Formation mechanisms of nano and microcones by laser radiation on surfaces of Si, Ge, and SiGe crystals
© Medvid et al.; licensee Springer. 2013
Received: 28 March 2013
Accepted: 6 May 2013
Published: 4 June 2013
In this work we study the mechanisms of laser radiation interaction with elementary semiconductors such as Si and Ge and their solid solution SiGe. As a result of this investigation, the mechanisms of nanocones and microcones formation on a surface of semiconductor were proposed. We have shown the possibility to control the size and the shape of cones both by the laser. The main reason for the formation of nanocones is the mechanical compressive stresses due to the atoms’ redistribution caused by the gradient of temperature induced by strongly absorbed laser radiation. According to our investigation, the nanocone formation mechanism in semiconductors is characterized by two stages. The first stage is characterized by formation of a p-n junction for elementary semiconductors or of a Ge/Si heterojunction for SiGe solid solution. The generation and redistribution of intrinsic point defects in elementary semiconductors and Ge atoms concentration on the irradiated surface of SiGe solid solution in temperature gradient field take place at this stage due to the thermogradient effect which is caused by strongly absorbed laser radiation. The second stage is characterized by formation of nanocones due to mechanical plastic deformation of the compressed Ge layer on Si. Moreover, a new 1D-graded band gap structure in elementary semiconductors due to quantum confinement effect was formed. For the formation of microcones Ni/Si structure was used. The mechanism of the formation of microcones is characterized by two stages as well. The first stage is the melting of Ni film after irradiation by laser beam and formation of Ni islands due to surface tension force. The second step is the melting of Ni and subsequent manifestations of Marangoni effect with the growth of microcones.
KeywordsLaser radiation Microcones Nanocones Thermogradient effect
Semiconductor nanostructures are the most investigated object in solid state physics due to their promising application in microelectronics and optoelectronics. Today we have some well-developed methods for the formation of nanostructures: MBE , CVD , ion implantation , and laser ablation . The above-mentioned methods need subsequent thermal annealing of the structures in a furnace. Nanostructure growths by these methods need a lot of time and a high-vacuum or a special environment, for example, inert Ar gas. As a result, nanocrystals grow with uncontrollable parameters, broad size distribution, and chaotically, the so-called self-assembly. Therefore, one of the important tasks for nanoelectronic and optoelectronic growth is the elaboration of new methods for the formation of nanostructures in semiconductors with controlled features.
On the other hand, laser technology is of interest both fundamentally because laser radiation of a semiconductor can lead to different and sometimes opposite results, for example, annealing defects after ion implantation or creating new additional defects and from a device viewpoint , since it can be used for annealing B/n-Si or F/p-Si structures during p-n junction formation which is appropriate for many kinds of microelectronic devices .
Moreover, our recent investigations have shown that laser radiation can be successfully applied for formation of cone-like nanostructures [7–10] with laser intensity, which do not cause melting of the material. The 1D-graded band gap structure in elementary semiconductors was formed due to quantum confinement effect . Furthermore, it has been shown that irradiation by laser of Si single crystal with intensity which exceeds melting of material leads to formation of microcones, which are possible to use for solar cells, the so-called black Si . The lack of understanding of the interaction effects of laser radiation with a semiconductor limits laser technology application in microelectronics . So the aims of this research are to show a new possibility for formation of nanocones and microcones on a surface of elementary semiconductors (Si, Ge) and their solid solution by laser radiation, and to propose the mechanism of cones formation.
Materials and methods
For the formation of nanocones in the experiments on i-type Ge single crystals with resistivity ρ = 45 Ω cm, Na = 7.4 × 1011 cm−3, Nd = 6.8 × 1011 cm−3, where Na and Nd are acceptor and donor concentrations, and samples with the size of 16.0 × 3.0 × 2.0 mm3 were used. The samples were mechanically polished with diamond paste and chemically treated with H2O2 and CP-4 (HF/HNO3/CH3COOH in volume ratio of 3:5:3).
Different intensities, pulse durations, and wavelengths of nanosecond Nd:YAG laser were used to irradiate the samples (pulse repetition rate at 12.5 Hz, power of P = 1.0 MW and wavelength of λ = 1,064 nm). The diameter of the spot of the laser beam was 3 mm, and point-to-multipoint method was used for irradiation of the samples. All experiments of nanocone formation were performed in ambient atmosphere at pressure of 1 atm, T = 20°C, and 60% humidity. Current–voltage (I-V) characteristics were measured for the nonirradiated and irradiated samples with nanocones formed on a surface of i-Ge samples. The measurements of the I-V characteristics were performed by soldering 99% tin and 1% antimony alloy contacts directly on the irradiated surface of Ge with the tin contacts on the opposite side. Measurements of I-V characteristics were done at room temperature and atmospheric pressure.
The structure consisting of Ni catalyst with thicknesses d = 30 nm deposited on commercial Si(111) single crystals were used for formation of microcones. Pulsed Nd:YAG laser for treatment Ni/Si structure with following parameters was used: wavelength of λ = 1,064 nm, pulse duration of τ = 150 ms, pulse repetition rate of 12.5 Hz, power at P = 1.0 MW, laser intensity of I = 4 MW/cm2. The threshold intensity of microcones formation is 3.15 MW/cm2. The samples were treated by laser radiation in scanning mode with step of 20 μm. All experiments of microcones formation were performed in ambient atmosphere at pressure of 1 atm, T = 20°C, and 60% humidity.
Investigations of the reflection obtained from the surface with decorated microcones structure were done with Avantes AvaSpec-2048 UV/VIS/NIR spectrometer (Avantes Inc., Apeldoorn, The Netherlands) in the wavelength range of 200 to 1,100 nm [spectrometer based on AvaBench-75 symmetrical Czerny-Turner construction (Avantes Inc., Apeldoorn, The Netherlands) with 2,048 pixel CCD detector and resolution of 1.4 nm].
Surface morphology and chemical analysis of the samples by scanning electron microscope (SEM) with integrated energy dispersive X-ray spectrometer (SEM-EDX) Hitachi S-900 (Hitachi America, Ltd., Brisbane, CA, USA) were used. Photoluminescence (PL) measurements were performed by equipment Fluorolog-3, using photo detector Hamamatsu R928 and xenon lamp (450 W) (Hamamatsu Photonics GmbH, Herrsching, Germany).
Results and discussion
The surface microstructuring of ordinary Si by pulsed femtosecond laser-induced plasma [25, 26] or chemical vapor deposition with catalytic metal on Si  is used for black Si formation. We proposed a new laser method, which is simpler and cheaper comparison with above-mentioned methods .
Experimentally, we have shown the possibility to control the size and the shape of cones both by the laser radiation and the semiconductor parameters.
Nanocone formation mechanism in semiconductors is characterized by two stages. The first stage is characterized by formation of n-p junction for elementary semiconductors or Ge/Si heterojunction for SiGe solid solution. The second stage is characterized by formation of nanocones due to mechanical plastic deformation of the compressed Ge layer on Si and in elementary semiconductor compressed n-type top layer.
The mechanism of the formation of microcones is characterized by two stages. The first stage is melting of Ni film after irradiation by laser beam and formation of Ni islands due to surface tension force. The second step is melting of Ni and subsequent manifestations of Marangoni effect with growth of microcones.
AM is the head of Semiconductors Laboratory at Riga Technical University. PO is the lead researcher in Semiconductor Laboratory at Riga Technical University. ED is a Ph D student in Riga Technical University. RJG is an associate professor at Kaunas University of Applied Sciences. IP is an associate professor at Kaunas University of Technology.
Atomic force microscope
Quantum confinement effect
Scanning electron microscope
Authors AM and PO gratefully acknowledge the financial support by the European Regional Development Fund within the project ‘Sol–gel and laser technologies for the development of nanostructures and barrier structures’, 2010/0221/2DP/184.108.40.206.0/10/APIA/VIAA/145 and Latvian Council of Science according to the grant 10.0032.6.2. ED thanks for the support of this work by the European Social Fund within the project ‘Support for the implementation of doctoral studies at Riga Technical University’. RJ thanks the Research Council of Lithuania for Postdoctoral fellowship that was funded by the European Union Structural Funds project ‘Postdoctoral Fellowship Implementation in Lithuania.’
- Talochkin AB, Teys SA, Suprun SP: Resonance Raman scattering by optical phonons in unstrained germanium quantum dots. Phys Rev 2005, 72: 115416–11154.View ArticleGoogle Scholar
- Wu XL, Gao T, Bao XM, Yan F, Jiang SS, Feng D: Annealing temperature dependence of Raman scattering in Ge+−implanted SiO2 films. J Appl Phys 1997, 82: 2704. 10.1063/1.366089View ArticleGoogle Scholar
- Hartmann JM, Bertin F, Rolland G, Semeria MN, Bremond G: Effects of the temperature and of the amount of Ge on the morphology of Ge islands grown by reduced pressure-chemical vapor deposition. Thin Sol Film 2005, 479: 113–120. 10.1016/j.tsf.2004.11.204View ArticleGoogle Scholar
- Yoshida T, Yamada Y, Orii T: Electroluminescence of silicon nanocrystallites prepared by pulsed laser ablation in reduced pressure inert gas. J Appl Phys 1998, 83: 5427–5432. 10.1063/1.367373View ArticleGoogle Scholar
- Dumitras DC: Nd YAG Laser. Rijeka: InTech; 2012:318.View ArticleGoogle Scholar
- Shah RR, Hollingsworth DR, DeJong GA, Crosthwait DL: P-N junction and Schottky barrier diode fabrication in laser recrystallized polysilicon on SiO2. Electron Device Lett, IEEE 1981, 2: 159–161.View ArticleGoogle Scholar
- Medvid A, Dmytruk I, Onufrijevs P, Pundyk I: Quantum confinement effect in nanohills formed on a surface of Ge by laser radiation. Phys Status Solidi C 2007, 4: 3066–3069. 10.1002/pssc.200675477View ArticleGoogle Scholar
- Medvid A, Dmitruk I, Onufrijevs P, Pundyk I: Properties of nanostructure formed on SiO2/Si interface by laser radiation. Solid State Phenom 2008, 131–133: 559–562.View ArticleGoogle Scholar
- Medvid’ A, Onufrijevs P, Lyutovich K, Oehme M, Kasper E, Dmitruk N, Kondratenko O, Dmitruk I, Pundyk I: Self-assembly of nanohills in Si1 − x Ge x /Si hetero-epitaxial structure due to Ge redistribution induced by laser radiation. J Nanosci Nanotechnol 2010, 10: 1094–1098. 10.1166/jnn.2010.1849View ArticleGoogle Scholar
- Medvid A, Mychko A, Pludons A, Naseka Y: Laser induced nanostructure formation on a surface of CdZnTe crystal. J Nano Res 2010, 11: 107–112.View ArticleGoogle Scholar
- Medvid’ A, Onufrijevs P, Dauksta E, Kyslyi V: “Black silicon” formation by Nd:YAG laser radiation. Adv Mater Res 2011, 222: 44–47.View ArticleGoogle Scholar
- Medvid’ A: Chapter 2. Laser induced self-assembly nanocones’ formation on a surface of semiconductors. In Laser Growth and Processing. Edited by: Vainos N. London: Woodhead; 2012:85–112.View ArticleGoogle Scholar
- Medvid A, Mychko A, Strilchyk O, Litovchenko N, Naseka Y, Onufrijevs P, Pludonis A: Exciton quantum confinement effect in nanostructures formed by laser radiation on the surface of CdZnTe ternary compound. Phys Status Solidi C 2009, 6: 209–212. 10.1002/pssc.200879869View ArticleGoogle Scholar
- Li J, Lin-Wang : Comparison between quantum confinement effect of quantum wires and dots. Chem Mater 2004, 16: 4012–4015. 10.1021/cm0494958View ArticleGoogle Scholar
- Medvid A: Redistribution of point defects in the crystalline lattice of a semiconductor in an inhomogeneous temperature field. Defect and Diffusion Forum 2002, 210–212: 89–102.View ArticleGoogle Scholar
- Medvid’ A, Onufrijevs P, Dauksta E, Barloti J, Ulyashin AG, Dmytruk I, Pundyk I: P-N junction formation in ITO/p-Si structure by powerful laser radiation for solar cells applications. Adv Mater Res 2011, 222: 225–228.View ArticleGoogle Scholar
- Mada Y, Inoue N: p-n Junction formation using laser induced donors in silicon. Appl Phys Lett 1986, 48: 1205. 10.1063/1.96982View ArticleGoogle Scholar
- Blums J, Medvid A: The generation of donor centres using double frequency of YAG:Nd laser. Phys Status Solidi 1995, 147: K91-K94. 10.1002/pssa.2211470242View ArticleGoogle Scholar
- Kiyak SG: Formation of p-n junction on p-type Ge by millisecond laser pulses. Phys Tech Semiconduct 1984, 18: 1958–1964.Google Scholar
- Claeys C: Germanium-Based Technologies: from Materials to Devices. London: Elsevier; 2007.Google Scholar
- Cheung K, Cheung NW: Extraction of Shottky diode parameters from forward current–voltage characteristics. Appl Phys Lett 1986, 49: 85–87. 10.1063/1.97359View ArticleGoogle Scholar
- Koynov S, Brandt M, Stutzmann M: Black nonreflecting silicon surfaces for solar cells. Appl Phys Lett 2006, 88: 203107–1–203107–3.Google Scholar
- Kosyachenko LA: Solar Cells - Silicon Wafer-Based Technologies. Intech: Rijeka; 2011.View ArticleGoogle Scholar
- Yamamoto K, Sakamoto A, Nagano T, Fukumitsu K: NIR sensitivity enhancement by laser treatment for Si detectors. Nuclear Instr Meth Phys 2010, A624: 520–523.View ArticleGoogle Scholar
- Halbwax M, Sarnet T, Delaporte P, Sentis M, Etienne H, Torregrosa F, Vervisch V, Perichaud I, Martinuzzi S: Micro and nano-structuration of silicon by femtosecond laser: application to silicon photovoltaic cells fabrication. Thin Sol Film 2008, 516: 6791–6795. 10.1016/j.tsf.2007.12.117View ArticleGoogle Scholar
- Liu S, Zhu J, Liu Y, Zhao L: Laser induced plasma in the formation of surface-microstructured silicon. Mater Lett 2008, 62: 3881. 10.1016/j.matlet.2008.05.012View ArticleGoogle Scholar
- Jeon M, Uchiyama H, Kamisako K: Characterization of tin-catalyzed silicon nanowires synthesized by the hydrogen radical-assisted deposition method. Mater Lett 2009, 63: 246–248. 10.1016/j.matlet.2008.10.005View ArticleGoogle Scholar
- Bennett TD, Krajnovich DJ, Grigoropoulos CP, Baumgart P, Tarn AC: Marangoni mechanism in pulsed laser texturing of magnetic disk substrates. J Heat Tran 1997, 119: 589–596. 10.1115/1.2824146View ArticleGoogle Scholar
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