2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 1EE 235/NSE 203Lec. 10-11• Motivation and Density of states • Quantum Dots– Stranski-Krastanow Self-Assembled QDs• Molecular beam epitaxy (MBE) • Metal-organic chemical vapor deposition (MOCVD)– Colloidal QDs2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 2Density of States1975 : R.Dingle and C.HenryUSA Patent Application1982 : Y.Arakawa and H.Sakaki, Appl. Phys. Lett.,2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 3Fermi-Dirac DistributionElectrons in thermal equilibrium distribute themselves according to the Fermi-Dirac distribution, i.e., the probability fe(E,T) of finding an electron in a state of energy E at a temperature T is given bykBT ~ 26.5 meVµ is Fermi energykBis Boltzmann’s constant.Fermi-Dirac distribution for holes2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 4Electron Energy DistributionThe number of electrons, n(E), per unit energy interval is,X =2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 53-, 2-, 1-, and 0- dimensional SystemsImpact of Inhomog. broadeningThermal populationDimensionalitydensity of statesEnergy 2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 6QW Gain spectra2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 7Threshold Current Densitiesof Semiconductor Lasersafter Ledentsov et al., IEEE J. Sel. Top. Quantum El. 6, 439 (2000)Threshold Current Density (A/cm²)2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 8Epitaxial QD Lasers and SOAs• Application drivers:– Low cost 1.3-1.5 um wavelength lasers and semiconductor optical amplifiers for telecom applications.• Potential advantages– Lasers• Temperature insensitive Æ do not need to add temperature controllers• Low chirp (frequency change with modulation amplitude) Ætransmits through longer distance in optical fibers• High differential gain Æ high speed Æ large transmission bandwidth–SOA• Broad spectral gain (200 nm)• Gain is insensitive to signal power2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 9Lasing oscillation of quantum dot lasers at 1.3Lasing oscillation of quantum dot lasers at 1.3µµmmFuFujitsuFujitsu2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 10High speed modulationINQIE, University of TokyoRCAST&IIS, University of TokyoQuantization of electronic states in semiconductor lasers were dQuantization of electronic states in semiconductor lasers were discussed in 1976. iscussed in 1976. But, electrons have freedom of motions.But, electrons have freedom of motions.Early work on quantum effects in semiconductor lasers)exp()(),,( zikyikxgzyx zy−−=φ)exp(),(),,( zikyxgzyx z−=φQuantum Wire Quantum Wire Quantum Well Quantum Well INQIE, University of TokyoRCAST&IIS, University of TokyoQuantum dots proposed in 1982Experimental demonstrationDH lasers in high magnetic field (1982)QW lasers in high magnetic field (1983)The concept of full confinement broughtartificial atoms in semiconductor devices which can be controlled by current injection.INQIE, University of TokyoRCAST&IIS, University of TokyoAppl.Phys.Lett. 47 (1985) 1099.The first report on SK-grown InAs/GaAs quantum dots2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 14Some facts of QD laser technology development• 1985 Observation of InGaAs clusters in GaAsL. Goldstein, et al, Appl. Phys. Lett. 47(10), 1985 “Growth by molecular beam epitaxy and characterization of InAs/GaAs strained-layer superlattices”,.• 1993 Bright PL intensity from such clustersD. Leonard et al Appl. Phys. Lett. 63(23), 1993• 1994 First lasing with QD active mediumA.Yu.Egorov et al, Semiconductor 28, 1994N.Kirstaedter et al, Electron. Lett. 30, 1994• 1998 1.3 µm QD laser (Atomic Layer Epitaxy)D.L.Huffaker et al, Appl. Phys. Lett. 73(18), 1998• 1999 1.3 µm QD laser (Quantum dots in Quantum Well or DWELLTM)L.F.Lester et al Photon. Technol. Lett. 11(8), 1999A.R.Kovsh et al, Semiconductor, 1999 / Zhukov et al, Appl.Phys.Lett. 75, 1999Quantum Dot start-ups• 2001 ZIA Lasers Ltd, Albuquerque, New Mexico, USA (22 mln USD pumped in) – team from University of New Mexico (Profs.Lester and Malloy)• 2003 NL Nanosemiconductot GmbH (5 mln Euro pumped in) – team from Ioffe Inst. (Prof.Ledentsov)Most cited paper in EL !!!1.3 µm as a driving force for GaAs OE R&D2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 15EE 235/NSE 203Lec. 10-11• Density of states • Quantum Dots: Fabrication and Devices – Stranski-Krastanow Self-Assembled QDs• Molecular beam epitaxy (MBE) • Metal-organic chemical vapor deposition (MOCVD)– Colloidal QDs2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 16MBE technology Pump(ion-, cryo-, turbo-, sublimate-, diffuse-)e-gunHEED screenSubstrateholderShuttersEffusion cellsIon gauge Cryo-shirtsVacuum (1e-10 Tr) is better than in between Earth and MarsD= 1``3``3x2`` or 4``4x8`` or 7x6`` or 15x4``1984198019912000Capacity of a reactor2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 172008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 18Reflection High Energy Electron DiffractionA high energy beam (5-100keV) is directed at the sample surface at a grazing angle. The electrons are diffracted by the crystal structure of the sample and then impinge on a phosphor screen mounted opposite to the electron gun. The resulting pattern is aseries of streaks. The distance between the streaks being an indication of the surface lattice unit cell size.2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 192008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 202008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 21In-situ control by high energy electron diffraction during MBE process2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 22Energy minimization as a driving force2008/4/6 EE 235/NSE203 Nanoscale Fabrication; Lec. 11; Prof. Chang-Hasnain 23Growth, lithography, etching (and regrowth)Growth on high index surfacesGrowth on prepatternedsubstratesStranski-KrastanovgrowthStrain induced lateral confinementFabrication of Nanostructures: Change of Technology ParadigmComplex
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