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材料制备方法的选择,主要考虑所选方法是否工艺简单、重复性好、稳定性好,是否适合大批量生产、高效节能,制备的材料是否具有较高的质量从而可以满足研究和实际应用的需要等。已被报道的SnTe材料的不同生长方法、材料形态及其特性如表1所示[23-41],SnTe薄膜和SnTe纳米结构常用制备方法包括分子束外延法(Molecular beam epitaxy, MBE)、化学气相沉积法(Chemical vapor deposition,CVD)、物理气相沉积法(Physical Vapor Deposition,PVD)、液相合成法、熔融退火法以及直接合金法等。
表 1 碲化锡制备方法、材料形态及其特性
Table 1. Preparation methods, material morphology and properties of tin telluride
Preparation methods Morphological structure Features Year Ref. MBE SnTe-based films and superlattices The structure parameters of the PbTe/SnTe superlattice were
determined by the selected buffer layer material1997 [23] MBE Si (111) substrate/
SnTe thin filmThe electronic structure of the film was adjustable by
changing thickness and lead doping level2014 [24] MBE BaF2 (001) substrate/
SnTe filmBy increasing the growth temperature, the film has higher
mobility and lower carrier concentration2014 [25] MBE Sapphire substrate/Bi2Te3 buffer layer/SnTe film Dirac electrons on the SnTe (111) surface was gained by transmission measurements on a high quality film grown on the Bi2Te3 buffer layer 2014 [26] MBE
BaF2substrate/SnTe
filmBy optimizing the growth conditions and film thickness, the carrier concentration is reduced, which conduced to study the surface magnetic transport characteristics 2015 [27] MBE GaAs (111) A substrate/CdTe/
SnTe filmSingle-phase very low hole concentration of SnTe (111) can be
obtained by optimizing the growth temperature of SnTe and
CdTe layers and the growth rate of SnTe2016 [28] MBE Substrate/Bi2Te3 buffer layer/SnTe film An efficient photoconductive photodetector was prepared
based on 10 nm TCI SnTe2017 [29] CVD SnTe nanowire The exposed surface of SnTe micro-nano structure can be adjusted by experimental parameters such as temperature 2014 [30] CVD SnTe nanoribbon The controlled growth of crystal surface of SnTe nanocrystals {100} can be realized by Bi doping 2016 [31] CVD SnTe thin film/n-Si Nps heterojunction A photovoltaic photodetector was prepared based on
SnTe/Si Nps heterojunction2017 [32] PVD SnTe thin film/n-Si heterojunction A photovoltaic photodetector was prepared based on
SnTe/Si heterojunction2017 [33] PVD SnTe flake A field effect transistor photodetector was prepared based on
SnTe single crystal2018 [34] PVD SnTe thin film/n-Bi2Se3 heterojunction A photovoltaic photodetector was prepared based on
SnTe/Bi2Se3 heterojunction2020 [19] Hot wall epitaxy SnTe-based films and superlattices The prepared EuTe/SnTe SL showed a high mobility of 2720 cm2/(V·S) at room temperature. The Seebeck coefficients of SnTe/PbSe and SnTe/PbS SLs can be close to those of PbSe and PbS 2009 [35] Solution-phase synthesis SnTe quantum dot By changing the growth temperature, concentration of reaction mixture, etc., the average diameter of SnTe NCs was adjustable within 4.5-15 nm, and the band gap correspondingly is 0.8-0.38 eV. It can be
used in near-infrared photoelectric devices2007 [36] Solution-based synthesis SnTe nanostructure The shape/size controlled preparation of SnTe nanotubes, nanorods and nanowires promotes the application of colloidal infrared active nanomaterials in practical technologies 2015 [37] Vapor-liquid−
solid growthSnTe nanoplates SnTe nanoplate were prepared with large {100} or {111} surface areas, allowing selective study of the surface states on these surfaces.
The phase transition from rock salt structure to rhombic structure
was observed at low temperature2014 [38] Solid solution alloying Sn 1.03−x Mg x Te ingot Adjusting the SnTe electron band structure by Mg doping, the Seebeck coefficient was improved and the thermoelectric property was optimized 2014 [39] Microwave solvothermal method Se/Cd co-doped SnTe octahedral particles By using the strategy of co-doping selenium and cadmium, the energy band structure of SnTe was optimized to improve the
power factor and thermoelectric optimization value2017 [40] Alloying Ge doped SnTe alloy The local structure distortion and related ferroelectric instability of SnTe were adjusted by Ge doping, and the ultra-low lattice thermal conductivity was aquired to optimize the thermoelectric performance of SnTe 2019 [41] -
高质量薄膜材料的获得对于潜在的器件应用至关重要。分子束外延是指在超高真空下,源材料经过高温蒸发产生的分子束流经衬底表面吸附、迁移、成核以及外延生长单晶薄膜的方法。由于MBE方法生长环境洁净、衬底温度低、制备的薄膜晶体质量好以及可精确控制掺杂浓度和膜层组分等优点,很适宜用来制备原子级超薄层或多层异质结构的光电薄膜材料。
缓冲层材料的选择对MBE制备高质量的薄膜至关重要。在异质外延时,由于衬底和外延薄膜材料不同,二者存在晶格失配,引入缓冲层的目的是释放薄膜中的应力、减小位错失配,缓冲层的生长直接影响到后续外延薄膜的制备质量。早在1997年,波兰科学院物理研究所的J. SADOWS等人在BaF2 (111) 衬底及SnTe,Pb0.5Sn0.5Τe和PbTe不同缓冲层上制备了(50 Å SnTe)/(50 Å PbTe)超晶格,结果发现缓冲层材料的选择在很大程度上决定了整个结构的电学参数[23]。2014年,清华大学的Yan等人[24]利用MBE方法首次在Si (111)衬底上制备出了SnTe高质量薄膜,通过改变薄膜厚度和铅掺杂水平使薄膜的电子结构可调。由于Sn空位和Te取代Sn,非故意掺杂的SnTe是p型半导体材料,在小于1 µm的厚度时,薄膜往往是高度粒状和粗糙的,这会显著降低载流子迁移率,为解决该问题,很多研究之前是集中在SnTe薄膜的缓冲层使用和化学掺杂上,而研究者后来发现通过优化MBE制备SnTe薄膜时的工艺参数可有效降低载流子浓度和增加迁移率。2014年,美国东北大学物理系的B. A. Assaf等人[25]用MBE方法制备SnTe薄膜时发现提高生长温度不仅改善了薄膜的表面形貌和结晶质量,而且载流子浓度也随之降低,当载流子浓度为p=8×1019 cm−3时,霍尔迁移率可达760 cm2/(V·S)。2016年,Ryota Akiyam等人报道了用MBE方法在CdTe上沉积SnTe(111)层,通过优化SnTe、CdTe层的生长温度以及SnTe的生长速率,获得了仅在(111)方向生长的SnTe单相,表面平整度比在BaF2衬底上生长的有很大改善[28]。2017年,国防科技大学的 Jiang等人[24]报道了一种利用MBE方法制备晶圆规模的SnTe薄膜(5 mm×2 mm)的可控方法,即在生长SnTe膜之前,先在绝缘的钛酸锶(STO)(111)衬底上生长四、五层Bi2Te3薄膜(4 nm)以减少晶格的失配,再生长10 nm的SnTe薄膜[29],并基于SnTe薄膜制备了高效光导型探测器,为优化这些器件用于宽带和灵敏的光电应用提供了指导。
MBE制备方法非常先进,但它也有自身地一些局限性:MBE设备昂贵、操作复杂、生长速率慢以及制备的晶圆规模的SnTe薄膜很难被转移到包括柔性衬底的其他衬底上,这限制了它的兼容性和实际应用,不利于实现产业化生产。
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化学气相沉积法是指利用含有构成薄膜元素的一种或几种气态或液态反应物(单质或化合物)的蒸气,在衬底表面上进行化学反应生成薄膜的方法。CVD方法的特点是设备简单易操作、制备的薄膜重复性和均匀性较好、沉积温度较低以及通过改变气相组成可实现薄膜化学成份可控等。
合理设计具有明确表面的半导体纳米晶体是实现下一代光电探测器、热电和自旋电子器件的关键,SnTe纳米晶体其表面晶面(surface facets)决定了它的表面状态。然而,大多数可用的SnTe纳米晶是由热力学稳定的{100}面组成的,生长具有{111}面的均匀纳米晶体具有挑战性。2014年中国科学院大学的Muhammad Safdar[30]等人用CVD方法获得了具有明显的高对称晶体表面的SnTe纳米线和微晶体,其微纳结构的暴露面可以通过改变CVD过程中的实验参数如沉积温度来调制,在不添加金催化剂的情况下,在高温沉积区域,SnTe为具有{100}面的立方块,而在较低的生长温度下,SnTe为具有{111}面的八面体。该研究为可控合成SnTe半导体微纳结构材料提供了指导。2016年,澳大利亚昆士兰大学的Yi-Chao Zou等人[31]在表面能计算的指导下,使用CVD制备了Bi掺杂SnTe纳米结构,其表面晶面通过Bi掺杂进行调制,实验结果得到了具有明显{111}表面的Bi掺杂SnTe纳米带,为今后发展晶面可控纳米结构提供了机会。2017年,苏州大学的Suhang Gu等人利用CVD方法首次在硅纳米柱表面生长了SnTe薄膜,形成的高质量SnTe/Si纳米柱(Nanopillars)异质结光伏型光电探测器可实现从紫外到近红外的宽谱探测,响应速度超快,探测率高[32]。
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物理气相沉积是指在真空条件下进行的物理气相反应生长方法,或是在低气体放电条件下使用固体材料作为源材料, 经过“蒸发或溅射”后, 以物理方法实现物质从源材料沉积到衬底上的薄膜的可控原子转移过程。PVD方法主要分为真空蒸发镀膜法、真空溅射镀膜法以及真空离子镀膜法。相比于溅射镀膜法,蒸发法具有的优点是:真空度较高、沉积速率较高以及制备的薄膜质量较高。而溅射镀膜法也有优点:通过调整工艺参数易实现膜厚可控、工艺重复性较好、制备多元合金薄膜时化学成分易控以及所沉积的薄膜对衬底的附着力较好等。
2017年,山东师范大学的张宏斌等人在没有使用任何催化剂的情况下,采用PVD方法在Si上制备了具有(111)面和(100)面的SnTe薄膜,该薄膜呈现立方岩盐晶体结构且无其他相的存在,其Sn/Te原子比为1∶1.06,说明薄膜中存在一定数量的Sn空位,导致p型载流子的输运。衬底温度对PVD制备SnTe纳米片的形貌有很大影响,为得到适于制备光电探测器的SnTe纳米片,需要对生长SnTe的温度进行探索[33]。2018年,中国科技大学的张凯等人采用PVD法,在Si/SiO2衬底上对生长SnTe的温度做了探索,发现随生长温度不同,制备出的样品其形貌差异很大。生长温度低于300 ℃时得到具有线状结构表面的SnTe,其表面不够平整,不利于光电器件的制备;而生长温度过高为600 ℃时得到的是紧密堆积方块状SnTe厚纳米片,同样不适于光电器件的制备及性能测试;而生长温度是480 ℃时, 所有SnTe纳米片都均匀分布在整个衬底上,表面干净平整,厚度大小均匀,可很好的满足不同尺寸光电器件的制备需求[34]。2020年,山东师范大学同一团队的张宏斌等人在SiO2衬底上采用一种离位两步PVD的生长策略在无催化剂的情况下制备了高质量的SnTe/Bi2Se3异质结构,在垂直异质结的区域获得了干净的界面,这种新型异质结构不仅利用了拓扑绝缘体对光的有效吸收,而且为研究p型和n型拓扑表面态之间的能带耦合效应提供了理想平台[19]。
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还有一些其他的方法比如液相合成法[36-40]、熔融退火法、直接合金法[41]等也用于制备SnTe薄膜及其纳米结构。但是,液相合成法制备的材料面积要么是太小以至于无法在其上进行器件制作,要么是晶体质量不好无法进行表面态的探索。而熔融退火法、直接合金法等制备的SnTe材料是多用于热电应用领域的探索,而未见用于光电器件方面的研究。
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SnTe材料的性质决定了它的应用,而性质又与材料结构紧密相关。如图2(a)所示,SnTe半导材料具有三种晶型结构,分别为菱方结构的α-SnTe[42]、盐岩结构(面心立方结构)的β-SnTe[22, 43]和斜方结构的γ-SnTe[42],其具体的空间群和晶格参数如表2所示[44-45]。α-SnTe是低温相,在小于100 K时存在;β-SnTe在100 k以上存在,而在高压条件下(>18 kbar的压力),β-SnTe可沿[111]方向发生畸变转变为γ-SnTe。由于具有面心立方结构的β-SnTe在室温和大气压下是稳定的相,因此通常用于光电探测器件的是这种结构。
图 2 SnTe的结构及表征:(a) 不同结构相变;(b) 面心立方结构的SnTe布里渊区;(c) 面心立方结构的SnTe能带结构;(d) 随厚度或应变可调的带隙;(e) X射线光电子能谱;(f) X射线衍射图谱;(g) 高分辨透射电子显微镜图
Figure 2. Structure and characterization of SnTe: (a) Different phase transitions; (b) FCC Brillouin zone; (c) Band dispersion; (d) Strain- and layer-dependent band gap; (e) XPS spectra; (f) XRD pattern; (g) HRTEM image
表 2 SnTe不同相的晶体结构
Table 2. Crystal structure of different phases of SnTe
Phases Crystal structures Space groups Lattice parameters α-SnTe Rhombohedral structure R3m α = 89.895°, a = 6.325 Å (1Å = 0.1 nm), β-SnTe Rock-salt Cubic structure Fm3m α = 90°, a = 6.3268 Å γ-SnTe Orthorhombic structure Pnma α = 90°, a = 11.95 Å, b = 4.37 Å, c = 4.48 Å SnTe是第一个被理论预测并已被实验证实的拓扑晶体绝缘体,具有高度对称的晶体结构,拥有无带隙的拓扑表面态和窄带隙体态,且无带隙的表面态仅仅存在于那些镜面对称的表面如(100)、(110)、(111),其螺旋形的多重表面态和强健的拓扑保护特性在制备无能耗光电器件方面可应用,图2(b)和(c)分别是SnTe面心立方结构的布里渊区和能带结构[43],它在面心立方布里渊区具有特殊的镜像对称性。SnTe是窄带隙半导体材料,在室温下其体带隙为0.18 eV,可制备从紫外光、可见光到中红外波段的宽谱光电探测器;并且通过改变SnTe薄膜厚度或所受应力使带隙可调,如图2(d)所示[46]。SnTe的结构通常采用X射线衍射(X-Ray diffraction,XRD)、高分辨透射电子显微镜(High resolution transmission electron microscope,HRTEM)以及光电子能谱(X-ray photoelectron spectroscopy,XPS)等手段来表征;非故意掺杂的SnTe由于Sn空位和Te取代Sn从而呈现出P型半导体,Sn:Te通常小于1,如图2(e)XPS谱所示[32];图2(f)和(g)的XRD[32]和HRTEM图[30]表明了SnTe具有(111)、(100)等拓扑面。
Preparation, structure and properties of tin telluride and its research progress in infrared photodetection (Invited)
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摘要: Ⅳ-Ⅵ族碲化锡化合物是直接带隙半导体材料,在室温和大气压条件下具有稳定存在的面心立方结构。作为拓扑晶体绝缘体,碲化锡具有高度对称的晶型结构、螺旋形的多重表面态和强健的拓扑保护特性、无带隙的拓扑表面态和窄带隙体态、室温下高的迁移率等优异性能,在制备无能耗、宽谱(从紫外光、可见光到红外光)、超快响应的新型光电探测器领域有巨大潜力。文中从适宜应用于光电探测器件的角度出发,对碲化锡材料的制备方法、晶体结构、性质进行了阐述,对近年来碲化锡在红外光电探测领域的研究进展进行了总结,展望了其在光电探测领域的发展前景,并提出了碲化锡作为光电器件亟需深入研究的几个方面。Abstract: As Ⅳ-Ⅵ compound, tin telluride belongs to direct band gap semiconductor materials. Under the condition of room temperature and atmospheric pressure, tin telluride has a stable face-centered cubic crystal structure. Being a topological crystal insulator, tin telluride has a highly symmetrical crystal structure. Due to its helical multiple surface states and strong topological protection characteristics, tin telluride can be used to fabricate new electronic devices without energy consumption. Moreover, on account of its excellent properties such as band-gap free topological surface state and narrow band gap posture, it has great potential in the field of preparing new photodetectors with wide spectral response from ultraviolet, visible light to infrared. In addition, because of its high mobility at room temperature, tin telluride is expected to be used for high performance photoelectric detection with ultra-fast response speed. In this review, the preparation methods, crystal structures and properties of tin telluride materials were summarized from the point of view that they were suitable for photodetectors. And the research progress of tin telluride in infrared photoelectric detection in recent years was summarized. Then the development potential of tin telluride in the field of photodetectors was prospected, and several aspects that need to be further studied as photodetectors were also put forward.
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Key words:
- SnTe /
- material preparation /
- photoelectrical properties /
- photodetectors
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图 2 SnTe的结构及表征:(a) 不同结构相变;(b) 面心立方结构的SnTe布里渊区;(c) 面心立方结构的SnTe能带结构;(d) 随厚度或应变可调的带隙;(e) X射线光电子能谱;(f) X射线衍射图谱;(g) 高分辨透射电子显微镜图
Figure 2. Structure and characterization of SnTe: (a) Different phase transitions; (b) FCC Brillouin zone; (c) Band dispersion; (d) Strain- and layer-dependent band gap; (e) XPS spectra; (f) XRD pattern; (g) HRTEM image
图 3 SnTe的形貌、光学、电学及热电性质:(a) SnTe微晶;(b) 基于SnTe纳米线双端器件的I-V曲线;(c) 磁导Δρ/ρ0–B曲线;(d) 7.2 nm和14 nm直径的SnTe纳米晶体的红外吸收光谱;(e) SnTe薄膜的霍尔载流子浓度;(f) SnTe薄膜的霍尔迁移率;(h) SnTe热电材料的功率因数
Figure 3. Morphology, optical, electrical and thermoelectric properties of SnTe: (a) SnTe microcrystals; (b) Current−voltage curves; (c) Magneto-conductance Δρ/ρ0–B curves; (d) IR absorption spectra of 7.2 nm and 14 nm SnTe NCs; (e) Hall carrier density; (f) Hall mobility; (h) Power factor
图 4 SnTe光伏型器件及其光电特性:(a) SnTe/Si异质结器件示意图;(b) 典型的电流-电压特性;(c)SnTe/Si异质结构的能带图;(d) SnTe/Si器件的截面图;(e) SnTe/Si器件的光电流开关行为;(f)外量子效率图;(g) SnTe/Bi2Se3异质结构示意图;(h) 异质结构横截面的HRTEM图像;(i) SnTe/Bi2Se3的狄拉克能带图
Figure 4. SnTe photovoltaic detector and its photoelectric properties: (a) Scheme of SnTe/Si heterostructure device; (b) Typical I–V characteristics; (c) Energy band diagram; (d) Cross section diagram of SnTe/Si devices; (e) Photocurrent switching behavior of the device; (f) EQE spectrum; (g) Schematic drawing of the SnTe/Bi2Se3 heterostructure; (h) HRTEM image of the heterostructure cross-section; (i) Dirac band diagrams of SnTe/Bi2Se3
图 5 SnTe光导型器件及其光电特性: (a)光导型探测器的示意图;(b)光导型探测器的光学显微镜图;(c) 在405 nm光照下的光响应图;(d) 3.8 µm光照下的光响应图;(e)光电流随激光功率强度的变化关系;(f) 柔性SnTe近红外单个纳米片光电探测器原理图;(g) AFM图;(h)在980 nm激光照射下光电流随激光功率强度的变化关系;(i)不同弯曲角度的SnTe纳米片在980 nm激光照射下的光电流
Figure 5. SnTe photoconductive detector and its photoelectric properties: (a) Schematic diagram of the photodetector; (b) OM image of the detector; (c) Time-dependent photo-response with 405 nm; (d) Time-dependent photo-response with 3.8 µm; (e) The laser power intensity dependence of the photocurrent; (f) Schematic diagram of flexible SnTe NIR single nanoplate photodetectors; (g) Representative AFM image; (h) Dependence of laser intensity on the photocurrent under the illumination of a 980 nm laser; (i) Photocurrent of SnTe nanoplate photodetectors bending with different radii under the illumination of a 980 nm laser
图 6 SnTe 场效应晶体管器件及其光电特性: (a) SnTe基光电探测器原理图;(b) SnTe纳米片的SEM图像;(c) SnTe纳米片的AFM图像;(d) 4650nm光照下的光响应图;(e) SnTe基柔性光电探测器的光响应测量;(f) 柔性器件的光电流图;(g) 在暗条件和980nm激光照射下SnTe探测器的转移特征曲线;(h) 典型的噪声-栅极电压图;(i) 依赖于栅极电压的响应率和探测率
Figure 6. SnTe FET photodetector and its photoelectric properties: (a) Diagrammatic drawing of the SnTe-based photodetector; (b) SEM image; (c) AFM image; (d) Time-dependent photo-response with 4650 nm; (e) Photoresponse measurements of the SnTe-based flexible photodetectors; (f) Time-dependent photocurrent of the flexible device; (g) Transfer curves of SnTe detectors; (h) Typical noise as a function of gate voltage; (i) Gate voltage dependent responsivity and detectivity
表 1 碲化锡制备方法、材料形态及其特性
Table 1. Preparation methods, material morphology and properties of tin telluride
Preparation methods Morphological structure Features Year Ref. MBE SnTe-based films and superlattices The structure parameters of the PbTe/SnTe superlattice were
determined by the selected buffer layer material1997 [23] MBE Si (111) substrate/
SnTe thin filmThe electronic structure of the film was adjustable by
changing thickness and lead doping level2014 [24] MBE BaF2 (001) substrate/
SnTe filmBy increasing the growth temperature, the film has higher
mobility and lower carrier concentration2014 [25] MBE Sapphire substrate/Bi2Te3 buffer layer/SnTe film Dirac electrons on the SnTe (111) surface was gained by transmission measurements on a high quality film grown on the Bi2Te3 buffer layer 2014 [26] MBE
BaF2substrate/SnTe
filmBy optimizing the growth conditions and film thickness, the carrier concentration is reduced, which conduced to study the surface magnetic transport characteristics 2015 [27] MBE GaAs (111) A substrate/CdTe/
SnTe filmSingle-phase very low hole concentration of SnTe (111) can be
obtained by optimizing the growth temperature of SnTe and
CdTe layers and the growth rate of SnTe2016 [28] MBE Substrate/Bi2Te3 buffer layer/SnTe film An efficient photoconductive photodetector was prepared
based on 10 nm TCI SnTe2017 [29] CVD SnTe nanowire The exposed surface of SnTe micro-nano structure can be adjusted by experimental parameters such as temperature 2014 [30] CVD SnTe nanoribbon The controlled growth of crystal surface of SnTe nanocrystals {100} can be realized by Bi doping 2016 [31] CVD SnTe thin film/n-Si Nps heterojunction A photovoltaic photodetector was prepared based on
SnTe/Si Nps heterojunction2017 [32] PVD SnTe thin film/n-Si heterojunction A photovoltaic photodetector was prepared based on
SnTe/Si heterojunction2017 [33] PVD SnTe flake A field effect transistor photodetector was prepared based on
SnTe single crystal2018 [34] PVD SnTe thin film/n-Bi2Se3 heterojunction A photovoltaic photodetector was prepared based on
SnTe/Bi2Se3 heterojunction2020 [19] Hot wall epitaxy SnTe-based films and superlattices The prepared EuTe/SnTe SL showed a high mobility of 2720 cm2/(V·S) at room temperature. The Seebeck coefficients of SnTe/PbSe and SnTe/PbS SLs can be close to those of PbSe and PbS 2009 [35] Solution-phase synthesis SnTe quantum dot By changing the growth temperature, concentration of reaction mixture, etc., the average diameter of SnTe NCs was adjustable within 4.5-15 nm, and the band gap correspondingly is 0.8-0.38 eV. It can be
used in near-infrared photoelectric devices2007 [36] Solution-based synthesis SnTe nanostructure The shape/size controlled preparation of SnTe nanotubes, nanorods and nanowires promotes the application of colloidal infrared active nanomaterials in practical technologies 2015 [37] Vapor-liquid−
solid growthSnTe nanoplates SnTe nanoplate were prepared with large {100} or {111} surface areas, allowing selective study of the surface states on these surfaces.
The phase transition from rock salt structure to rhombic structure
was observed at low temperature2014 [38] Solid solution alloying Sn 1.03−x Mg x Te ingot Adjusting the SnTe electron band structure by Mg doping, the Seebeck coefficient was improved and the thermoelectric property was optimized 2014 [39] Microwave solvothermal method Se/Cd co-doped SnTe octahedral particles By using the strategy of co-doping selenium and cadmium, the energy band structure of SnTe was optimized to improve the
power factor and thermoelectric optimization value2017 [40] Alloying Ge doped SnTe alloy The local structure distortion and related ferroelectric instability of SnTe were adjusted by Ge doping, and the ultra-low lattice thermal conductivity was aquired to optimize the thermoelectric performance of SnTe 2019 [41] 表 2 SnTe不同相的晶体结构
Table 2. Crystal structure of different phases of SnTe
Phases Crystal structures Space groups Lattice parameters α-SnTe Rhombohedral structure R3m α = 89.895°, a = 6.325 Å (1Å = 0.1 nm), β-SnTe Rock-salt Cubic structure Fm3m α = 90°, a = 6.3268 Å γ-SnTe Orthorhombic structure Pnma α = 90°, a = 11.95 Å, b = 4.37 Å, c = 4.48 Å -
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