Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B50: Semiconductor Nanowires: Optical and Electronic Properties |
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Sponsoring Units: DCMP Chair: Roberto Myers, The Ohio State University Room: Mile High Ballroom 1D |
Monday, March 3, 2014 11:15AM - 11:27AM |
B50.00001: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 11:27AM - 11:39AM |
B50.00002: Carrier dynamics in silicon nanowires studied using optical-pump terahertz-probe spectroscopy Alexandre Beaudoin, Bassem Salem, Thierry Baron, Pascal Gentile, Denis Morris The advance of non-contact measurements involving pulsed terahertz radiation presents great interests for characterizing electrical properties of a large ensemble of nanowires. In this work, N-doped and undoped silicon nanowires (SiNWs) grown by chemical vapour deposition (CVD) on quartz substrate were characterized using optical-pump terahertz probe (OPTP) transmission experiments. Our results show that defects and ionized impurities introduced by N-doping the CVD-grown SiNWs tend to reduce the photoexcited carrier lifetime and degrade their conductivity properties. Capture mechanisms by the surface trap states play a key role on the photocarrier dynamics in theses small diameters' ($\sim $100 nm) SiNWs and the doping level is found to alter this dynamics. We propose convincing capture and recombination scenarios that explain our OPTP measurements. Fits of our photoconductivity data curves, from 0.5 to 2 THz, using a Drude-plasmon conductivity model allow determining photocarrier mobility values of 190 and 70 cm$^{2}$/V$\cdot $s, for the undoped and N-doped NWs samples, respectively. [Preview Abstract] |
Monday, March 3, 2014 11:39AM - 11:51AM |
B50.00003: Field-effect transistors based on Si:P nanowires with axially graded doping Jorge Barreda, Timothy Keiper, Mei Zhang, Peng Xiong Phosphorus-doped Si nanowires (NWs) have been synthesized via the vapor-liquid-solid method. Local electrical transport measurements along the length of the NWs reveal a systematic reduction of the electrical conductivity in the growth direction. These results, along with structural characterizations by SEM and AFM, point to a graded doping profile along the length of the NWs [1] as the origin of the spatial variation of the electronic properties. Due to the inherent doping gradient, Cr/Au and Cr/Ag contacts on the NWs evolve systematically from ohmic contacts on the highly-doped side (where growth starts) to Schottky junctions on the lower-doped side (where growth ends). Field-effect transistors (FETs) have been fabricated from individual as-grown Si NWs. By patterning a series of electrodes along the length of a NW, both channel-limited and Schottky barrier-limited devices were obtained from a single NW. In particular, by using two electrodes located at opposite ends of a NW, FETs limited by a single Schottky junction were consistently realized. These devices, in which the Schottky junction acts as the drain terminal and the ohmic contact as the source terminal, exhibit excellent gate modulation due to the tuning of the Schottky barrier. [1] Daniel E. Perea et al., Nature Nanotechnology 4, 315-319 (2009). [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B50.00004: Quasiballistic hole transport in Ge/Si core/shell nanowires Dharmraj Kotekar Patil, Zhaoen Su, Binbin Tian, Minh Nguyen, Jinkyoung Yoo, Shadi Dayeh, Sergey Frolov We investigate low temperature hole transport in Ge/Si core/shell nanowires. We study devices with annealed (Ni) and unannealed (Ti/Al) contacts. We observe Coulomb blockade and analyze the capacitive and quantum energy scales in Ge/Si nanowire quantum dots. In devices with Ni contacts, we study diameter and shell thickness dependence on hole mobility at low temperature. We observe Fabry-Perot oscillations indicating a quasi-ballistic transport regime. We also investigate subband-resolved transport of holes as a function of magnetic field magnitude and orientation. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B50.00005: Analysis of spin-orbit coupling effects in the Pt-Si nanowires on Si(110) surface Sehoon Oh, Hyungjun Lee, Hyoung Joon Choi We study Pt-induced nanowires on Si(110) surface by using an ab-initio pseudopotential density-functional method. A thick slab of Si atoms is considered with Pt atoms added on the Si surface. Atomic structures of Pt-induced nanowires are determined by the total-energy minimization. We calculate surface band structures near the Fermi level and simulate scanning tunneling microscopy (STM) images and angle-resolved photoemission spectra (ARPES). We analyze the effects of the spin-orbit interaction on the electronic structure qualitatively as well as quantitatively. This work was supported by NRF of KOREA (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2013-C3-008). [Preview Abstract] |
Monday, March 3, 2014 12:15PM - 12:27PM |
B50.00006: Substrate effect on the band gap of semiconducting atomic wires Adam J. Simbeck, Saroj K. Nayak The electronic structure of free-standing and supported semiconducting atomic wires is investigated using a combination of first-principles density functional theory (DFT) and many-body perturbation theory (MBPT). The band gaps predicted from DFT for SiH$_{\mathrm{2}}$ and GeH$_{\mathrm{2}}$ atomic wires are unaffected by the presence of the substrate, whereas the gaps calculated using MBPT under the \textit{GW} approximation are reduced by about 1eV when the wires are supported. The reduction in the band gap is attributed to a change in the electronic correlation energy, which can be understood as a screened Coulomb interaction. These results highlight the importance of the role played by the substrate in manipulating the electronic and optical properties of quantum confined Si and Ge systems. [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B50.00007: Optical and Electrical Characterization of Quantum Dots Decorated ZnO Nanowires for Energy Conversion Richard Mu, Anthony Mayo, Haiyang Xu, Yichun Liu Significant progress has been made recently in understanding optoelectronic properties of metallic and semiconducting quantum dots and their interactions with their surrounding nano-environments. It is shown that nanostructured photovoltaic devices do have clear advantages over the bulk counterparts to address energy challenges facing humanity. They require much less mass, not exclusively limited by materials of choice, and favoring integration for multifunctionality to be able to effectively harvest solar energy by tuning the optical gap and enhancing photon absorption across section through various nanomaterials syntheses. The other challenge is to be able to purposely control and manipulate the energy transfer pathways for particular needs. As for nanostructured photovotaic devices, charge and exciton transports must be carefully evaluated. The knowledge of charge and exciton mobility, coherent and incoherent hopping due to electronic coupling, energy redistribution and partition in may be the critical steps. CdTe and Si functionalized bare ZnO nanowires, and core/shell have been fabricated with Glazing Angle Deposition technique as the model systems. A series materials characterization techniques (confocal Raman, optical, photoluminancence and electrical) have been conducted to provide valuable information about the nanostructure. Results will be presented and discussed along with their scientific implications. [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B50.00008: Size and strain dependence of electronic properties in ultrathin ZnO nanowires Xihong Peng, Andrew Copple, Qun Wei One dimensional nanostructures of group II-VI semiconductors, in particular ZnO, have drawn broad research interests in recent years due to their potential applications in nano-electronics and nano-optics. In this project, electronic structures of ultrathin wurtzite ZnO nanowires were studied using first-principles Density Functional Theory (DFT) calculations. It was found that the nanowire axial lattice constants shrink compared to that of bulk ZnO. The band gap opens for small nanowires due to the quantum confinement effect. In addition, the band gap can be further tuned using uniaxial strain. The effective masses of the electron and the hole in ZnO can be manipulated not only by the size of nanowire, but also through the applied strain. The results were cross checked using different DFT methods, including GGA, DFT$+$U, and hybrid functionals. [Preview Abstract] |
Monday, March 3, 2014 12:51PM - 1:03PM |
B50.00009: Insights into Optical Quality of GaAs/AlGaAs MOCVD Nanowires Yi-Hsin Chiu, Nicholas G. Minutillo, Greg Smith, John A. Carlin, Ezekiel Johnston-Halperin, Fengyuan Yang GaAs nanowires (NWs) are promising candidate materials for future optoelectronic device applications and fundamental physics study. In order to fully realize this potential it is important to identify a growth regime that yields high quality structural, electronic and optical characteristics. Here we explore the impact of growth temperature on NW optical quality for both (100) and (111)B oriented GaAs substrates. Au catalyzed GaAs/AlGaAs core/shell NWs are grown by metalorganic chemical vapor deposition (MOCVD) within a substrate temperature window of 410 $^{\circ}$C to 470 $^{\circ}$C. We find that, contrary to expectation, the optical quality depends on substrate orientation with (100) wire quality decreasing monotonically with increasing temperature while (111)B wire quality peaks at 430 $^{\circ}$C. This result suggests that the orientation of the NW ensembles plays a critical role in precursor diffusion and subsequent point defect density. [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B50.00010: Photocurrent spectroscopy of confined quantum states in single quantum well tube nanowire devices Bekele Badada, Teng Shi, Leigh Smith, Howard Jackson, Jan Yarrison-Rice, Qiang Gao, H. Hoe Tan, Chennupati Jagadish We investigate optical transitions in GaAs/AlGaAs core-multishell nanowires Quantum Well Tubes (QWT) devices using photocurrent spectroscopy (PC) at low temperature (10K). The GaAs quantum well layer was embedded inside a thick AlGaAs shell surrounding a 50 nm diameter GaAs NW. The single nanowire devices were fabricated by standard photolithography followed by deposition of Ti (20nm)/Al (500nm) metal contacts on either end the nanowire. We present results for two sets of quantum well tubes having quantum well widths of 8nm and 4nm. The QWT nanowire devices exhibit very low (sub pA) dark current and are extremely photosensitive. PC measurements of the QWT devices exhibit photocurrent peaks corresponding to excitons confined to the GaAs core as well as ground and excited states of electrons and holes confined to the quantum well tube, and also in the barrier. Comparisons of the PC spectra with PL and PLE measurements on the same devices show that the peaks associated with the PC spectra show a close correspondence. [Preview Abstract] |
Monday, March 3, 2014 1:15PM - 1:27PM |
B50.00011: Temperature-dependent photoluminescence imaging of GaAs/AlGaAs heterostructure quantum well tubes Teng Shi, Howard Jackson, Leigh Smith, Jan Yarrison-Rice, Nian Jiang, Hoe Tan, Qiang Gao, Chennupati Jagadish Two sets of GaAs/AlGaAs core-multi shell nanowire quantum well tubes (QWTs) grown by MOCVD, with QW widths of 2nm and 6nm are dispersed onto a 4mm diameter hemispherical solid immersion lens. We obtain high spatial resolution photoluminescence (PL) images of single nanowires (NWs) from 10 K up to 120 K. High spectral resolution PL spectra reveal several narrow emission lines on high energy side of the 2nm QWT at low temperatures. In the 6nm QW, such narrow emission lines are not observed. Spatially-resolved PL images show that these localized states are randomly distributed along the NW long axis. Temperature-dependent PL imaging indicates that the quantum dot emissions disappear at temperatures above 50K. The recombination lifetime for electrons and holes in the QWT for the 2nm and 6nm QWTs are 500ps and 800 ps, respectively. We observe the recombination lifetime increases slightly with increasing temperature. [Preview Abstract] |
Monday, March 3, 2014 1:27PM - 1:39PM |
B50.00012: Ab initio study of substitutional doping of III-V nanowires Bob Schoeters, Geoffrey Pourtois, Bart Partoens Using \textit{ab initio} calculations we study the impact of substitutional dopants in thin III-V nanowires. In this study we focus on 4 different technologically relevant III-V nanowires: GaAs, InSb, InP and InGaAs, doped with either C, Si, Ge, Be, Mg or Zn. We determine the energetically most favorable positions for these dopants by looking at their formation energies. These preferred locations indicate whether a dopant will segregate to the surface or the center of the nanowire. This can have a large impact on the electronic properties, since it will lead to an inhomogeneous doping distribution. We can explain the preferential positions as a competition between a chemical and a relaxation effect. However, in reality these nanowires contain several defects, such as antisites, vacancies, dangling bonds at the nanowire surface, \dots. Therefore we also investigate the impact of these defects on the localization of the dopants. Finally we study the impact of these dopants on the electronic structure. [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 1:51PM |
B50.00013: Transient Rayleigh Scattering Spectroscopy measurement of Carrier Dynamics in Zincblende and Wurtzite Indium Phosphide nanowires Yuda Wang, Mohammad Montazeri, Howard Jackson, Leigh Smith, Jan Yarrison-Rice, Tim Burgess, Suriati Paiman, Hoe Tan, Qiang Gao, Chennupati Jagadish Pump-probe transient Rayleigh spectroscopy is used to study the carrier dynamics of ZB {\&} WZ InP nanowires. Utilizing a wavelength-tunable pulse laser as probe and by adjusting the pump-probe pulse time delay, the change of the Rayleigh scattering efficiency as a function of excitation energy and time delay is measured from a single nanowire. The results are analyzed using an absorption coefficient calculated by a band-to-band transition model and the index of refraction obtained by the Kramers-Kronig relation. The temperature of the electron-hole plasma (EHP) cools via the emission of longitudinal optic (LO) and acoustic phonons. The LO phonon cooling dominates at early times when the carrier temperatures are high, after which the acoustic phonon interactions begins to dominate. The carrier concentrations of the split-off band in ZB InP and C band in WZ InP appears to be 1-2 orders of magnitude smaller than that of the HH, LH or A, B valence bands. Such measurements provide a detailed picture of electron and hole densities and temperatures as a function of time after excitation. [Preview Abstract] |
Monday, March 3, 2014 1:51PM - 2:03PM |
B50.00014: Population Dynamics of Excitons in Polytype Wurzite-Zincblende InP Nanowires Hans-Peter Wagner, Masoud Kaveh, Wolfgang Langbein, Qian Gao, Chennupati Jagadish, Gerd Duscher We investigate the population dynamics of excitons in polytype wurzite/zincblende (WZ/ZB) InP nanowires using heterodyne four-wave-mixing (HFWM) in three-beam configuration at LN temperature. The photon energy of exciting 100 fs pulses was set to 1.44 eV and 1.49 eV, resonant to excitons in ZB and WZ segments, respectively. Pump pulse fluences were varied from 0.16 to 3.2 $\mu $J/cm$^{\mathrm{2}}$. At 1.44 eV pulse energy the HFWM amplitude shows a rapid initial decay on a sub-picosecond time-scale indicating a fast conversion of ZB excitons into spatially indirect excitons at the WZ/ZB interface. For longer delays the HFWM amplitude reveals a nearly mono-exponential decay time of 2 ns at lowest pump fluence which is assigned to the lifetime of indirect electron-hole pairs. With increasing pulse fluence the decay dynamics becomes multi-exponential which is attributed to state filling of higher-energy indirect excitons. At 1.49 eV pulse energy the HFWM amplitude reveals an additional rapid decay on a 10 ps time-scale which is tentatively assigned to the trapping of A-excitons at point-defects in the WZ segments. The observed dynamics is modeled by coupled rate-equations. [Preview Abstract] |
Monday, March 3, 2014 2:03PM - 2:15PM |
B50.00015: Inelastic electron and Raman scattering from the collective excitations in quantum wires Manvir Kushwaha The nanofabrication technology has taught us that an $m$-dimensional confining potential imposed upon an $n$-dimensional electron gas paves the way to a quasi-($n$-$m$)-dimensional electron gas, with $m \le n$ and $1\le n, m \le 3$. This is the road to the (semiconducting) quasi-$n$ dimensional electron gas systems we have been happily traversing on now for almost two decades. Achieving quasi-one dimensional electron gas (Q-1DEG) led us to some mixed moments in this journey: while the reduced phase space for the scattering led us believe in the route to the faster electron devices, the proximity to the 1D systems left us in the dilemma of describing it as a Fermi liquid or as a Luttinger liquid. No one had ever suspected the potential of the former, but it took quite a while for some to convince the others on the latter. A {\em realistic} Q-1DEG system at the low temperatures is best describable as a Fermi liquid rather than as a Luttinger liquid. This has motivated us to employ the Bohm-Pines' full RPA to develop a systematic methodology for the inelastic electron and light scattering from the collective (plasmon) excitations in Q-1DEG [or quantum wires]. We will discuss in detail the results published in AIP Advances {\bf 3}, 042103 (2013). [Preview Abstract] |
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