Composition and kinetic characteristics of vapour phase during mercuric iodide growing

The results of thermodynamical analysis of the vapour phase are presented for mostly often used growth conditions. It is shown that the vapour phase may contain: HgI₂(g), Hg(g), I₂(g), I(g). However, the degree of decomposition does not exceed one percent. Moverover, the following dependences are calculated and presented in a graphic form for HgI₂ + I₂ vapour mixture: the coefficient of dynamic viscosity from composition and temperature; the coefficient of diffusion with temperature and pressure; the coefficient of heat conductivity from composition and temperature.     

Vapor growth of doped mercuric iodide crystals by the Temperature Oscillation Method

Crystals of HgI₂ are grown from the vapor phase using the Temperature Oscillation Method. Techniques to dope the crystals with Hg, I₂, NH₄I, SbI₃, PbI₂, and TeI₄ during growth are described. Evaluation of the external morphology indicates that HgI₂ can incorporate a relatively large excess of Hg. Increasing the iodine concentration in the crystals introduces morphological break- down of the vapor/solid interface.     

Mass transport in the three-thermal-zone solute transport method

The mass transport process of the three-thermal-zone solute transport method is analyzed theoretically in this paper. The growth rate of a crystal is depending on the temperature gradient and the size of the curcible. Comparing with the normal temperature gradient solute transport method, this technique can be used to grow crystals in better quality.     

AlN bulk single crystal growth on 6H-SiC substrates by sublimation method

Large and thick AlN bulk single crystals up to 43 mm in diameter and 10 mm in thickness have been successfully grown on 6H-SiC (0 0 0 1) substrates by the sublimation method using a TaC crucible. Raman spectrum indicates that the polytype of the grown AlN single crystals is a Wurtzite-2H type structure, and the crystals do not include any impurity phases. The quality at the top of the crystal improves as crystal thickness increases along the 〈0 0 0 1〉 direction during growth: a low etch pit density (7×10⁴ cm⁻²) and a small full width at half maximum for a 0002 X-ray rocking curve (58 arcsec) have been achieved at a thickness of ∼8 mm. The possible mechanism behind the improvement in the AlN crystal quality is also discussed.     

Growth of high-purity ZnTe single crystals by the sublimation travelling heater method

A travelling heater method (THM) was developed to grow high-purity ZnTe from the vapor phase. This crystal growth method is called the “sublimation THM”. The temperature of the sublimation interface was set at 815°C and the temperature of the growth interface was varied from 785 to 800°C. The growth rate was 3 mm/day. Under these conditions, it was found that the growth process was mainly due to surface nucleation. Characteristics of the crystals were compared with those of solution-THM and vapor phase epitaxially grown crystals. The free-exciton line at 2.381 eV strongly appears and a doublet structure in neutral- acceptor bound exciton at 2.375 eV is clearly resolved with splitting energy of about 0.7 meV. We thus conclude that the THM from the vapor phase is suitable for preparing ZnTe single crystals which have excellent luminescent properties.     

Bulk crystals of PbTe synthesized by the iodide method

Bulk crystals have been prepared for the first time from PbTe synthesized by low-temperature iodide method. Their basic structural, physico-chemical and electrical parameters as a result of certain technology conditions have been investigated.     

Numerical simulation of a new SiC growth system by the dual-directional sublimation method

A new SiC growth system using the dual-directional sublimation method was investigated in this study. Induction heating and thermal conditions were computed and analyzed by using a global simulation model, and then the values of growth rate and shear stress in a growing crystal were calculated and compared with those in a conventional system. The results showed that the growth rate of SiC single crystals can be increased by twofold by using the dual-directional sublimation method with little increase in electrical power consumption and that thermal stresses can be reduced due to no constraint of the crucible lid and low temperature gradient in crystals.     

Growth of bismuth tri‐iodide platelets by the physical vapor deposition method

The work reports the growth of single BI₃ crystals with platelets habit. Platelets were grown by physical vapor deposition (PVD) in a high vacuum atmosphere and with argon, polymer or iodine as additives. Crystals grew in the zone of maximum temperature gradient, perpendicular to the ampoule wall. Crystals grown with argon as additive show a very shining surface, have hexagonal (0 0 l) faces, sizes up to 20 x 10 mm² and thicknesses up to 100 μm. They were characterized by optical microscopy and scanning electron microscopy (SEM). Dendritic‐like structures were found to be their main surface defect. SEM indicates that they grow from the staking of hexagonal unities. Electrical properties of the crystals grown under different growth conditions were determined. Resistivities up to 2 x 10¹² Ωcm (the best reported value for monocrystals of this material) were obtained. X‐ray response was measured by irradiation of the platelets with a ²⁴¹Am source of 3.5 mR/h. A comparison of results according to the growth conditions was made. Properties of the crystals grown by this method are compared with the ones measured for others previously grown from the melt. Also, results for bismuth tri‐iodide platelets are compared with the ones obtained for mercuric and lead iodide platelets. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Method of X-ray spectral microanalysis of PbTe and SnTe obtained by the iodide method

This an examination of the characteristics of the X-ray spectral microanalysis of the tellurides of lead and thin, obtained by the iodide method. It was demonstrated that applying the method of calculating the composition in relation to the relative intensity of the characteristic X-ray radiations of the analytical lines TeL_α and IL_α secures the possibility of analyzing relief surfaces. Besides that, the method makes it possible to make calculations without using numerous traditional semi-empirical expressions under conditions of changes in the values of the accelerating voltage.     

Optical and structural properties of lead iodide thin films prepared by vacuum evaporation method

Thermally processed lead iodide (PbI₂) thin films were prepared by the vacuum evaporation method in a constant ambient. Measured thickness of the film was verified analytically from the optical transmittance data in a wavelength range between 300 and 1600 nm. From the Tauc relation for the non‐direct inter band transition, the optical band gap of the film was found to be 2.58 eV for film thickness 300 nm. X‐ray diffraction analysis confirmed that PbI₂ films are polycrystalline, having hexagonal structure. The low fluctuation in Urbach energy indicates that the grain size is quite small. The present findings are in agreement with the other results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stability of growth conditions and α-HgI2 crystal habit during growing by temperature oscillation method

On the basis of analysis of the experimental data, it is shown that:

• the crystal growth rate is mainly determined by diffusion in vapour phase;
• the limitation of the growth process by transport leads to an unremitting change of the growth conditions, being the cause of slowing down the growth and the change of the growth rates ratio of the crystallographically different facets, the latter evokes refaceting;
• the limitation of the growth by the transport process is the factor reducing the perfection of the structure and the maximum sizes of single crystals.

     

On iodine behaviour in bulk crystals of PbTe and SnTe synthesized by the iodide method

In order to explain the peculiar characteristics of iodidely synthesized PbTe and SnTe crystals a model for their interaction with iodine is suggested. It is based on the assumption that PbI and I, respectively SnI and I, resulting from the PbI₂ (SnI₂) dissociations, are incorporated independently and specifically in the crystals: in PbTe prevails the PbI-incorporation; in SnTe — the incorporation of I + V_Sn. This difference is connected with the thermodynamic stability of the PbTe and SnTe crystal lattices.     

Investigation of the acoustic attenuation in lead and tin tellurides obtained by the iodide method

The products of the reaction for obtaining lead telluride and tin telluride, synthesized by the iodide method, were analyzed by the method of acoustic attenuation (internal friction). The results of the investigations are in agreement with the model, suggested earlier, of self-alloying of tellurides by metallic component.     

X-ray study of the reaction products in obtaining lead telluride by a low-temperature iodide method

Results from X-ray studies of the products of the reaction in obtaining lead telluride by the iodide method are presented. It is demonstrated that PbI₂ condenses at the flow of the inert gas on the cool parts of the reactor at the isothermal annealing of the synthesized material. This is in agreement with the assumption about the self-alloying of PbTe as a result of the higher solubility of Pb under conditions of dissolving PbI₂ in lead telluride.     

Crystal growth of SnO2 by chemical transport method

Single crystals of SnO₂ were grown by the chemical transport method from the powder prepared by heating hydrous stannic oxide. The transport reactions were carried out when iodine and sulfur were simultaneously used as transporting agent, and fine crystals of a few millimeters in dimensions were grown after a ten-day transport; the transport proceeded from 1100°C (charge) to 900°C part in a silica ampoule. The crystals were identified as SnO₂ (cassiterite) by the Weissenberg method. Thermodynamic calculations led to the equilibrium $\text{SnO}{}_2\text{(s) + I}{}_2\text{(g)}\text{+}\text{1}\text{2}\text{S}{}_2\text{(g)}\text{?}\text{SnI}{}_2\text{(g) + SO}{}_2\text{(g)}$ for this transport reaction.     

Stoichiometric single crystal growth of AgGaS2 by iodine transport method and characterization

High quality single crystals of ternary AgGaS₂ (AGS) semiconductor with chalcopyrite structure have been grown by chemical vapor transport (CVT) technique using iodine as a transporting agent at different growth zone temperatures. The powder X‐ray diffraction and single crystal X‐ray diffraction studies indicate that the as‐grown AGS crystals belong to the tetragonal (chalcopyrite) system with (112) plane as the dominant peak. The full width at half maximum (FWHM) of the X‐ray rocking curve for the as‐grown AGS single crystal is 5 arcsec. The energy dispersive X‐ray analysis (EDAX) and optical transmission spectra of as‐grown AGS single crystals grown at different conditions show the almost same composition and band gap (2.65 eV). Photoluminescence (PL) spectra of as‐grown AGS single crystals show prominent band edge emission at 2.61 eV. The resistivity of the as‐grown AGS single crystal has been measured. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Epitaxial growth of CuInSe2 single crystal by halogen transport method

CuInSe₂ single crystals were epitaxially grown on (001) GaP, (001) GaAs, and (110) GaP by the halogen transport method. The orientation relationships in the growth on the (001) and (110) faces were (a) [001]_CuInSe2 [001]_sub and [100]_CuInSe2 [100]_sub (c-axis orientation growth), and (b) [110]_CuInSe2 [110]_sub and [001]_CuInSe2 [001]_sub, respectively. On (001) InP, the orientation relationships between the layer and substrate consist of two sets: (c) [100]_CuInSe2 [001]_sub and [001]_CuInSe2 [010]_sub, and (d) [100]_CuInSe2 [001]_sub and [001]_CuInSe2 [ 00]_sub (a-axis orientation growth). The above results, i.e., c-axis growth on (001) GaP and (001) GaAs and a-axis growth on (001) InP, could be explained by a criterion of the minimum lattice mismatch between grown layers and substrates. A series of growth experiments on (001) GaAs indicated that appropriate gas etching of the substrate surface and growth temperature were required for obtaining twin-free single-crystal epitaxial CuInSe₂.     

Melt menisci during single-crystal tube growth by the Stepanov method

The stability of the liquid menisci formed during the growth of single-crystal tubes by the Stepanov method and, in particular, by the floating zone method used to purify crystals, has been investigated. The results obtained can be used in practice to grow crystals by various capillary shaping methods.