Metalorganic Chemical Vapor Deposition Growth of High-Quality InAs/GaSb Type II Superlattices for Mid-IR Photodetector Applications
X. B. Zhang , A. Petschke, S. Mou , C. Xu , J. H. Ryou , S. L. Chuang , K. C. Hsieh, and R. D. Dupuis 1) Center for Compound Semiconductors and School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Drive NW, Atlanta, GA, 30332-0250, USA 2) Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, 208 North Wright Street, Urbana, IL 61801, USA
Metal organic chemical vapor deposition of metaphorphic InAs GaSb superlattices on (0 0 1) GaAs substrates for mid-IR photodetector applications
Abstract InAs/GaSb superlattices (SLs) were grown on (0 0 1) GaAs substrates by metal organic chemical vapor deposition. A thin low temperature (LT) GaSb nucleation layer followed by a 250 nm thick high temperature (HT) GaSb buffer layer were introduced before the growth of the SLs and their growth conditions were optimized. The effects of growth temperature and GaSb growth rate on the morphology and structural properties of the SL were systematically studied. Atomic force microscopy, photoluminescence, transmission electron microscopy and X-ray diffraction were used to characterize the grown structures. Generally, nanopipes, about 100 nm in diameter, were found in the grown structures and their formation depends strongly on the growth temperature and the GaSb growth rate in growing the SL. By optimizing these parameters, high-quality InAs/GaSb SLs without nanopipes and with sharp interfaces have been realized.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.