A. Tromson-Carli

Solution hardening and dislocation density reduction in CdTe crystals by Zn addition

Solution hardening due to the incorporation of Zn in CdTe is studied theoretically by means of a model which starts from the differences between the Cd-Te and Zn-Te bond lengths. The critical resolved shear stress (CRSS) for plastic deformation is calculated for the entire composition range. Plastic deformation experiments performed at room temperature on CdTe, Zn0.04Cd0.96Te and Mn0.1Cd0.9Te crystals confirm that the Zn alloy is harder (by a factor of four) while the Mn alloy does not show any hardening effect. These results are complemented by microhardness measurements which give CRSS values in ZnxCd1-xTe in qualitative agreement with the model. Finally the superior crystalline quality of Zn0.04Cd0.96Te is demonstrated by a lower dislocation density (5x104 cm-2) and a narrower rocking curve width (25 arc sec).

Growth by solid phase recrystallization and assessment of large ZnSe crystals of high purity and structural perfection

Some physical properties of ZnSe resulting from the ionicity of its chemical bond make it difficult its melt-growth, suggesting the use of low temperature growth. Among the classical techniques of low temperature growth, solution and vapor growth are shown to present some limitations. Solid state recrystallization is presented as an attractive alternative for the growth of large ZnSe crystals of high purity and structural perfection, as shown from photoluminescence and X-ray diffraction measurements.

Growth of large, high purity, low cost, uniform CdZnTe crystals by the “cold travelling heater method”

Abstract The cold travelling heater method (CTHM) has been used to grow CdZnTe crystals (x Zn = 0.04 and 0.20) of 2 inch diameter, which is the largest diameter ever used in THM. A simple model confirms that convection is the dominant mechanism of matter transport in THM, justifying the use of the accelerated crucible rotation technique (ACRT), in which is imposed a forced convection regime, to enlarge the size of the crystals and increase the growth rate. In order to obtain single crystals, solid state recrystallization (SSR) has been applied for the first time to CdTe. Ingots of excellent axial and radial uniformity have been obtained by CTHM, as well as crystals purer than the Bridgman grown ones, from 5N elements as source material at ten times lower price than the 6N ones classically used for Bridgman growth. SSR crystals have been found also of lower purity than the CTHM ones. It follows that contamination in CdTe growth is expected to occur not only from the starting elements but particularly from the high temperatures used. The main agents of high temperature contamination are shown to be Li and Cu. Some mosaic structure of the crystals comes from the off-stoichiometric THM growth conditions and could be avoided by SSR annealing under Cd vapour pressure.

Growth of AlSb on insulating substrates by metal organics chemical vapour deposition

Abstract Aluminium antimonide thin films were grown on different insulating substrates, i.e. silica, CaF 2 , BaF 2 , Al 2 O 3 , GaAs, by metal organics chemical vapour deposition (MO-CVD). Epitaxial AlSb thin films were successfully grown on CaF 2 and GaAs. In the process, the metal alkyls trimethylaluminium (TMA) and trimethylantimony (TMSb) are the sources of Al and Sb, respectively. The thermodynamic study of the system Al-Sb-C-H shows that AlSb could be deposited for given values of the partial pressures of Al, Sb and C in the vapour phase. Other condensed phases could appear, Al 4 C 3 , Sb.

Horizontal Bridgman growth of large high quality Cd1−yZnyTe crystals

Abstract High quality Cd0.96Zn0.04Te single crystals, as demonstrated from X-ray diffraction measurements, have been grown by the horizontal Bridgman (HB) method in glassy carbon boats. The relevance of this crucible material has been shown from contact angle measurements with liquid CdTe and Cd1−yZnyTe. Nevertheless, its thermal conductivity, which is higher than that of silica, is shown to favour a growth interface concavity. The use of [110]-oriented seeds, after determination of the preferential growth axis of CdTe crystals grown by the HB method, has allowed us to control supercooling and to grow single crystals of controlled growth direction. A residual pressure of hydrogen in the growth tube is shown to inhibit any parasitic growth on the Cd1−yZnyTe ingot surface and to act on the compensation state of the crystals.

Evaluation of triisobutylaluminium for the epitaxial growth of AlSb compared to trimethylaluminium

Abstract Epitaxial layers of AlSb were grown from metal organics using trimethylantimony (TMSb) and either trimethylaluminium (TMA) or triisobutylaluminium (TiBA). The two Al alkyl sources were compared. Growth with TiBA resulted in epilayers of AlSb on GaSb that did not contain a second phase of Al 4 C 3 . However, AlSb formed using TMA always contained Al 4 C 3 .

Crystal growth and characterization of CdTe doped with transition metal elements

Abstract CdTe and Cd0.96Zn0.04 Te crystals doped with vanadium, and with other transition elements like cobalt and nickel, have been grown by a vertical asymmetric Bridgman technique. The segregation coefficient of V, determined from the concentration profiles measured along the ingot growth axis, is found between 1.2 and 5.5×10−2 depending on the initial concentration. SIMS imagery reveals the presence of vanadium precipitates of ∼ 20 μm diameter in the V-rich part of the ingots. As a result of the large V-concentration, the crystals present a mosic crystallographic structure, evidenced by a multipeak spectrum in X-ray double diffraction. An increase in the Vickers micro-hardness of CdTe:V beside pure CdTe was observed and interpreted by considerations upon the bonding lengths. A systematic investigation of the optical absorption, measured at 77 K, was conducted as a function of crystal growth parameters. The observed bands are attributed to d → d ∗ transitions of V2+ (3d3) and V3+ (3d2) ions on Cd sites.

C and CH4 as Transport Agents for the CVT Growth of ZnO Crystals

ZnO is a wide-bandgap (3.437 eV at 2 K) semiconductor which has many applications in optoelectronic devices, such as blue and UV light emitters. ZnO bulk can be used as a substrate for the homoepitaxial growth and as alternative substrate for the heteroepitaxial growth of GaN. From thermodynamic and experimental studies, we have demonstrated that carbon and hydrocarbides such as methane act as efficient chemical transport agents of ZnO. We have observed that the transport rate does not roughly depend on the initial amount of carbon, but is approximately proportional to the temperature difference, AT, between source and crystal. cm-sized ZnO crystals have been grown after adjusting the main parameters of growth. The quality of crystals is assessed from structural, chemical and physical characterisation. Electrical measurements performed on our crtystals show carrier concentrations lying around 10 18 cm -3 at 300 K, with resistivities varying from 0.05 Ω cm to 50 Ω cm for a temperature changing from 4.2 K to 300 K. The maximum mobility measured at room temperature was 183 cm 2 /Vs.

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.

Seed-free growth of (1 1 1) oriented CdTe and CdZnTe crystals by solid-state recrystallization

Abstract Solid-state recrystallization (SSR) is proposed as a novel method of CdTe bulk crystal growth which allows one to overcome the difficulties met in the growth of the compound which result from the ionic character of the Cd–Te chemical bond. A three-step strategy for CdTe SSR growth is described where the production of CdTe provides a source for the subsequent growth by sublimation of polycrystalline boules which are finally submitted to SSR. The material obtained after each step is characterized electrically, optically and chemically. Large CdTe crystals showing good structural properties have been obtained from this SSR technique, which is demonstrated to be also convenient for the growth of CdZnTe crystals.