Plate-shaped piezoelectric transformers were designed and manufactured with Pb(Mg 1=3 Nb 2=3 )O 3 -PbTiO 3 single crystals (PMN-PT). Theoretical analysis was performed using Mason's equivalent circuit model and finite element method (FEM) simulations. In the experiment, transformer performances, especially the power density, were compared among different materials, including lead zirconate titanate (PZT) ceramics, undoped PMN-PT, and manganese-doped PMN-PT (Mn-PMN-PT). High power density of 38 W/cm 3 was obtained using single crystals, which was 5 times that of hard PZT ceramics. The power level of the single crystal transformer showed a significant dependence on doping, poling direction, and cutting orientation. Results also verified that the high power performance was mainly determined by the electromechanical coupling coefficient and mechanical quality factor of the material.

Auger recombination (AR) in quantum well (ow) semiconductors is re-investigated taking into account a realistic band structure instead of the usual parabolic approximation. Since direct AR is negligible in ows phonon-assisted AR is treated. The theoretical results are in good agreement with experimental investigations. In contrast, the description of ows by a reduced heavy-hole mass is insufficient. The influence of AR on the temperature dependence of semiconductor lasers is discussed.

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