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Probing Electronic Band Structure and Quantum Confined States in Single Semiconductor Nanowire Devices

Badada, Bekele H

Abstract Details

2016, PhD, University of Cincinnati, Arts and Sciences: Physics.
We have used electrical transport measurements, photocurrent spectroscopy (PC), photoluminescence (PL) and photoluminescence excitation spectroscopies (PLE) to investigate electronic band structure and quantum confined states in single (MOCVD) grown semiconductor nanowires. The nanowires used in this study include Zn2As3, GaAs, GaAsSb, GaAs/AlGaAs core-shell and GaAs/AlGaAs core-multishell (Quantum well tube (QWT)) nanowires. Single nanowire devices were fabricated using photolithography to deposit metal contacts on either end of the nanowire to allow optoelectronic measurements. Electrical transport and photocurrent spectroscopy were used to characterize a novel II-V semiconductor nanowire device, Zn3As2, at room and low (10 K) temperature. Employing metal-semiconductor-metal modeling and self-consistent fitting, we have extracted relevant intrinsic semiconductor parameters from room temperature current-voltage characteristics. The extracted acceptor doping densities for nanowire and nanoplatelate devices are of 1.67×1018cm-3 and 7.41×1018cm-3 respectively. These values agree well with doping densities determined using transient Rayleigh scattering. The photocurrent spectra measurements reported here allow an estimation of the band gap of this material to be 1.13 eV which is in the near-infrared at 10 K. The electronic band structure of single GaAs nanowires was also characterized using photocurrent spectroscopy at room and low (10 K) temperature. In bare 100 nm diameter GaAs nanowire devices we observed the non-linear dark current arising from back-to-back Schottky behavior. We observed saturation of photocurrent as we increased the bias for fixed photon energy above the band gap at room temperature. We attributed this saturation to the diffusion length of minority carriers resulting in the complete extraction of photogenerated carriers at high biases. Photocurrent spectra at 10 K exhibit a peak near the band edge of GaAs ~1.5eV, in both bare GaAs core and GaAs/AlGaAs core-shell nanowire devices. This peak is the signature of an excitonic resonance contributing to below band gap absorption. In addition, the GaAs/AlGaAs photocurrent spectra provide a clear estimation of the Al concentration in the barrier. GaAsSb photocurrent spectra at 10 K were also measured which showed the onset of absorption at 0.9 eV. In addition, a peak observed at ~300meV above the band gap is related to the split off band consistent with a 40 %-45% Sb concentration found using EDX analysis. We explored the nature of exciton localization in single GaAs/AlGaAs QWT devices using PC, combined with simultaneous PL and PLE measurements. Excitons confined to GaAs quantum well tubes of 8 and 4 nm widths embedded into an AlGaAs barrier were seen to ionize at high bias levels. Spectroscopic signatures of the ground and excited states confined to the QWT were seen in PL, PLE, and PC data and were consistent with simple numerical calculations. The demonstration of good electrical contact with the QWTs enabled the study of quantum confined Stark effect shifts in the sharp emission lines of excitons localized to quantum dot-like states within the QWT. Atomic resolution cross-sectional TEM measurements and an analysis of the quantum confined Stark effect of these dots provided insights into the nature of the exciton localization in these nanostructures.
Leigh Smith, Ph.D. (Committee Chair)
Philip Argyres, Ph.D. (Committee Member)
Howard Everett Jackson, Ph.D. (Committee Member)
Frank Pinski, Ph.D. (Committee Member)
112 p.

Recommended Citations

Citations

  • Badada, B. H. (2016). Probing Electronic Band Structure and Quantum Confined States in Single Semiconductor Nanowire Devices [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470043382

    APA Style (7th edition)

  • Badada, Bekele. Probing Electronic Band Structure and Quantum Confined States in Single Semiconductor Nanowire Devices. 2016. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470043382.

    MLA Style (8th edition)

  • Badada, Bekele. "Probing Electronic Band Structure and Quantum Confined States in Single Semiconductor Nanowire Devices." Doctoral dissertation, University of Cincinnati, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470043382

    Chicago Manual of Style (17th edition)