Properties of Amorphous Transparent Conducting and Semiconducting Oxides from First Principles
"Amorphous transparent conducting and semiconducting oxides possess properties superior or comparable to their crystalline counterparts. The structure-property relationship in amorphous oxides is not nearly as well understood as in the case of the crystalline transparent conducting oxides. We have employedab initio molecular dynamics and a liquid quench approach to simulate amorphous oxide structures and performed density functional-based calculations to study the electronic properties of several amorphous conducting and semiconducting oxides with various cation compositions. The effect of amorphization in oxides was investigated by taking indium oxide as a progenitor of the system. From the thorough study it was confirmed that the distribution and connectivity of naturally coordinated indium polyhedra (InO6) depend on the cooling rates used in the quenching process. Also, it was shown experimentally that the transport properties depend strongly on the deposition temperature, in particular, the carrier Hall mobility is enhanced at the onset of the amorphous region to become similar to the mobility in crystalline In2O3. Our results have shown that the corresponding amorphous structure exhibits a long chain of the InO6 connected primarily via corner sharing, thus, highlighting the importance of the medium/long-range structural characteristics. To understand the effect of chemical composition on the structure and properties of amorphous oxides, In-X-O with X=Sn, Zn, Ga, Cd, Ge, Sc, Y, or La, were studied. The results reveal that the short-range structure of the metal-O polyhedra is preserved in the amorphous oxides; therefore, the extended nature of the conduction band, the key feature of transparent conducting oxide, is maintained. Unlike the case of crystalline transparent oxides, additional cation in amorphous oxides does not act as a dopant. Instead, the presence of X affects the number of naturally coordinated In atoms as well as the oxygen sharing between metal-oxygen polyhedra which ultimately affects the transport properties"--Abstract, page iv.
Ab Initio Moleculardynamics, Amorphous Oxides, Density Functional Theory, Electronic Structure, Semiconductors, Transparent Conductors, Physics
Missouri University of Science and Technology
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