embodiment 1, and the difference is that in the preparation step 5, the substrate is heated to 780° C. for nitriding, and the growth temperature in the preparation step 6 is maintained at 760° C.
  • FIG. 3 The diameter distribution and statistics of the manufactured high-quality GaN single crystal nanowires are shown in Fig. 3, and the top view of the SEM, the bird’s eye view of a depression angle of 20 degrees and the cross-sectional view are shown in Fig. 5.
  • Figure 5 shows the morphology of the GaN nanowires prepared at the annealing and nitriding temperature of 780°C, and the bottom GaN merging phenomenon becomes weaker.
  • the steps in this embodiment are basically the same as those in embodiment 1, and the difference is that in the preparation step 5, the substrate is heated to 880° C. for nitriding, and the growth temperature in the preparation step 6 is maintained at 760° C.
  • Figure 3 The diameter distribution and statistics of the manufactured high-quality GaN single crystal nanowires are shown in Figure 3, and the top view of the SEM, the bird's eye view of a depression angle of 20 degrees, and the cross-sectional view are shown in Figure 6.
  • Figure 6 shows the morphology of the GaN nanowires prepared at the annealing and nitriding temperature of 880°C. The merging of the bottom GaN is basically relieved, but the directivity becomes worse.
  • the steps of this embodiment are basically the same as those of embodiment 1, and the difference is that in the preparation step 6, the growth time of the GaN nanowires is changed to 8 hours.
  • Figure 7 shows that the single nanowire prepared by this method has a uniform diameter distribution and a hexagonal appearance.
  • Figure 8 shows that the atoms in a single nanowire are arranged in an orderly manner without dislocations.
  • Figure 9 shows that there are no edge dislocations and screw dislocations in a single nanowire.
  • Figure 10 shows that a single nanowire has a higher crystal quality under room temperature PL optical characterization.
  • Examples 1-5 effectively show that there is a better annealing and nitriding temperature range that can effectively avoid the bottom merging phenomenon of GaN nanowires, that is, the annealing and nitriding process is beneficial to form island-shaped AlN nucleation points and inhibit the AlN film produce.
  • the specific steps of the method for preparing high-quality single crystal GaN nanowires using PA-MBE include:
  • the Si substrate placed in the growth chamber is heated to 850°C at a heating rate of 15°C/min, and the baking reconstruction time is 1.0h;
  • the substrate is reduced to 600°C at a cooling rate of 20°C/min, the metal Al source baffle is opened, and the deposition time is 0.5min;
  • the specific steps of the method for preparing high-quality single crystal GaN nanowires using PA-MBE include:
  • the Si substrate placed in the growth chamber is heated to 1000°C at a heating rate of 25°C/min, and the baking reconstruction time is 0.6h;
  • the metal source baffle is quickly closed, and the substrate is cooled from the growth temperature to 250°C at a rate of 100°C/min, and then the film is taken.

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Abstract

提供一种采用PA-MBE(分子束外延技术)制备高质量单晶GaN纳米线的方法，在Si衬底上先生长岛状AlN成核点，再在岛状AlN成核点上生长GaN纳米线。其特征在于：首先对Si衬底进行退火处理以获得洁净的重构Si表面，然后通过开发和优化AlN的成核层的生长方法和技术来制备岛状AlN成核点，并通优化退火温度和氮化时间来调控其分布及形貌，最后在优化的岛状AlN成核点上制备GaN纳米线。生长过程中，通过固定金属源束流和较高的N 2等离子体流量来设定V/III；采用反射高能电子衍射花样对成核过程进行实时原位监测。再通过优化衬底温度来制备质量较高，具有六方形貌的GaN纳米线。

Description

一种控制GaN纳米线结构与形貌的分子束外延生长方法 技术领域
本发明涉及到采用PA-MBE制备高质量单晶GaN纳米线的方法，属于宽禁带半导体材料技术领域。
背景技术
作为第三代半导体，Ⅲ族氮化物直接带隙材料的禁带宽度较宽，其带隙覆盖了从近红外波段到紫外可见波段，是实现固态照明器件，紫外光电子器件的理想材料；同时，其较高的电子迁移率和热导率使其在高频高功率电力电子器件方面也被广泛研究。GaN纳米线由于其较大的比表面积、一维特性、低位错等特征日益受到科研工作这的广泛关注。基于GaN纳米线制备出来的纳米柱LED、光电探测器、纳米发电机、光催化水分解、光泵浦激光器等微纳结构器件在国际上也已陆续报道。Si基GaN纳米线在光电集成方面具有很大优势和广阔的市场前景。然而，生长出高质量的GaN纳米线材料是研究开发并提升GaN纳米线基器件的前提条件。早期GaN纳米线发展缓慢的主要原因之一是缺乏合适的成核层技术。直接生长在异质衬底上的GaN纳米线的形貌尺寸、沿直径方向均匀性、方向性、合并程度，成核层控制等问题一直是相关科研工作者积极探索的重要方向。
国际上，随着氮化技术、氮化铝(AlN)成核层技术、图形化衬底等技术的引入，加之更为有效的生长设备的探索成功，使得对GaN纳米线基材料及其相关器件的研究和制备有了突飞猛进。虽然国内对GaN纳米线的研究进展较国外稍晚，但时至今日，GaN纳米线基半导体材料及器件的研究也引起了众多高校及科研院所的足够重视，并获得丰硕的成果。现今GaN纳米线领域的研究主要集中在提高晶体生长质量、材料及器件应用基础性研究以及器件制作趋于实用化、产业化方面。
目前，广泛应用于高质量单晶GaN纳米线制备的技术主要包括：金属有机物化学汽相沉积(MOCVD)技术以及分子束外延(MBE)技术等。对于MOCVD外延技术，其良好的对纵向和横向生长速率的控制性和较高的生长速率使其在批量制备具有高长径比的GaN纳米线具有较大优势。然而，该技术在器件生长方 面也有一定弊端，比如采用金属有机化合物作为金属源，容易引入大量深能级杂质；互扩散比较严重，很难实现精确的界面控制。与之相应的，采用分子束外延(MBE)技术有如下特点：使用衬底温度低，生长速率慢，束流强度易于精确控制，组分和掺杂浓度可随着源的变化而迅速调整。这种技术可以实现原子层级生长从而精确控制厚度、结构与成分和形成陡峭的异质结构。对于采用PA-MBE在Si(111)面衬底上，通过引入退火和氮化过程来制备和改变岛状AlN成核点的分布和形貌，外延生长单晶GaN纳米线的技术，目前尚未查到相关的专利文献。
发明内容
本发明的目的是提供一种高质量GaN单晶纳米线的PA-MBE生长技术，通过引入退火和氮化过程来制备和改变岛状AlN成核点的生长、分布、及形貌，使得制备出的岛状AlN微晶分布趋于独立、均匀。
本发明采用的技术方案为：
一种采用PA-MBE(分子束外延技术)制备高质量单晶GaN纳米线的方法，在Si衬底上先生长岛状AlN成核点，再在岛状AlN成核点上生长GaN纳米线。
优选的，其步骤包括：
1)清洗Si衬底；
2)将放入Si衬底的MBE缓冲室抽真空，将衬底加热烘烤除气，除气时间不少于1.0h；
3)将放入生长腔室的Si衬底升温至850℃-1000℃范围内任一温度，烘烤重构时间不小于0.5h；
4)将Si衬底降温至600℃-660℃范围内任一温度，打开金属Al源挡板，在Si衬底上沉积一层超薄金属Al膜，厚度在1-4nm；
5)关闭金属Al源挡板，将衬底升温至680℃-880℃区间内任一值并稳定一段时间后向等离子体发生器引入高纯N 2；打开等离子体发生器，使其N等离子体起辉，而后打开N 2 Plasma挡板对衬底进行N化，在衬底上形成岛状AlN成核点；
6)关闭N 2 Plasma挡板，将衬底温度控制到至720℃-880℃区间内任一值后，同时打开金属Ga源和N 2 Plasma挡板，进入生长GaN纳米线的过程；
7)生长结束后迅速关闭金属源挡板，并将衬底从生长温度降温至100-250℃ 后取片。
优选的，步骤1)中将Si衬底放入BOE(缓冲氧化蚀刻液)或HF(氢氟酸)溶液中清洗5-10分钟。
优选的，步骤2)中真空度在1×10 -6Torr以下，衬底加热至500-600℃。
优选的，步骤3)中升温速率为15℃/min至25℃/min。
优选的，步骤4)中降温速率为15℃/min至25℃/min，沉积金属Al的时间为0.5min-2.5min。
优选的，步骤5)中升温速率为10℃/min至20℃/min，向等离子发生器引入高纯N 2时流量为2-4sccm，N 2纯度达到99.99999％，N化时N 2流量降至0.6-1.0sccm，N化时间控制在1.0min-3.0min。
优选的，步骤6)中升温/降温速率为8℃/min至15℃/min，金属Ga源的束流控制在1×10 -8Torr到1×10 -7Torr之间，生长时间为1.0-8.0h。
优选的，步骤7)中降温速率为50℃/min至100℃/min。
本发明中超薄金属Al膜厚度控制在1-4nm。利用有效的引入退火过程改变AlN成核层的生长及分布状态，采用优化的操作步骤，在(111)面单晶Si衬底上采用固定金属源束流、Plasma功率和N 2 plasma流量，控制金属Al膜的退火及氮化温度，形成岛状AlN成核点，然后在岛状AlN成核点上进行GaN纳米线的生长，控制生长温度，生长出高晶体质量，良好形貌的单晶GaN纳米线，利用MBE方法制备的单晶GaN纳米线达到原子层级外延生长，生长速率范围为0.028-0.056nm/s。退火步骤、氮化工艺参数控制及控制超薄Al膜层厚度是本发明制备岛状AlN成核点的关键。按照生长动力学原理，Ga原子优先在势能最低点处成核。本发明中，衬底上相比于岛状AlN成核点之外的区域，Ga原子在AlN上更稳定存在，所以GaN纳米线更倾向于在AlN上沉积生长。对于用AlN薄膜作衬底来说，AlN薄膜表面势能差异较小，都可以成为GaN纳米线的成核点，大量的成核点会导致生长出的GaN纳米线底部容易出现合并现象，影响纳米线的生长及晶体质量，因此在岛状AlN成核点上生长出的单晶GaN纳米线质量更高。优化衬底温度也有助于制备得到质量较高，具有六方形貌的GaN纳米线。本发明制备的高质量GaN单晶纳米线可重复实现，可推广到PA-MBE在(111)面单晶Si衬底上外延InGaN，AlGaN纳米线合金以及相关量子结构。
附图说明
图1为实施例1中高质量单晶GaN纳米线外延结构示意图；
图2为实施例1中制得的高质量GaN单晶纳米线的扫描电子显微镜(SEM)的俯视图、20度俯角的鸟瞰图以及截面图；
图3为实施例1-4中制得的高质量GaN单晶纳米线的直径分布及统计；
图4为实施例2中制得的高质量GaN单晶纳米线的扫描电子显微镜(SEM)的俯视图、20度俯角的鸟瞰图以及截面图；
图5为实施例3中制得的高质量GaN单晶纳米线的扫描电子显微镜(SEM)的俯视图、20度俯角的鸟瞰图以及截面图；
图6为实施例4中制得的高质量GaN单晶纳米线的扫描电子显微镜(SEM)的俯视图、20度俯角的鸟瞰图以及截面图；
图7为实施例5中制的高质量GaN单晶纳米线转移到Si衬底上的单根纳米线的SEM形貌图；
图8为实施例5中制得的高质量单根GaN纳米线沿g＝1-210的高分辨透射电镜的图像；
图9为实施例5中制得的高质量单根GaN纳米线沿着g＝0002和g＝01-10方向的明、暗场像图；
图10为实施例5中制得的高质量GaN纳米线在室温300K下的室温PL图；
其中1代表(111)面Si衬底；2代AlN成核层；3代表外延生长的高质量单晶GaN纳米线。
下面结合附图对本发明的实施方式作进一步阐述。
具体实施方式
实施例1
如图1结构所示，本采用PA-MBE制备高质量单晶GaN纳米线的方法的具体步骤包括：
1.)将Si衬底放入BOE中清洗5分钟。
2.)将放入Si衬底的MBE缓冲室真空度抽至优于1×10 -6Torr后，将衬底加热至600℃，烘烤除气时长1.0h；
利用束流探测器分析衬底表面的金属源束流，通过控制MBE内金属坩埚顶 部和底部的温度，将金属Ga源的束流控制在1×10 -7Torr；
3.)将放入生长腔室的Si衬底以20℃/min的升温速率升温至950℃，烘烤重构时长0.5h；
4.)将衬底以15℃/min的降温速率降至650℃，打开金属Al源挡板，沉积时间为2.0min；
5.)关闭金属Al源挡板，将衬底以10℃/min的升温速率升温至830℃并稳定2min后向等离子体发生器引入流量为3.0sccm的高纯N 2，纯度达到99.99999％；打开等离子体发生器，使其N等离子体起辉，而后降低引入的N 2流量至0.9sccm；打开N 2 Plasma挡板对衬底进行N化2.0min；
6.)关闭N 2 Plasma挡板，将衬底以8℃/min的升温速率升温至760℃后，同时打开金属Ga源和N 2 Plasma挡板，进入生长GaN纳米线的过程，生长时间设置在2h；
7.)生长结束后迅速关闭金属源挡板，并以50℃/min的速率将衬底从生长温度降温至200℃后取片。
生长的高质量单晶GaN纳米线的扫描电子显微镜(SEM)的俯视图、20度俯角的鸟瞰图以及截面图如图2中所示；GaN纳米线的直径分布及统计如图3所示。从图1中可以看出，GaN纳米线是从岛状AlN成核点上制备出来。从图2中可以看出，在830℃的退火和氮化温度下制备出来的分立的GaN纳米线具有良好的方向性。图4表面退火和氮化温度对于GaN纳米线的直径有重大影响。
实施例2
该实施例步骤与实施例1基本一致，其区别在于步骤1中将Si衬底置于HF溶液中清洗10分钟，制备步骤5中将衬底升温至730℃进行氮化，维持制备步骤6中生长温度760℃不变。
制的高质量GaN单晶纳米线的直径分布及统计如图3所示，SEM的俯视图、20度俯角的鸟瞰图以及截面图如图4中所示。图4表明了在730℃的退火和氮化温度下制备出来的GaN纳米线的形貌，底部GaN合并层较为明显。
实施例3
该实施例步骤与实施例1基本一致，其区别在于制备步骤5中将衬底升温至780℃进行氮化，维持制备步骤6中生长温度760℃不变。
制的高质量GaN单晶纳米线的直径分布及统计如图3所示，SEM的俯视图、20度俯角的鸟瞰图以及截面图如图5中所示。图5表明了在780℃的退火和氮化温度下制备出来的GaN纳米线的形貌，底部GaN合并现象变弱。
实施例4
该实施例步骤与实施例1基本一致，其区别在于制备步骤5中将衬底升温至880℃进行氮化，维持制备步骤6中生长温度760℃不变。
制的高质量GaN单晶纳米线的直径分布及统计如图3所示，SEM的俯视图、20度俯角的鸟瞰图以及截面图如图6中所示。图6表明了在880℃的退火和氮化温度下制备出来的GaN纳米线的形貌，底部GaN合并现象基本缓解，但方向性变差。
实施例5
该实施例步骤与实施例1基本一致，其区别在于制备步骤6中将GaN纳米线生长时间改为8h。
制的高质量GaN单晶纳米线转移到Si衬底上的单根纳米线的SEM形貌如图7所示；单根GaN纳米线沿g＝1-210的高分辨透射电镜的图像如图8所示。单根GaN纳米线沿着g＝0002和g＝01-10方向的明、暗场像如图9中所示；在室温300K下的室温PL如图10中所示。图7表明采用此方法制备的单根纳米线直径分布均匀且具有六方形貌。图8表明单根纳米线内原子排布有序，无位错产生。图9表明单根纳米线内没有刃位错和螺位错的存在。图10表明在室温PL光学手段表征下，单根纳米线具有较高的晶体质量。
实施例1-5有效表明：存在一个较佳的退火和氮化温度区间可以有效避免了GaN纳米线底部合并现象，即退火和氮化工艺有利于形成岛状AlN成核点并抑制AlN薄膜的产生。
实施例6
本采用PA-MBE制备高质量单晶GaN纳米线的方法的具体步骤包括：
1.)将Si衬底放入BOE中清洗8分钟。
2.)将放入Si衬底的MBE缓冲室真空度抽至优于1×10-6Torr后，将衬底加 热至500℃，烘烤除气时长1.5h；
利用束流探测器分析衬底表面的金属源束流，通过控制MBE内金属坩埚顶部和底部的温度，将金属Ga源的束流控制在5×10-8Torr；
3.)将放入生长腔室的Si衬底以15℃/min的升温速率升温至850℃，烘烤重构时长1.0h；
4.)将衬底以20℃/min的降温速率降至600℃，打开金属Al源挡板，沉积时间为0.5min；
5.)关闭金属Al源挡板，将衬底以15℃/min的升温速率升温至630℃并稳定2min后向等离子体发生器引入流量为2.0sccm的高纯N2，纯度达到99.99999％；打开等离子体发生器，使其N等离子体起辉，而后降低引入的N 2流量至0.6sccm；打开N 2 Plasma挡板对衬底进行N化1.0min；
6.)关闭N 2 Plasma挡板，将衬底以10℃/min的升温速率升温至720℃后，同时打开金属Ga源和N 2 Plasma挡板，进入生长GaN纳米线的过程，生长时间设置在1h；
7.)生长结束后迅速关闭金属源挡板，并以80℃/min的速率将衬底从生长温度降温至100℃后取片。
实施例7
本采用PA-MBE制备高质量单晶GaN纳米线的方法的具体步骤包括：
1.)将Si衬底放入HF中清洗6分钟。
2.)将放入Si衬底的MBE缓冲室真空度抽至优于1×10 -6Torr后，将衬底加热至550℃，烘烤除气时长1.0h；
利用束流探测器分析衬底表面的金属源束流，通过控制MBE内金属坩埚顶部和底部的温度，将金属Ga源的束流控制在1×10 -8Torr；
3.)将放入生长腔室的Si衬底以25℃/min的升温速率升温至1000℃，烘烤重构时长0.6h；
4.)将衬底以25℃/min的降温速率降至700℃，打开金属Al源挡板，沉积时间为2.5min；
5.)关闭金属Al源挡板，将衬底以20℃/min的升温速率升温至880℃并稳定3min后向等离子体发生器引入流量为4.0sccm的高纯N 2，纯度达到99.99999％； 打开等离子体发生器，使其N等离子体起辉，而后降低引入的N 2流量至1.0sccm；打开N 2 Plasma挡板对衬底进行N化3.0min；
6.)关闭N 2 Plasma挡板，衬底温度仍然控制在880℃，同时打开金属Ga源和N 2 Plasma挡板，进入生长GaN纳米线的过程，生长时间设置在4h；
7.)生长结束后迅速关闭金属源挡板，并以100℃/min的速率将衬底从生长温度降温至250℃后取片。

Claims (9)

  1. 一种采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：在Si衬底上先生长岛状AlN成核点，再在岛状AlN成核点上生长GaN纳米线。
  2. 根据权利要求1所述采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：其步骤包括：
    1)清洗Si衬底；
    2)将放入Si衬底的MBE缓冲室抽真空，将衬底加热烘烤除气，除气时间不少于1.0h；
    3)将放入生长腔室的Si衬底升温至850℃-1000℃范围内任一温度，烘烤重构时间不小于0.5h；
    4)将Si衬底降温至600℃-660℃范围内任一温度，打开金属Al源挡板，在Si衬底上沉积一层超薄金属Al膜，厚度在1-4nm；
    5)关闭金属Al源挡板，将衬底升温至680℃-880℃区间内任一值并稳定一段时间后向等离子体发生器引入高纯N 2；打开等离子体发生器，使其N等离子体起辉，而后打开N Plasma挡板对衬底进行N化，在衬底上形成岛状AlN成核点；
    6)关闭N 2 Plasma挡板，将衬底温度控制到至720℃-880℃区间内任一值后，同时打开金属Ga源和N 2 Plasma挡板，进入生长GaN纳米线的过程；
    7)生长结束后迅速关闭金属源挡板，并将衬底从生长温度降温至100-250℃后取片。
  3. 根据权利要求2所述的采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：步骤1)中将Si衬底放入BOE或HF溶液中清洗5-10分钟。
  4. 根据权利要求3所述的采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：步骤2)中真空度在1×10 -6 Torr以下，衬底加热至500-600℃。
  5. 根据权利要求4所述的采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：步骤3)中升温速率为15℃/min至25℃/min。
  6. 根据权利要求5所述的采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：步骤4)中降温速率为15℃/min至25℃/min，沉积金属Al的厚度为1-4nm。
  7. 根据权利要求6所述的采用PA-MBE制备高质量单晶GaN纳米线的方法，其 特征在于：步骤5)中升温速率为10℃/min至20℃/min，向等离子发生器引入高纯N 2时流量为2-4sccm，N 2纯度达到99.99999％，N化时N 2流量降至0.6-1.0sccm，N化时间控制在1.0min-3.0min。
  8. 根据权利要求7所述的采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：步骤6)中升温/降温速率为8℃/min至15℃/min，金属Ga源的束流控制在1×10 -8 Torr到1×10 -7 Torr之间，生长时间为1.0-8.0h。
  9. 根据权利要求8所述的采用PA-MBE制备高质量单晶GaN纳米线的方法，其特征在于：步骤7)中降温速率为50℃/min至100℃/min。
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LUDOVIC LARGEAU, ELISABETH GALOPIN, NOELLE GOGNEAU, LAURENT TRAVERS, FRANK GLAS, JEAN-CHRISTOPHE HARMAND: "N-Polar GaN Nanowires Seeded by Al Droplets on Si(111)", CRYSTAL GROWTH & DESIGN, vol. 12, no. 6, 21 May 2012 (2012-05-21), pages 2724 - 2729, XP055775182, ISSN: 1528-7483, DOI: 10.1021/cg300212d *

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