Seung-Yoon Lee

Oxygen-Controlled Seed Layer in DC Sputter-Deposited ZnO:Al Substrate for Si Thin-Film Solar Cells

Oxygen-controlled seed layer in Al-doped ZnO (ZnO:Al) thin films deposited by the industrially compatible dynamic dc magnetron sputter results in both enhanced electron mobilities and appropriate etched morphologies for the Si thin-film solar cells. At the relatively low deposition temperature of 300 °C, optimized ZnO:Al film grown on the seed layer has the carrier mobility of 45 cm2/V·s and proper postetching morphology with around 1-2-μm crater size. Reduced angular distribution of the (002) grains analyzed by the diffraction rocking curve is shown as the key structural feature for the improved carrier mobility. Finally, the performance of the microcrystalline Si solar cell on the developed ZnO:Al substrate shows high-efficiency potential of the tandem solar cell adapting this transparent conductive oxide substrate.

Enhancement of Crystallinity in ZnO:Al Films Using a Two-Step Process Involving the Control of the Oxygen Pressure

The ZnO:Al films were prepared using a two-step process through the control of oxygen pressure by DC-pulsed magnetron sputtering. The seed layers were prepared with various Ar to oxygen pressure, and the bulk layers were deposited under pure Ar. At the seed-layer condition of Ar/O2 = 24/1 (Ar rich), the seed layer showed grains that led to the formation of hillock, and the grains of seed layer were seem to act as nucleation sites for columnar growth of bulk layer. While, at the seed-layer condition of Ar/O2 =4/1 (oxygen rich), grains show large lateral growth with a nonuniform distribution, and a number of dislocations are shown in grains. As oxygen pressure during the deposition of seed layer increased, the decrease of local strain (or the increase of crystallinity) was observed. The etched surface showed the crater-like structure and the abrupt morphology change appeared at high oxygen pressure, which was likely due to nonuniform grain structure and/or the decrease in the number of chemical attack sites by the drastic decrease of grain boundary. The haze values increased with increasing oxygen pressure, which was explained by the change of crater size, as shown in the AFM image.

Phase change optical media with time-shifted multipulse write strategy for 1X-2X dual speed Blu-ray disc system

We have developed phase change optical media with appropriate write strategy for 1X-2X dual speed Blu-ray Disc system and for the future high speed phase change optical data storage. For recording layer, eutectic-based Ge(Sb70Te30)+Sb material was used and Sb/Te ratio and Ge content were optimized to obtain proper erasability and archival stability of recorded amorphous marks. The recording layer is wrapped up in GeN interface layers to obtain reasonable overwrite cyclability and higher crystallization speed. In addition, we designed appropriate write strategy so-called time-shifted multipulse(TSMP) where the starting positions of multipulse parts are shifted from reference clock. With this write strategy, the overall jitter characteristics of the disc was improved and especially we found that trailing edge jitter was improved much more than leading edge jitter. Thus feasibility of 1X-2X dual speed applicable Blu-ray Disc and its write strategy was demonstrated.