Development of a spin-injection device utilising Gadolinium Nitride

<p>In this thesis, the first steps in creating a realisable spin-injection transistor using ferromagnetic semiconductor electrodes are detailed. A spin-injection device utilising the ferromagnetic semiconductor gadolinium nitride has been designed, fabricated and electrically tested. In addition, an experimental setup for future measurements of a spin current in spin-injection devices was adapted to our laboratory-based off one developed by the Shiraishi group at Kyoto University. Issues encountered during fabrication were identified, and an optimal method for fabricating these devices was determined. Gadolinium nitride and copper were used to make the devices on Si/SiO2 substrates. The electrical integrity and applicability of the devices for future measurements of injected spin-current was determined through electrical device testing. Resistance measurements of electrical pathways within the device were undertaken to determine the successful deposition of the gadolinium nitride and copper. IV measurements to determine if the devices could withstand the current required for spin current measurements were done. The durability of the devices through multiple measurement types was observed. It was determined that although spin-injection devices utilising gadolinium nitride can be successfully fabricated, more work needs to be done to ensure that the electrical pathways through the copper and gadolinium nitride can be consistently reproducible to allow spin-injection measurements to be done.</p>

Development of a spin-injection device utilising Gadolinium Nitride

<p>In this thesis, the first steps in creating a realisable spin-injection transistor using ferromagnetic semiconductor electrodes are detailed. A spin-injection device utilising the ferromagnetic semiconductor gadolinium nitride has been designed, fabricated and electrically tested. In addition, an experimental setup for future measurements of a spin current in spin-injection devices was adapted to our laboratory-based off one developed by the Shiraishi group at Kyoto University. Issues encountered during fabrication were identified, and an optimal method for fabricating these devices was determined. Gadolinium nitride and copper were used to make the devices on Si/SiO2 substrates. The electrical integrity and applicability of the devices for future measurements of injected spin-current was determined through electrical device testing. Resistance measurements of electrical pathways within the device were undertaken to determine the successful deposition of the gadolinium nitride and copper. IV measurements to determine if the devices could withstand the current required for spin current measurements were done. The durability of the devices through multiple measurement types was observed. It was determined that although spin-injection devices utilising gadolinium nitride can be successfully fabricated, more work needs to be done to ensure that the electrical pathways through the copper and gadolinium nitride can be consistently reproducible to allow spin-injection measurements to be done.</p>

PHOTOPHYSICAL AND PHOTOCHEMICAL SYSTEMS WITH SEMICONDUCTORS FOR THE CONVERSION OF SOLAR ENERGY. A REVIEW

Electrochemical energy sources are an alternative to replace technology based on the burning of fossil fuels. In an elec-trochemical system the potential drop spreads over a very narrow region at an interphase, creating high electric fields.So, there are good technological reasons to study semiconductor / electrolyte interphases. Currently, one of the ways touse renewable resources is through photovoltaic technology that directly converts solar radiation into electrical energy.This technology is manufactured from semiconductors, generally silicon, following an extremely careful and expensivemanufacturing procedure. An option for photovoltaic devices is photoelectrochemical cells.These cells are made bythe contact of a semiconductor electrode with a solution, which can be easily prepared and offers the possibility oflow-cost manufacturing. Understanding how these devices work requires knowledge of the characteristics of semicon-ductors and how these materials behave in contact with an electrolytic solution and under illumination by sunlight. Thepresent work describes, through an updated review, the principles and applications of semiconductor electrodes as themain components in a photoelectrochemical solar cell (PEC), to carry out chemical reactions of technological interest.In addition, the elements that are required for the improvement in the performance and construction of the PEC are discussed.

Charge Injection and Dielectric Characteristics of Polyethylene Terephthalate Based on Semiconductor Electrodes

Employing a novel semiconductor electrode in comparison with the traditional semiconductor electrode made of polyethylene/ethylene-vinyl-acetate copolymer/carbon-black (PE/EVA/CB) composite, characteristic charge carriers are injected into polyethylene terephthalate (PET) as a polymer dielectric paradigm, which will be captured by specific deep traps of electrons and holes. Combined with thermal stimulation current (TSC) experiments and first-principles electronic-state calculations, the injected charges from the novel electrode are characterized, and the corresponding dielectric behavior is elucidated through DC conductance, electrical breakdown and dielectric spectrum tests. TSC experiments with novel and traditional semiconductor electrodes can distinguish the trapping characteristics between hole and electron traps in polymer dielectrics. The observable discrepancy in space charge-limited conductance and the stable dielectric breakdown strength demonstrate that the electron injection into PET film specimen is restricted by using the novel semiconductor electrode. Attributed to the favorable suppression on the inevitable electron injections from metal electrodes, adopting novel i-electrode can avoid the evident abatement of dipole orientation polarization caused by space charge clamp, but will engender the accessional high-frequency dielectric loss from dielectric relaxations of interface charges at i-electrodes.

Characteristics of the Nanosecond Overvoltage Discharge Between CuInSe2 Chalcopyrite Electrodes in Oxygen-Free Gas Media

The characteristics of the nanosecond overvoltage discharge ignited between semiconductor electrodes based on the CuInSe2 chalcopyrite compound in the argon and nitrogen atmospheres at gas pressures of 5.3–101 kPa are reported. Due to the electrode sputtering, chalcopyrite vapor enters the discharge plasma, so that some CuInSe2 molecules become destroyed, whereas the others become partially deposited in the form of thin films on solid dielectric substrates located near the plasma electrode system. The main products of the chalcopyrite molecule decomposition in the nanosecond overvoltage discharge are determined; these are atoms and singly charged ions of copper and indium in the excited and ionized states. Spectral lines emitted by copper and indium atoms and ions are proposed, which can be used to control the deposition of thin chalcopyrite films in the real-time mode. By numerically solving the Boltzmann kinetic equation for the electron energy distribution function, the electron temperature and density in the discharge, the specific losses of a discharge power for the main electronic processes, and the rate constants of electronic processes, as well as their dependences on the parameter E/N, are calculated for the plasma of vapor-gas mixtures on the basis of nitrogen and chalcopyrite. Thin chalcopyrite films that effectively absorb light in a wide spectral interval (200–800 nm) are synthesized on quartz substrates, by using the gas-discharge method, which opens new prospects for their application in photovoltaic devices.