세미나안내

[2014 01 10] 특별세미나

Understanding of point defects in oxides and their impact on electronic devices from first principles

MSE Graduate Students and Researchers

관리자 | 2014.01.10 11:30 | 조회 3072


Reception: MSE Graduate Students and Researchers

Reference: MSE Professors

Subject: MSE Special Seminar_ Dr. Minseok Choi

 

 Date: 2014. 1. 10(FRI), 16:00 ~ 17:00

 Place: Science Building, Room. 202 Multimedia Room

 Title: Understanding of point defects in oxides and their impact on electronic devices from first principles

 Speaker: Dr. Minseok Choi

Advanced Characterization and Analysis Group, Korea Institute of Materials Science (KIMS)

 Host of a Seminar: Prof. Junwoo Son

 

 Abstract

Using first-principles calculations based on density-functional theory, point defects in the structural, electrical, and optical properties of oxides have been studied. In this talk, our recent results for native donors in SrTiO3 will be presented. For SrTiO3, the issue of what cause the fascinating physical such as very high n-type conductivity, visible-light emission, and ferroelectricity without doping is still under debate. These properties have typically been attributed to the O vacancy or its complexes, but the role of these defects has not been well explored. Our calculations show that the off-centered Ti antisite is likely to form, even comparable with O vacancy, and introduces deep, localized states in the gap. Based on these results, we conclude that the experimentally observed properties could be related to the Ti antisite. We find that the O vacancy induces local octahedral rotation even in the cubic phase, with the electron localization near the vacancy. Such electronic structure provides an explanation for the n-type conductivity in reduced SrTiO3 and for the visible-light emission as well as the Ti antisite. We have also examined how point defects in gate dielectrics impact on the performance of metal-oxide-semiconductor (MOS) devices.  High-k oxides are intensively studied for industrial applications, such as alternative gate dielectrics in MOS devices. Promising results have been achieved with Al2O3/III-V and HfO2/Si MOS structures, which exhibit relatively low densities of interface states. However, the presence of carrier traps and fixed charges near the oxide/semiconductor interface still poses serious limitations in device performance. We investigate the effects of impurities in Al2O3 and HfO2, which could be introduced during the deposition process. By analyzing the position of the impurity levels with respect to the semiconductor band edges, the role of the impurities in the electrical properties of MOS devices is addressed. Our results show that the C impurity can act as carrier traps and/or lead to leakage current through the gate dielectric. N impurity is a likely source of fixed charge, but may be effective in alleviating the problem of carrier traps and fixed charges associated with native defects.

 

Department of Materials Science and Engineering



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