Person: Likovich, Edward Michael
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Likovich
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Edward Michael
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Likovich, Edward Michael
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Publication High-Current-Density Monolayer CdSe/ZnS Quantum Dot Light-Emitting Devices with Oxide Electrodes(Wiley-Blackwell, 2011) Likovich, Edward Michael; Jaramillo, Rafael; Russell, Kasey; Ramanathan, Shriram; Narayanamurti, VenkateshPublication Epitaxial Catalyst-Free Growth of InN Nanorods on c-Plane Sapphire(Springer-Verlag, 2009) Shalish, Ilan; Seryogin, G.; Yi, W.; Bao, J. M.; Zimmler, M. A.; Likovich, Edward Michael; Bell, David; Capasso, Federico; Narayanamurti, VenkateshWe report observation of catalyst-free hydride vapor phase epitaxy growth of InN nanorods. Characterization of the nanorods with transmission electron microscopy, and X-ray diffraction show that the nanorods are stoichiometric 2H–InN single crystals growing in the [0001] orientation. The InN rods are uniform, showing very little variation in both diameter and length. Surprisingly, the rods show clear epitaxial relations with the c-plane sapphire substrate, despite about 29% of lattice mismatch. Comparing catalyst-free with Ni-catalyzed growth, the only difference observed is in the density of nucleation sites, suggesting that Ni does not work like the typical vapor–liquid–solid catalyst, but rather functions as a nucleation promoter by catalyzing the decomposition of ammonia. No conclusive photoluminescence was observed from single nanorods, while integrating over a large area showed weak wide emissions centered at 0.78 and at 1.9 eV.Publication Growth of ZnO Nanowires Catalyzed by Size-Dependent Melting of Au Nanoparticles(Institute of Physics, 2009) Petersen, Eric W.; Likovich, Edward Michael; Russell, Kasey; Narayanamurti, VenkateshWe present a general approach to growing ZnO nanowires on arbitrary, high melting point (above 970 °C) substrates using the vapor–liquid–solid (VLS) growth mechanism. Our approach utilizes the melting point reduction of sufficiently small (5 nm diameter) Au particles to provide a liquid catalyst without substrate interaction. Using this size-dependent melting effect, we demonstrate catalytic VLS growth of ZnO nanowires on both Ti and Mo foil substrates with aspect ratios in excess of 1000:1. Transmission electron microscopy shows the nanowires to be single-crystalline, and photoluminescence spectra show high-quality optical properties. We believe this growth technique to be widely applicable to a variety of substrates and material systems.Publication Weak Localization and Mobility in ZnO Nanostructures(American Physical Society, 2009) Likovich, Edward Michael; Russell, Kasey; Petersen, Eric W.; Narayanamurti, VenkateshWe conduct a comprehensive investigation into the electronic and magnetotransport properties of ZnO nanoplates grown concurrently with ZnO nanowires by the vapor-liquid-solid method. We present magnetoresistance data showing weak localization in our nanoplates and probe its dependence on temperature and carrier concentration. We measure phase coherence lengths of 50–100 nm at 1.9 K and, because we do not observe spin-orbit scattering through antilocalization, suggest that ZnO nanostructures may be promising for further spintronic study. We then proceed to study the effect of weak localization on electron mobility using four-terminal van der Pauw resistivity and Hall measurements versus temperature and carrier concentration. We report an electron mobility of ∼100 cm2/V s at 275 K, comparable to what is observed in ZnO thin films. We compare Hall mobility to field-effect mobility, which is more commonly reported in studies on ZnO nanowires and find that field-effect mobility tends to overestimate Hall mobility by a factor of 2 in our devices. Finally, we comment on temperature-dependent hysteresis observed during transconductance measurements and its relationship to mobile, positively charged Zn interstitial impurities.Publication Magnetoresistance in an Asymmetric GaMnAs Resonant Tunneling Diode(American Physical Society, 2009) Likovich, Edward Michael; Russell, Kasey; Yi, Wei; Narayanamurti, Venkatesh; Ku, Keh-Chiang; Zhu, Meng; Samarth, NitinIn a GaMnAs/AlGaAs resonant tunneling diode (RTD) structure, we observe that both the magnitude and polarity of magnetoresistance are bias dependent when tunneling from a three-dimensional GaMnAs layer through a two-dimensional GaMnAs quantum well. This magnetoresistance behavior results from a shift of negative differential resistance features to higher bias as the relative alignment of the GaMnAs layer magnetizations is changed from parallel to antiparallel. Our observations agree with recent predictions from a theoretical analysis of a similar n-type structure by Ertler and Fabian, and our results suggest that further investigation into ferromagnetic RTD structures may result in significantly enhanced magnetoresistance.Publication Direct Injection Tunnel Spectroscopy of a p-n Junction(American Institute of Physics, 2009) Likovich, Edward Michael; Russell, Kasey; Narayanamurti, Venkatesh; Lu, Hong; Gossard, Arthur C.We demonstrate spectroscopic measurements on an InGaAs p-n junction using direct tunnel injection of electrons. In contrast to the metal-base transistor design of conventional ballistic electron emission spectroscopy (BEES), the base layer of our device is comprised of a thin, heavily doped p-type region. By tunneling directly into the semiconductor, we observe a significant increase in collector current compared to conventional BEES measurements. This could enable the study of systems and processes that have thus far been difficult to probe with the low-electron collection efficiency of conventional BEES, such as luminescence from single-buried quantum dots.