Mbe Growth and Characterization of Lwir HgCdTe
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MBE GROWTH AND CHARACTERIZATION OF LWIR HgCdTe M.B. LEE, J. DECARLO, D.DIMARZIO, and M.KESSELMAN Grumman Corporate Research Center, Bethpage, NY 11714-3580 ABSTRACT We have grown high-mobility LWIR HgCdTe thin films on CdTe substrates, using molecular beam epitaxy (MBE). The structural, optical, and electrical properties of these epilayers were determined by SEM, DCRC, FTIR, and Hall effect measurements. For films of 10 to 11 Am thick and composition X value ranging from 0.152 to 0.172, the highest mobility observed was 7.5 x 105 cm 2 /V-sec, and the FWHMs of the rocking curves were 75 to 110 arcsec. We also have carried out the temperature-dependent EXAFS study of HgCdTe. INTRODUCTION In spite of recent advances in the growth of other materials with long wavelength infrared (LWIR) detection potential [1,2], HgCdTe remains the most promising detector material for the spectral range of 8-12 gim. Molecular beam epitaxy (MBE) is a growth technique in which all important growth parameters can be precisely controlled. Therefore, it is ideally suited for the growth of LWIR HgCdTe, for which optimal deposition conditions must be carefully maintained for long growth periods. In this paper, we describe the experimental conditions for MBE growth and the procedures used for epilayer characterization. The structural, optical, and electrical properties are summarized. Finally, the quality of these epilayers is compared with other published results. EXPERIMENTAL TECHNIQUES The HgCdTe epilayers were deposited in a RIBER 2300 MBE system on 1 cm x 1 cm CdTe (100) substrates purchased from II-Vl Corporation. Double crystal rocking curve (DCRC) measurements of the substrates indicated that the FWHM of the (400) reflection spot was about 50 arcsec. The substrates were degreased and etched with 1.5 % bromine/methanol solution for 90 sec prior to mounting in the growth chamber. Within the growth chamber, the substrates were first annealed at 320°C for 90 min. A CdTe buffer layer, 0.5 gm thick, was grown on each substrate before the depositing of HgCdTe. HgCdTe epilayer deposition was carried out at 200 0C, and the substrate temperature was maintained throughout the growth period to within 0.2 0 C. IR transmission data were taken with a Mattson Cygnus 100 FTIR spectrometer, which uses a special wafer-scanning software. The Van der Pauw technique was used to measure the electrical properties of the epilayers. Indium micro-ball cold wire bonding was used for electrical connection to the sample. Mat. Res. Soc. Symp. Proc. Vol. 161. ©1990 Materials Research Society
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The electrical transport properties were measured over a temperature range of 10 to 270 K and in a magnetic field from 1000 to 8000 Gauss. EXAFS experiments were carried out at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory over temperatures ranging from 10 K to 300 K. RESULTS Table I summarizes the growth conditions for three LWIR HgCdTe epilayers that will be discussed in this paper. The growth conditions for all three samples were identica
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