G. Didier

Growth and characterization of Cd1−xMnxTe and MnTe crystals; contribution to the CdTe-MnTe pseudo-binary phase diagram determination

Abstract Large MnTe single crystals were grown by a modified Bridgman method and by THM. Large homogeneous Cd−1xMnxTe single crystals were grown by the Bridgman method with x = 0.01 to 0.75, and their electrical conductivity and Hall effect were measured. The CdTe-MnTe pseudo-binary phase diagram was studied by DTA and electron microprobe measurements. The solid solution range extends up to x = 0.77. The two phase field is remarkably narrow, accounting for the homogeneity of the Bridgman ingots.

Growth of ZnTe by stoichiometric and off stoichiometric zone refining

Abstract A method of fractionated synthesis is developed for ZnTe. Large crystals are grown by two zone melting methods: the travelling solvent method (TSM) and the vertical zone refining technique. The influence of the crystallization temperature on the carrier concentration of the crystals is shown. A complex center [V Zn –donor] is assumed to be involved.

“Cold travelling heater method”, a novel technique of synthesis, purification and growth of CdTe and ZnTe

Abstract A new method of synthesis, growth and purification, called “cold travelling heater method” (CTHM) was devised for CdTe and ZnTe. The source material is constituted of a Cd (or Zn) rod surrounded by Te powder. The optimum growth conditions have been determined for the growth of CdTe and ZnTe ingots up to diameters of 30 and 20 mm, respectively. Their excellent purity, in view of the modest purity of the starting elements used, is attested by electrical and photoluminescence measurements. In a brief preliminary study, the growth of (Hg,Cd)Te and (Hg,Zn)Te is shown to be possible by CTHM, but the ingots obtained suffer from a lack of homogeneity.

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.

Low-temperature growth of ZnSe crystals

Abstract ZnSe single crystals have been grown at “low temperature” (800–900°C) by chemical vapour transport (CVT) with iodine as the chemical agent, and by the Travelling Heater Method (THM) with PbCl 2 as the solvent. The pseudo-binary PbCl 2 -ZnSe and PbBr 2 -ZnSe phase diagrams have been partially determined by DTA. The electron concentration of CVT crystals has been found to depend only on the annealing temperature. An activation energy of 1.14 eV can be obtained from this result and associated with the electric activation of iodine atoms. The purification effect of THM has been very pronounced for lithium.

Properties of CdTe crystals grown by THM using Cd as the solvent

Abstract CdTe crystals have been grown using Cd as the solvent (crystals A). Several physical properties (photoluminescence, electrical transport properties, DLTS) of these crystals have been compared to those of crystals grown by THM using Te as the solvent (crystals B). The purity level of crystals A is slightly higher than that of crystals B. Both crystals A and B are found to have rather poor crystalline quality from cathodoluminescence and X-ray topography observations. The effect of annealing of crystals A and B under saturated Cd vapour pressure has been studied. A and B are shown to react to the annealing in an opposite way. This could be explained by the presence of precipitates of different type according to the solvent used during the growth process.

Simultaneous synthesis and growth by THM of large HgTe crystals of high purity

Abstract Large mercury telluride crystals are grown, by the travelling heater method directly from mercury and tellurium as source material. Their purity is attested by the electrical characteristics measured after appropriate annealing.

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.

Low resistive ZnSe substrates

Doping by annealing of ZnSe single crystals grown by solid phase recrystallisation in a mixture of Al and Zn at 860°C has been studied. The properties of doped ZnSe crystals assessed by secondary ions mass spectroscopy, scanning electron microscopy (electron channelling patterns (ECP) and cathodoluminescence (CL)), double crystal X-ray diffraction (rocking curve) and Hall effect measurements depend strongly on the geometry of the crystal which is annealed. In the best case, CL spectra show only the donor-bound exciton line (2.67 eV at 300 K; 2.77 eV at 100 K) indicating thus, together with ECP and rocking curve FWHM (35 arcsec), the high crystalline quality of the (100)-doped substrates. From Hall effect measurements, a free electron concentration of 5 × 10 17 cm -3 and an electron mobility of 200 cm -2 V -1 s -1 (resistivity 6.3 × 10 -2 Ω cm) at 300 K are determined.