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Nanowires and ultrafast lasers : 2.5 years at the ANU
Transcript of Nanowires and ultrafast lasers : 2.5 years at the ANU
2.5 years at the ANU Patrick Parkinson What is the nanoscale? Introducing ... Nanowires Gold nanoparticle assisted,
Metal-organic-chemical-vapour deposition (MOCVD) How are they made? So, why nanowires? 1D allows for vertical integration into conventional electronics
1D objects can be seen and moved (unlike 0D objects)
Nanowires can be made to be smaller, faster, better and cheaper than bulk components
1 dimensionality is cool! Techniques Nanowires in action Highlights of 2011-2012 Electrically contacted nanowires Quantum tube nanowires Selective growth and positioning Nanolasers Nanowire solar cells Quantum effects
Integration with conventional electronics
Low cost, high efficiency solar cells
Electrically pumped lasers
...Novel physics! Outlook for the future... Take home message: Nanowires have become a crucial tool for fundamental and practical study of emerging nanoscale physics and engineering... Acknowledgements Amira Ameruddin
Jaret Lee Rex Li
Xiaoming Yuan And all of EME and ANFF!
Ubiquitous in modern world
large scale integration
High efficiency (inherent laser cavity) What do our nanolasers look like? So... do we have lasing? 1) Narrow laser linewidth : 2) Laser interference: Ongoing work with three techniques Focussed ion-beam deposition Electron-beam lithography Quick
Can cause damage
Basically useless for either real world or model system devices! At present, can contact ~15 devices per chip. Around 1 day per run.
Both 2 and 4 point probe devices have been made Direct-laser write lithography Also - new techniques for in-situ contacting using direct-laser writing and luminescence
Not strong science, but can contact 1 wire/5mins sucessfully. Only 2 point probe. Quantum tube? Where do we put it? So, does it work? Quantum wells are ultra-narrow, 2-dimensional regions of material where electrons are confined in one dimension... So? Almost ALL modern electronics rely on these!
High frequency transistors
High efficiency laser pointers What if we wrap a quantum well around a wire?
All the advantages of quantum wells
New coupling phenomenon
Of use for nanolasers, too! Nano-everything...
what devices can we make with had great quality nanowires? What would a nanowire solar cell look like? Can we really do this? our nanowires grow randomly on the substrate ... is there anything we can do? Selective-area grown MOCVD MOCVD growth - introduce the chemicals needed to make the nanowires, like Gallium and Arsenic, or Indium and Phosphine as two gases.... and wait for the chemical reaction How about an analogy? 6um Scanning electron micrograph Nanowire 'core' Nanowire 'shell' Nanowire 'cap' Optical microscope image (1000x) A huge number of modern devices rely on quantum wells!
LEDs, lasers, photodetectors... and more BCB (plastic) Nanowire tips peeking through... Solar cell power comes from the wires Thanks Qian! More blue More red Transmission Electron micrograph 50nm Gold 'seed' Meter scale
Humans x1000 - mm scale
Ants x100,000 - 10 micrometer scale
Human Hair x1Million - 1 micrometer scale
Red blood cells x10 Million - 100nm scale
HIV Virus Nanotechnology! Why do we care?
We want access to new physical, chemical, engineering and biological regime.
We need to be able to fabricate and control things on this length scale. Small things can be inherently cheap, fast, and...small! Gain medium Below threshold Above threshold Yes - although requires advanced traditional micro-electronics techniques. Advantages include uniformity, precise positioning more complex structures... Why nanolasers? and they are a great playground for exploring the nanoworld! x1 Billion - atoms University of Warwick, UK and IBM Zurich Normal nanowire 'Quantum tube' wire SURFACE AREA low power lasing! ANU Reactor People : Fu Lan, Hao Wang People involved: Fu Lan, Qian Gao, Kun Peng, Ian Wenas People involved: Me, Kun Peng IOP Nanotechnology 23, 335704 Study (currently undergoing review)
Can we make nanowire PVs better using longer lifetime nanowires? Device 1: Old best NWs
Device 2: New best NWs Where is the extra current coming from? Use multiphoton photocurrent microscopy. Carriers are generated using two photon absorption to give 3D photocurrent map: Carrier Lifetime optimisation Growing method Diameter (d) Lifetime (τ) Smax (cm/s) *Ref
Au (MOCVD) 50 nm 1.8 ± 0.1 ns 6.9 × 102 Here
Au (MOCVD) 50 nm 30 ps 4.2 × 104 P. Parkinson
Au (MOCVD) 50 nm 1.02 ± 0.42 ns 1.3 × 103 N. Jiang2SA (MOCVD) 90 nm 1.3 ns 1.7 × 103 C. Chang27Au (MBE) 106 ± 18 nm 9 ± 1 ps 2.9 × 105 S. Breuer22Au(MBE) 40 nm 0.8 ns 1.25 × 103 L. Ahtapodov29
Ga (MBE) 150 ± 25 nm 2.5 ± 0.1 ns 1.5 × 103 S. Breuer22Ga (MBE) 80 ~ 180 nm 1.5 ± 0.3 ns 1.6 × 103 L. Prechtel 31** An ongoing feature - better quality nanowires are needed for optoelectronic behaviour. Two paths:
Improve the core
Reduce the surface recombination velocity through passivation Where are we at? Concentrate on shell growth Less dependance upon shell thickness, stronger correlation in shell time (left) 3min shell growth (right) 8min growth In conclusion... GaAs/AlGaAs core-shell nanowires with carrier lifetime of 1.9ns at room temperature can be fabricated - approaching bulklike
It appears that interface quality is of critical importance for this application; it seem that this is determined by shell growth time and interdiffusion arising from this APL99, 234106 + Manuscript in Preparation Manuscript with referees... Manuscript in preparation Time-resolved photoluminescence
measurements Photoconductivity of nanostructures Single nanowire devices New results = technique + materials (+theory) Materials Raw materials:
GaAs/InGaP (oxygen resistant passivation) Micro-PL Photocurrent Non-linear effects