J.‐L. Staudenmann

Molecular beam epitaxial growth of a novel strained‐layer superlattice system: CdTe‐ZnTe

CdTe‐ZnTe strained‐layer superlattices have been grown for the first time using the molecular beam epitaxy technique. The superlattices have been grown at 285 °C. They have been characterized by electron and x‐ray diffraction. The presence of satellite peaks in the x‐ray spectra shows that the superlattices are of excellent quality despite the large mismatch between CdTe and ZnTe along the growth axis (Δa/a=6.4%). X‐ray oscillation patterns show that the superlattices are three‐dimensional crystals.

Layer intermixing in HgTe‐CdTe superlattices

High‐temperature x‐ray diffraction measurements on HgTe‐CdTe superlattices grown by molecular beam epitaxy have been made to determine the extent of intermixing of the individual HgTe and CdTe layers. In situ interdiffusion measurements were carried out at 110, 162, and 185 °C and estimates of the interdiffusion coefficient were made. We find appreciable intermixing of the HgTe and CdTe layers at temperatures as low as 110 °C. Such results have serious implications for the use of this material in optoelectronic devices.

Interdiffusion in HgTe–CdTe superlattices

Semiconductor superlattices comprised of alternating HgTe and CdTe layers have been proposed as a tunable narrow band gap semiconductor for long wavelength optoelectronic applications. Growth of this novel superlattice material has been reported by several laboratories. Its usefulness as a narrow band gap optical material, however, has not been established. A main issue of concern is the interdiffusion of the constituent Hg, Cd, and Te atoms across the heterointerfaces of the superlattice structure. To determine the extent of this interdiffusion we have carried out, for the first time, temperature dependent x‐ray diffraction measurements on HgTe–CdTe superlattices. Peak intensities of the superlattice satellites were monitored as a function of annealing temperature and time to yield estimates of the interdiffusion coefficient D(T). Our results indicate there is appreciable intermixing of the HgTe and CdTe layers at temperatures as low as 110 °C. Such results have serious implications for the use of this m...

Photo-MOCVD growth of HgTe-CdTe superlattices

Abstract HgTe-CdTe superlattices have been grown by photo-assisted metalorganic chemical vapor deposition (MOCVD). The substrate temperatures used were 182°C and 240°C. Superlattices were obtained despite low growth rates requiring long growth times, up to 12 h. Superlattice structures were verified by cross-sectional transmission electron microscope (TEM) and diffractometer X-ray diffraction patterns. The X-ray diffraction patterns showed satellite peaks up to third order. A grid-like array of dislocations at the substratelayer interface, suggesting operation of a dislocation-blocking mechanism, was observed. The electrical properties of superlattices grown at higher temperature (240°C) were improved compared with those grown at lower temperature (182°C) and had n-type conductivity as grown, with carrier concentrations ≈10 16 cm -3 and mobilities ≈10 4 cm 2 V -1 s -1 . Infrared transmission/reflection measurements showed that the superlattice absorption edge was shifted to longer wavelengths compared with the homogeneous alloy of the same CdTe fraction ( x -value), as expected.

Thermal stability among HgTe/CdTe, Hg1−xCdxTe/CdTe, and Hg1−xMnxTe/CdTe superlattices

In situ interdiffusion measurements on X‐alloyed Hg1−xXxTe/CdTe superlattices reveal that superlattices with x>0 are more stable than HgTe/CdTe superlattices (X=Cd and Mn for the present study). These alloyed superlattices have, therefore, a better chemical stability and hence, longer device lifetime than the nonalloyed ones, allowing for technological developments to proceed. It is hypothesized that the differences between Fourier components of the diffusion coefficients D(T) are due to Cd and Mn substitutions which presumably slow down interstitial and vacancy motions.

Static atomic displacements in a CdTe epitaxial layer on a GaAs substrate

A (001)CdTe epitaxial layer on a (001)GaAs substrate was studied by x‐ray diffraction between 10 and 360 K. The CdTe growth took place at 380 °C in a vertical gas flow metalorganic chemical vapor deposition reactor. Lattice parameters and integrated intensities of both the substrate and the epitaxial layer using the (00l) and (hhh) Bragg reflections reveal three important features. Firstly, the GaAs substrate does not exhibit severe strain after deposition and it is as perfect as a bulk GaAs. Secondly, the CdTe unit cell distorts tetragonally with a⊥>a∥ below 300 K. The decay of the (00l) reflection intensities as a function of the temperature yields a Debye temperature of 142 K, the same value as for bulk CdTe. Thirdly, a temperature‐dependent isotropic static displacement of the Cd and the Te atoms is introduced to account for the anomalous behavior of the (hhh) intensities.

Evidence for GaAs substrate strain caused by a CdTe epitaxial layer

Abstract The 400 Bragg intensities of a 3 μm thick single crystal CdTe epitaxial layer on a [100] GaAs substrate have been measured between 6.8 and 380 K. The results clearly show that the Debye temperature of the substrate surface is higher than that of the bulk substrate which implies that the substrate surface is strained. This contrasts with common thinking that only the interface of the epitaxial layer is strained by the deposition.

Characterization of thin films, epitaxial layers, and superlattices using the precession camera

Abstract This article describes a simple method to provide qualitative structural information on thin films, epitaxial layers, and superlattices using the Buerger precession camera. This method is especially useful for epitaxially grown films because it gives a rapid and easy-to-interpret photograph of the reciprocal space of all the components at once: substrate, film or buffer layer, and/or superlattice. A wide variety of examples - Al on Si, Ge on Si, CdTe epitaxial layers on GaAs, CdTe/ZnTe superlattices on GaAs, and Mo/Ni superlattices on mica - are used to illustrate the present technique.

Anomalous temperature dependence of lattice parameters of metalorganic chemical vapor deposition CdTe grown on GaAs

It is reported that the lattice parameters of a 3‐μm‐thick [1,0,0] single crystal CdTe epitaxial layer on a [1,0,0] single crystal GaAs substrate behave anomalously below 120 K. The epilayer used in this experiment was deposited at 410 °C by metalorganic chemical vapor deposition. This x‐ray lattice parameter study was done in the temperature range between about 8 and 300 K. Our results show that the lattice parameters perpendicular to the surface of both the GaAs substrate and the CdTe epilayer shrink four times more than the corresponding bulks when the samples are cooled down to 10 K. It is further seen that there is no compensation effect between the elements of the composite system; that is, the lattice parameters of the two materials change in the same direction as if the composite system—the epilayer and the thickness of the substrate which is probed by the x rays—would behave as a new material with entirely new physical properties.

X-Ray Diffraction of CdTe Epitaxial Layers on GaAs Substrates as a Function of Temperature

A (0,0,1) epitaxial layer of CdTe on a (0,0,1) GaAs substrate has been studied as a function of temperature by x-ray diffraction. Lattice parameters and integrated intensities of Bragg reflections were measured between 10 K and 360 K using a wavelength of 0.7093 Å (Mo Kα). The lattice parameters were measured parallel and perpendicular to the interface. The changes of the integrated intensities with temperature give information about the thermal vibrations. Average Debye temperatures for the substrate and epilayer are 232±2 K and 142±2 K, respectively. These data are compared with data from CdTe and GaAs single crystals in order to understand how strain is propagated and/or relieved in the composite system.