Nanoscience galore: hybrid and nanoscale photonics

Transcription

1 Nanoscience galore: hybrid and nanoscale photonics Pavlos Lagoudakis SOLAB, 11 June 2013

2 Hybrid nanophotonics Nanostructures: light harvesting and light emitting devices 2

3 Hybrid nanophotonics Nanostructures: light harvesting and light emitting devices Hybrid semiconductor materials:. epitaxial heterostructures/bulk crystals. colloidal QDs and/or organic semiconductors 3

4 Bulk, organic and colloidal nanocrystal semiconductor materials molecule nanoparticle bulk solid LUMO conduction band energy E E E g HOMO valence band H 2 C HO O CH HC CH HC O CH 2 OH 5 nm

5 Utilise best of both worlds Colloidal QDs/organic High absorption Color tunability High quantum yield Low cost Low carrier mobility Epitaxial Semiconductors High carrier mobility

6 Hybrid nanophotonics Nanostructures: light harvesting and light emitting devices Hybrid semiconductor materials:. epitaxial heterostructures/bulk crystals. colloidal QDs and/or organic semiconductors Energy transfer between constituents:. radiative pumping. non-radiative dipole-dipole coupling (RET) RET: Resonance Energy Transfer 6

7 Resonance Energy Transfer

8 Hybrid semiconductor nanostructures Phys. Rev. Lett. 102, (2009) Appl. Phys. Lett. 94, (2009) Advanced Materials 22, (5) 602 (2010) Physical Review Letters 107, (2011) organic-inorganic, colloidal-epitaxial semiconductors weak coupling of electronic transitions 9

9 (rate R -6 ) 10

10 Non-radiative energy transfer (RET) Hu et al Quarterly reviews of biophysics 35,1 (2002) LUMO acceptor Donor QW CB ET HOMO VB Energy transfer rate H. Kuhn, J. Chem. Phys. 53, 101 (1970). overlap between donor emission and acceptor absorption R n n=6 for point dipoles n=2 2D to 2D 14

11 Hybrid QW/nanophosphor LEDs 16

12 QW excitations: unbound electron hole pair regime 18

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14 Exciton Transfer in Hybrid Heterostructures (a) CdS ET QW + _ + _ ET k ET ET efficiency: 60K k r Energy Rohrmoser et al Applied Physics Letters 2007

15 QW excitons to J-band excitons Energy transfer rate: A: 4nm B: 6.5nm Population decay (photoluminescence) A: 4nm η A =0.23 and η B =0.39 black QW only red hybrid 25

16 Hybrid Heterostructures in NIR tracking energy transfer at the acceptor site Time correlated single photon counting surface states black organic only red hybrid dashed model Coupled states through non-radiative energy transfer from quantum wells to organic emitter describe transfer dynamics to acceptor (dashed line): Chanyawadee all rates are derived from photoluminescence and fluorescence decay measurements 26 Chanyawadee et al PRB 2008

17 Testing the concept of dimensionality 28

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27 Excitons in the QW potential landscape free exciton (2D) with wave vector k Potential landscape of imperfect QW localized exciton (0D) with localization length Lloc Rindermann et al Phys Rev Lett 107,

28 Resonance Energy transfer vs exciton localisation 41

29 Hybrid QD/QW structure NCs QW energy transfer rate minimum barrier width R n patterned QW shorter donor-acceptor distance 43

30 Hybrid colour conversion LED 2 µ m Surface-textured LEDs PL 457 nm Colloidal QDs FL 618 nm PL Intensity (arb. units) Absorption (arb. units) Chanyawdee et al; Advanced Materials 22, (5) Wavelength (nm)

31 Fluorescence decay of QDs Unetched QWs: no RET Etched QWs: RET enabled Chanyawdee et al; Advanced Materials 22, (5)

32 Fluorescence decay of QDs ket ( kqw + ket ) t knct It () ( e e ) k k k NC QW ET Carrier injection due to nonradiative energy transfer Chanyawdee et al; Advanced Materials 22, (5)

33 Hybrid colour conversion LED GB patent Unetched QWs + QDs Etched QWs + QDs 47

34 Hybrid LED with F8BT blue and yellow complimentary colours: --->mix white shallow-etched LED deep-etched LED

35 Hybrid photovoltaics Carrier generation QD layer organic/ncs p-doped layer intrinsic layer n-doped layer Energy transfer Radiative energy transfer Nonradiative energy transfer Carrier extraction pin heterostructure 49

36 Hybrid QD/patterned QW structure 850 nm p+ GaAs p+ AlGaAs i- AlGaAs i- MQW 1350 nm 80x80 mm 2 pattern 20 µ m 2 µ m i- AlGaAs channels n+ GaAs 570 nm width 1.4 µm depth Chanyawadee et al Physical Review Letters 102,

37 Photoluminescence decay of QWs PL Intensity (norm.) flat QW patterned QW QDs + patterned QW Time (ns) Longer rise time indicates energy transfer nqdi (0) keti ( kqdi + keti ) t kqw t I( t) = ( e e ) + f ( t) QDs passivate k k channel k surface QW QDi ETi Chanyawadee et al Physical Review Letters 102,

38 Photocurrent conversion efficiency S ( 1 a H P ) I = I e I a P C 6-fold enhancement of photocurrent conversion efficiency 64% generated from nonradiative energy transfer Chanyawadee et al Physical Review Letters 102, Chanyawadee

39 Hybrid NC/patterned bulk GaAs device 760 nm p+ GaAs p+ AlGaAs p+ GaAs i- GaAs 1850 nm n+ GaAs photoluminescence peak of CdTe NCs : 734 nm PIN device : 823 nm Chanyawadee et al; Applied Physics Letters 94,

40 Hybrid NC/patterned bulk GaAs device RT photocurrent increases in hybrid structures photocurrent enhancement is higher in patterned device Chanyawadee et al; Applied Physics Letters 94,

41 Outlook: RET optoelectronic devices Photovoltaics Silicon HPVs (TSMC), surface treatment, organic sem., blends Lighting application surface passivation/surface-textured LEDs, organic phosphors, organic/qd lasers 55

42 Acknowledgements Laboratories for Hybrid Optoelectronics the people Martin Charlton: Nano-fabrication Industrial collaborations: IBM-Zurich, Luxtaltek, Q-cells David Lidzey (The University of Sheffield) Ian Watson, Martin Dawson (Univ. Strathclyde) Mohamed Henini (University of Nottingham) Dmitry Talapin (University of Chicago) Horst Weller (University of Hamburg) Andrey Rogach (University of Hong Kong) Alexander Eychmuller, (Uni of Dresden) Hiroshi Amano (Nagoya Uni, Japan) Galia Pozina GaN nanofabrication Optical spectroscopy Microscopy Funding: EU-FP7: ITN-Icarus, NoE Nanophotonics for energy efficiency 56