Search

First-principles calculations based on a truncated Coulomb hybrid functional were used to elucidate Y 2 O 3 doping of HfO 2. We calculated the formation enthalpies as well as density of states of nearly 1200 defective structures of two phases of HfO 2 : room-temperature monoclinic and high-temperature cubic structures. For dilute doping, the monoclinic phase is retained and electron trapping states are introduced near the conduction band minimum. For doping concentrations near to 12.5 at. %, the cubic phase is stabilized and the gap is free from charge trapping defect states, making it a suitable high-dielectric constant material for complementary metal-oxide semiconductor applications. [ABSTRACT FROM AUTHOR]

Bournonite (CuPbSbS3) and enargite (Cu3AsS4) have recently been used as absorber layers in thin-film photovoltaic devices due to their ideal bandgap and ferroelectric properties. An understanding of the ferroelectric domain structure in these materials is required so that the benefits of the internal depolarizing electric fields can be fully exploited. Here, the atomic structure and electronic properties of domain walls (DWs) are elucidated through a combined aberration-corrected scanning transmission electron microscopy and density functional theory study. ∼90° and 180° DWs are observed in bournonite. As the 180° DW is charge neutral, it cannot contribute to the anomalous photovoltaic effect that leads to high open circuit voltages. The ∼90° DW shows a slight offset across the boundary, but the contributions of this to the anomalous photovoltaic effect are negligible. The DWs are also electrically passive, i.e., they do not result in significant recombination and do not block charge carrier transport. A high density of stacking faults (SF) was, however, observed in enargite. The SFs have a large number of defect states within the bandgap, which would lower the device efficiency through Shockley–Read–Hall recombination. [ABSTRACT FROM AUTHOR]