LPE of Isolated Pb0,85Sn0.15Te Islands on PbTe

In recent years the importance of selective epitaxy has continuously increased. It is a tool for controlling the production of semiconductor structures as required. This method has been demonstrated and investigated by LPE as well as VPE and MBE. Usually substrates are used having either preferentially etched channels or windows in masks to predetermine the site. In the present paper epitaxy of Pb_0.85Sn_0.15 Te deposits growing in isolated islands on PbTe substrates by means of LPE is investigated.     

Double crystal topographic investigations of PbTe grown by the travelling heater method (THM)

THM-grown PbTe and PbTe: Tl were examined near the (n, —n)-position by means of X-ray double crystal arrangement. The half-width of the rocking curves of Tl doped PbTe is larger than that of undoped PbTe by factor two. Long range and local lattice plane distortions, as well as disturbances induced during preparation, in the from of dislocation slip lines and greatly disoriented areas were observed.     

TSM-gewachsene Halbleiter-Einkristalle aus (Pb0,8Sn0,2)Te

By means of the Travelling Solvent Method (TSM) the authors succeeded in growing PbSnTe solid solution crystals using a simple working growing principle. Imperfections and constitution as well as electrical properties of the crystals have been investigated. The results lead to the conclusion that one can grow homogeneous, nearly perfect crystals having low carrier densities and high carrier mobilities in a relatively short time which seems to be the main advantage of the experimental techniques used. Representative values of electrical crystal parameters are p₇₇ ≦ 10¹⁷ cm⁻³, n₇₇ ≦ 10¹⁷ cm⁻³; pμ₇₇ ⋍ 1,6 × × 10⁴cm²/Vs; dimensions: 1 × 4 × 4 mm³.     

On the substructure of epitaxial (Pb,Sn)Te films grown on KCl cleavage faces

The X-ray diffraction rocking curve analysis has been employed for the measurement of crystallite sizes of (Pb, Sn)Te films for different thickness, epitaxially grown on KCl cleavage faces by the hot-wall technique. The size of the coherently scattering regions parallel to the reflecting planes did not depend on film thickness and agreed with the mean distance of nuclei just before coalescence, investigated by means of replica electron microscopy. The results are consistent with a model of stalk-like growth of crystallites in film growth direction.     

Investigations for Sn diffusion in Pb1−xSnxTe and PbTe

By annealing Pb_1−xSn_xTe and PbTe isothermally in a quartz ampoule Sn diffused from Pb_1−xSn_xTe into PbTe. The profiles obtained have been investigated by means of an electron beam microanalyser, and the coefficients of diffusion have been determined at various temperatures. The diffusion of Sn can be explained by the expressions: D_PbSnTe = 1.5 · 10⁻¹ exp (−1.8 eV/kT) cm² s⁻¹ (0,14 < x < 0,18) D_PbTe = 5,5 · 10⁻⁴ exp (−1.5 eV/kT) cm² s⁻¹. N-type layers are observed at the surface of Pb_1−xSn_xTe specimens.     

Distribution of Pb2+ ions in KCl single crystals grown by bridgman method

Basing on the Pb²⁺ concentrations in the ”︁pure”︁ ends of single KCl crystals, at various dopant concentrations in the original melts, as well as on the Pb²⁺ concentrations along the crystals, the distribution coefficient of the dopant ions is estimated. The origin of possible deviations of experimental data from those calculated according to eq. (1) is discussed and the neccessity of introducing an appropriate correction factor is pointed out (eq. (2)).     

Growth of 2-methyl-4-nitroaniline (MNA) crystals by the bridgman method

Organic single crystals of 2-methyl-4-nitroaniline (MNA) up to 3 mm in diameter and 20 mm in length have been successfully grown by the Bridgman method using the purified reagent by sublimation. The crystals are transparent and yellow in colour by controlling the growth conditions. In the spectra of yellow coloured crystals no absorption peak is observed until about 450 nm. Also, the crystals of MNA have the two cleavage planes (311 ) and (010).     

Crystal growth of rare-earth orthovanadate (RVO4) by the floating-zone method

Single crystals of rare-earth orthovanadate, RVO₄ where R=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, with the cross-sectional size of about 7×7 mm² and 20–50 mm length have been successfully grown by the floating-zone method. Fluorescence properties at room temperature and dielectric and elastic properties along the c-axis of some grown crystals have been reported.     

Influence of gravitation on the processes of heat and mass transfer in solution crystal growth by the travelling heater method (THM) (III)

The effect of the natural and thermocapillary convection on the vortex configuration in solution during growth of PbTe crystal by the travelling heater method is considered. The estimation of the parameters of growth process (i. e. axial temperature gradients, gravitational acceleration, degree of the solution's surface contact with ampoule), when the vortex configuration undergoes qualitative variation, is given. In terms of the one-dimensional thermodiffusive problem solution the effect produced by the convective stirring on the position of growing and dissolving interfaces is described.     

Physical Properties of Pb0.8Sn0.2Te :In Epitaxial Layers

A study was made of dislocation density, Hall effect, conductivity, and photoeffects in In-doped Pb_0.78Sn_0.22Te epitaxial layers. From an analysis of R_H vs T the existence of resonant as well as deep levels is concluded, dependent on In content and defect structure. Samples with about 0.4 at.% In which are not compensated, exhibit photoresponse as well as luminescence.     

Sphalerite-type Cd(Te,Se) crystallised by self-selecting vapour growth

Monocrystals of sphalerite-type CdTe_1-xSe_x were grown by self-selecting vapour growth SSVG in the horizontal configuration. As measured on a series of points of a (110) split plane, the “rocking curve” half-width was below 30 arcsec, while the lattice parameter measurements demonstrated the molar fraction x varying within 0.0024 (0.24 %). The values of x obtained from photoluminescence spectra taken from samples of different quality were in the ranges of 0.0034 (0.34 %) and 0.0047 (0.47 %). On the basis of the photoluminescence measurements, the maximum difference in x within the crystallised material was estimated to be 0.01 (1 %).     

The texture of GaSb ingots grown by the bridgman method

Crystallographic features of GaSb grown by the Bridgman procedure were investigated by scanning electron microscopy. Chemical etching and the electron channelling method were used to determine the position and crystallographic orientation of crystallites. A pronounced 〈110〉 texture was detected which was misaligned by 5÷28° with respect to the main axes of the ingots. Boundaries were categorized according to the orientation change accross them. Results were compared. The majority of small angle boundaries are probably caused by thermal stresses induced dislocation migration.     

Influence of Gravitation on the Processes of Heat and Mass Transfer in Solution Crystal Growth by the Travelling Heater Method (THM) (II)

The two-dimensional quasi-stationary thermodiffusive hydrodynamic problem of the crystal PbTe growth from solution by the travelling heater method has been solved. Computation is given for the temperature field distribution in crystal and solution. The picture of fluxes in solution was obtained under free convection for different lengths of solvent zone. It is shown that in the absence of absence of gravitation at the growing interface in solution there occurs a constitutional supercooling, whereas the free convection removes it, which leads to greater morphological stability of a growing crystal face.     

Influence of Gravitation on the Processes of Heat and Mass Transfer in Solution Crystal Growth by the Travelling Heater Method (THM) (I)

In axially symmetric and planar cases the formulation is given of a two-dimensional hydrodynamic thermodiffusive problem on the crystal PbTe growth from solution by the travelling heater method. The analysis of the one-dimensional thermo-diffusive problem solution is presented. The dependences were obtained of the growing and dissolving interface positions relative to the heater on the heater travel rate for different lengths of solvent zone.     

Melt growth and post‐grown annealing of semiinsulating (CdZn)Te by vertical gradient freeze method

We present results of development of CdZnTe semi‐insulating crystals prepared by Vertical Gradient Freeze method in a 4‐zone furnace. We applied the way of growth of the crystal from the top when the first crystallization seed is created on the surface of the melt. The typical height of the crystals is 5 cm. Resistivity and photoconductivity profiles measured along the growth axis by contactless method are compared and their mutual correlation is explained based on a model of relative shift of the Fermi level and the midgap level present in the material. The influence of the Fermi level on electron trapping and recombination is summarized. We present here results of a two‐step annealing method aimed at reduction of Te inclusions while keeping the resistivity high. We employed CdTe:Cl VGF grown samples to eliminate Te inclusions observed in as grown crystals by two‐step post grown annealing in Cd and Te atmosphere and present a model of the processes leading to high resistivity material after annealing.     

Crystal growth of progesterone metastable and stable polymorphs by polymer induced herteronucleation (PIHn) method

The selective crystallization of progesterone polymorphs prepared by Polymer‐Induced Heteronucleation (PIHn) method was investigated. Polyvinyl alcohol (PVA), hydroxypropyl methylcellulose (HPMC), dextran, gelatin, polyisoprene (PI), and acrylonitrile/butadiene copolymer (NBR) were used as heteronucleants. Crystallizations were conducted from 0.5, 10 and 40 mg mL⁻¹ solutions in chloroform at room temperature by solvent evaporation. The samples were characterized by X‐ray powder diffraction, differential scanning calorimetry, infrared spectroscopy and scanning electron microscopy. Form 2 was obtained from 0.5 mg mL⁻¹ solution in almost all polymers. A mixture of both polymorphs crystallized from the three concentrations on gelatine; from 10 and 40mg mL⁻¹ on PVA and HPMC and, from 10 mg mL⁻¹ solutions on NBR. Form 2 crystallized on HPMC was stable for three months under ambient stress conditions (40ºC and 75% RH). These results are good evidence that the tailoring of new formulations and devices with progesterone the metastable and more soluble form 2 is possible.     

Phase transitions of p-type (Pb,Sn,Ge)Te-based alloys for thermoelectric applications

p-type (Pb,Sn,Ge)Te-based alloys for thermoelectric applications were prepared using Bridgman technique. Second-order, rhombohedral to cubic phase transitions are involved, as evaluated from anomalies in the temperature dependence values of Seebeck coefficient, electrical conductivity, heat flow and the elongation, in the vicinity of the phase transition temperature, T_c. The correlation between these anomalies in both the electronic and thermodynamic properties was interpreted by means of the relationship of Fermi energy to the chemical potential (or to the molar Gibbs free energy).     

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.