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采用离子束溅射沉积的方法在Si衬底上生长Ge量子点, 观察到量子点的生长随Ge原子层沉积厚度θ的增加经历了两个不同的阶段. 当θ在6—10.5个单原子层(ML)范围内时, 量子点的平均底宽和平均高度随θ增加同时增大, 生长得到高宽比较小的圆顶形Ge量子点, 伴随着量子点的生长, 二维浸润层的厚度同时增大, 量子点的分布密度缓慢增加; 当θ在11.5—17 ML范围内时, 获得高宽比较大的圆顶形Ge量子点, 量子点以纵向生长为主导, 二维浸润层的离解促进量子点的成核和长大, 量子点的分布密度随θ的增加快速增大; 量子点在θ由10.5 ML增加到11.5 ML时由一个生长阶段转变到另一个生长阶段, 其分布密度同时发生6.4倍的增加. 离子束溅射沉积Ge量子点的生长演变与在热平衡状态下生长的量子点不同, 在量子点的不同生长阶段, 其表面形貌和分布密度的变化特点是在热力学条件限制下表面原子动态演变的结果, θ的变化是引起系统自由能改变的主要因素. 携带一定动能的溅射原子对生长表面的轰击促进表面原子的扩散迁移, 同时压制量子点的成核, 在浸润层中形成超应变状态, 因而, 改变体系的能量和表面原子的动力学行为, 对量子点的生长起重要作用.The Ge quantum dots on Si substrate are prepared by ion beam sputtering deposition (IBSD). The growth evolution is observed to experience two stages with Ge coverage (θ) increasing. When θ increases from 6 monolayers (ML) to 10.5 ML, the average base width and height of quantum dots both increase, and the dome shape dots with small aspect ratio values are obtained. As the dots grow up, Ge atoms are also accumulated in the wetting layer, which contributes to the observed quantum dot density increasing mildly during this stage. When θ is in a range from 11.5 ML to 17 ML, vertical growth dominates the dot evolution. Another dome shape quantum dots are prepared with large aspect ratio values. Ge coverage gain results in the dot density increasing rapidly. A wetting layer decomposition process is demonstrated to give significant effect on that. The growth transition occurs as θ increases from 10.5 ML to 11.5 ML, and the dot density is enhanced 6.4 times in this course. So it is concluded that the evolution of Ge quantum dot prepared by IBSD is very different from that deposited on the thermal equilibrium condition. The observed characters of the dot shape and size distribution result from the kinetic behaviors of the surface atoms which are restricted by the thermodynamic limitation. Ge coverage is the one of the most important factors which can change the free energy. On the other hand, the energic sputtered atom bombardment enhances surface diffusion and defers nucleation of three-dimensional islands until the superstrain wetting layer is formed, which can also change the system free energy and the surface atom kinetic behaviors. So the growth evolution of Ge quantum dots prepared by IBSD is related so much with the effect of atom bombardment on the quantum dot growth.
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Keywords:
- Ge quantum dot /
- ion beam sputtering deposition /
- surface morphology /
- behavior of surface atoms
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[2] Yang H B, Tao Z S, Lin J H, Lu F, Jiang Z M, Zhong Z Y 2008 Appl. Phys. Lett. 92 111907
[3] Rokhinson L P, Tsui D C, Benton J L 1999 Appl. Phys. Lett. 75 2413
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[22] Chung H C, Liu C P, Lai Y L 2008 Appl. Phys. A 91 267
[23] Leonard D, Pond K, Petroff P M 1994 Phys. Rev. B 50 11687
[24] Daruka I, Tersoff J, Barabási A L 1999 Phys. Rev. Lett. 82 2753
[25] Jin G, Liu J L, Wang K L 2003 Appl. Phys. Lett. 83 284
[26] Barabási A L 1999 Mater. Sci. Eng. B 67 23
[27] Zhang Y W, Brower A F 2001 Appl. Phys. Lett. 78 2706
[28] Johansson J, Seifert W 2002 J. Crys. Growth 234 132
[29] Zhang Y, Drucker J 2003 J. Appl. Phys. 93 9583
[30] Floro J A, Lucadamo G A, Chason E, Freund L B, Sinclair M, Twesten R D, Hwang R Q 1998 Phys. Rev. Lett. 80 4717
[31] Rickman J M, Srolovitz D J 1993 Surf. Sci. 284 211
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[1] Eaglesham D J, Cerullo M 1990 Phys. Rev. Lett. 64 1943
[2] Yang H B, Tao Z S, Lin J H, Lu F, Jiang Z M, Zhong Z Y 2008 Appl. Phys. Lett. 92 111907
[3] Rokhinson L P, Tsui D C, Benton J L 1999 Appl. Phys. Lett. 75 2413
[4] Tong S, Lee J Y, Kin H J, Liu F, Wang K L 2005 Opt. Mater. 27 1097
[5] Larsson M, Elfving A, Holtz P O, Hnsson G V, Ni W X 2003 Surf. Sci. 532-535 832
[6] Kamins T I, Carr E C, Williams R S, Rosner S J 1997 J. Appl. Phys. 81 211
[7] Ross F M, Tromp R M, Reuter M C 1999 Science 286 1931
[8] Medeiros-Ribeiro G, Bratkovski A M, Kamins T I, Ohlberg D A A, Williams R S 1998 Science 279 353
[9] Capellini G, De Seta M, Evangelisti F 2003 J. Appl. Phys. 93 291
[10] Shchukin V A, Ledentsov N N, Kopev P S, Bimberg D 1995 Phys. Rev. Lett. 75 2968
[11] Kamins T I, Medeiros-Ribeiro G, Ohlberg D A A, Williams R S 1999 J. Appl. Phys. 85 1159
[12] Dobbs H T, Vvedebsky D D, Zangwill A, Johansson J, Carlsson N, Seifert W 1997 Phys. Rev. Lett. 79 897
[13] Koduvely H M, Zangwill A 1999 Phys. Rev. B 60 R2204
[14] Song H Z, Usuki T, Nakata Y, Yokoyama N, Sasakura H, Muto S 2006 Phys. Rev. B 73 115327
[15] Vailionis A, Cho B, Glass G, Desjardins P, Cahill D G, Greene J E 2000 Phys. Rev. Lett. 85 3672
[16] Chen K M, Jesson D E, Pennycook S J, Thundat T, Warmack R J 1997 Phys. Rev. B 56 R1700
[17] Meyer F, Schwebel C, Pellet C, Gautherin G, Buxbaum A, Eizenberg M, Raizman A 1990 Thin Solid Films 184 117
[18] Mosleh M, Meyer F, Schwebel C, Pellet C, Eizenberg M 1994 Thin Solid Films 246 30
[19] Choil C H, Hultman L, Barnett S A 1990 J. Vac. Sci. Technol. A 8 1587
[20] Sasaki K, Takahashi Y, Ikeda T, Hata T 2002 Vacuum 66 457
[21] Xiong F, Pan H X, Zhang H, Yang Y 2011 Acta Phys. Sin. 60 088102 (in Chinese) [熊飞, 潘红星, 张辉, 杨宇 2011 60 088102]
[22] Chung H C, Liu C P, Lai Y L 2008 Appl. Phys. A 91 267
[23] Leonard D, Pond K, Petroff P M 1994 Phys. Rev. B 50 11687
[24] Daruka I, Tersoff J, Barabási A L 1999 Phys. Rev. Lett. 82 2753
[25] Jin G, Liu J L, Wang K L 2003 Appl. Phys. Lett. 83 284
[26] Barabási A L 1999 Mater. Sci. Eng. B 67 23
[27] Zhang Y W, Brower A F 2001 Appl. Phys. Lett. 78 2706
[28] Johansson J, Seifert W 2002 J. Crys. Growth 234 132
[29] Zhang Y, Drucker J 2003 J. Appl. Phys. 93 9583
[30] Floro J A, Lucadamo G A, Chason E, Freund L B, Sinclair M, Twesten R D, Hwang R Q 1998 Phys. Rev. Lett. 80 4717
[31] Rickman J M, Srolovitz D J 1993 Surf. Sci. 284 211
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