Efficiency a-Si:H solar cell. Detailed theory

We develop a detailed formalism to photoconversion efficiency η of hydrogenated amorphous silicon ( a-Si:H ) based solar cells with a contact grid. This efficient three-dimensional model allows firstly optimization of the p i n sandwich in terms of carrier mobilities, thickness of the layers, doping levels and others. Secondly, geometry of the grid fingers that conduct the photocurrent to the bus bars and ITO/SiO₂ layers has been optimized, and the effect of non-zero sun beam incidence angles has been included as well. The model allows optimization of the amorphous Si based solar cells in a wide range of key parameters

Ohmic contacts based on Pd to indium phosphide Gunn diodes

Experimental data on manufacturing the ohmic contacts Au–Ti–Pd–n⁺-InP, formed using vacuum deposition of metal onto a heated to 300 °C substrate representing an epitaxial n⁺-n-n⁺⁺-n⁺⁺⁺-InP structure. The specific contact resistance measured at room temperature was about 7·10⁻⁵ Ohm·cm². Voltage-current characteristics within the temperature range 110 to 380 K are linear. Gunn diodes with such contacts, which were made as a straight mesa-structure in a pulsed mode (pulse duration of 100 ns, pulse ratio of 1000, operating current of 2.2 A), generated the microwave power ~10 mW in the V-band

Local threshold field for dendritic instability in superconducting MgB2 films

Using magneto-optical imaging the phenomenon of dendritic flux penetration in superconducting films was studied. Flux dendrites were abruptly formed in a 300 nm thick film of MgB2 by applying a perpendicular magnetic field. Detailed measurements of flux density distributions show that there exists a local threshold field controlling the nucleation and termination of the dendritic growth. At 4 K the local threshold field is close to 12 mT in this sample, where the critical current density is 10^7 A/cm^2. The dendritic instability in thin films is believed to be of thermo-magnetic origin, but the existence of a local threshold field, and its small value are features that distinctly contrast the thermo-magnetic instability (flux jumps) in bulk superconductors.Comment: 6 pages, 6 figures, submitted to Phys. Rev.

New technological possibilities to prepare InP epitaxial layers, as well as ohmic and barrier contacts to them, and the properties of microwave diodes made on their basis

A novel technological approach to fabrication of n-InP autoepitaxial films LPE-grown on porous n⁺-InP substrates, as well as ohmic and barrier contacts to them using (quasi)amorphous TiBx interstitial phases, is proposed. We demonstrate the advantages of TiBx−n-n⁺-n⁺⁺-InP Schottky-barrier diodes made on porous substrates over those made on the standard rigid substrates, as well as the possibility to make Gunn diodes (intended for the 120−150 GHz frequency range) on the InP epitaxial structures grown on porous substrates

Structural and electrical-physical properties of the ohmic contacts based on palladium to n⁺ -n-n⁺⁺ -n⁺⁺⁺ -InP

Presented in this paper are experimental data on structural properties of contact metallization and temperature dependence of the specific contact resistance for ohmic contacts Au–Ti–Pd–n⁺-InP and Au–Ti–Ge–Pd-n⁺-InP prepared using the method of successive thermal evaporation of metals in oil-free vacuum in one process cycle onto the n⁺-n-n⁺⁺-n⁺⁺⁺-InP epitaxial structure heated to 300 °C. It has been theoretically and experimentally shown that within the temperature range 250…380 K the current transport mechanism in the ohmic contacts Au–Ti–Pd–n⁺-InP is thermal-field one, and in the ohmic contacts Au–Ti–Ge–Pd-n⁺-InP it is caused by conductivity along metal shunts linked with dislocations. According to the X-ray diffraction data, the density of these dislocations in the near-contact InP area is ~10⁹ cm⁻²

Novel technological possibilities for growth of GaAs autoepitaxial films, and properties of Gunn diodes made on their basis

The n⁺-n-n⁺-n⁺⁺-GaAs epitaxial structures were MBE-grown on porous nanostructured and traditional (standard) heavily doped n⁺⁺-GaAs substrates. On their basis, we fabricated the Gunn diodes generating power output in the 44−59 GHz (first harmonic) and 101−104 GHz (second harmonic) frequency ranges. For both harmonics, the power output of the Gunn diodes grown on porous substrates was shown to be from 20 to 30 % higher than those grown on the flat ones

Adlayers of palladium particles and their aggregates on porous polypropylene hollow fiber membranes as hydrogenization contractors/reactors

Principal approaches for the preparation of catalytic membrane reactors based on polymer membranes containing palladium nanoparticles and for the description of their characteristics are presented. The method for the development of adlayers composed of palladium nanoparticles and their aggregates on the surface of hydrophobic polypropylene porous hollow fiber membranes is proposed, and their comprehensive study is performed. Various regimes of the deposition of palladium on individual fibers and on membrane surface inside membrane modulus are considered. The sizes of primary Pd particles range from 10 to 500 nm, and dimensions of their aggregates vary from 200 nm to tens of microns. The sizes of primary particles in a free state and in their aggregates are estimated by the methods of X-ray analysis and scanning electron microscopy. The proposed approach is used for the preparation of catalytic membrane contactors/reactors for the removal of dissolved oxygen from water. In the systems under study, the limiting stage of dissolved oxygen removal is concerned with diffusion-controlled delivery of oxygen to the surface of catalytic particles. © 2010 Elsevier B.V. All rights reserved