Sung-Won Cho

Growth mode and structural characterization of GaSb on Si (001) substrate: A transmission electron microscopy study

Growth mode and structural properties of GaSb layers grown on silicon substrate by molecular beam epitaxy method are investigated by transmission electron microscopy. It is found that the GaSb grows to three-dimensional islands and grains are tilted to reduce a lattice mismatch through twin boundaries when they are directly grown on Si substrate. A low-temperature (LT) AlSb buffer plays a key role in transferring the growth mode from a three-dimensional island to a layer-by-layer structure. When the LT AlSb layer is used as a buffer, 90° misfit dislocations, with the Burgers vector b of 1∕2a⟨110⟩, are observed on the interface.

Highly efficient phosphorescent polymer OLEDs fabricated by screen printing

We demonstrate the use of screen printing in the fabrication of highly efficient phosphorescent polymer organic light-emitting devices (OLEDs) based on a green-emitting Ir(ppy)3 and a host polymer PVK. We incorporate PBD in the polymer host as an electron-transporting dopant and a-NPD as a hole-transporting dopant. The best screen-printed single-layer device exhibits very high peak luminous efficiency of 63 cd/A at a relatively high operating voltage of 17.1 V at the luminance of 650 cd/m 2 . We observed the highest luminance of 21,000 cd/m 2 at 35 V. Due to the high operating voltage, despite of the high peak luminous efficiency the peak power efficiency was found to be 12.2 lm/W at the luminance of 470 cd/m 2

High aspect ratio via etching conditions for deep trench of silicon

Abstract Deep trench etching of silicon was investigated as a function of platen power, operational pressure and the SF6:C4F8 gas flow rate. Their effects on the etch rate, etch profile and scallops were also studied. As the platen power was increased from 5 to 30 W, the etch rate was increased from 0.54 to 2.51 μm/min. However, the etch rate was decreased at platen power higher than 30 W. As the pressure was increased from 10 to 25 mTorr, the etch rate was increased from 1.93 to 2.69 μm/min but the etch rate was decreased at the pressure higher than 35 mTorr. As the SF6:C4F8 gas flow rate was increased from 50:50 to 200:160 sccm, the etch rate was increased from 1.91 to 2.31 μm/min and at the SF6:C4F8 gas flow rate of 260:220 sccm, it was decreased to 2.21 μm/min.

Influence of hydrogen on SiON thick film for silica waveguide deposited by PECVD and annealing effect

Abstract Silicon oxynitride (SiON) films containing various hydrogen concentrations were deposited in a plasma enhanced chemical vapor deposition (PECVD) reactor using SiH 4 and N 2 O as precursor gases. In this work, the influence of annealing temperature on the optical and physical properties of SiON films is presented. It can be seen that the refractive index for the as-deposited SiON and annealed SiON films can be varied continuously between 1.4554 and 1.4513 at a wavelength of 1552 nm by using a prism coupler. The silicon content of the films is independent of the annealing temperature and for all layers it is approximately 33%. As annealing temperature increased, the oxygen content of the films increased from 64 to 66.2%, and the nitrogen content decreased from 1.98 to 0.02%.

N2 doped SiO2–SiON planar waveguides deposited by PECVD method

Abstract Silica based planar lightwave circuits (PLCs) have been applied to various kinds of wave-guided optical passive devices. Silicon dioxide (SiO2) and silicon oxynitride (SiON) thick films have been deposited by plasma enhanced chemical vapor deposition (PECVD). SiO2 and SiON films were obtained at low temperatures (

Refractive index control of core layer using PECVD and FHD for silica optical waveguide

Abstract Silicon oxynitride (SiON) and GeO 2 –SiO 2 layers as core layers deposited using the plasma-enhanced chemical vapor deposition (PECVD) and flame hydrolysis deposition (FHD), respectively. For PECVD technique, the deposition rate monotonically rises with increasing r.f. power from approximately 4.5 μm/h at the power of 60 W to 5.9 μm/h at the power of 180 W. As r.f. power increased from 60 to 180 W, refractive index (RI) of SiON films decreased from 1.5312 to 1.4620. For FHD technique, the RI increases from 1.4615 to 1.4809 with the increase in the GeCl 4 flow rate from 30 to 100 sccm. Material grown by two processes, FHD and PECVD, exhibited the similar etching characteristics by inductively coupled plasma etching.

Effect of helium on spatial plasma parameters in low pressure argon-helium plasma

Spatial distributions of the electron energy probability function were measured using a Langmuir probe in side-type argon-helium inductively coupled plasma. Collisional dominated electron heating and a concave shape of plasma density profile were observed at 10 mTorr pure argon. As the helium proportion increased, the electron heating and density profile changed to collisionless dominated heating and a convex shape respectively, and the same tendency was shown when the pressure decreased in the pure argon plasma. These changes were due to the decrease in the e-n collision frequency and the expansion of the electron power dissipation region.

Power dependence of electron density at various pressures in inductively coupled plasmas

Experimental observation of the electron density variation in inductively coupled plasmas with the electron energy probability function (EEPFs) was performed at various gas pressures at two RF powers (25 W and 200 W). The measured EEPFs at high power discharges (200 W) showed a Maxwellian distribution, while evolution of the EEPFs from a bi-Maxwellian distribution to a Druyvesteyn-like distribution was observed at low RF powers (25 W) with increasing pressure. A discrepancy of the electron density variation between the two RF powers was observed. This difference is explained by the modified collisional loss and the Bohm velocity from the EEPF of the bi-Maxwellian distribution and the Druyvesteyn–like distribution.

Investigation of plasma diagnostics using a dual frequency harmonic technique

Plasma diagnostic methods using harmonic currents analysis of electrostatic probes were experimentally investigated to understand the differences in their measurement of the plasma parameters. When dual frequency voltage ( ω1,ω2) was applied to a probe, various harmonic currents ( ω1, 2ω1,ω2, 2ω2,ω2±ω1,ω2±2ω1) were generated due to the non-linearity of the probe sheath. The electron temperature can be obtained from the ratio of the two harmonics of the probe currents. According to the combinations of the two harmonics, the sensitivities in the measurement of the electron temperature differed, and this results in a difference of the electron temperature. From experiments and simulation, it is shown that this difference is caused by the systematic and random noise.

Experimental verification of the Boltzmann relation at the wall in inductively coupled plasmas

The radial profiles of the electron density at the bottom wall were measured from the center to the edge at argon 3 mTorr with an RF power of 200 W. Since the Boltzmann relation in terms of the fluid picture only describes the behavior of the confined particles, the escaping electrons, which are not confined in plasmas, were not expected to follow the Boltzmann relation. However, unexpected results were observed. The spatial profiles of the density of escaping electrons and the floating potential were well described by the Boltzmann relation with the electron temperature. Moreover, it was concluded that the behavior of the escaping electrons is also described by the generalized Boltzmann relation in terms of the kinetic model.