laser diodes - Graz University of Technologyhadley/psd/lectures16/jan31.pdf · Spontaneous emission...
Transcript of laser diodes - Graz University of Technologyhadley/psd/lectures16/jan31.pdf · Spontaneous emission...
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laser diodes
http://www.aliexpress.com/item/445nm-laser-diode/767127021.html
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Spontaneous emission
Spontaneous emission dominates in fluorescent lighting and light emitting diodes. In a gas, the conservation of momentum is easily maintained. For a semiconductor, a direct bandgap material is necessary.
Recombination time = 1/W Recombination rate
2 1h E E
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Stimulated emission
Stimulated emission is responsible for the coherent light of lasers.
Wstimulated() =Wspontaneous() . nph()
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Optical cavity
https://en.wikipedia.org/wiki/Laser_construction#/media/File:Lasercons.svg
http://www.jinsunglaser.com/content.php?db=m2_2&prod=30&no=84&page=1
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Laser diode
The faces of the crystal are cleaved to make mirrors.
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Vertical-cavity surface-emitting laser (VCSEL)
http://wwwold.fi.isc.cnr.it/users/giovanni.giacomelli/Semic/Samples/samples.html
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laser diodes
Ibach & Lueth, Solid-State Physics
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Stimulated emission
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Quantum cascade lasers
Energy levels depend on the width of the wells so lasers can be made at many frequencies (mid to far infrared 2.75 - 250 m). Many colors can be made with one materials system.Window in atmosphere at 5 m used for point-to-point communications.
Quantum wells
e Tunneling
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Quantum cascade lasers
http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=1096486
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Galaxy Tab
Encapsulation technology
OLEDs
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Prof. Günther Leising
Electroluminescence in poly(p-phenylene)
poly(3-hexylthiophene)
In 1992, Leising et al. for the first time reported on blue electroluminescence from OLEDs containing poly(p-phenylene) (PPP).
G. Grem, G. Leditzky, B. Ullrich and G. Leising, Adv. Mater. vol.4 p. 36 (1992).
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OLEDs
GlassITO anode
Aluminum cathode
Cathode is typically a low work function material Al, Ca - injects electrons
Anode is typically a high work function material ITO - injects holes
Cathode
Anode
Eg
Hole transport layer
Electron transport layerEmission layer
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Q-dot LEDs
Coe-Sullivan, et al. Advanced Functional Materials, 10.1002/adfm.200400468
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Nanoparticle OLEDs
Appl. Phys. Lett. 92, 183305 (2008)
Semiconductor nanosphere (Me-LPPP) OLEDs
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Efficient lighting
Very efficientMany colors possibleNo toxic chemicals
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Flexible, transparent, wearable displays
Folding displayTransparent AMOLED
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Equivalent circuit
Solar cell
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Solar spectrum
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Shockley–Queisser limit
http://en.wikipedia.org/wiki/Shockley-Queisser_limit
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Biofuel efficiency ~ 1%Grid parity will be reached in the next 10 years
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Perovskite solar cells
methylammonium lead trihalide ABX3CH3NH3PbX3, where X is I, Br or ClOptical bandgap 1.5 - 2.3 eV
+ Cheaper to fabricate than Si solar cells. (silicon cells require > 1000 C)
- Contains leadAlso less efficient CH3NH3SnI3 version
- Not stable
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Printable solar cells
Konarka CD labor - TU Graz
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organic solar cells
http://www-ssrl.slac.stanford.edu/science-highlight/2011/january/effects-thermal-annealing-morphology-polymer%E2%80%93fullerene-blends-organic
Excitons
Bulk heterojunction
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Organic microprocessor
Institute of Solid State PhysicsTechnische Universität Graz
A modern desktop computer has the processing power of a mosquito brain.