docTransmission Electron Microscopy characterization of InAs(Bi)
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Transmission Electron Microscopy characterization of InAs(Bi)
Universidad de Cádiz I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast Transmission Electron Microscopy characterization of InAs(Bi)/GaAs QDs David L. Sales ([email protected]) D. F. Reyes, M. Roldán, S. I. Molina, D. González, F. Bastiman, C. Hunter • Imaging Bi atoms IV. Image simulation II Workshop on Bi-Containing Semiconductors | David L. Sales | 1 | 30 Introduction Previous TEM work in GaAsBi I. Introduction •Previous GaAsBi works • Framework • Molecular beam epitaxy of GaAsBi on (311)B GaAs substrates II. Methodology & Materials • Techniques 1 µm 1 µm (b) • Microscopes • Sample structure (c) GaAsBi GaAsBi II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms GaAs GaAs (001) Z-contrast (311)B IV. Image simulation M. Henini et al. Appl. Phys. Lett. 91, 251909 2007 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 2 | 35 Introduction Previous TEM work in GaAsBi J. F. Rodrigo et al. Applied Surface Science 256 (2010) 5688–5690 I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 3 | 35 Introduction Previous TEM work in GaAsBi D. L. Sales et al. Appl. Phys. Lett. 98, 101902 (2011) I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 4 | 35 Introduction Framework I. Introduction • Materials Science & Engineering Group •Previous GaAsBi works • Computational Intelligence systems • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast STEM Group • Imaging Bi atoms IV. Image simulation 8/14/2011 (Dr. Pennycook’s group) Dr. F. Bastiman II Workshop on Bi-Containing Semiconductors | David L. Sales | 5 | 35 Methodology and materials I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 6 | 35 Methodology & Materials Experimental techniques I. Introduction •Previous GaAsBi works A • Framework II. Methodology & Materials • Techniques B A • Microscopes • Sample structure B B II. (Preliminary) Results • PL C • CTEM C • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 B II Workshop on Bi-Containing Semiconductors | David L. Sales | 7 | 35 Methodology & Materials Transmission electron microscopes I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes JEOL 2010 FEG JEOL 2011 LaB6 JEOL 1200 EX VG-HB603 VG-HB501 NION UltraSTEM II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 Aberration-corrected • Sample structure II Workshop on Bi-Containing Semiconductors | David L. Sales | 8 | 35 Methodology & Materials Sample structure I. Introduction • MBE growth @ Sheffield •Previous GaAsBi works • Framework II. Methodology & Materials 50 nm GaAs • Techniques • Microscopes ≈2.2 ML InAs(Bi) 400ºC • Sample structure II. (Preliminary) Results 580ºC P3: 0% Bi P4: 1% Bi P5: 2% Bi P7: 4% Bi 80 nm GaAs buffer • PL • CTEM • Z-contrast • Imaging Bi atoms (100) GaAs Substrate IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 9 | 35 (Preliminary) Results P1: InAs QW P3: InAsQDs P6: InAs(Bi) QDs (1%Bi) P5: InAs(Bi) QDs (2%Bi) PL I. Introduction •Previous GaAsBi works P2: InAsQDs (500ºC) P7: InAs(Bi) QDs (4%Bi) • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 Sample % Bi λ peak (nm) FWHM (meV) P3 0 1055 69 P4,P6 1 1062 76 P5 2 1065 84 P7 4 1227 53 II Workshop on Bi-Containing Semiconductors | David L. Sales | 10 | 35 (Preliminary) Results Conventional TEM Analysis I. Introduction •Previous GaAsBi works 0% Bi • Framework II. Methodology & Materials 50 nm • Techniques • Microscopes • Sample structure 1% Bi II. (Preliminary) Results • PL 50 nm • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 2% Bi 50 nm 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 11 | 35 (Preliminary) Results Density of planar defects I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast Sample (cm-2) 0% Bi < 5·108 1% Bi < 1.6·109 2% Bi 1.9·109 4% Bi 2·109 Reducing PL intensity • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 12 | 35 Sample P7 (4% Bi) Methodology & Materials HRTEM Analysis Z-contrast TD I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 13 | 30 (Preliminary) Results Basic STEM Analysis I. Introduction •Previous GaAsBi works vacuum • Framework II. Methodology & Materials • Techniques GaAs • Microscopes • Sample structure In(Ga)As(Bi) QDs II. (Preliminary) Results • PL • CTEM • Z-contrast GaAs • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 14 | 35 500 I. Introduction • Framework II. Methodology & Materials • Techniques 2.2 nm 400 x 10^4 Intensity •Previous GaAsBi works 450 50 nm 350 300 GaAs GaAs 250 200 0 10 20 30 40 50 nm 60 70 80 90 100 • Microscopes • Sample structure 5100 II. (Preliminary) Results 5.84 5050 4.58 6.78 13.73 5000 • PL 4950 x 10^3 • CTEM • Z-contrast • Imaging Bi atoms 4900 4850 4800 IV. Image simulation 4750 4700 14/08/2011 20nm 0 5 10 15 20 25 30 35 nm 40 45 50 55 60 65 II Workshop on Bi-Containing Semiconductors | David L. Sales | 15 | 30 (Preliminary) Results Summing up I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL Sample Height (nm) Diameter (nm) 0% Bi 1.7 6.4 1% Bi 1.6 6.1 2% Bi 1.6 6.2 4% Bi 2.3 8.3 • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 Bigger and better developed (faceted) QDs Red-shift contribution II Workshop on Bi-Containing Semiconductors | David L. Sales | 16 | 35 (Preliminary) Results Aberration corrected STEM - HAADF I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 17 | 35 (Preliminary) Results Why HAADF? I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 18 | 35 (Preliminary) Results Why HAADF? I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • For a ternary alloy: – Linear relationship Intensity quotient (R) vs. Composition. • Techniques Re ( x) = 1.005 + 0.229 x • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation Column-by-column compositional mapping by Z-contrast imaging S. I. Molina et al. Ultramicroscopy 109 (2009) 172–176 8/14/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 19 | 35 (Preliminary) Results I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure Element Z Z2 As 33 1089 Bi 83 6889 Ga 31 961 dumbbell + II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 20 | 35 I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques GaAs0.96Bi0.04 • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms (311)B GaAs IV. Image simulation II Workshop on Bi-Containing Semiconductors | David L. Sales | 21 | 30 14/08/2011 I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques GaAs0.96Bi0.04 • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms (311)B GaAs IV. Image simulation II Workshop on Bi-Containing Semiconductors | David L. Sales | 22 | 30 14/08/2011 (Preliminary) Results I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results Element Z Z2 As 33 1089 Bi 83 6889 Ga 31 961 In 49 2401 dumbbell + • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 23 | 35 I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation _ + (Preliminary) Results Image processing I. Introduction •Previous GaAsBi works • Determining R factors: • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL IAs/Bi = R(x) IGa/In • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 Minimize variations due to: • Same local thickness • Same amorphous layer • Same experimental image conditions II Workshop on Bi-Containing Semiconductors | David L. Sales | 27 | 35 I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation Image Simulations The next step… I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes Solving the Schrödinger stationary equation 2 ∆ Ψ + [ Et − Vˆ ] Ψ = 0 2 m0 • Sample structure II. (Preliminary) Results • PL by FFT multislice method (Ishizuka’s code) • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 STEM image simulations II Workshop on Bi-Containing Semiconductors | David L. Sales | 29 | 35 The SICSTEM software A Paralell HAADF-STEM Simulation Sw Workshop on Bi-Containing Semiconductors | David L. Sales | 30 | 35 Cádiz University supercomputer I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation • Hewlett-Packard (2007) – 320 Xeon Woodcrest cores running at 3GHz – 3.75 Tflops (position 327 in Top500 last year) – Each node 8 or 16 Gb RAM – Total RAM = 700 GB – 2.5 TB disk capacity II Workshop on Bi-Containing Semiconductors | David L. Sales | 31 | 35 Image Simulations Create the supercell I. Introduction •Previous GaAsBi works • Framework • 50,600 atoms • 5x5x40 nm II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 32 | 35 Image Simulations I. Introduction •Previous GaAsBi works • Framework • Aprox. time for simulation:12 hours. • High resolution: 182 pix/nm II. Methodology & Materials • Techniques • Microscopes • Sample structure II. (Preliminary) Results • PL • CTEM • Z-contrast • Imaging Bi atoms IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 33 | 35 Image Simulations I. Introduction •Previous GaAsBi works • Framework II. Methodology & Materials • Techniques • Microscopes • • Include 1 Bi atom instead of As in different layers Debye Waller estimations using L.-M. Peng / Micron 30 (1999) 625–648. 99 83 • Sample structure 67 II. (Preliminary) Results • PL 51 35 • CTEM • Z-contrast • Imaging Bi atoms 19 3 IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 34 | 35 Image Simulations I. Introduction •Previous GaAsBi works • Focusing at layer 25 • Detecting Bi at layers 3 and 19 • Framework II. Methodology & Materials • Techniques • Microscopes 99 83 • Sample structure 67 II. (Preliminary) Results • PL 51 35 • CTEM • Z-contrast • Imaging Bi atoms 19 3 IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 35 | 35 Image Simulations I. Introduction •Previous GaAsBi works • Focusing at layer 40 • Detecting Bi at layers 3, 19 and 35 • Framework II. Methodology & Materials • Techniques • Microscopes 99 83 • Sample structure 67 II. (Preliminary) Results • PL 51 35 • CTEM • Z-contrast • Imaging Bi atoms 19 3 IV. Image simulation 14/08/2011 II Workshop on Bi-Containing Semiconductors | David L. Sales | 36 | 35 ¡Muchas gracias! Cádiz (Spain)
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