Impact of firing on surface passivation of p-Si by SiO2/Al and SiO2/SiNx/Al stacks

Firing impacts on surface passivation provided by a SiO2 and SiO2/SiNx stack with evaporated Al films are studied by capacitance-based techniques on MIS capacitors. For devices with insulator layers consisting solely of as-deposited SiO2, the densities of either interface states (Dit) or fixed charges (Qfc) are hardly influenced by firing. Capping the SiO2 layer with a SiNx layer results in a shift of the peak activation energy of Dit toward the valence band (Ev) of Si. Firing this SiO2/SiNx stack leads to an increase of Qfc, a reduction of Dit, and a moderate shift of peak activation energy of Dit toward Ev. Co-firing with the Al film on top significantly reduces the Qfc, Dit, and Dit peak activation energy, which is resulting from the atomic hydrogen passivation. These results are of particular interest for the development of solar cells with rear surface passivation and local contacts

K2 Y F5 crystal symmetry determined by using rare-earth ions as paramagnetic probes

The electron paramagnetic resonance angular dependences for Gd3+ and Ce3+ centers in K2 Y F5 crystals show that the Y3+ site has monoclinic Ch symmetry in these crystals. This site symmetry is compatible with the crystal structure having the Pnam space group. From the zero-field splitting parameters of the Gd3+ center, it is deduced that the symmetry of the Y3+ sites is close to trigonal around the b axis, distorted by the overall orthorhombic symmetry of the crystal structure. This information is required for the identification of radiation-induced centers in this material, which shows favorable properties for applications as thermoluminescent dosimeter. © 2007 The American Physical Society

Transferred hyperfine interactions for Yb3+ ions in CsCa F 3 and Cs2 NaY F6 single crystals: Experimental and ab initio study

The results of an electron-nuclear double resonance study of the cubic paramagnetic Yb3+ center in Cs2 NaY F6 and CsCa F3 single crystals are presented. The values and signs of the transferred hyperfine interaction (THFI) parameters for several neighboring shells are determined. It is found that the relevant parameters for the two studied matrices differ, in spite of the fact that the nearest environment of the rare earth ion is nearly identical. A first-principles theoretical analysis is performed for the THFI parameters of the first coordination shell of F- ions. Several mechanisms of metal ion-ligand coupling are considered and it is found that one of them, ligand polarization, explains the difference observed for the THFI parameters in Cs2 NaY F6 and CsCa F3. © 2009 The American Physical Society