介质衬底上生长h-BN二维原子晶体的研究进展

doi:10.15541/jim20190086

摘要/Abstract

摘要：

六方氮化硼(h-BN)二维原子晶体以其独特的结构、优异的性质以及广泛的应用前景引起了人们的普遍关注。高质量h-BN材料的制备是其性质研究与实际应用的前提。机械剥离的h-BN尺寸有限, 普遍采用的化学气相沉积(CVD)技术通常以过渡金属为衬底, 器件应用时需要将h-BN转移到其它衬底上。因此, 在介质衬底上直接生长h-BN成为二维材料研究领域的一个重要发展方向。本文总结了近年来介质衬底(包括: Si基衬底、蓝宝石衬底和石英衬底等)上直接生长h-BN二维原子晶体的主要进展。人们采用CVD、金属有机气相外延法(MOVPE)、物理气相沉积法(PVD)等方法, 通过提高生长温度、衬底表面处理、两步生长等工艺实现了介质衬底上直接生长h-BN。此外, 还介绍了介质衬底上h-BN二维原子晶体的主要应用。

关键词: 六方氮化硼, 二维材料, 介质衬底, 直接生长, 综述

Abstract:

In recent years, hexagonal boron nitride (h-BN) two-dimensional (2D) atomic crystal has attracted considerable attention due to its unique structure, novel property and potential applications. The synthesis of high quality h-BN determines how far we can go for property research and practical applications. However, the sizes of h-BN domains obtained by mechanical exfoliation were limited to several micrometers. Transition metal substrates are usually used in the CVD growth of 2D h-BN layers, and thus a transfer process is required for fabricating h-BN-based electronic devices. Therefore, it is strongly desirable to directly synthesize 2D h-BN on dielectric substrates. In this article, we review recent process on the direct growth of h-BN by CVD, MOVPE, PVD on different dielectric substrates, including silicon-based substrates, sapphire, quartz, etc. Several approaches, such as, increasing substrate temperature, oxide-assisted nucleation, and surface nitridation were adopted to directly grow h-BN on dielectric substrates. Besides, we also summarized the main applications of 2D h-BN grown on dielectric substrates.

Key words: h-BN, 2D material, dielectric substrates, direct growth, review

中图分类号:

TM23
O782

张兴旺, 高孟磊, 孟军华. 介质衬底上生长h-BN二维原子晶体的研究进展[J]. 无机材料学报, 2019, 34(12): 1245-1256.

ZHANG Xing-Wang, GAO Meng-Lei, MENG Jun-Hua. Research Progress of Direct Growth of Two-dimensional Hexagonal Boron Nitride on Dielectric Substrates[J]. Journal of Inorganic Materials, 2019, 34(12): 1245-1256.

图/表 7

表1 采用不同方法在介质衬底上制备h-BN二维晶体的优缺点

Table 1 Comparison of different methods for preparing 2D h-BN on dielectric substrates

Preparation method	Advantages	Disadvantages
CVD	Low equipment cost, suitable for preparing large area sample	The complicated process, the interrelated growth parameters, many by-products
MOVPE	The cold wall reaction chamber which can prevent precursors from reacting on the inner wall	Highly toxic precursors, high growth temperature (>1000 ℃)
PLD, ALD and Magnetron sputtering	Easy to control the process, the low growth temperature (250-700 ℃)	The poor material quality, mostly amorphous
MBE	High material quality	Expensive equipment and high growth temperature (>1300 ℃)
Two-step method	The lower growth temperature (500-1000 ℃), simple process, suitable for preparing large area and patterned sample	Impurities are introduced during spin coating

图1 (a)SiO2衬底上生长20 min的h-BN的AFM图(插图为对应的傅里叶变换图像)[26]; (b)Si衬底上BN纳米片的SEM照片[27]; (c)在蓝宝石衬底上使用纳米晶石墨烯合成h-BN的示意图及其TEM、HRTEM照片[28]; (d)SiO2衬底和(e)石英衬底上h-BN的照片[29,30]; (f)蓝宝石衬底上h-BN的照片; (g)蓝宝石衬底上h-BN的低能电子衍射图; 沿不同方向生长的h-BN的HRTEM照片: (h)垂直于Al2O3(11ˉ20)方向, (i)平行于Al2O3(11ˉ20)方向[31]

Fig. 1 (a) AFM image of h-BN on SiO2 for 20 min with inset image showing the FFT data[26]; (b) SEM image of the BN sheets grown on Si[27]; (c) Synthesis of h-BN film on sapphire substrate using nc-G and corresponding cross-sectional TEM and HRTEM images[28]; Camera view of h-BN on (d) SiO2 and (e) quartz surface[29,30]; (f) Photograph of EM-h-BN on sapphire substrate; (g) LEED pattern of h-BN grown on sapphire substrate; HR-TEM images of multilayer h-BN grown (h) perpendicular to Al2O3 (11ˉ20) and (i) parallel to Al2O3 (11ˉ20)[31]

图2 (a)1000 ℃下生长30 min的BN薄膜的AFM形貌及粗糙度[35]: (a1)V/III = 450, (a2)V/III = 2250; (b)BN薄膜的截面TEM照片[35]: (b1)V/III = 450, (b2)V/III = 2700; (c)在(c1)流量连续和(c2)流量交替模式下, 生长8 h的h-BN薄膜的表面形貌[36,37]

Fig. 2 (a) AFM micrographs with line scans and surface roughness measured on BN films grown at 1000 ℃ for 30 min[35]: (a1) V/III = 450, (a2) V/III = 2250; (b) Cross sectional TEM images of BN layer deposited using (b1) V/III ratio of 450 and (b2) 2700[35]; (c) Surface topography of h-BN films deposited for 8 h (c1) under continuous flow conditions and (c2) using FM scheme[36,37]

图3 (a)PLD设备示意图以及热解石墨衬底上h-BN和蓝宝石衬底上a-BN的截面TEM照片[42]; (b)蓝宝石衬底上非晶BN薄膜的高分辨SEM照片[43]; (c)Si衬底上h-BN薄膜的截面TEM照片[44]; (d)Si衬底上h-BN层状结构的高分辨TEM照片[44];在 (e~f)1690 ℃下生长3 h, (e)蓝宝石衬底和(f)热解石墨衬底上h-BN的AFM图[45]

Fig. 3 (a) Schematic of PLD setup and the cross-sectional TEM image of h-BN on HOPG and a-BN on sapphire[42]; (b) High magnification SEM image of an amorphous BN film deposited on sapphire substrate[43]; (c) Cross-sectional TEM image of h-BN film on Si[44]; (d) High-magnification TEM image of the h-BN layered structure on Si[44]; (e-f) AFM images of h-BN grown on (e) sapphire and (f) HOPG for 3 h, 1690 ℃[45]

图4 (a)通过扩散-偏析方法生长h-BN的原理图[47]和(b)沉积-转换两步法合成h-BN薄膜的工艺流程图[48]

Fig. 4 (a) Growth mechanism of h-BN by diffusion and segregation[47] and (b) schematic illustration of process flow for synthesis of h-BN films by a two-step method[48]

图5 (a)RMS随V/III比例变化的关系图; (b)不做表面氮处理与氮处理10 min条件下, BN厚度随V/III比例变化的关系图(插图是V/III比例为2250时, BN厚度随生长时间变化的关系图); (c)蓝宝石衬底上h-BN的截面STEM照片及对应区域的衍射图; (d)Si3N4/Si衬底上h-BN的照片; (e)Si3N4/Si, SiO2/Si和Si衬底上h-BN厚度与生长时间的关系图[30, 49-53]

Fig. 5 (a) Plot of RMS determined by AFM vs. V/III; (b) Thickness vs. V/III for BN films grown on sapphire with and without the pre-growth nitridation process with insetshowing thickness vs. growth time for films grown using a V/III ratio of 2250; (c) Cross-sectional STEM image of h-BN grown on sapphire and diffraction patterns for selected areas I and II; (d) Camera view of h-BN on Si3N4/Si; (e) Variations of h-BN film thickness at different CVD growth times for Si3N4/Si, SiO2/Si, and Si substrates[30, 49-53]

图6 (a)h-BN光探测器的响应光谱及其212 nm光照和暗态下的I-V曲线[60]; (b)转移下来的薄膜的光学显微镜图及其柔性器件的照片[61]; (c)偏压30 V下, h-BN MSM探测器的响应光谱和响应时间[62]; (d)量子阱器件的设计、释放和转移过程示意图[67]; (e)转移后器件的EL光谱[68]

Fig. 6 (a) Response spectrum of the h-BN detector and I-V curves under 212 nm laser irradiation and dark condition[60]; (b) Microscope image of the transferred film and the photograph of the flexible metal-semiconductormetal device[61]; (c) The relative spectral response and photocurrent decay kinetics of h-BN MSM detector measured at Vb = 30 V (Inset showing a microscope image of the h-BN MSM photodetector)[62]; (d) Schematic illustrations of the MQW materials design, release and transfer processes[67]; (e) Electroluminescence spectra from the transferred LED[68]

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