Sang Chil Lee

Mechanism of light emission and manufacturing process of vertical-type light-emitting diode grown by hydride vapor phase epitaxy

We developed a vertical-type light-emitting diode (LED) in which the substrate is removed using a hydride vapor phase epitaxy (HVPE) apparatus consisting of a multi-graphite boat filled with a mixed source and a high-temperature (T ≈ 900 °C) RF heating coil outside the source zone. The new chip-growth process with a significant reduction in the number of production steps is completed in only four steps, namely, photolithography, epitaxial layer growth, sorting, and metallization. We analyze the emission mechanism of these lights from measurement results to validate the characteristics of the light emitted from these vertical-type blue LEDs and white LEDs (WLEDs) without substrates, and propose that this mixed-source HVPE method may be a promising production technique for LEDs.

The hysteretic voltage gap for a single-electron dual-junction-array trap with stray capacitances

The hysteretic voltage gap ΔV(m) - the difference between the threshold voltages for single-charge-soliton tunnelling into and escape from a single-electron dual-junction-array trap (which consists of 2N gated small junctions with equal junction capacitances C, equal stray capacitances C0, equal input gate capacitances C1, and coupling capacitance CC) through an m-junction cotunnelling process - is investigated for various charge solitons including a single electron, an exciton, and a combined soliton. Our results show that ΔV(m) has a strong dependence on m, C0/C, C1/C, CC/C, and N, and that no hysteresis loop exists beyond a critical value ηc of C0/C. For finite stray capacitance and strong coupling capacitance, the exciton can be a candidate for use in constructing more stable single-electron circuits, as in the case of no stray capacitance and weak coupling capacitance previously discussed in the literature.