Jan M. Yarrison-Rice

Polarization and temperature dependence of photoluminescence from zincblende and wurtzite InP nanowires

A.M., L.V.T., T.B.H., H.E.J., L.M.S., and J.M.Y.-R. acknowledge support from the Institute for Nanoscale Science and Technology of the University of Cincinnati and the National Science Foundation through Grant Nos. EEC/NUE 0532495 and ECCS 0701703. The Australian authors acknowledge support from the Australian Research Council. Y.K. acknowledges support by the Korean Science and Engineering Foundation KOSEF through Grant No. F01- 2007-000-10087-0.

Temperature dependence of photoluminescence from single core-shell GaAs–AlGaAs nanowires

This work was supported by the University of Cincinnati. Australian authors gratefully acknowledge the financial support from the Australian Research Council.

Carrier Dynamics and Quantum Confinement in type II ZB-WZ InP Nanowire Homostructures

We use time-resolved photoluminescence from single InP nanowires containing both wurtzite (WZ) and zincblende (ZB) crystalline phases to measure the carrier dynamics of quantum confined excitons in a type-II homostructure. The observed recombination lifetime increases by nearly 2 orders of magnitude from 170 ps for excitons above the conduction and valence band barriers to more than 8400 ps for electrons and holes that are strongly confined in quantum wells defined by monolayer-scale ZB sections in a predominantly WZ nanowire. A simple computational model, guided by detailed high-resolution transmission electron microscopy measurements from a single nanowire, demonstrates that the dynamics are consistent with the calculated distribution of confined states for the electrons and holes.

Unexpected Benefits of Rapid Growth Rate for III-V Nanowires

In conventional planar growth of bulk III-V materials, a slow growth rate favors high crystallographic quality, optical quality, and purity of the resulting material. Surprisingly, we observe exactly the opposite effect for Au-assisted GaAs nanowire growth. By employing a rapid growth rate, the resulting nanowires are markedly less tapered, are free of planar crystallographic defects, and have very high purity with minimal intrinsic dopant incorporation. Importantly, carrier lifetimes are not adversely affected. These results reveal intriguing behavior in the growth of nanoscale materials, and represent a significant advance toward the rational growth of nanowires for device applications.

Nearly intrinsic exciton lifetimes in single twin-free GaAs/AlGaAs core-shell nanowire heterostructures

S.P., M.A.F., H.E.J., L.M.S., and J.M.Y.-R. acknowledge the financial support of the University of Cincinnati and the National Science Foundation through Grant Nos. EEC/NUE- 0532495, ECCS-0701703, and DMR/MWN-0806700. H.J.J., Q.G., H.H.T., C.J., X.Z., and J.Z. acknowledge support from the Australian Research Council and the Australian National Fabrication Facility.

The effect of V/III ratio and catalyst particle size on the crystal structure and optical properties of InP nanowires

InP nanowires were grown on 111B InP substrates by metal-organic chemical vapour deposition in the presence of colloidal gold particles as catalysts. Transmission electron microscopy and photoluminescence measurements were carried out to investigate the effects of V/III ratio and nanowire diameter on structural and optical properties. Results show that InP nanowires grow preferably in the wurtzite crystal structure than the zinc blende crystal structure with increasing V/III ratio or decreasing diameter. Additionally, time-resolved photoluminescence (TRPL) studies have revealed that wurtzite nanowires show longer recombination lifetimes of approximately 2500 ps with notably higher quantum efficiencies.

Direct Measure of Strain and Electronic Structure in GaAs/GaP Core−Shell Nanowires

Highly strained GaAs/GaP nanowires of excellent optical quality were grown with 50 nm diameter GaAs cores and 25 nm GaP shells. Photoluminescence from these nanowires is observed at energies dramatically shifted from the unstrained GaAs free exciton emission energy by 260 meV. Using Raman scattering, we show that it is possible to separately measure the degree of compressive and shear strain of the GaAs core and show that the Raman response of the GaP shell is consistent with tensile strain. The Raman and photoluminescence measurement are both on good agreement with 8 band k.p calculations. This result opens up new possibilities for engineering the electronic properties of the nanowires for optimal design of one-dimensional nanodevices by controlling the strain of the core and shell by varying the nanowire geometry.

Optical, Structural, and Numerical Investigations of GaAs/AlGaAs Core–Multishell Nanowire Quantum Well Tubes

The electronic properties of thin, nanometer scale GaAs quantum well tubes embedded inside the AlGaAs shell of a GaAs core-multishell nanowire are investigated using optical spectroscopies. Using numerical simulations to model cylindrically and hexagonally symmetric systems, we correlate these electronic properties with structural characterization by aberration-corrected scanning transmission electron microscopy of nanowire cross sections. These tubular quantum wells exhibit extremely high quantum efficiency and intense emission for extremely low submicrowatt excitation powers in both photoluminescence and photoluminescence excitation measurements. Numerical calculations of the confined eigenstates suggest that the electrons and holes in their ground states are confined to extremely localized one-dimensional filaments at the corners of the hexagonal structure which extend along the length of the nanowire.

Room temperature photocurrent spectroscopy of single zincblende and wurtzite InP nanowires

The InP nanowires are grown by vapor-liquid-solid growth catalyzed by 20 and 50 nm gold nanoparticles on an InP substrate at 400 C using metal-organic chemical-vapor deposition. The 50 nm nanowires were grown with a V/III ratio of 350, while the 20 nm nanowires were grown at a V/III ratio of 700. 9 Extensive cw and time-resolved PL measurements at low temperatures have shown that the 20 nm wires are predominantly WZ, while the 50 nm nanowires are predominantly ZB, with some twins and stacking faults present as determined by high-resolution transmission electron microscopy imaging. 3,4,9 To obtain individual nano

High efficiency photonic crystal based wavelength demultiplexer

A highly efficient design of a two-channel wavelength demultiplexer in the visible region is presented with finite-difference time-domain simulations. The design process is described in detail with particular attention to the challenges inherent in fabrication of an actual device. A 2D triangular lattice photonic crystal with 75nm air pores in a silicon nitride planar waveguide provides the confinement for visible light. The device losses due to fabrication errors such as stitching misalignment of write fields during e-beam lithography and variation in air pore diameters from etching are modeled using realistic parameters from initial fabrication runs. These simulation results will be used to guide our next generation design of high efficiency photonic crystal based demultiplexing devices.