Richard J. Stirn

Heteroepitaxial growth of Cd1−xMnxTe on GaAs by metalorganic chemical vapor deposition

In this letter we report on preliminary results of heteroepitaxial growth of the dilute magnetic semiconductor alloy Cd1−xMnxTe on GaAs by metalorganic chemical vapor deposition. Dimethylcadmium (DMCd), diethyltellurium (DETe), and tricarbonyl (methylcyclopentadienyl) manganese (TCPMn) were used as source materials. The TCPMn had to be heated to as high as 140 °C to provide the required vapor pressure. Films with Mn atomic fractions up to 30% have been grown over the temperature range 410–450 °C. Results of optical absorption/transmission, photoluminescence, and x‐ray diffraction measurements are presented along with a scanning electron micrograph showing good surface morphology of the grown layers.

Practical antireflection coatings for metal-semiconductor solar cells

The metal‐semiconductor solar cell is a potential candidate for converting solar energy to electrical energy for space and terrestrial application. In this paper, a method for obtaining parameters of practical antireflection (AR) coatings for the metal‐semiconductor solar cells is given. This method utilizes the measured equivalent index of refraction obtained from ellipsometry, since the surface to be AR coated has a multilayer structure. Both the experimental results and theoretical calculations of optical parameters for Ta2O5 AR coatings on Au‐GaAs and Au‐GaAs0.78P0.22 solar cells are presented for comparison.

A Schottky‐barrier solar cell on sliced polycrystalline GaAs

Antireflecting‐metal‐oxide‐semiconductor (AMOS) technology has been applied to sliced wafers of polycrystalline GaAs having grain sizes of about 100 μm. Simulated AM1 sunlight efficiencies up to 14% were obtained, and studies using the scanning electron microscope showed that grain boundaries have minimal effect on short‐circuit current density. However, current‐voltage characteristics show some influence on open‐circuit voltage.

Low‐temperature deposition of low resistivity ZnSe films by reactive sputtering

Low resistivity semiconducting films of ZnSe have been deposited at temperatures as low as 120 °C using dc magnetron co‐sputtering of Zn and In (dopant) targets in a reactive atmosphere of H2Se/Ar. Yellowish transparent films of ZnSe on glass and conductive transparent oxide‐coated glass substrates were obtained having a room‐temperature resistivity as low as 20 Ω cm. Atomic absorption analysis showed a Zn to Se ratio of 49.8:49.0 and In concentration of about 1% for the reactively sputter‐deposited ZnSe:In films on glass. Optical absorption/transmission measurements yielded an energy band gap of about 2.65 eV at room temperature. X‐ray diffraction results indicated highly oriented polycrystalline films on glass with the c axis parallel to the plane of the film.

Recent improvements in AMOS solar cells

Several improvements in AMOS cell fabrication processes have been developed. These improvements consist of a new chemical surface preparation, a new form of oxide layer and a better antireflecting coating. It was found that AMOS cells with the chemical surface treatment NHH (NH4OH: H2O2:H2O = 1:1:10) and SHH (H2SO4:H2O2:H2O = 10:1:1), prior to oxidation, yield a lower reverse saturation current, higher open-circuit voltage, near-unity diode ideality factor and a higher degree of consistency. The performance of AMOS cells made by physically-deposited oxide layers is comparable, if not superior, with that of water-vapor grown oxide cells. The thermal degradation of open-circuit voltage in AMOS cells with the improved technology is also less pronounced. The application of antireflection coatings has been improved by the use of laser flash evaporation so as to eliminate the previously observed degradation in open-circuit voltage.

Comment on ``Temperature Dependence of Hole Velocity in p GaAs''

A comparison of magnetoresistance mobility values and their temperature dependence with theoretical values of the conductivity mobility was made in a recent publication. Reasons are discussed why such a comparison is unwarranted, particularly when multiple‐carrier conduction is present.

Optimum Anti Reflection Coating For Anti Reflection-Coated Metal-Oxide-Semiconductor (AMOS) Solar Cells

The Antireflection-coated Metal Oxide Semiconductor (AMOS) solar cell is an attractive candidate for converting solar energy to electrical energy for space and terrestrial applications because of its simplicity, high solar-energy conversion efficiency (15%), and adaptability to low-cost thin-film structure, when the semiconductor is made of direct bandgap material. The high energy conversion efficiency of the AMOS cell is partially due to its relatively good minority carrier collection efficiency and, hence, good current out-put, when a direct bandgap material like GaAs is used. Obviously, the amount of sunlight which can be coupled into the solar cell must be maximized by a suitable antireflection (AR) coating. In this paper, comprehensive methods for obtaining parameters of an optimum single-layer AR coating on an AMOS solar cell to match the entire sunlight spectrum, rather than a single wavelength, will be given. In this method, therefore, the effects of a solar spectrum, spectral response of the solar cell and optical properties of the solar cell are collectively considered.

Practical Anti-Reflection Coating For Metal Semiconductor Solar Cells

The metal-semiconductor solar cell is a possible candidate for converting solar to electrical energy for terrestrial application. In this paper, a method for obtaining optical parameters of practical anti-reflection coatings for the metal-semiconductor solar cell, is given. This method utilizes the measured index of refraction obtained from ellipsometry since the surface to be AR coated has a multi-layer structure. Both the experimental results and theoretical calculation of optical parameters for Ta205 anti-reflection coatings on Au-GaAs and Au-GaAs.78P.22 solar cells are presented for comparison.