Search

Heterojunction solar cells were fabricated by electrochemical deposition of p-type, cuprous oxide (Cu2O) absorber on sputtered, n-type ZnO layer. X-ray diffraction measurements revealed that the as-deposited absorber consists mainly of Cu2O, but appreciable amounts of metallic Cu and cupric oxide (CuO) are also present. These undesired oxidation states are incorporated during the deposition process and have a detrimental effect on the photovoltaic properties of the cells. The open circuit voltage (VOC), short circuit current density (jSC), fill factor (FF) and power conversion efficiency (η) of the as-deposited cells are 0.37 V, 3.71 mA/cm2, 35.7% and 0.49%, respectively, under AM1.5G illumination. We show that by thermal annealing in vacuum, at temperatures up to 300 °C, compositional purity of the Cu2O absorber could be obtained. A general improvement of the heterojunction and bulk materials quality is observed, reflected upon the smallest influence of the shunt and series resistance on the transport properties of the cells in dark and under illumination. Independent of the annealing temperature, transport is dominated by the space-charge layer generation-recombination current. After annealing at 300 °C the solar cell parameters could be significantly improved to the values of: VOC = 0.505 V, jSC = 4.67 mA/cm2, FF = 47.1% and η = 1.12%.

The switching behavior of the amorphous CoFeB/Ru/CoFeB artificial antiferromagnet (AFi) at submicron sizes is investigated, where additional shape anisotropy and the mangnetostatic edge coupling are also considered. The AFi has an increased coercivity with respect to a single layer of amorphous CoFeB and switching asteroids comparable to single layers are observed in samples with a high new moment.

Large tunnel magnetoresistance of approximately 60% in sputter-deposited junctions with plasma oxidized, polycrystalline MgO barriers and Co50Fe50 FM electrodes is demonstrated. These junctions present a resistance-area product approximately two orders of magnitude lower than AlO(sub x) junctions.

Research into magnetostatic interactions between the soft and the hard magnetic electrodes in magnetic tunnel junctions using artificial ferrimagnets is presents. The local stray fields linked with domain wall situated in the AFi layers were found to be responsible to the local pinning of domain wall in the detection layer during its reversal.

Research into micromagnetic characteristics arising during the reversal of an artificial ferrimagnet used as a hard layer of a magnetic tunnel junction is presented. An analytical model has been developed which takes account of different tunneling paths linked with local magnetization structures.

Research into properties of very thin insulating Al oxide films, serving as barriers in magnetic tunnel junctions, is presented. It was possible to emphasize the link between the local transport properties of the tunnel barrier and the quantities obtained from measuring patterned micronic junctions.

In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n-doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling junctions. [ABSTRACT FROM AUTHOR]

In this work we study Al-oxide-based tunnel junctions with amorphous Co60Fe20B20 and polycrystalline Co90Fe10 ferromagnetic (FM) electrodes. Focus is given on the evolution of the tunnel magnetoresistance and barrier characteristics (resistance-area product, effective thickness, height, and asymmetry) as a function of the annealing temperature up to 400 °C. Junctions with two CoFeB electrodes show the largest thermal stability of the tunnel magnetoresistance. Substituting firstly one and then both CoFeB electrodes with CoFe leads to an increasingly faster degradation of the spin-dependent transport upon annealing. The observed differences suggest an improved interface quality between the amorphous FM and the Al oxide. [ABSTRACT FROM AUTHOR]

The inelastic, spin-dependent tunneling in magnetic junctions with AlOx barrier and Co50Fe50 ferromagnetic (FM) electrodes is discussed. There is less decline of JMR with temperature for the annealed junctions and the maximum decrease of JMR is measured for the overoxidised as-deposited junctions.

A powerful technique for controlling the oxidation of ultrathin metallic layers is described. This technique consists of depositing the metallic layer to be oxidized on top of the soft magnetic layer of a bottom spin valve.

Magnetic tunnel junctions are fabricated, that use Co/Ru/Co and Co/Ru/CoFe artificial ferrimagnet (AFi) systems as hard magnetic electrodes. Together with the enhanced thermal stability, up to 350 degree Celsius of the junctions involving the Co/Ru/CoFe system potential use as magnetic sensors is discussed.