Mechanism of polarization pinning in vertical cavity surface emitting lasers using focused ion beam etching

Photoluminescence experiments have identified strain as the origin for polarization pinning in vertical cavity surface emitting lasers post-processed by focused ion beam etching. Theoretical models were applied to deduce the strain in devices. Post-annealing was used to optimize polarization pinning.

Self-assembled artificial pinning centres in thick YBCO superconducting films

Strong, artificial pinning centres are required in superconducting films of large thickness for power applications in high magnetic fields. One of the methods for the introduction of pinning centres in such films is substrate decoration, i.e., growing nanoscale islands of certain materials on the substrate prior to the deposition of the superconducting film. Two other methods are building up a layered distribution of a second phase and homogeneous incorporation of second phase inclusions from a compositional target. In this paper, we compare the effectiveness of these methods in terms of the type of the self-assembly of nanoparticles. The comparison is made over a large set of YBa2Cu3O7 films of thickness up to 6.6 μm deposited with Au, Ag, Pd, LaNiO3, PrBa2Cu 3O7, YBCO, BaZrO3 and Gd2Ba 4CuWOy nanoparticles. It is found that substrate-decoration self-assembly is able to provide higher critical current in low magnetic field than the incorporation of homogeneous second phase in the sample microstructure. By specific modification of substrate decoration we achieved the self-field critical current per centimetre of width of 896 A/cm at 77.3 K and 1620 A/cm at 65 K in a film of thickness of 4.8 μm. © 2010 IOP Publishing Ltd.

Flux line lattice structure and behavior in antiphase boundary free vicinal YBa2Cu3O7-delta thin films

Field angle dependent critical current, magneto-optical microscopy and high resolution electron microscopy studies have been performed on YBa2Cu3O7-delta thin films grown on miscut substrates. High resolution electron microscopy images show that the films studied exhibited clean epitaxial growth with a low density of antiphase boundaries and stacking faults. Any antiphase boundaries (APBs) formed near the film substrate interface rapidly healed rather than extending through the thickness of the film. Unlike vicinal films grown on annealed substrates, which contain a high density of antiphase boundaries, magneto-optical imaging showed no filamentary flux penetration in the films studied. The flux penetration is, however, asymmetric. This is associated with intrinsic pinning of flux strings by the tilted a-b planes and the dependence of the pinning force on the angle between the local field and the a-b planes. Field angle dependent critical current measurements exhibited the striking vortex channeling effect previously reported in vicinal films. By combining the results of three complementary characterization techniques it is shown that extended APB free films exhibit markedly different critical current behavior compared to APB rich films. This is attributed to the role of APB sites as strong pinning centers for Josephson string vortices between the a-b planes. (C) 2003 American Institute of Physics.