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MOVPE Droplets Heteroepitaxial Growth Model S. Shusterman E. Cohen, N. Elfassy, D. P. Kumah, Y. Yacoby, R. Clarke, Y. Paltiel Q 3 N Applied Physics Department Center for nano science and nano technology, HUJI, Israel E L a b Quantum Nano Engineering Lab 9/17/2020
Motivation and Goal • Self-assembled quantum dots (SAQDs) Scientific and applicative interest Fine tuning of their opto-electronic properties Size, shape, chemical composition, strain fields Growth process 4 Q 4 N E L a b Quantum Nano Engineering Lab 9/17/2020
Outline • DHE growth mode. • Critical issues and possible problems • Characterization methods – HR TEM + Peak Pair Algorithm (PPA) – Kelvin Probe Force Microscopy (KPFM) – X-ray Coherent Bragg Road Analysis (COBRA) • DHE growth model Q 5 N E L a b Quantum Nano Engineering Lab 5 9/17/2020
Stranski-Krastanov growth mode surface free energy of deposited material surface free energy of substrate interface energy strain energy of the layer S-K growth method can be useful for materials systems with 5 -7% lattice mismatch Q 6 N E L a b Quantum Nano Engineering Lab 6 9/17/2020
Droplet hetero-epitaxy (DHE) growth mode • First stage of the growth: low melting point group II- III- or IV element nano-droplets formation on the substrate. • Second stage of the growth: N. Koguchi, et al, J. Cryst. Growth, 111, 688, (1991). T. Mano, et al, Jpn. J. Apll. Phys. 33, 4580 (2000). V. Mantovani, et al, J. Appl. Phys. 96, 4416 (2004). Q 7 N reaction of these droplets with one or more group V- or VI elements in the gas phase (liquidphase-epitaxy-like crystallization) E L a b Quantum Nano Engineering Lab 7 9/17/2020
Parameters that influence optical and electrical properties • Size and shape of QD – Band gap change due to Quantum effect – Shift from direct to indirect transitions • Composition – Band gap and offset change due to elements intermixing • Crystalline structure • Presents of strain and growth defects – Band gap change due to different ordering – Band gap variations due to strain we need methods for characterization and control composition and strain with sub nanometer resolution! Q 8 N E L a b Quantum Nano Engineering Lab 8 9/17/2020
Droplet Hetero-Epitaxy (DHE) In. Sb/Ga. As In. As/Ga. Sb 30 nm In. Sb/In. Sb 30 nm (high density) 40 nm 200 nm (low density) 200 nm Q 9 Highly strained N E L a b Low strain Quantum Nano Engineering Lab 500 nm No strain 9 9/17/2020
Dot’s characterization by TEM c) c) (a) HRTEM image of DHE dot The growth is epitaxial, concave shape of dot (b) The dot lattice constant calculated from FFT is different from expected 1 – Ga. As substrate a. Ga. As=5. 74± 0. 02 Å, 2 – QD a. Dot = 6. 06± 0. 03 Å (a. In. Sb= 6. 479 Å a. In. As= 6. 058 Å) 3 – Ga. As cap layer acap = 5. 73± 0. 04 Å. Q N E 10 L a b Quantum Nano Engineering Lab 10 9/17/2020
Strain determined using Peak Pairs algorithm 1) Misfit dislocations 2) Strain distribution a) 3 z 2 3 x z Q 11 Nx E L a b 1 P. L. Galindo, 11 et al, Quantum Nano Engineering Lab 9/17/2020 Ultramicroscopy, 107, 1186 (2007).
Strain determined using Peak Pairs algorithm a) a) b) z z x x (a) Displacement fields map in X direction. (b) Displacement fields map in Z direction. The different colors in dot-substrate interface in X and Z maps indicate the presence of strain. Q N E 12 L a b S. Shusterman, A. Raizman, A. Sher, Y. Paltiel, A. Schwarzman, O. Azriel, A. Boag, Y. Rosenwak P. L. Galindo, Europhys Letters 88 66003 (2009). 12 Quantum Nano Engineering Lab 9/17/2020
Contact potential difference (CPD) Q N E 13 L a b Quantum Nano Engineering Lab 13 9/17/2020
In. Sb nano-dots grown on In. Sb (unstrained system) topography Q N E 14 L a b CPD S. Shusterman, A. Raizman, Y. Paltiel, A. Sher, A. Schwarzman, E. Lepkifker and Y. Rosenwaks, Nanoletters, 7, 2089 (2007). Quantum Nano Engineering Lab 14 9/17/2020
In. Sb nano-dots on Ga. As (strained hetero-system) topography CPD QS. Shusterman, A. Raizman, Y. Paltiel, A. Sher, A. Schwarzman, E. Lepkifker and Y. Rosenwaks, N E 15 L a b Nanoletters, 7, 2089 (2007). Quantum Nano Engineering Lab 15 9/17/2020
Simple CPD calculation First SC material (In. Sb in our case): =4. 07 e. V =4. 06 e. V Eg 1 – In. Sb band gap , Ga. Sb =4. 59 e. V 1 – In. Sb affinity Second SC material (substrate): Eg 2 – substrate band gap, 2 – substrate affinity, =4. 90 e. V 0. 73 e. V In. Sb 0. 18 e. V In. As Ga. As 0. 35 e. V 1. 42 e. V offset - valence band offset of In. Sbsubstrate system Q N E 16 L a b Quantum Nano Engineering Lab 16 9/17/2020
Comparison of the simulated and the measured CPD Q N E 17 L a b S. Shusterman et al. , Nanoletters, 7, 2089 (2007). Quantum Nano Engineering Lab 17 9/17/2020
Summary so far • DHE is a very flexible method • Dots of different sizes and composition can be grown on any substrate. • HRTEM results show that the growth is complicated (strain dislocations, composition change) • Kelvin probe gradient of composition and strain We need a non destructive method to map these effects within sub nano resolution Q N E 18 L a b Quantum Nano Engineering Lab 18 9/17/2020
Surface X-ray diffraction n Surface X-ray diffraction (SXRD) ¨ Phase problem ¨ Direct phase retrieval Detailed atomic structure Walther et al. Phys. Rev. Lett. 86, 11 (2001) methods Keizer et al. App. Phys. Lett 96, 6 (2010) Q N E 19 L a b Quantum Nano Engineering Lab 19 9/17/2020
COBRA (Coherent Bragg Rod Analysis) • Total electron density consists of: – Substrate with known structure – Epitaxial layer with unknown electron density • Assumption: unknown part varies slowly relative to the known part Q N E 20 L a b Quantum Nano Engineering Lab 20 9/17/2020
COBRA (Coherent Bragg Rod Analysis) • What we get? Electron density “folded” in 2 dimensions to substrate-defined unit cell n Anomalous scattering Height Q N Electron Density E 21 L a b Quantum Nano Engineering Lab 21 9/17/2020
Results – In. As/Ga. As Group IIIVelements Group elements(Ga/In) (As) 0. 5 Ga K-Edge (Ebeam=10. 36 ke. V) As K-Edge (Ebeam=11. 86 ke. V) Electron Density [a. u. ] 0. 4 G-III (In/Ga) 0. 2 0. 1 0 -30 Q N G-V (As) 0. 3 E 22 L a b -20 -10 0 10 Height [angstrom] 20 30 Cohen et al. App. Phys. Lett. 98, 24 22 (2011) Quantum Nano Engineering Lab 40 9/17/2020
Results – In. As/Ga. As 1 x (In Concentration) • Substrate/dot materials intermixing 0. 5 0 In. As -20 Q N 0 10 20 Height [angstrom] E 23 L a b Ga. As -10 Quantum Nano Engineering Lab 23 30 9/17/2020
Results – In. As/Ga. As Group III elements (Ga/In) r 1 Electron Density [a. u. ] 0. 5 r 2 0. 4 0. 3 0. 2 Tersoff Phys. Rev. B 63, 20 Spencer, (2001) 0. 1 0 -30 Q 24 N E L a b -20 -10 0 10 Height [angstrom] 20 30 40 Shusterman et al. EPL 88, 6 24 (2009) Quantum Nano Engineering Lab 9/17/2020
Results – Other Systems • In. Sb/Ga. As n In. As/Ga. Sb (lattice matched system) Kumah et al. Nat. Nano 4 (2009) Eyal Cohen et al. (2012) Q N E 25 L a b Quantum Nano Engineering Lab 25 9/17/2020
Growth Model • In. Sb/Ga. As (1) (2) (3) Q n In. As/Ga. Sb (lattice matched system) (1) (2) (3) (4) N 26 E 26 L a b Quantum Nano Engineering Lab 9/17/2020
Conclusions • Droplet Hetero-Epitaxy is very fixable and sensitive to surfactants, temperature, intermixing • We have developed new arsenal of unique methods to characterize self-assembled quantum dots; Kelvin probe, Non-destructive COBRA, HRTEM pair peak algorithm. • A detailed growth model enables the growth control Q N E 27 L a b Quantum Nano Engineering Lab 27 9/17/2020
Many thanks to http: //aph. huji. ac. il/people/paltiel/index. html Our Group: Dr. Shira Yochelis, Naomi Elfassy, Eyal Cohen, Eran Katzir , Avner Neubauer, Ayelet Strauss, Guy Koplovitz, Oren Ben Dor, Odelya Koslovsky, Yaalat Chen. Zohar, Ido Eisnberg, Yuval Shifriss, Ohad Westrich And Sergey Shusterman Applied Physics Division, Solid State Physics Group, Soreq NRC, Israel Yizhak Yacoby, Racah Institute of Physics, HUJI Roy Clarke, Divine Kumah, Naji Husseini, Chris Schelpütz, Yongsoo Yang, University of Michigan, Ann Arbor, MI Financing: , ISF-BICORA, DARPA, MOD, Israel Taiwan, Magneton Capital Nature , FTA and Peter Brojde center Q N E 28 L a b Quantum Nano Engineering Lab 9/17/2020
Let Us Meet Again We welcome all to our future group conferences of Omics group international Please visit: www. omicsgroup. com www. Conferenceseries. com http: //optics. conferenceseries. com/ Q N E 29 L a b Quantum Nano Engineering Lab 9/17/2020
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