Yoon Bong Hahn

Mechanistic Study and Characterization of 3C-SiC(100) Grown on Si(100)

Single crystal cubic SiC(100) thin films were grown on Si(100) from thermal cracking of tetramethylsilane (TMS) as a function of growth temperature reactor pressure, source gas flow rate, and Si/C atomic ratio in a radio frequency-inductive chemical vapor deposition reactor. The orientation of as-grown SiC films mostly followed that of the Si substrate. However, the growth of SiC( 111) was detected in the films grown at high TMS flow rates and high Si/C atomic ratios. The thickness of the SiC film was increased with the growth temperature, reactor pressure, TMS flow rate, and Si/C atomic ratio. Voids were formed in the silicon side of the SiC/Si interface, hut disappeared when the reactor pressure TMS flow rate, and Si/C ratio were increased. The formation of voids was attributed to the outdiffusion of Si atoms from the Si substrate. The stresses and strains generated in the grown films were also investigated in terms of the growth conditions. The formation mechanism of voids at the SiC/Si interface was discussed on the basis of the experimental observations.

Dry etching of SrBi2Ta2O9 thin films in Cl2/NF3/O2/Ar inductively coupled plasmas

A parametric study of high density plasma etching of SrBi2Ta2O9 (SBT) thin films was carried out in a planar type inductively coupled plasma (ICP) etcher with different chemistries of Cl2/Ar, Cl2/NF3/Ar, and Cl2/NF3/O2/Ar. The etch rate was a strong function of gas concentration, ICP source power, and rf chuck power. Both Cl2/NF3/Ar and Cl2/NF3/O2/Ar plasmas showed maximum etch rates of ∼1600 A/min at 5 mTorr, 700 W ICP power, and 150 W rf chuck power. The addition of NF3 and O2 into the Cl2/Ar mixture played an important role in not only enhancing the etch rate, but also smoothing the etched surface by reducing the kinetic energy of ions. Electrical properties of the SBT films were quite dependent of plasma chemistries: Cl2/NF3/O2/Ar showed the least damage in the films and resulted in overall the best polarization-electric field hysteresis loop compared to other chemistries.

Kinetic study of 3C-SiC growth on Si by pyrolyzing tetramethysilane in low pressure radio frequency-induction heated chemical vapor deposition reactor

Single crystal 3C-SiC films were grown on Si(111) substrate using tetramethylsilane [TMS,(CH3)4Si] in a low pressure radio frequency-induction heated chemical vapor deposition reactor. The growth rate of 3C-SiC film increased with increasing TMS flow rate and growth temperature. The growth kinetics of 3C-SiC film was determined by analyzing the experimental data on the growth rate. The growth reaction of 3C-SiC film was the first order of TMS partial pressure in the reactor. The reaction rate controlling step changed from the surface reaction in the temperature range of 1100–1250 °C to the diffusion of reactive gases at higher temperatures above 1250 °C. The activation energies were 72.2 kcal/min for the surface reaction-controlling step and 38.2 kcal/min for the diffusion-controlling step. At the growth temperatures, TMS was dissociated into hydrogen, Si atoms, and hydrocarbon gases such as CH3⋅, CH4, C2H2, and C2H4. The effective reactive species for the growth of 3C-SiC turned out to be gaseous Si atom...

Cl2-based dry etching of GaN films under inductively coupled plasma conditions

Dry etching of undoped, n- and p-type GaN films was carried out in Cl2-based inductively coupled plasmas (ICPs) using different rf excitation frequencies of 100 kHz and 13.56 MHz, in which the rf chuck power source operates. The etch rates with lower frequency of 100 kHz are somewhat greater than those with a higher frequency of 13.56 MHz due to higher ion bombarding energy with lower frequency. The highest etch rates with the 100 kHz frequency were obtained at moderately high ICP power of 700 W: ∼9300 A/min of n-GaN, ∼5300 A/min of p-GaN, and ∼7100 A/min of undoped GaN. The 13.56 MHz frequency of rf chuck power source produced maximum etch rates of ∼7900 A/min of n-GaN, ∼5800 A/min of p-GaN, and 6100 A/min of undoped GaN at 20 mTorr, 700 W ICP, and 150 W rf power. The surface roughness was relatively independent of the chuck power up to 150 W in 13.56 MHz and showed fairly smooth morphology (rms 1.1–1.3 nm), while etching at higher rf power (>200 W) produced rougher surface.

Effect of dry etching conditions on surface morphology and optical properties of GaN films in chlorine-based inductively coupled plasmas

Dry etching of undoped, n- and p-type GaN films has been carried out in a planar type inductively coupled plasma (ICP) system. The effect of etching conditions on surface morphology and optical properties of GaN films etched in Cl2/Ar discharges was studied. All the GaN films showed overall similar etching behavior at 700 W ICP, 150 W rf, 40 mTorr, and 25% Cl2. The surface roughness was relatively independent of the rf power up to 150 W, resulting in quite smooth morphology (root-mean-square roughness 1.1–1.3 nm), while etching at higher chuck powers (>200 W) produced rougher surfaces due to increased ion bombardment. The lattice disorder and point defect density were lower during the ICP etching compared with reactive ion etching. The intensity of the band edge peak of as-grown n-GaN was decreased after the ICP etching, and the extent of intensity decrease was inversely proportional to the applied chuck power. By contrast, the as-grown p-GaN showed a weak intensity of band edge emission, but the peak shi...

Growth characteristics and deposition mechanism of SrTiO3 thin films by plasma enhanced metalorganic chemical vapor deposition

Dielectric SrTiO3 thin films were deposited on Pt/Si and Ir/Si substrates by plasma enhanced metalorganic chemical vapor deposition using high purity Ti(O-i-C3H7)4, Sr(tmhd)2, and oxygen. The deposition rates were quite dependent on bubbler temperature, substrate temperature, and rf source power. The dissociation of Ti(O-i-C3H7)4 was substantially enhanced by increasing the rf source power, while that of Sr(tmhd)2 increased with the substrate temperature. Surface morphology showed a smooth surface and good adhesion at the interface. Based on the growth characteristics of films, it was found that the deposition of SrTiO3 films was controlled by the decomposition rate of Sr(tmhd)2 on the substrate surface.Dielectric SrTiO3 thin films were deposited on Pt/Si and Ir/Si substrates by plasma enhanced metalorganic chemical vapor deposition using high purity Ti(O-i-C3H7)4, Sr(tmhd)2, and oxygen. The deposition rates were quite dependent on bubbler temperature, substrate temperature, and rf source power. The dissociation of Ti(O-i-C3H7)4 was substantially enhanced by increasing the rf source power, while that of Sr(tmhd)2 increased with the substrate temperature. Surface morphology showed a smooth surface and good adhesion at the interface. Based on the growth characteristics of films, it was found that the deposition of SrTiO3 films was controlled by the decomposition rate of Sr(tmhd)2 on the substrate surface.

Improvement of electrical and optical properties of ingan/ganbased lightemitting diodes with triangular quantum well structure

Substantial improvement of electrical and optical properties of InGaN/GaN multiple quantum wells (MQWs) was obtained with a triangular band structure. Transmission electron microscopy (TEM) images from the–50 nm. The light-emitting diodes (LEDs) with the triangular QWs showed a lower operation voltage, a higher light output power, and higher intensities and narrower line widths of electroluminescence spectra than those with the rectangular QWs. Very bright and uniform light emission from the triangular MQW LEDs was also observed at a low injection current, but spatially non-uniform emission from the rectangular ones.

Controllable Synthesis of ZnO Nanonails by Vapor-Solid Process: Growth Mechanism and Structural and Optical Properties

Single-crystalline with good optical properties aligned ZnO nanonails were grown on steel alloy substrate without the use of metal catalyst or additives by the thermal evaporation process using high purity metallic zinc powder and oxygen as source materials for zinc and oxygen, respectively. Detailed morphological studies by FESEM revealed that the obtained nanonails are grown in a high density over the whole substrate surface and are exhibiting perfect hexagonal-shaped caps. The diameters of the nanonails at their tops and bases are ranges from 120∼160nm and 50∼70 nm, respectively. The detailed structural characterizations confirmed that the synthesized nanostructures are single-crystalline and grown along the c-axis direction. Raman scattering and room-temperature photoluminescence studies demonstrated the wurtzite hexagonal phase and good optical properties, respectively for the grown nanonails.