R. Triboulet

Undoped high‐resistivity cadmium telluride for nuclear radiation detectors

Starting with highly purified feed material, single crystals of semiinsulating CdTe were grown by the use of the traveling heater method, without external chemical compensation. Evaluation of the crystals by the use of electrical and optical measurements showed decisive improvements in quality. Nuclear radiation detectors prepared by the use of this material resulted in an energy resolution (FWHM), at room temperature, of 4.6 and 8.5 keV for γ rays at energies of 122 and 662 keV, respectively. The energy resolution at 122 keV decreased to 3.8 keV at a temperature of −30°C. No polarization effect was observed.

Cdte and CdZnTe crystal growth by horizontal bridgman technique

By means of the horizontal modified Bridgman technique, CdTe and CdZnTe crystals have been grown. The conditions of synthesis have been described and a modified gradient freeze technique has been experimented and proposed. By modifying the transverse gradient, nature of the boat, gas overpressure and temperature cycles, different growths have been compared. A computerized power recording was found to be extremely sensitive in spotting any thermal accidents. With an optimization of these different factors, we have obtained large single crystals: they gave (111) substrates up to 28 cm2. A new and fast optical technique with a He-Ne laser has been used for studying all orientation parameters. The substrates have been characterized by double X-ray diffraction, photoluminescence and electrical measurements.

Growth and characterization of bulk HgZnTe crystals

Abstract Bulk Hg 1− x Zn x Te crystals have been grown by THM with a longitudinal homogeneity of ±0.02 mol for x = 0.15 corresponding to the 10 μm detection wavelength. The hardness of the material, higher than for (Hg,Cd)Te, reveals a higher bonding strength. The first opto-electronic parameters measured are close to those found in (Hg,Cd)Te.

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.

(Hg,Zn)Te: A new material for IR detection

Abstract The properties of MZT are analyzed according to the concept of stability after specifying it through considerations related to the Zn-Te bond. in comparison with MCT, direct single crystal growth is shown possible by THM. The ingots are of better longitudinal homogeneity and the crystals of better crystalline quality. Lower interdiffusion coefficients are found from interdiffusion experiments the results of which are interpreted by introducing a large term of interaction between cations. The better stability of the surfaces is demonstrated from electrochemical experiments and the better bonding strength from hardness data. An intense absorption excitonic line, in the absorption spectra, accounts for less non radiative recombination. Excellent implanted IR photodiodes confirm the importance of this material.

Twin-free (Cd, Mn)Te substrates

Abstract The complete pseudo-binary CdTe-MnTe phase diagram was drawn up by DTA. It shows a phase transition in the solid state from a high temperature phase, not unambiguously identified, to the low temperature ZB one. Bridgman grown (Cd, Mn)Te crystals present a high twinning density while those grown by THM, at a temperature lower than the phase transition one, were shown to be of twin free ZB structure, and highly purified beside the Bridgman ones. Microhardness measurements confirm that Mn destabilizes the Cd-Te bond. Twin-free (Cd Mn)Te crystals, with X-ray double crystal rocking curves of average FWHM ⋍ 30 arc sec, appear nevertheless of reasonable substrate quality.

High efficiency n‐Cd(Se,Te)/S=photoelectrochemical cell resulting from solution chemistry control

High efficiency (12.7%) CdSe0.68Te0.32/cesium polysulfide photoelectrochemical cells are demonstrated in this work. Crystals of the ternary alloy Cd(Se, Te) of type n type were synthesized by the traveling heater method. The nature of the polysulfide electrolyte, based on Cs polysulfide without excess hydroxide and containing small amounts of copper ions, is shown to be of particular importance in determining the cell efficiency. Reasonable output stability of the cell was obtained under accelerated tests.

CdTe growth by “multipass thm” and “sublimation thm”

Abstract Two methods of growth, derived from the classical THM, lead to significant improvements in the perfection of CdTe crystals. A greater purity is obtained with the Multipass THM whereas the modified Sublimation THM reduces the stoichiometric departure. Results on the materials physical characterisation are given which establish the advantages of the methods.

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).

Influence of the mercury vapor pressure on the isothermal growth of HgTe over CdTe

The theory developed in the preceding article is applied to the epitaxial growth of HgTe on a CdTe substrate under isothermal EDRI conditions. In the absence of excess mercury, two different growth conditions can be distinguished. In the high‐temperature case, pure HgTe is present at the surface of the epitaxial layer and the layer thickness is proportional to the square root of the Hg vacancy diffusion coefficient and of the vacancy concentration gradient. At low temperature (<450 °C), a CdHgTe solid solution exists at the surface of the epitaxial layers; its thickness depends linearly on the coefficient of interdiffusion and on the mercury concentration gradient at the surface. Mercury in excess influences the rate of interdiffusion, the evaporation of mercury from the substrate, and therefore the interdiffusion coefficient as well as the layer thickness and the surface composition. It was found that the interdiffusion coefficient D (varying between 0.5 μ2/h for cadmium‐rich alloys and 100 μ2/h for merc...