Specular HgTe–CdTe superlattice epilayers have been obtained on two 2-in. diam GaAs or sapphire wafers per growth run using a horizontal metalorganic chemical vapor deposition (MOCVD) reactor in which the pyrolysis of the organometallics is induced by a cracking susceptor suspended above the substrates. This enables growth of superlattices below 300 °C using the standard precursors dimethyl cadmium, diethyl telluride, and elemental mercury. Annealing the superlattices at 350 °C converts them to homogeneous Hg1−xCdxTe. Compositional profiles obtained by Rutherford backscattering, sputter Auger depth profiling, and e-beam analysis of ultramicrotomed thin cross sections, were used to study interdiffusion of the CdTe and HgTe layers during growth and annealing. Arrays of metal–semiconductor field effect transistors (MESFETS) and photoconductive detectors with room temperature peak responsivity between 1.3 and 1.6 μm have been prepared from incompletely interdiffused material grown on semi-insulating GaAs without thick buffer layers. Device processing used mesa technology and a KI:I2:HBr etchant developed for its selectivity with respect to Hg1−xCdxTe . Capping layers of CdTe and HgTe deposited at low temperatures have been investigated as dielectric and ohmic contacts, respectively. Electrical analyses by Hall and C–V measurements are presented. Room temperature electron mobilities up to 27 500 cm2 /V s and resistivities of 1–2 Ω cm have been observed for the HgTe layers. Information on crystallinity and defect structure of the epilayers was obtained by selected area electron channeling patterns, high-resolution transmission electron microscopy (HRTEM), Rutherford backscattering spectroscopy (RBS) and four-circle, double-crystal, and triple-crystal x-ray diffraction. Compositional profiles in the 100 cm2 deposition area were obtained by wavelength dispersive x-ray analysis (WDX), Fourier transform infrared (FTIR) spectrometry and inductively coupled plasma atomic emission spectrometry (ICPAES).
Ultramicrotome techniques are used to prepare thin cross sections of a {111} epilayer of CdTe deposited by metalorganic chemical vapor deposition onto a {100} GaAs substrate. The structure of these samples is investigated by transmission electron microscopy using high-resolution (HRTEM) and diffraction contrast, and the polarity of the {111} layer by convergent beam electron diffraction (CBED) and characteristic x-ray emission under various electron channelling conditions, or ALCHEMI. Rutherford backscattering and channelling experiments on the bulk film confirm the presence of a multiply twinned lamellar structure as observed by electron beam techniques. Strong channeling confirms that the crystallinity is good, and that no significant concentration of defects occurs. HRTEM images of the {111} epilayer from the interface across the lamellar twins show few dislocations or crystal defects. Diffraction contrast indicates the presence of a periodic strain in the GaAs and parallel to the interface. CBED and ALCHEMI results confirm that the layer is B type, and that the lamellar twins do not invert phase.
In this work, we present a new approach to determining Poisson's ratio of AlAs. This approach requires the growth of a particular structure with a multiple quantum well (MQW) -lOx[500A GaAs/800A AlGa1As] followed by two single layers -O.5 AlAs and O.5 AlGa1As on a GaAs substrate. The X-ray rocking curves of the as-grown sample give the perpendicular lattice constants in the two single epilayers, and following chemical etching to remove the two single layers, X-ray diffraction (XRD) measurement of the MQW is used to determine the Al fraction x. With this data, we obtain a value for Poisson's ratio of AlAs which is VA1AS 0.255 0.003 assuming Vegard's law and a linear variation of the AlGa1As lattice constant with x. However we obtain VARS -0328 0.003 if, as proposed by Z. R. Wasilewski', a nonlinear relationship with the bowing parameter c1 .245x iO is assumed. The value of 0.328 is in good agreement with most recent results obtained which do not assume Vegard's law. Our results therefore support the violation ofVegard's law in describing the relationship between the lattice constant of AlGaAs and its composition.
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