低维量子结构的制备及电学性质研究
摘要
硅衬底上自组织生长的锗硅量子点(GeSi QDs)在光电子、微电子和单电子器件领域有着重要的应用前景。GeSi量子点的电学性质研究不仅仅在基础研究中有着重要的意义,其对器件性能的影响使得在工业上也广泛受到关注。其电学性质受各种各样因素的影响,这些因素即包括量子点本身的组分分布、应力分布、几何结构等等,也包括外界测试时附加的偏压、接触压力等因素的影响。本文采用导电原子力显微镜(CAFM)对自组织生长的GeSi单量子点的电流分布进行测试,研究了偏压和接触压力对其电流分布的影响,并结合静电力显微镜(EFM)和扫描开尔文显微镜(SKM)的结果,对其导电机制进行了探讨。
为了进一步弄清GeSi量子点的电学特性对形貌、组分分布等依赖关系,我们利用纳米小球模板加反应离子束刻蚀的方法,制备了纯硅量子点。利用CAFM、EFM、SKM对纯硅量子点的电学性质进行研究,并与GeSi量子点的结果进行比较。
石墨烯,自首次成功制备以来,就备受关注,但研究通常都着眼在石墨单层的横向输运上,不同层数的石墨薄层的电学性质变化往往被忽略,我们成功运用了为人们所熟知的物理剥离法,在300nm厚的氧化硅表面自行制备了石墨单层和石墨多层样品,并用扫描电容显微镜(SCM), EFM, SKM等手段对不同厚度的进行了电学性质的分析和比较。
得到的主要结果包括以下几点：
1.通过CAFM对单个圆顶型锗硅量子点的导电分布测试的结果显示其电流分布为一环形,即衬底不导电,量子点的腰部导电性明显好于中心。不同偏压的测试表明,其腰部的电流值与偏压有明显的正相关,而中心随电压变化不大,这一现象在尺寸稍大的量子点中比尺寸稍小的更为明显。不同作用力下的电流分布显示了量子点导电性随接触压力的变大而变好对于任何尺寸的量子点都适用。EFM和SKM结果也从另外的方面证实了大点的导电性优于小点的结果。对其机理的深入探讨正在进行中。
2.将纳米小球模板与反应离子刻蚀相结合,我们给出了一种操作简单,成本低廉的纯硅纳米结构的普遍加工方法,过程中没有金属杂质的引入,并可以通过制备过程中实验参数的选择实现用统一的流程制作无杂质的纯硅量子点,量子环,量子围墙,量子凹坑等结构。
3.对纯硅量子点的电学性质测试给出了与GeSi量子点相同的结论,即大点导电性优于小点；电势、静电力不出现电流分布中的环状特征而是呈圆饼状。综合考虑对各种量子结构的电学性质测试,我们发现了量子结构的电学性质对几何形状的依赖关系。
4.制备了300m氧化硅表面上的石墨单层、多层样品,通过光学显微镜照片辅助定位,用AFM对单层石墨及多层石墨进行形貌表征。研究了不同层数的石墨薄层的电学性质,发现其静电力分布、表面势分布以及载流子浓度是与层数相关的,其机理有待进一步深入研究。
Self-assembled silicon-germanium quantum dots (GeSi QDs) have important applications in optoelectronics, microelectronics, and single electron device fields. Electrical properties of GeSi QDs are of great significance not only in fundamental researches, but also on device performances in industry. The electrical properties were related to many factors including the internal properties of quantum dots itself, such as the component distribution, stress distribution, geometry characteristic, etc., and external situation, such as test bias voltage, force between tip and sample and so on. In this thesis, conductive atomic force microscope (CAFM) was used to analysis the current distribution of individual GeSi QDs, and current distributions under different bias voltages and applied forces. Together with electrostatic force microscopy (EFM) and scanning Kelvin microscopy (SKM), the mechanism of conductive characteristic is discussed.
In order to further understanding the electrical properties in relation with the geometrical characteristic or component distribution, we use nanosphere lithography combined with reaction ion etching to fabricate pure silicon quantum dots. CAFM, EFM and SKM are carried out to study the electrical properties of pure silicon quantum dots. The results are also compared with GeSi QDs' results.
石墨烯,since its first successfully fabricated, has drawn a mess concern all over the world, but studies usually focus on the horizontal transport in the石墨烯,layer number dependent electrical properties of few-layer-graphite (FLG) is often overlooked. We have successfully used the well known physical dissection method to fabricate single-layer石墨烯and FLG on the surface of 300nm thick silicon oxide. With scanning capacitance microscopy (SCM), EFM and SKM, layer number dependent electrical properties were studied.
Following results are obtained:
1. Conductive atomic force microscope measurement on a single dome-like GeSi QDs show that the current distribution of GeSi QDs is ring-shaped, which means the substrate is not as conductive as the dots, while at the same time, the waist of quantum dots has a better conductivity than the center of the dots. Different bias voltages tests showed that the current at the waist of quantum dots have a significant positive relationship with the bias voltage, while the center vary only a little. This phenomenon is more apparently in the larger quantum dots than in the smaller ones. Current distribution under different forces shows the electrical conductivity of quantum dots become well with higher pressure is suitable for all size of dots. EFM and SKM also provide evidence that big QDs have better conductivity than small QDs. But ring distribution does not appear in the distribution of static electric force or surface potential.
2. With the notion of nano-sphere lithography and reactive ion etching, we give a simple, low-cost method of fabricating nano-structure of pure silicon in general, the process is free from metal impurities. With this method a unified process can be make to fabricate metal-impurity-free silicon quantum dots, quantum rings, quantum walls and quantum pits.
3. The results of pure silicon QDs show the same features as the GeSi QDs, that is, big QDs have a better conductivity than small QDs; surface potential and static electric force has a round distribution instead of ring distribution. Think together with the other results we test on all the other nano-structures, the current distribution is dominated by geometrical properties.
4. We have successfully fabricated石墨烯and few-layer-graphite (FLG) on the silicon substrate with a 300nm thick SiO2 layer on top. With the help of optical microscope, we use AFM to identify石墨烯and FLG. Also, SCM, EFM and SKM is brought in to investigate the electrical properties of石墨烯and FLG, the results show that the static electric force, surface potential and carrier density is positive related to the layer numbers.
为了进一步弄清GeSi量子点的电学特性对形貌、组分分布等依赖关系,我们利用纳米小球模板加反应离子束刻蚀的方法,制备了纯硅量子点。利用CAFM、EFM、SKM对纯硅量子点的电学性质进行研究,并与GeSi量子点的结果进行比较。
石墨烯,自首次成功制备以来,就备受关注,但研究通常都着眼在石墨单层的横向输运上,不同层数的石墨薄层的电学性质变化往往被忽略,我们成功运用了为人们所熟知的物理剥离法,在300nm厚的氧化硅表面自行制备了石墨单层和石墨多层样品,并用扫描电容显微镜(SCM), EFM, SKM等手段对不同厚度的进行了电学性质的分析和比较。
得到的主要结果包括以下几点：
1.通过CAFM对单个圆顶型锗硅量子点的导电分布测试的结果显示其电流分布为一环形,即衬底不导电,量子点的腰部导电性明显好于中心。不同偏压的测试表明,其腰部的电流值与偏压有明显的正相关,而中心随电压变化不大,这一现象在尺寸稍大的量子点中比尺寸稍小的更为明显。不同作用力下的电流分布显示了量子点导电性随接触压力的变大而变好对于任何尺寸的量子点都适用。EFM和SKM结果也从另外的方面证实了大点的导电性优于小点的结果。对其机理的深入探讨正在进行中。
2.将纳米小球模板与反应离子刻蚀相结合,我们给出了一种操作简单,成本低廉的纯硅纳米结构的普遍加工方法,过程中没有金属杂质的引入,并可以通过制备过程中实验参数的选择实现用统一的流程制作无杂质的纯硅量子点,量子环,量子围墙,量子凹坑等结构。
3.对纯硅量子点的电学性质测试给出了与GeSi量子点相同的结论,即大点导电性优于小点；电势、静电力不出现电流分布中的环状特征而是呈圆饼状。综合考虑对各种量子结构的电学性质测试,我们发现了量子结构的电学性质对几何形状的依赖关系。
4.制备了300m氧化硅表面上的石墨单层、多层样品,通过光学显微镜照片辅助定位,用AFM对单层石墨及多层石墨进行形貌表征。研究了不同层数的石墨薄层的电学性质,发现其静电力分布、表面势分布以及载流子浓度是与层数相关的,其机理有待进一步深入研究。
Self-assembled silicon-germanium quantum dots (GeSi QDs) have important applications in optoelectronics, microelectronics, and single electron device fields. Electrical properties of GeSi QDs are of great significance not only in fundamental researches, but also on device performances in industry. The electrical properties were related to many factors including the internal properties of quantum dots itself, such as the component distribution, stress distribution, geometry characteristic, etc., and external situation, such as test bias voltage, force between tip and sample and so on. In this thesis, conductive atomic force microscope (CAFM) was used to analysis the current distribution of individual GeSi QDs, and current distributions under different bias voltages and applied forces. Together with electrostatic force microscopy (EFM) and scanning Kelvin microscopy (SKM), the mechanism of conductive characteristic is discussed.
In order to further understanding the electrical properties in relation with the geometrical characteristic or component distribution, we use nanosphere lithography combined with reaction ion etching to fabricate pure silicon quantum dots. CAFM, EFM and SKM are carried out to study the electrical properties of pure silicon quantum dots. The results are also compared with GeSi QDs' results.
石墨烯,since its first successfully fabricated, has drawn a mess concern all over the world, but studies usually focus on the horizontal transport in the石墨烯,layer number dependent electrical properties of few-layer-graphite (FLG) is often overlooked. We have successfully used the well known physical dissection method to fabricate single-layer石墨烯and FLG on the surface of 300nm thick silicon oxide. With scanning capacitance microscopy (SCM), EFM and SKM, layer number dependent electrical properties were studied.
Following results are obtained:
1. Conductive atomic force microscope measurement on a single dome-like GeSi QDs show that the current distribution of GeSi QDs is ring-shaped, which means the substrate is not as conductive as the dots, while at the same time, the waist of quantum dots has a better conductivity than the center of the dots. Different bias voltages tests showed that the current at the waist of quantum dots have a significant positive relationship with the bias voltage, while the center vary only a little. This phenomenon is more apparently in the larger quantum dots than in the smaller ones. Current distribution under different forces shows the electrical conductivity of quantum dots become well with higher pressure is suitable for all size of dots. EFM and SKM also provide evidence that big QDs have better conductivity than small QDs. But ring distribution does not appear in the distribution of static electric force or surface potential.
2. With the notion of nano-sphere lithography and reactive ion etching, we give a simple, low-cost method of fabricating nano-structure of pure silicon in general, the process is free from metal impurities. With this method a unified process can be make to fabricate metal-impurity-free silicon quantum dots, quantum rings, quantum walls and quantum pits.
3. The results of pure silicon QDs show the same features as the GeSi QDs, that is, big QDs have a better conductivity than small QDs; surface potential and static electric force has a round distribution instead of ring distribution. Think together with the other results we test on all the other nano-structures, the current distribution is dominated by geometrical properties.
4. We have successfully fabricated石墨烯and few-layer-graphite (FLG) on the silicon substrate with a 300nm thick SiO2 layer on top. With the help of optical microscope, we use AFM to identify石墨烯and FLG. Also, SCM, EFM and SKM is brought in to investigate the electrical properties of石墨烯and FLG, the results show that the static electric force, surface potential and carrier density is positive related to the layer numbers.
引文
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[22]S. M. Weeks, F.Y. Ogrin, W. A. Murray and P. S. Keatley, Langmuir 23,1057 (2007).
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[24]C. L. Cheung, R. J. Nikolic, C. E. Reinhardt and T. F. Wang, Nanotechnology 17,1339(2006).
[2]S. Pasic-acute and K. Ilakovac, Phys. Rev. A 55,4248 (1997).
[3]D. Dovinos and D. Williams, Phys. Rev. B 72,085313 (2005).
[4]I. Tanaka, I. Kamiya, H. Sakaki, N. Qureshi, S. J. Allen, and P. M. Petroff, Appl. Phys. Lett.74,844(1999).
[5]J. Oh and R. J. Nemanich, J. Appl. Phys.92,3326 (2002).
[6]W. I. Park, G. C. Yi, J. W. Kim, and S. M. Park, Appl. Phys. Lett.82,4358 (2003).
[7]F. Xue, J. Qin, J. Cui, Y. L. Fan, Z. M. Jiang, and X. J. Yang, Surf. Sci.592,65 (2005).
[8]R. Wu, F.H. Li, Z.M. Jiang and X.J. Yang, Nanotechnology 17,5111 (2006).
[9]N. Vourdas, D. Kontziampasis, G. Kokkoris, V. Constantoudis, A. Goodyear, A. Tserepi, M. Cooke and E. Gogolides, Nanotechnology 21,085302 (2010).
[10]J. Yoo, K. Kim, M. Thamilselvan, N. Lakshminarayn, Y. K. Kim, J. Lee, K. J. Yoo and J. Yi, J. Phys. D 41,125205 (2008).
[11]Z. P. Huang et al., Adv. Mater.19,744 (2007).
[12]Aurelie Pierret et al., Nanotechnology 21,065305 (2010).
[13]Xiaofeng Peng and Itaru Kamiya, Nanotechnology 19,315303 (2008).
[14]Z.A.K. Durrani and M.A. Rafiq, Microelectronic Engineering,86,456 (2009).
[15]K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, and A. K. Geim, PNAS 102,10451 (2005).
[16]K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, A. A. Firsov, Science 306,666 (2004).
[17]P. Blake, E. W. Hill, A. H. Castro Neto, K. S. Novoselov, D. Jiang, R. Yang, T. J. Booth, and A. K. Geim, Appl. Phys. Lett.91,063124 (2007).
[18]K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos and A. A. Firsov, Nature 438,197 (2005).
[19]V. P. Gusynin and S. G. Sharapov, Phys. Rev. Lett.95,146801 (2005).
[20]S. Sonde, F. Giannazzoa, V. Raineri and E. Rimini, J. Vac. Sci. Technol. B,27, 868 (2009).
[21]Sujit S. Datta, Douglas R. Strachan, E. J. Mele, and A. T. Charlie Johnson, Nano Lett.9,7 (2009).
[22]S. M. Weeks, F.Y. Ogrin, W. A. Murray and P. S. Keatley, Langmuir 23,1057 (2007).
[23]P. X. Chen, Y. L. Fan and Z. Y. Zhong, Nanotechnology 20,095303 (2009).
[24]C. L. Cheung, R. J. Nikolic, C. E. Reinhardt and T. F. Wang, Nanotechnology 17,1339(2006).