Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8TEM and XSTM Characterization ofEmbedded InAs Quantum DotsDepartment of Materials Science & Engineering University of California at BerkeleyMatt LowryPresented for NSEC203/EEC235April 16, 2008MotivationDepartment of Materials Science & Engineering University of California at BerkeleyOptical & electrical properties depend on shape, size, composition, and symmetryAFM vs. XSTM vs. TEMChanges due to cappingIn segregationTEM averaging effectsXSTM cleavage planesOptimize growth strategies for potential applicationsGood microscopy is difficultCross-Sectional Scanning Tunneling Microscopy (XSTM)Department of Materials Science & Engineering University of California at Berkeleyhttp://www.insp.upmc.fr/axe1/Dispositifs%20quantiques/AxeI2_more/PRINCIPLE/STSprin.HTMRaster tipI ~ exp (-kz)Image or topographyShape and Size DeterminationDepartment of Materials Science & Engineering University of California at BerkeleyFull and truncated pyramidal quantum dotsCleaved on (110) planesOnly model 2 was observedD.M. Bruls, et al., Appl. Phys. Lett. 81, 1708 (2002).Composition DeterminationDepartment of Materials Science & Engineering University of California at BerkeleyStress relaxes on free surface due to 7% lattice mismatchInxGa1-xAs alloy with linear In gradient60%-100% In gradient from bottom to topLattice constantIncrease of 35pm across dot due to In content increaseD.M. Bruls, et al., Appl. Phys. Lett. 81, 1708 (2002).Multi-Directional Analysis of an Isolated Quantum DotDepartment of Materials Science & Engineering University of California at BerkeleyMulti-directional analysis to detect asymmetriesSplitting of exciton statesInAs dot with GaAs capFocused Ion Beam used to isolate a quantum dot in a micropillar80nm X 80nm pillar with 5nm amorphous regionT. Kita, et al., Appl. Phys. Lett. 90, 041911 (2007).TEM of an Isolated Quantum DotDepartment of Materials Science & Engineering University of California at BerkeleyT. Kita, et al., Appl. Phys. Lett. 90, 041911 (2007). Along [110] : 21nm Along [-110] : 23nmAnisotropic growth due to facetingPreferential strain in [-110]Asymmetry of diffraction patterns [110] Zone Axis [-110] Zone AxisConclusionsDepartment of Materials Science & Engineering University of California at BerkeleyCross-sectional STM has allowed for the determination of shape, size, and composition of InAs quantum dots embedded in GaAs.A combined FIB/TEM approach has allowed for the determination of asymmetric crystal strain in an isolated InAs quantum dot embedded in GaAs.Both procedures are applicable to other systemsBetter characterization will hopefully aid in fulfilling the promise of
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