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Low-Frequency Noise and Lateral Transport Studies of In 0.35 Ga 0.65 As/GaAs

Low-Frequency Noise and Lateral Transport Studies of In 0.35 Ga 0.65 As/GaAs Quantum Dot Heterostructures. Vasyl P. Kunets , T. Al. Morgan, Yu. I. Mazur, V. G. Dorogan, P. M. Lytvyn, M. E. Ware, D. Guzun, J. L. Shultz, and G. J. Salamo.

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Low-Frequency Noise and Lateral Transport Studies of In 0.35 Ga 0.65 As/GaAs

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  1. Low-Frequency Noise and Lateral Transport Studies of In0.35Ga0.65As/GaAs Quantum Dot Heterostructures Vasyl P. Kunets, T. Al. Morgan, Yu. I. Mazur, V. G. Dorogan, P. M. Lytvyn, M. E. Ware, D. Guzun, J. L. Shultz, and G. J. Salamo Arkansas Institute for Nanoscale Materials Science and Engineering, University of Arkansas, Fayetteville, Arkansas 72701

  2. Outline • Motivation (low-frequency noise from conductivity fluctuations : from bulk to QDs) • Sample growth (self-assembled quantum dots) • Electronic studies of QD heterostructures • photoluminescence • temperature dependent Hall effect • low frequency noise spectroscopy • Summary

  3. n-type L d Ee - W t V i number of carriers fluctuation mobility fluctuations Origins of Low-Frequency Noise in Bulk Semiconductors motivation

  4. E E thermionic emission GaAs EWL 2D WL InGaAs WL B EF tunneling E0 0D QDs InGaAs QDs x N(E) Low-Frequency Noise in Heterostructures with Quantum Dots multi-layer InGaAs QDs • What conductivity mechanisms are important in the presence of QDs? • Carrier hopping random-telegraph noise • Tunneling in-plane of QDs shot noise • What model (n or ) is valid for 1/f noise in heterostructures with QDs? • Self-assembled heteroepitaxy and the generation-recombination noise motivation

  5. RHEED Measurements for In0.35Ga0.65As 0 ML InGaAs – reference sample FM growth 6 ML InGaAs – QW sample 9 ML InGaAs – QD sample 150 nm GaAs:Si, Nd = 71016 cm-3 11 ML InGaAs – QD sample SK growth 13 ML InGaAs – QD sample N ML In0.35Ga0.65As 20 nm GaAs spacer 20 nm GaAs spacer 500 nm GaAs:Si, Nd = 71016 cm-3 500 nm GaAs buffer GaAs S.I. (001) substrate Growth of QD Heterostructures by Solid Source MBE self-assembled quantum dots

  6. Correlation between AFM Statistical Analysis and Photoluminescence NQD = 3.8  1010 cm-2 height = 34 Å NQD = 8.4  1010 cm-2 height = 47 Å • PL red shift with coverage • PL line-shape correlates with size distribution from AFM NQD = 7.2  1010 cm-2 height = 54 Å • higher density of quantum dots BUT LOWER integral PL intensity Electronic properties of self-assembled quantum dots

  7. 2DEG Donor States Transition from QW to QDs Examined by Temperature Dependent Hall Effect • Transition from bulk GaAs to quantum well and to QDs is observed in mobility vs. temperature trends Electronic properties of self-assembled quantum dots

  8. Noise Spectrum Analyzer SR785 LNA FFT SR560 GPIB LabView RL» Rsample 24 V conduction band NSD e c E0 NSA valence band Deep Level Defects (Low Frequency Noise Spectroscopy) Electronic properties of self-assembled quantum dots

  9. Evolution of G-R Signatures with Varying InGaAs Coverage Defect A, evolution with temperature f = 20 Hz Electronic properties of self-assembled quantum dots

  10. conduction band NSD EF e c E0 Deep Level Energies activation energy energy of the local level below EC Electronic properties of self-assembled quantum dots

  11. Five Different Traps are Resolved and Quantitatively Characterized • The activation energies of all traps, their densities and capture cross sections were obtained Electronic properties of self-assembled quantum dots

  12. Summary, Outcome and Acknowledgements • Lateral transport and noise characteristics of QW and QD heterostructures were studied and compared to bulk GaAs material • Analysis of g-r noise temperature dependence in heterostructures allowed five different traps with activation energies of 0.8 eV, 0.54 eV, 0.35 eV, 0.18 eV and 0.12 eV located in GaAs to be resolved • Trap with EA0.12 eV located in GaAs spacer layer is caused by high deposition of InGaAs • The noise spectroscopy is a very sensitive technique applicable for characterization of nanostructures • This research resulted in the fabrication of infrared-photodetector (9 ML) that can be operated at room temperature (B.S. Passmore, J. Wu, M.O. Manasreh, V.P. Kunets, P.M. Lytvyn, and G.J. Salamo, IEEE Electron Device Letters 29 224 (2008)) • Authors are grateful for the financial support of the National Science Foundation under Grant No. DMR-0520550 summary

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