Sungkuk Choi

Abnormal variation of the growth rate under high NH3 injected regime in the growth of GaN by NH3-source MBE

Unusual growth-rate variation during GaN formation using gas-source MBE has been discussed with respect to the chemical reactions occurring in the transition layer. A series of samples were prepared to confirm the assumption by verifying the growth regime and the impacts on the crystal quality of the GaN film. We found that the growth rate can be varied along with the amount of NH3 supply even under NH3-rich condition with a fixed Ga flux. Two growth conditions were investigated for their impact on the transition layer. One was the atomic force microscopy result, which revealed that the adatom migration length is closely related to the transition layer formation. The other one is the photoluminescent spectra, which revealed that the luminescence property of GaN is strongly related to the transition layer.

A Study on the In-situ Separation of GaN by Using Thermal Decomposition

The free-standing GaN (FS-GaN) substrate was fabricated by using an in-situ self-separation technique that was accomplished by using the thermal decomposition of GaN. For the self-separation of GaN, a decomposable buffer layer (DBL) was introduced between the sapphire substrate and the overgrown thick-GaN, and self-separation of GaN happened during the high-temperature GaN growth. The thick GaN was almost unaffected by the thermal stress during the separation from sapphire substrate, so we could fabricate low-defect and high-quality FS-GaN. In this study, the DBL growth temperature (Tg: 700 ◦C) and the thermal annealing temperature (T ∼ 900 ◦C) were optimized. The reduced thermal stress was confirmed by using cathodoluminescence. Also, the values of the full widths at half maximum for the (002) and the (102) ω-rocking curves were 67 and 96 arcsec, respectively, and a low etch pit density (6 × 10 cm−2) was observed, both of which indicate the feasibility of this method for fabricating FS-GaN.

The Effect of V/III Ratio on Growth Mechanism of Gas Source MBE

Growth mechanism of GS-MBE(Gas source-Molecular Beam Epitaxy) has been investigated. We observed that the growth rate of GaN films is changing from 520 nm/h to 440 nm/h by the variation of V/III ratio under nitrogen-rich growth condition. It was explained that the amount of hydrogen on the growth front varies by the ammonia flow, and gallium hydrides are generated on the surface by a reaction of hydrogen and gallium, resultantly the amount of gallium supplying is changing along with the flow. Reflection high energy electron diffraction (RHEED) observation was used to confirm the N-rich condition. The crystal quality of GaN was estimated by photoluminescence (PL) and X-ray diffraction (XRD).

Growth of O- and Zn-polar ZnO films by DC magnetron sputtering

Department of Nano-semiconductor Engineering, National Korea Maritime University, Busan 606-791, Korea*Department of Offshore Plant Management, National Korea Maritime University, Busan 606-791, Korea**Division of Electrical and Electronics Engineering, National Korea Maritime University, Busan 606-791, Korea***PAN-Xal Co., Ltd., Suwon 443-380, Korea****Center for Interdisciplinary Research, Tohoku University, Sendai 980-8577, Japan

Two-way optical communication system in which each Si photo-diode plays two roles of light-receiver and light-emitting diode

We developed a unique and simple two-way optical transmission system in which each Si photo-diode plays two roles of photo-receiver and light-emitting diode. Such a system may lead to realization of fully monolithic Si OEIC.