Bonghwan Chon

Photoluminescent characteristics of Ni-catalyzed GaN nanowires

The authors report on time-integrated and time-resolved photoluminescence (PL) of GaN nanowires grown by the Ni-catalyst-assisted vapor-liquid-solid method. From PL spectra of Ni-catalyzed GaN nanowires at 10K, several PL peaks were observed at 3.472, 3.437, and 3.266eV, respectively. PL peaks at 3.472 and 3.266eV are attributed to neutral-donor-bound excitons and donor-acceptor pair, respectively. Furthermore, according to the results from temperature-dependent and time-resolved PL measurements, the origin of the PL peak at 3.437eV is also discussed.

Electrical properties and near band edge emission of Bi-doped ZnO nanowires

Electrical transport of Bi–ZnO nanowires shows n-type semiconducting behavior with a carrier concentration of ∼3.5×108cm−1 (2.7×1019cm−3) and an electron mobility of 1.5cm2∕Vs. The carrier concentration is one order of magnitude larger than that of undoped ZnO nanowires, indicating that Bi acts as donor rather than the usual acceptor in ZnO films. The low mobility may be in association with electron scatterings at the boundaries from small size effect of nanowires. Near band edge emission in photoluminescence spectrum of Bi–ZnO nanowires is redshifted relative to undoped ZnO nanorods as a result of enhanced carrier concentration. The donor-acceptor pair transition associated with Bi was also observed at 3.241eV.

Structural characterization and low temperature growth of ferromagnetic Bi–Cu codoped ZnO bicrystal nanowires

Ferromagnetic Bi–Cu codoped ZnO nanowires were fabricated at temperatures as low as 300°C via a vapor phase transport using the mixture of Zn, BiI3 and CuI powders. They are grown as a bicrystal, along the [011¯2] direction, have a width of 40–150nm, and a length of a few microns. The investigation of the growth mechanism proposes that the synergy of BiCu and iodine/iodide induces the formation of bicrystallinity. The photoluminescence measurement shows the cooperative effect of Bi and Cu ions. The ferromagnetism observed in this study is the result of the combined effect of structural defects, the substitution of Cu into Zn site along the c axis, and codoping of Bi.

Excitonic origin of enhanced luminescence quantum efficiency in MgZnO/ZnO coaxial nanowire heterostructures

The effect of exciton transport on luminescence efficiency was investigated by time-resolved photoluminescence and spatially resolved cathodoluminescence spectroscopy. The internal quantum efficiency of ZnO nanowire (NW) increased from 45% to 56% due to formation of a MgZnO/ZnO coaxial NW heterostructure. MgZnO shell layer formation induced a decrease in the exciton diffusion length and diffusion coefficient from 150 to 120 nm and 9.8 to 6.4 cm2/s, respectively. The change in exciton transport characteristics indicated that exciton transport, in addition to the surface passivation effect, was an important factor determining the luminescence efficiency in the coaxial NW heterostructure.

Ferromagnetic ZnO bicrystal nanobelts fabricated in low temperature

Zinc oxide bicrystal nanobelts were fabricated via a vapor phase transport of a powder mixture of Zn, BiI3, and MnCl2∙H2O at temperatures as low as 300°C. The bicrystal nanobelts, growing along the [011−3] direction, have the widths of 40–150nm and lengths of tens of microns. The energy dispersive x-ray spectroscopy result verifies that the bicrystal nanobelts contain higher concentration of both Bi and Mn along the grain boundary. The investigation of the growth mechanism proposes that MnBi may induce the formation of bicrystal nanobelts. Photoluminescence spectra show that the ultraviolet emission of the bicrystal nanobelts has a blueshift of 18meV as compared to Bi–ZnO nanowires at 10K. The bicrystal nanobelts also exhibit ferromagnetism at room temperature.

Exciton scattering mechanism in a single semiconducting MgZnO nanorod.

Excitonic phenomena, such as excitonic absorption and emission, have been used in many photonic and optoelectronic semiconductor device applications. As the sizes of these nanoscale materials have approached to exciton diffusion lengths in semiconductors, a fundamental understanding of exciton transport in semiconductors has become imperative. We present exciton transport in a single MgZnO nanorod in the spatiotemporal regime with several nanometer-scale spatial resolution and several tens of picosecond temporal resolution. This study was performed using temperature-dependent cathodoluminescence and time-resolved photoluminescence spectroscopies. The exciton diffusion length in the MgZnO nanorod decreased from 100 to 70 nm with increasing temperature in the range of 5 and 80 K. The results obtained for the temperature dependence of exciton diffusion length and luminescence lifetime revealed that the dominant exciton scattering mechanism in MgZnO nanorod is exciton-phonon assisted piezoelectric field scattering.

Photoluminescent characteristics of MgxZn1−xO (0 ⩽ x ⩽ 0.18) nanorods

We report on continuous wave and time-resolved photoluminescent characteristics of MgxZn1−xO (0 ≤ x ≤ 0.18) alloy nanorods grown on Si substrates using catalyst-free metal–organic chemical vapor deposition. Low temperature time-integrated photoluminescence (PL) spectra of the alloy nanorods clearly exhibited a dominant PL peak of a single MgxZn1−xO phase without showing any PL peak from ZnO. In addition, dominant PL peak positions of the alloy nanorods were blueshifted with increasing Mg content in the nanomaterials. Using temperature-dependent PL spectra and time-resolved PL spectra of MgxZn1−xO nanorods, we discuss the composition fluctuations in MgxZn1−xO (0 ≤ x ≤ 0.18) nanorods.