Engineering topics
Publications and source records attributed to Stirn, R. J..
A new fabrication process is being developed which significantly improves the efficiency of metal-semiconductor solar cells. The resultant effect, a marked increase in the open-circuit voltage, is produced by the addition of an interfacial layer oxide on the semiconductor. Cells using gold on n-type gallium arsenide have been made in small areas (0.17 sq cm) with conversion efficiencies of 15% in terrestrial sunlight.
The metal-semiconductor solar cell is a possible candidate for converting solar to electrical energy for terrestrial application. A method is given for obtaining optical parameters of practical antireflection coatings for the metal-semiconductor solar cell. This method utilizes the measured refractive index obtained from ellipsometry since the surface to be AR coated has a multilayer structure. Both the experimental results and theoretical calculation of optical parameters for Ta2O5 antireflection coatings on Au-GaAs and Au-GaAs(0.78)P(0.22) solar cells are presented for comparison.
Photovoltaic devices have been fabricated for solar and short-wavelength laser energy conversion using the thin metal film-semiconductor (Schottky barrier) approach. Studies of the metal film optical characteristics and the voltage outputs were emphasized. Air mass zero efficiencies of 8 to 9% in GaAs and laser conversion efficiencies of 25% at 4880 A in GaAs(0.6)P(0.4) are presently measured, with projected efficiencies of 15 and 45%, respectively. The techniques, if applied successfully to semiconductor thin films, could have an impact in solar energy terrestrial application.
An investigation is conducted concerning the mechanisms by which a steady flow of current proceeds through the contact when an external voltage is applied. The main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons. A high-field domain analysis is conducted together with experimental studies. Particular attention is given to the range in which tunneling predominates.
The formation of space charge in the barrier region is discussed. This region extends to a distance, x-sub o, equal to 200 A plus twice the mean free path of majority carriers. The conventional transport equation can be used only for x greater than x-sub o, and the carrier density at x-sub o represents a boundary condition for the bulk. Its change as a function of applied voltage, temperature, and light intensity in photoconducting CdS is discussed. The time dependence of the space-charge formation in the region between 0 and x-sub o is analyzed. It is shown under which conditions the individuality of the metal contact is observable.
Precise values of the reverse saturation currents in silicon solar cells and magnitudes of the diffusion and recombination components have been obtained. The recombination current as well as leakage current due to shunting are shown to be nonuniform across the cell. The diffusion lengths calculated from the diffusion current components agree well with diffusion lengths measured independently in similar material. Models are given demonstrating the effect of recombination and shunting currents on the dark current-voltage characteristics of solar cells.
Precise values of the reverse saturation currents in solar cells and magnitudes of the diffusion and recombination components have been obtained. The recombination current as well as leakage current due to shunting are shown to be nonuniform across the cell and to be responsible for up to 30% loss in efficiency for the average cell in a Jupiter-type environment. Models are given demonstrating the effect of recombination and shunting currents on dark and light characteristics of solar cells.
Future costs of silicon solar cells are projected on the basis of more than a thousand-fold increase in volume. If no major application of new manufacturing technology is made, the cost remains excessive for any large scale energy system. However, the development of a multiple-ribbon crystal growth process could permit a 300-fold reduction in cell costs to about $375/kW of cell output.
Device for metering variety of metals for high vacuum evaporation designed for thin film metal- insulator-metal diodes fabrication
Mechanism using a helix sequentially feeds prescribed amounts of metal charges into an evaporation boat used for flash vapor deposition of the evaporants onto a substrate in a vacuum chamber. The helix is advanced by external manual controls extending through sealed feed- through devices into the chamber wall.
Photoconductor concepts, and properties of recrystallized evaporated cadmium sulfide layers