Chang Hyun Bae

Origin of the slow photoresponse in an individual sol-gel synthesized ZnO nanowire

Photocurrent of a single ZnO nanowire synthesized by a sol-gel route was investigated. In vacuum, the dark current was bigger but the photoresponse was slower than that in air, attributed to the release of the available charge carriers by the desorption of water molecules and the decrease of the exchange rates of molecular ions. Under the steady radiation of the ultraviolet light (λ=325nm), a gradual decrease of the photocurrent was noticeable, which can be explained in terms of the annihilation of the carriers by the replacement of hydroxyl groups (OH−) by O2−, resulting in the decrease of charge carriers.

Er3+ photoluminescence from Er-doped amorphous SiOx films prepared by pulsed laser deposition at room temperature: The effects of oxygen concentration

We have fabricated Er-doped amorphous SiOx films by laser ablation of a Si:Er2O3 target in He atmosphere. The photoluminescence intensity at 1.54 μm was highly dependent on the oxygen content in the film, which turned out to be changed significantly by the ambient He pressure. Also, we have adopted time-of-flight quadrupole mass spectroscopy to obtain kinetic energies of ionic species in a plume produced by laser ablation. Si and Er ions do not overlap spatially as they expand toward the Si substrate and Er ions impinge on the preformed SiOx layer.

Array of luminescent Er-doped Si nanodots fabricated by pulsed laser deposition

Ordered arrays of Er-doped Si nanodots were fabricated by pulsed laser deposition using an anodic aluminum oxide (AAO) nanopore membrane. Er-doped Si (Si:Er) nanodots with an average diameter of 60–80nm and a periodicity of 100nm were uniformly assembled into hexagonally ordered nanopores of AAO membrane. Photoluminescence (PL) spectra taken from Si:Er nanodots showed an emission peak at 1.54μm, which is due to intra-4f shell transition (I13∕24→I15∕24) of Er3+ ions. Postannealing of nanodot arrays up to 500°C resulted in the enhancement of PL intensities without enlargement or aggregation of the nanodots.

Fabrication of Nanodot Arrays on Si by Pulsed Laser Deposition Using Anodic Aluminum Oxide Nanopore Membrane as Mask

We demonstrate the fabrication of metal and semiconductor nanodot arrays on Si by pulsed laser deposition using an anodic alumina membrane as a mask. A Hexagonal-close-packed nanopore membrane mask was fabricated by the anodic oxidation of aluminum sheet. Pulsed laser deposition of Ag, Ni, ZnO, and Er-doped Si (Si:Er) nanodots was performed on a Si substrate to which an alumina membrane mask adheres by van der Waals interaction. Highly ordered arrays of Ag, Ni, ZnO, and Si:Er nanodots with average diameters ranging from 55 to 86 nm and a periodicity of ~100 nm were obtained. Also, the time-resolved images of laser-produced plasma plumes were analyzed to examine the dynamical properties of the ejected materials.

A time-of-flight quadrupole mass spectrometric study of Cn+(n=1–24) ions produced by laser ablation of a graphite target

Mass spectral distributions and time-of-flight spectra of Cn+ (n=1–24) ions escaping from a carbon plasma plume generated by laser (λ=1064 nm) ablation of a graphite target are analyzed to shed light on their formation mechanisms, expansion dynamics, and laser–plume interaction. In particular, by shining the whole or a slice of the plume with a photodissociation laser (λ=266 nm) delayed with respect to the ablation laser, we examine the effects of the laser–plume interaction on the mass distribution as well as photodissociation channels of carbon-cluster cations. Also, we present experimental data that show a clear linear dependence of the velocities of Cn+ ions on 1/M. This result confirms that Cn+ ions are mainly accelerated by a transient local electric field in the plume.

Enhancement of light emission from silicon nanocrystals by post-O2-annealing process

This study investigated the effects of the post-O2-annealing process on light emission from silicon nanocrystals. Using pulsed laser ablation in an O2-filled atmosphere, the SiOx (x<2) thin layers were synthesized prior to O2-annealing. We observed a strong photoluminescence from the silicon nanocrystals embedded in the annealed layers at 500 °C, which depended on the post-O2-annealing time. We also found that the interface property between the silicon nanocrystal and stoichiometric SiO2 matrix is critical for efficient light emission. The electroluminescence spectra in the visible range were obtained above the on-current density of 0.7 A/cm2 under several forward-bias voltages. The blueshift in the electroluminescence was attributed to the band-filling effect under high current injection mode. The external emission efficiency was estimated to be about 0.3% by using the band-filling model.

Er3+ Photoluminescence from Er-doped Silicon-Rich Silicon Oxide Films Deposited by Laser Ablation of a Si:Er Target in an Oxygen Atmosphere

We have developed a new pulsed laser deposition method for fabricating Er-doped silicon-rich silicon oxide (SRSO:Er) films. A target composed of a pure Si disk and an Er metal strip was ablated by a line-focused laser beam in oxygen atmosphere. The oxygen concentration that determines the relative concentrations of the three phases (Si–Si, SiOx, and SiO2) in the film was easily controlled by varying the ambient oxygen pressure. The photoluminescence intensity at 1.54 µm from Er3+ ions was strongly dependent on the amount of the Si–Si phase in the SRSO:Er films.