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Investigation of zincblende, wurtzite, and mixed phase InP nanowires by photocurrent, photoluminescence and time-resolved photoluminescence spectroscopies

Pemasiri, Karunananda
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377873494

Abstract Details

2013, PhD, University of Cincinnati, Arts and Sciences: Physics.
We use photocurrent, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy to investigate the optoelectronic properties of single zincblende (ZB), wurtzite (WZ) and mixed-phase (ZB/WZ) InP nanowires at low temperatures (10K). In this project, InP nanowires were grown by vapor-liquid-solid method using 20nm and 50nm gold nanoparticles as catalyst at 400C. ZB nanowires (50nm), WZ nanowires (20nm) and ZB/WZ mixed-phase nanowires (50nm) were grown at V/III ratios 350, 700 and 700 respectively. PL and TRPL spectroscopy of individual ZB, WZ and ZB/WZ mixed-phase InP nanowires at 10K were studied by exciting single nanowires with a titanium-sapphire laser. From PL and TRPL spectroscopy, we have observed emission at the band edges of ZB and WZ InP at ~1.42eV and 1.504eV respectively, consistent with previous measurements. For ZB/WZ mixed-phase InP nanowires, we observe a change in PL emission energy from the ZB band edge to the WZ band edge as a function of excitation power consistent with the nature of the mixed phase nanowires. TRPL measurements show a dramatic increase of the recombination lifetime from 170ps for excitons in the continuum above the conduction and valence band barriers to more than 8400ps for electrons confined in quantum potential wells defined by monolayer-scale ZB sections and holes confined in quantum potential wells defined by the predominant WZ sections of the nanowire. Using detailed HRTEM measurements from 657nm length of a nanowire, we calculate a complete set of electrons and hole confined states using an eigenfunction expansion method analysis of which demonstrates that the observed energy-dependent dynamics are consistent with the type-II nature of the confined electron and hole wavefunctions. Photocurrent spectroscopy in single InP nanowire devices have been carried out to investigate their electronic band structure. Photolithography was used to fabricate Ohmic Ti/Al contact pads separated by ~4 microns on several ZB or WZ InP nanowires. I-V characteristics confirm highly photosensitive nanowire devices with Ohmic contacts. Using a tunable (1.30-1.75eV) CW-laser, we obtain photocurrent at fixed bias-voltage as a function of excitation energy by broad illumination of the InP nanowire device. At room temperature, we find that the photocurrent for all nanowire devices drops exponentially for photon energies below the fundamental band edge, showing evidence for an Urbach-edge. We find that the WZ energy gap (~1.42eV) is ~70meV above the ZB energy gap (~1.35eV) at 300K, consistent with previous PL measurements. At low temperatures (10K), the ZB device shows strong evidence for excitonic resonance peaks at 1.425eV and 1.539eV relevant to the degenerate heavy and light holes band and the split-off band. The WZ device shows three excitonic peaks at 1.504eV, 1.530eV, and 1.655eV corresponding to the A, B and C valence band energies, respectively. These energies coincide with recent photoluminescence excitation measurements. In some WZ InP nanowire devices, the A, B and C peaks have been observed at ~20-40meV higher energies than above, suggesting a possible quantum confinement in 20nm nanowires. The polarization dependence of photocurrent spectra measured from 275nm ZB nanowire and 20nm WZ nanowire shows very good agreement with theoretical absorption of light by nanowires as a function of diameter and photon energy.
Leigh Smith, Ph.D. (Committee Chair)
Howard Everett Jackson, Ph.D. (Committee Member)
Rostislav Serota, Ph.D. (Committee Member)
L.C.R. Wijewardhana, Ph.D. (Committee Member)
Jan Yarrison-Rice, Ph.D. (Committee Member)
131 p.
Physics
Photocurrent; Photoluminescence; Time-resolved photoluminescence; optical properties; nanowires; spectroscopy

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Citations

  • Pemasiri, K. (2013). Investigation of zincblende, wurtzite, and mixed phase InP nanowires by photocurrent, photoluminescence and time-resolved photoluminescence spectroscopies [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377873494

    APA Style (7th edition)

  • Pemasiri, Karunananda. Investigation of zincblende, wurtzite, and mixed phase InP nanowires by photocurrent, photoluminescence and time-resolved photoluminescence spectroscopies. 2013. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377873494.

    MLA Style (8th edition)

  • Pemasiri, Karunananda. "Investigation of zincblende, wurtzite, and mixed phase InP nanowires by photocurrent, photoluminescence and time-resolved photoluminescence spectroscopies." Doctoral dissertation, University of Cincinnati, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377873494

    Chicago Manual of Style (17th edition)

ucin1377873494
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This open access ETD is published by University of Cincinnati and OhioLINK.