R. Druilhe

Thermodynamic analysis of Zn-Cd-Te, Zn-Hg-Te and Cd-Hg-Te: phase separation in ZnxCd1−xTe and ZnxHg1−xTe

The thermodynamic coherent analysis of all data in Zn-Cd-Te, Zn-Hg-Te and Ce-Hg-Te ternaries, combined with that in the corresponding binaries, is understood by using a subregular associated liquid model and the Onda-Ito model in the pseudoregular approximation for the pseudobinary alloys. A clustering tendency is found which decreases from ZnxCd1−xTe to ZnxHg1−xTe, whereas CdxHg1−xTe is nearly ideal. A miscibility gap is predicted for ZnxCd1−xTe and ZnxCd1−xTe alloys below 428 and 329°C, respectively. Transmission electron microscopy studies on (100) MOCVD ZnxCd1−xTe layers grown at 365°C show such a phase separation: the corresponding relative lattice mismatch ((3.3 ± 0.2)%) is very near the predicted one (3.8%).

Hydrogen-arsenic interactions in MOVPE-grown CdTe : effects of rapid thermal annealing

Abstract Short thermal treatments (5 and 30 s) have been performed on MOVPE grown CdTe layers doped with arsenic in the concentration range 8 × 10 16 to 7 × 10 18 cm −3 . In the as-grown state most of the As atoms form with hydrogen neutral AsH pairs characterized by a local vibrational mode (LVM) at 2022 cm −1 . The hole concentration increases with annealing temperature and reaches a maximum for an annealing temperature of 500–550°C where the LVM intensity comes to zero. Almost full activation of the arsenic is obtained in the lowest doped layer. However the maximum hole concentration is limited to (1.5–2) × 10 17 cm −3 in the more doped layers, well below the concentration of As atoms involved in the pairs in the original state. Possible explanations are presented which imply short range precipitation or existence of a relaxed inactive As state.

Effect of the {h11} orientations and polarities of GaAs substrates CdTe buffer layer structural properties

Abstract CdTe layers were grown by metallo-organic chemical vapour deposition on GaAs substrates of different ( {h11} ) orientations and polarities. The morphology and structural properties of the epilayers were investigated using several techniques, namely scanning electron microscopy, transmission electron microscopy and double crystal X-ray diffraction. The best results were obtained for epitaxy on (211) A and (311) B substrate orientations. The occurrence of twinning in the cases of opposite polarity, i.e. (211) B and (311) A, was attributed to the presence of single dangling bonds on the etched substrate surfaces.

MOVPE growth and characterization of Hg0.7Cd0.3Te layers

The MOVPE growth of Hg0.7Cd0.3Te(MCT) layers is described. On 2 inch GaAs substrates, a graded composition buffer layer together with growth interruptions during the IMP deposition is found to reduce the density of pyramidal defects. It is found from SIMS measurements that Ga is transported from the GaAs substrates via the vapour phase into the layers. Lamella twins parallel to the surface, in (111) MCT layers grown on (100) GaAs substrates, are found to initiate electrically active centers. Carrier concentrations and mobilities comparable to those reported so far, whatever the growth technique used, are found from electrical measurements: ni ⋍ 1016cm−3 with μ300K⋍ 104cm2/V·s,n77Klying between 3×1014 and 2×1015 cm−3 with μ77K in the (2−12)×104cm4/V·s range. A uniformity of ±0.01 mol over large areas of ⋍ 10 cm2 is found from FTIR spectrometry. Photoconductors have been made from these layers, with performances comparable to those of bulk crystal devices.

Thin films of binary metal oxides by chemical vapor deposition from organometallic chelates

Abstract Thin films of Fe2O3 and NiO were epitaxially deposited on single crystals of Al2O3 and MgO, respectively, by chemical vapor deposition (CVD) from the respective metal acetylacetonates. Optical absorption spectra of the transparent films in the visible and ultra-violet region are reported.

Annealing kinetics of hydrogenated As acceptors in MOVPE grown CdTe

The kinetics of electrical activation of hydrogenated arsenic acceptors in MOVPE grown cadmium telluride layers was studied for arsenic doping in the range to . Thermal annealings were performed in the temperature interval 150-C with a duration from 1 s to 1 h. The hole concentration in the annealed samples was determined by the van der Pauw method and As-H pair concentration was deduced from the intensity of the LVM absorption line at , detected by Fourier transform spectrometry. Short annealing experiments (<1 min) showed a continuous increase in hole concentration with time and temperature, limited to about (1- at a temperature of C. The concentration of As-H pairs concurrently decreased but at a higher rate. Longer annealings usually led to a decrease in hole concentration while the As-H pair concentration either continued to drop or recovered depending on the value of arsenic doping. These results were interpreted in the framework of a theoretical analysis which took into account several processes: dissociation-recombination of impurity-hydrogen pairs, electronic ionization of arsenic impurities and electrical compensation due to the formation of arsenic-vacancy complexes. It was proposed that arsenic ionization takes place in two steps, the first one corresponding to a thermally activated conversion process and the second one to hole emission. The microscopic nature of the intermediary neutral impurity state is not known at present.

Chemical transport of FeCr2S4

Abstract FeCr 2 S 4 single crystals were grown by vapor transport in a closed system using first Cl 2 and a mixture of HCl+Cl 2 . Thermodynamic calculations show that chemical transport is only possible using HCl+Cl 2 as transport agent. Composition of the gas phase in equilibrium with the solid is derived from thermodynamic calculations.

Incorporation of hydrogen in CdTe and HgTe epitaxial layers grown by MOCVD

Abstract The incorporation of hydrogen into MOCVD-grown layers of CdTe, HgTe and CdHgTe using H2 as the vector gas has been studied. Concentrations of incorporated H going from 6.5 × 1017 cm-3 to 5 × 1018 cm-3 have been found by SIMS in CdTe layers. This concentration decreases with increasing growth temperature and decreasing bond strength of the host material.

In situ reflectance anisotropy studies of the growth of CdTe and other compounds by MOCVD

Using reflectance anisotropy (RA), we investigate in situ the metal-organic chemical vapor deposition (MOCVD) of CdTe and ZnTe on GaAs (100). RA transient signatures are observed at the beginning of the heteroepitaxy of lattice-mismatched semiconductors: CdTe on ZnTe and ZnTe on GaAs. RA records also exhibit a fast initial variation (δ/r=10−3) during the homoepitaxial growth of these II–VI compounds. In order to clearly understand those phenomena, surface coverage is analyzed by alternating the precursor flows. Large RA signals (δ/r=10−2) correlated with the 3D growth of ZnTe on GaAs are observed, before the material relaxation. These signals can be interpreted in terms of surface roughness evolution within the framework of the effective medium theories (EMT). Moreover, ex situ spectroscopic measurements of CdTe layers are performed and simulated; a good agreement is obtained between EMT models and experiments.

Low temperature growth of (Cd,Hg) Te layers by MOVPE

Abstract MCT layers have been grown for the first time at 250°C using DATe, DMCd and mercury. First the buffer layer CdTe grown at 365°C using DIPTe and DMCd is studied with an emphasis on the influence of the substrate orientation. Indeed the surface morphology and the crystalline quality may change dramatically as a function of the substrate orientation. Then the low temperature MOVPE growth of (Cd,Hg)Te is described: different compositions were achieved and the crystalline and electronic properties are presented.