A. Marbeuf

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%).

Consistent approach of II–VI equilibrium phase diagrams: Application to Zn-Se, Cd-Te, Hg-Te and Cd-Hg-Te systems

The molar mixing functions of some II–VI liquids (Zn-Se, Cd-Te, Hg-Te, Cd-Hg-Te) are obtained by fitting partial pressure data, liquidus lines (binary case) and liquidus surfaces of CdxHg1−xTe(s) alloys. Constraints, at the melting point of the zincblende, amongst all the data yield up to six independent parameters per binary, assuming Redlich-Kister polynomia forms for mixing functions in an associated solution model. The associated character is then found to decrease from Zn-Se to Hg-Te melts. Ternary interactions are taken into account in the Cd-Hg-Te liquid, whereas pseudobinary alloys appear nearly ideal.

Photo-assisted growth of ZnTe by metalorganic chemical vapour deposition

Abstract The metalorganic chemical vapour deposition (MOCVD) photo-assisted growth of ZnTe using a xenon lamp has been performed at atmospheric pressure under hydrogen as a carrier gas. Epitaxial growth was achieved on (100) GaAs, (100) GaSb and (100) ZnTe substrates with diethylzinc (DEZn) and diethyltellurium (DETe) as precursors. We have studied the growth rate as a function of the growth temperature, the partial pressure of precursors, the inlet partial pressure ratio R = VI/II, the light intensity and the energy of the irradiating photons. A growth rate enhancement has been observed for illuminated layers grown on GaAs and ZnTe substrates in comparison with those grown without illumination. We have not observed any measurable enhancement for layers grown onto (100) GaSb. The growth rate as a function of the light intensity increases for intensities higher than 20 mW / cm 2 and saturates for P > 120 mW / cm 2 . We relate the growth rate enhancement to irradiating photons with an energy higher than the band gap of ZnTe at the growth temperature.

EXAFS study of terbium activated zinc sulfide thin films

This paper reports that in order to establish the nature of luminescent centers in green-emitting electroluminescent thin film structures based on terbium-activated zinc sulfide, extended x-ray absorption fine structure (EXAFS) measurements were carried out using x-ray radiation from the 1.85 GeV-200 mA DCI storage ring in Orsay. Analysis of the EXAFS spectra at the Tb L{sub III} edge gives direct evidence for the presence of Tb-containing clusters in films prepared by the Atomic Layer Epitaxy process. The polycations TbO{sup +} forming the cluster are very similar to those found in the crystal structure of Tb{sub 2}O{sub 2}S.

Low temperature phase diagram of the Ga1−xInxAsySb1−y system

Abstract The phase diagram of the Ga1−xInxAsySb1−y quaternary alloy was calculated in the range 400–800°C by a progressive thermodynamic analysis combining binary data and generating ternary and quaternary systems; the mixing functions of the liquid phase are expressed in Redlich-Kister polynomial form, whereas the solid phase is described by a short-range order and substrate-induced strain in the delta lattice parameter (DLP) model. Our calculation give a solid phase miscibility gap smaller than predicted by previous calculations. A comparison with published data concerning the liquid phase epitaxy of GaInAsSb shows that, in fact, no growth was performed inside the miscibility gap of this alloy by LPE.

Growth kinetics during metal-organic chemical vapour deposition of ZnTe

Abstract ZnTe films are grown by metal-organic chemical vapour deposition starting from pyrolysis of a mixture of diethylzinc (DEZn) and diethyltellurium (DETe) diluted with H2. The decomposition process of these two organometallic precursors is monitored with a mass spectrometer; DEZn leads to n− C 4 H 10 with other hydrocarbons (C2H4 and C2H6) as reaction products and DETe leads to C2H4. When both organometallic precursors are present, a strong hysteresis loop of the signal intensity when heating and cooling the susceptor has been recorded, as a result of a catalytic reaction between the gas phase and the surface. The experimental growth rate V at 400 °C vs. organometallic concentration is described in terms of a kinetic model involving pyrolysis processes and a surface-catalysed reaction. The model explains the asymmetric behaviour of V; for a given DETe pressure (10−4 atm), the ZnTe growth rate as a function of DEZn partial pressure passes through a maximum ( p max DEZn ≈ 10 −4 atm ; V max ≈ 2.4 μ m h −1 ), whereas, at the same constant DEZn partial pressure, V follows a sublinear law with the increase in DETe partial pressure and saturates to V = 4.3 μ m h −1 .

Composition profiles and growth kinetics of GaxIn1−xP LPE layers: Experiments and theoretical approach

GaxIn1-xP epilayers of various ranges of composition (0.5 ⩽ x < 1) have been grown on GaP, GaAs and GaP0.40As0.60 substrat es by cooling saturated melts. A model combining the bulk diffusion kinetics of solutes and the attachment kinetics at the liquid-solid interface accounts for the experimental alloying composition profiles in the layers (very different depending on the composition range) and for the relative layer thickness variations.

XPS study of the ZnxHg1−xTe alloys: Core levels and valence-band offset

The X-ray photoemission study of the Zn(3d52), Hg(5d52) and Te(4d52)> core levels for ZnxHg1−x Te bulk crystals has been carried out in the complete x composition range. The corresponding binding energies relative to the valence-band maximum are measured as a function of x. Because of a relaxation in the lattice of the alloy, neither of the cation levels are affected by alloying on an absolute energy scale. By combining their shifts, the natural valence-band offset is deduced: its value (ΔEv = 0.17 eV) appears smaller than the CdxHg1−xTe value (ΔEv) = 0.35 eV). Between ZnTe and HgTe, the main part of the variation of the va ence-band maximum is found for semimetallic compositions. The deeper Te(4d52) level position varies in the same manner, but with a small bowing resulting from the disorder.

Liquid phase epitaxy of ZnSe in Sn: Calculation of the ternary phase diagram and electronic properties

Abstract The ternary equilibrium diagram Zn-Sn-Se has been calculated for a liquid of composition xZn =xSe = 10-2 to 5x10-2. For each binary system the liquid mixing energies (mixing enthalpy, excess entropy), are determined from literature data and by minimization of the total free enthalpy (Simplex method). The ternary diagram is generated in the same way with the help of the solubility measurements of ZnSe in Sn done by Rubenstein (1968) and us. Our experiments were performed in a special close tube arrangement also used for ZnSe epitaxy from tin solution. Epitaxial layers were prepared at temperature around 950°C on ZnSe substrates. Photoluminescence and electrical measurements indicate the material is donor doped. Chemical analysis reveals a profile of Al with a maximum near the substrate interface. That points out the importance of substrate purity in II-VI compounds epitaxy.

Anodic photodissolution of GaP single crystal electrodes in aqueous media

Abstract In this work, we show the influence of etching on the process of anodic dissolution of a GaP single crystal in an alkaline medium. The photodissolution of the electrode was studied from electrochemical measurements and the process was explained in terms of the influence of surface defects and particularly of dislocations.