Large area depositon of Cd1-xZnxTe on GaAs and Si substrates by metalorganic chemical vapor deposition

Results of large-area (up to 1000 cm²/run) Cd_1-xZn_xTe heteroepitaxy on both GaAs and GaAs/Si substrates by metalorganic chemical vapor deposition (MOCVD) are presented. Cd_1-xZn_xTe (x = 0-0.1) films exhibited specular surface morphology, 1% thickness uniformity (standard deviation), and compositional uniformity (Δx) of ±0.002 over 100 mm diam substrates. For selected substrate orientations and deposition conditions, the only planar defects exhibited by (lll)B Cd_1-xZn_xTe/GaAs/Si films were lamella twins parallel to the CdTe/GaAs interface; these do not propagate through either the Cd_1-xZn_xTe layer or subsequently deposited liquid phase epitaxy (LPE) HgCdTe layer(s). Background Ga and As-impurity levels for Cd_1-xZn_xTe on GaAs/Si substrates were below the secondary ion mass spectroscopy detection limit. Preliminary results of HgCdTe liquid phase epitaxy using a Te-rich melt on Si-based substrates resulted in x-ray rocking curve linewidths as narrow as 72 arc-sec and etch-pit densities in the range 1 to 3 x 10⁶ cm².     

Growth and characterization of AlxGa1−xAs Bragg reflectors by LP-MOCVD

Using a moderate-sized LP-MOCVD production reactor, we have demonstrated the growth of Bragg reflector structures that reflect nearly 100% of the light at the design wave-length of 850 nm. The designs studied consist of alternating layers of Al_0.10Ga_0.90As and Al_0.85Gao_0.15As, with up to 30 periods. Characterization data show the structures to be highly reproducible and uniform, with good agreement between data obtained by double-crystal x-ray rocking curve analysis, cross-sectional transmission electron microscopy, and optical-reflectance spectroscopy. GaAs solar cells utilizing Bragg reflectors have been fabricated and characterized.     

GaAs/Ge tandem-cell space concentrator development

GaAs/Ge monolithic tandem two-junction concentrators are being developed by optimizing separate one-junction GaAs and Ge cells that simulate the GaAs top cell and Ge bottom cell of the tandem. Separation allows easier analysis of the tandem's top and bottom cells than if these two junctions were in series. The best GaAs top cell has an independently measured AM1.5D efficiency of 28.7% at 200 suns and 25°C (24.5% AM0 at 170 suns), a record for a monolithic cell without a prismatic cover. The Ge bottom cells have a GaAs optical filter (but no GaAs junction) to replicate the spectrum that the Ge cell sees when incorporated into a tandem. The best Ge-under-GaAs bottom cell efficiency is 4.6% AM0 at 103 suns. Evidence that the 900-1800-nm response seen from the Ge bottom cell is due to a p-n junction in the Ge and not a GaAs/Ge heterojunction is presented     

Analysis of AlGaAs/GaAs solar cell structures by opticalreflectance spectroscopy

The control of the thickness and composition of the GaAs cap and AlGaAs window layers is essential to the fabrication of high-efficiency AlGaAs/GaAs heteroface solar cells. The use of optical reflectance spectroscopy for the analysis of these structures is presented. The calculation of the reflectance of a system of thin films is described along with the computer program, REFIT, for the analysis of GaAs cell structures. Results are presented for structures at different stages in the solar cell fabrication process, and the method is applied to the analysis of the oxidation of high AlAs mole fraction AlGaAs layers     

Growth of (GaAs)1_x(Ge2)x by metalorganic chemical vapor deposition

We report deposition of (GaAs)_{1_x}(Ge₂)_x on GaAs substrates over the entire alloy range. Growth was performed by metalorganic chemical vapor deposition at temperatures of 675 to 750°C, at 50 and 760 Torr, using trimethylgallium, arsine, and germane at rates of 2–10 μ/h. Extrinsic doping was achieved using silane and dimethylzinc in hydrogen. Characterization methods include double-crystal x-ray rocking curve analysis, Auger electron spectroscopy, 5K photoluminescence, optical transmission spectra, Hall-effect, and Polaron profiling. Results achieved include an x-ray rocking curve full-width at half maximum as narrow as 12 arc-s, Auger compositions spanning the alloy range from x = 0.03 to x = 0.94, specular surface morphologies, and 5K photoluminescence to wavelengths as long as 1620 nm. Undoped films are n type, with n ≈ 1 × 10¹⁷ cm⁻³. Extrinsic doping with silane and dimethylzinc have resulted in films which are n type (10¹⁷ to 10¹⁸ cnr⁻³) or p type (5 × 10¹⁸ to 1 × 10²⁰ cm⁻³). Mobilities are generally ≈ 50 cm²/V-s and 500 cm²/V-s, for p and n films, respectively.     

Sport psychiatry in childhood and adolescence: an overview

This review explores the importance and relevance of sport during childhood and adolescence, utilizing traditional stage theories of development. The literature supports the notion that sport is a necessary study as a health issue and a preventative tool in the field of psychiatry. Play and sport in childhood and adolescence enhance development physically, mentally, and socially. Participating in athletics encourages the development of leadership skills, self-esteem, muscle development and overall physical health. There is a lack of literature in the important area of sport psychiatry especially when considering beneficial, not deficit oriented youth athletic development. Child psychiatrists need to begin researching sport in order to develop a comprehensive understanding of how athletics can enhance the mental and physical health of youth.