Browsing by Author "Jagadish, Chennupati"
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Item Embargo A comparative study of transistors based on wurtzite and zincblende InAs nanowires(IEEE, 2010) Williams, Marc; Burke, Adam M.; Joyce, Hannah J; Micolich, Adam Paul; Tan, Hoe Hark; Jagadish, ChennupatiWe report a comparative study of the electronic properties of nominally identical nanowire field-effect transistor (NW-FET) devices produced using 50 nm diameter InAs nanowires that differ only in phase: ZB on the one hand, and WZ on the other. We find much higher current densities in the ZB NW-FETs, and on/off ratios of up to 100.Item Open Access A comparison of impurity-free and ion-implantation-induced intermixing of InGaAs/InP quantum wells(American Institute of Physics (AIP), 2000-11-01) Dao, Lap Van; Gal, Michael; Carmody, C; Tan, Hoe Hark; Jagadish, ChennupatiWe have compared the time integrated photoluminescence (PL) and the time resolved PL of several lattice matched InGaAs/InP quantum wells intermixed either by ion implantation or an impurity-free method. We have found that the carrier capture rates into quantum wells and carrier relaxation from the wells depend on the type of intermixing used. Our results indicate that the carrier lifetimes are significantly longer in samples intermixed by the impurity-free methods, while the carrier collection efficiency of the quantum wells is more efficient in samples intermixed by ion implantation.Item Open Access A comparison of low-energy as ion implantation and impurity-free disordering induced defects in N-type GaAs epitaxial layers(The Japan Society of Applied Physics, 2003) Deenapanray, P.N.K; Svensson, B.G; Tan, Hoe Hark; Jagadish, ChennupatiWe have compared the electrical properties of n-type GaAs layers disordered by either 40 keV As ion implantation or an impurity-free process employing an SiO2 capping layer. Current–voltage and capacitance–voltage measurements on Au Schottky barrier diodes fabricated on the processed layers showed that the impurity-free method retained the much better electrical quality of the GaAs epitaxial layers. Different sets of defects were observed in the implanted samples and impurity free disordered samples, which meant that the charge transfer across the Schottky barriers was different in the two cases. Our results further reveal that the concentrations and diffusion lengths of defects created by ion implantation were much larger. The impurity-free method retains the better electrical quality of the semiconductor material.Item Embargo A Comparison of the Mechanical properties and the impact of contact induced damage in a- and c- Axis ZnO Single crystals(Materials Research Society, 2007) Coleman, Victoria A; Bradby, Jodie; Jagadish, Chennupati; Phillips, Matthew R; J Christen; C Jagadish; D C Look; T Yao; F BertranNanoindentation studies were conducted on a-axis oriented ZnO single crystals. The mechanical properties and deformation mechanisms were monitored and compared to previously determined data from c-axis material. Hardness and modulus values reveal that a-axis ZnO is significantly softer than c-axis material (hardness of 2 ± 0.2 GPa), and behaves more plastically. Additionally, the influence of contact induced damage on the defect structure of a-axis material was examined using cathodoluminescence spectroscopy and monochromatic imaging to monitor the luminescence from indent sites. Deformation directly under the indent site enhanced the occurrence of red luminescence, and was attributed to a native defect in ZnO that has a higher formation energy than the defects responsible for the green and yellow visible defect bands, which were present in ZnO during growth and clustered to the indent site during annealing.Item Metadata only A Deep Level Transient Spectroscopy Study of Vacancy-related Defect Profiles in Channeled Ion Implanted Silicon(Institute of Electrical and Electronics Engineers (IEEE Inc), 2003) Lay, M D H; McCallum, Jeffrey C; de Azevedo, Gustavo; Deenapanray, Prakash; Jagadish, Chennupati; Michael GalItem Embargo A novel hybrid fabrication approach for three-dimensional photonic nanostructures(RMIT Publishing, 2012) Staude, Isabelle; Decker, Manuel; Ventura, Michael James; Jagadish, Chennupati; Neshev, Dragomir; Gu, Min; Kivshar, YuriItem Metadata only A Partially Depleted Absorber Photodiode with Graded Doping Injection Regions(Institute of Electrical and Electronics Engineers (IEEE Inc), 2004) Li, Xiao-Lei; Li, N; Demiguel, S; Zheng, X; Campbell, J C; Tan, Hoe Hark; Jagadish, ChennupatiA partially depleted absorber photodiode with graded absorption injection regions is reported. The 880-nm-thick In0.53Ga0.47As absorption region consists of a depletion layer and graded n- and p-type undepleted injection regions. Under backside illumination at 1.55-μm wavelength, an 8-μm-diameter photodiode exhibited an increase in bandwidth with increasing photocurrent. A saturation current bandwidth product of 990 mA · GHz and a responsivity of 0.67 A/W were achieved.Item Embargo A plasmonic staircase nano-antenna device with strong electric field enhancement for surface enhanced Raman scattering (SERS) applications(Institute of Physics Publishing, 2012) Li, Ziyuan; Hattori, Haroldo; Parkinson, Patrick; Tian, Jie; Fu, Lan; Tan, Hoe Hark; Jagadish, ChennupatiIn this paper, a staircase plasmonic nano-antenna device is analysed both theoretically and experimentally. The tapered nano-antenna cavity with a grating leads to electric field enhancement factor (EF) as high as 31 close to 830nm. The integration of a metallic grating aids the coupling of light coming from the vertical direction to the nano-antenna, increasing the electric field in the nano-antenna by a factor of 3. The smallest air gap width between the metallic regions of the fabricated nano-antenna is about 35nm, fabricated using focused ion beam system. The small air gaps in the nano-antennas can generate very high intensity electric fields which can be used in applications in biological sensing and imaging, nanoparticle manipulations and enhancement of nonlinear effects. In this paper, to experimentally demonstrate that with the integration of a well designed grating and reflectors, the resonance inside the nano-antenna cavity is increased significantly, we exploit one application of this device: the enhancement of surface enhanced Raman scattering (SERS). The present structure can lead to SERS EFs above 1 million.Item Open Access A transmission electron microscopy study of defects formed through the capping layer of self-assembled InAs/GaAs quantum dot samples(American Institute of Physics (AIP), 2006-06-01) Stewart Sears, Kalista; Wong-Leung, Yin-Yin; Tan, Hoe Hark; Jagadish, ChennupatiPlan-view and cross-sectional transmission electron microscopy have been used for a detailed study of the defects formed in capped InAs/GaAs quantum dot (QD) samples. Three main types of defects, V-shaped defects, single stacking faults, and stacking fault pyramids, were found to form under growth conditions that led to either very large, indium enriched, or coalesced islands. All three types of defects originate at the buried quantum dot layer and then travel through the GaAs cap to the surface on the {111} planes. The V-shaped defects were the most common and typically consisted of two pairs of closely spaced 60° Shockley partials with a <211> line direction. The two pairs originate together at the buried QD layer and then travel in “opposite” directions on different {111} planes. The second type of defect is the single stacking fault which consists of a single pair of partial dislocations separated by an ≈ 50 nm wide stacking fault. Finally, both complete and incomplete stacking fault pyramids were observed. In the case of the complete stacking fault pyramid the bounding dislocations along the [110], [11¯0], [101¯], and [101] directions were identified as stair rods. A possible mechanism for the stacking fault pyramid formation, which can also account for the creation of incomplete stacking fault pyramids, is presented.Item Embargo Achieving Straight Growth of InAs-on-GaAs Nanowire Heterostructures(American Chemical Society, 2011) Messing, Maria E; Wong-Leung, Yin-Yin (Jennifer); Zanolli, Zeila; Joyce, Hannah J; Tan, Hoe Hark; Gao, Qiang; Wallenberg, L Reine; Johansson, Jonas; Jagadish, ChennupatiOne of the main motivations for the great interest in semiconductor nanowires is the possibility of easily growing advanced heterostructures that might be difficult or even impossible to achieve in thin films. For III-V semiconductor nanowires, axial heterostructures with an interchange of the group III element typically grow straight in only one interface direction. In the case of InAs-GaAs heterostructures, straight nanowire growth has been demonstrated for growth of GaAs on top of InAs, but so far never in the other direction. In this article, we demonstrate the growth of straight axial heterostructures of InAs on top of GaAs. The heterostructure interface is sharp and we observe a dependence on growth parameters closely related to crystal structure as well as a diameter dependence on straight nanowire growth. The results are discussed by means of accurate first principles calculations of the interfacial energies. In addition, the role of the gold seed particle, the effect of its composition at different stages during growth, and its size are discussed in relation to the results observed.Item Open Access An ion-implanted InP receiver for polarization resolved terahertz spectroscopy(Optical Society of America, 2007-05-24) Castro-Camus, E; Lloyd-Hughes, J; Fu, Lan; Tan, Hoe Hark; Jagadish, Chennupati; Johnston, Michael BWe report on the construction, optical alignment and performance of a receiver which is capable of recording the full polarization state of coherent terahertz radiation. The photoconductive detector was fabricated on InP which had been implanted with Fe+ ions. The device operated successfully when it was gated with near infrared femtosecond pulses from either a Ti:sapphire laser oscillator or a 1 kHz regenerative laser amplifier. When illuminated with terahertz radiation from a typical photoconductive source, the optimized device had a signal to noise figure of 100:1 with a usable spectral bandwidth of up to 4 THz. The device was shown to be very sensitive to terahertz polarization, being able to resolve changes in polarization of 0.34 degrees. Additionally, we have demonstrated the usefulness of this device for (i) polarization sensitive terahertz spectroscopy, by measuring the birefringence of quartz and (ii) terahertz emission experiments, by measuring the polarization dependence of radiation generated by optical rectification in (110)-ZnTe.Item Metadata only An order of magnitude increase in the quantum efficiency of (Al)GaAs nanowires using hybrid photonic–plasmonic modes(American Chemical Society, 2015-01-14) Mokkapati, Sudha; Saxena, Dhruv; Jiang, Nian; Li, Li; Tan, Hark Hoe; Jagadish, ChennupatiWe demonstrate 900% relative enhancement in the quantum efficiency (QE) of surface passivated GaAs nanowires by coupling them to resonant nanocavities that support hybrid photonic-plasmonic modes. This nonconventional approach to increase the QE of GaAs nanowires results in QE enhancement over the entire nanowire volume and is not limited to the near-field of the plasmonic structure. Our cavity design enables spatially and spectrally tunable resonant modes and efficient in- and out-coupling of light from the nanowires. Furthermore, this approach is not fabrication intensive; it is scalable and can be adapted to enhance the QE of a wide range of low QE semiconductor nanostructures.Item Embargo Analysis of multi-wavelength photonic crystal single-defect laser arrays(IEEE, 2010) Liu, Danyu; Hattori, Haroldo; Fu, Lan; Tan, Hoe Hark; Jagadish, ChennupatiItem Open Access Analysis of optically pumped compact laterally coupled distributed feedback lasers with three symmetric defect regions(American Institute of Physics, 2007-10-25) Hattori, Haroldo; Tan, Hoe Hark; Jagadish, ChennupatiThis article analyzes compact laterally coupled distributed feedback DFB lasers with three defect regions. These devices are more flexible and smaller than conventional DFB lasers, having typical lengths between 20 and 50 m and a width less than 1 m lateral gratings are inserted in a single-mode waveguide . We optimize the defect regions to achieve an improved performance. In other words, an adequate choice of phase shifts may lead to single-mode operation, lower threshold optical power, higher quantum differential efficiency, and more uniform field distribution. This device is designed to operate under optical pumping.Item Open Access Analytical expression for the quantum dot contribution to the quasistatic capacitance for conduction band characterization(American Institute of Physics, 2008-07-30) Buda, Ma; Iordache, G; Mokkapati, Sudha; Fu, Lan; Jolley, Greg; Tan, Hoe Hark; Jagadish, Chennupati; Buda, MiThis paper demonstrates an analytical expression for the quasistatic capacitance of a quantum dot layer embedded in a junction, where the reverse bias is used to discharge the initially occupied energy levels. This analysis can be used to determine the position and the Gaussian homogeneous broadening of the energy levels in the conduction band, and is applied for an InGaAs/GaAs quantum dot structure grown by metal organic chemical vapor deposition. It is shown that the Gaussian broadening of the conduction band levels is significantly larger than the broadening of the interband photoluminescence (PL) transitions involving both conduction and hole states. The analysis also reveals a contribution from the wetting layer both in PL and modeled C-V profiles which is much stronger than in typical molecular beam epitaxy grown dots. The presence of a built-in local field oriented from the apex of the dot toward its base, contrary to the direction expected for a strained dot with uniform composition (negative dipole), is also derived from fitting of the C-V experimental data.Item Embargo Anelastic behavior in GaAs semiconductor nanowires(American Chemical Society, 2013) Chen, Bin; Gao, Qiang; Wang, Yan-Bo; Liao, Xiao-Zhou; Mai, Yiu-Wing; Tan, Hoe Hark; Zou, Jin; Jagadish, Chennupati; Ringer, Simon P.The mechanical behavior of vertically aligned single-crystal GaAs nanowires grown on GaAs(111)B surface was investigated using in situ deformation transmission electron microscopy. Anelasticity was observed in nanowires with small diameters and the anelasItem Metadata only Annealing kinetics of vacancy-related defects in low-dose MeV self-ion-implanted n-type silicon(American Physical Society, 2001) Pellegrino, P; Leveque, P; Lalita, J; Hallen, A; Jagadish, Chennupati; Svensson, Bengt GunnarSilicon samples of n-type have been implanted at room temperature with 5.6-MeV 28Si ions to a dose of 2 × 108 cm-2 and then annealed at temperatures from 100 to 380 °C. Both isothermal and isochronal treatments were performed and the annealing kineticsItem Metadata only Anomalous diffusion of intrinsic defects in K+ implanted ZnO using Li as tracer(Materials Research Society, 2012) Vines, Lasse; Neuvonen, P.T.; Kuznetsov, A Yu; Wong-Leung, Yin-Yin (Jennifer); Jagadish, Chennupati; Svensson, Bengt GunnarPotassium (K) ions have been implanted in hydrothermally grown ZnO to a dose of 1 × 1015 cm-2, followed by isochronal annealing in a tube furnace (30min) and by rapid thermal annealing (30s) on two separate samples. For annealing temperatures below 700°Item Embargo Antimony Induced {112}A Faceted Triangular GaAs1-xSbx/InP Core/Shell Nanowires and Their Enhanced Optical Quality(John Wiley & Sons Ltd., 2015) Yuan, Xiaoming; Caroff, Philippe; Wang, Fan; Guo, Yanan; Wang, Yuda; Jackson, Howard E; Smith, Leigh M; Tan, Hoe Hark; Jagadish, ChennupatiMid-infrared GaAs1-xSbx/InP core/shell nanowires are grown coherently with perfectly twin-free zinc blende crystal structure. An unusual triangular InP shell with predominantly {112}A facets instead of {112}B facets is reported. It is found that this polarity preference is due to the surfactant role of Sb, which inhibits InP shell growth rate in the 〈112〉A directions. This behavior reveals a new degree of control and tunability allowed in manipulating nanowire facet geometry and polarity in radial heterostructures by a simple means. Tuning the Sb composition in the core yields controllable intense photoluminescence emission in both the 1.3 and 1.5 μm optical telecommunication windows, up to room temperature for single nanowires. The internal quantum efficiency of the core/shell nanowires is experimentally determined to be as high as 56% at room temperature. Transient Rayleigh scattering analysis brings complementary information, revealing the photoexcited carrier lifetime in the core/shell nanowire to be ≈100 ps at 300 K and ≈800 ps at 10 K. In comparison, the carrier lifetime of core-only nanowire is below the detection limit of the system (25 ps). The demonstrated superior optical quality of the core/shell nanowires and their ideal emission wavelength range makes them highly relevant candidates for near-infrared optoelectronic applications.Item Embargo Arrayed nanoantennas for efficient broadband unidirectional emission enhancement(Institute of Electrical and Electronics Engineers (IEEE Inc), 2012) Maksymov, Ivan; Staude, Isabelle; Miroshnichenko, Andrey; Decker, Manuel; Tan, Hoe Hark; Neshev, Dragomir; Jagadish, Chennupati; Kivshar, YuriPlasmonic Yagi-Uda nanoantennas are narrowband because their bandwidth is compromised by their unidirectionality. We propose and study arrayed nanoantennas offering broadband unidirectional emission enhancement with a high radiation efficiency.