MRS, 2008 Fall Meeting Supported by DMR Grant Low-Frequency Noise and Lateral Transport Studies of In 0.35 Ga 0.65 As/GaAs Studies of In 0.35 Ga 0.65 As/GaAs Quantum Dot Heterostructures 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

MRS, 2008 Fall Meeting Supported by DMR Grant Outline Motivation (low-frequency noise from conductivity fluctuations : from bulk to QDs) elf-assembled quantum dots) Sample growth (self-assembled quantum dots) Electronic studies of QD heterostructures photoluminescence temperature dependent Hall effect low frequency noise spectroscopy Summary Summary

MRS, 2008 Fall Meeting Supported by DMR Grant Origins of Low-Frequency Noise in Bulk Semiconductors motivationn-type L t W V - dd EeEe iiii number of carriers fluctuation mobility fluctuations

MRS, 2008 Fall Meeting Supported by DMR Grant Low-Frequency Noise in Heterostructures with Quantum Dots motivation multi-layer InGaAs QDs E x E0E0 EFEF GaAs InGaAs WL E WL BB tunneling thermionic emission InGaAs QDs N(E) E 0D QDs 2D WL What conductivity mechanisms are important in the presence of QDs? What conductivity mechanisms are important in the presence of QDs? Carrier hopping random-telegraph noise Carrier hopping random-telegraph noise Tunneling in-plane of QDs shot noise Tunneling in-plane of QDs shot noise Self-assembled heteroepitaxy and the generation-recombination noise Self-assembled heteroepitaxy and the generation-recombination noise What model (  n or  ) is valid for 1/f noise in heterostructures with QDs? What model (  n or  ) is valid for 1/f noise in heterostructures with QDs?

MRS, 2008 Fall Meeting Supported by DMR Grant self-assembled quantum dots Growth of QD Heterostructures by Solid Source MBE GaAs S.I. (001) substrate 500 nm GaAs buffer 500 nm GaAs:Si, N d = 7  cm nm GaAs spacer 150 nm GaAs:Si, N d = 7  cm -3 N ML In 0.35 Ga 0.65 As N ML In 0.35 Ga 0.65 As RHEED Measurements for In 0.35 Ga 0.65 As 0 ML InGaAs – reference sample 6 ML InGaAs – QW sample 9 ML InGaAs – QD sample 11 ML InGaAs – QD sample 13 ML InGaAs – QD sample FM growth SK growth

MRS, 2008 Fall Meeting Supported by DMR Grant Correlation between AFM Statistical Analysis and Photoluminescence Electronic properties of self-assembled quantum dots N QD = 3.8  cm -2 height = 34 Å N QD = 8.4  cm -2 height = 47 Å N QD = 7.2  cm -2 height = 54 Å PL red shift with coverage PL line-shape correlates with size distribution from AFM higher density of quantum dots BUT LOWER integral PL intensity

MRS, 2008 Fall Meeting Supported by DMR Grant Electronic properties of self-assembled quantum dots 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 Donor States 2DEG

MRS, 2008 Fall Meeting Supported by DMR Grant Electronic properties of self-assembled quantum dots Deep Level Defects (Low Frequency Noise Spectroscopy) LNAFFT Noise Spectrum Analyzer SR785 GPIB LabView SR V R L » R sample conduction conductionbandvalenceband NSDNSDNSDNSD NSANSANSANSA E0E0E0E0 cccc eeee

MRS, 2008 Fall Meeting Supported by DMR Grant Evolution of G-R Signatures with Varying InGaAs Coverage Electronic properties of self-assembled quantum dots f = 20 Hz Defect A, evolution with temperature

MRS, 2008 Fall Meeting Supported by DMR Grant Deep Level Energies Electronic properties of self-assembled quantum dots NSDNSDNSDNSD E0E0E0E0 cccc eeee EFEFEFEF conduction conductionbandactivationenergy energy of the local level below E C

MRS, 2008 Fall Meeting Supported by DMR Grant Five Different Traps are Resolved and Quantitatively Characterized Electronic properties of self-assembled quantum dots The activation energies of all traps, their densities and capture cross sections were obtained The activation energies of all traps, their densities and capture cross sections were obtained

MRS, 2008 Fall Meeting Supported by DMR Grant Summary, Outcome and Acknowledgements summary 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 E A  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 (2008)) (B.S. Passmore, J. Wu, M.O. Manasreh, V.P. Kunets, P.M. Lytvyn, and G.J. Salamo, IEEE Electron Device Letters (2008)) Authors are grateful for the financial support of the National Science Foundation under Grant No. DMR