Traveling Heater Method Research Articles

Microscopic solid inhomogeneities in Al xGa 1−xSb bulk crystal grown from metallic solutions

In Al xGa 1−xSb crystals grown by the travelling heater method (THM), spatially resolved photoluminescence and cathodoluminescence measurements were carried out at 77 and 20 K, respectively, to detect the AlSb distribution at convective type I and kinetic type II striations (resolution about 4 μm in diameter). The AlSb microscopic segregation effects in the riser area of type II striations can be explained with the non-steady-state step exchange model.

Melt and metallic solution crystal growth of CuInSe 2

In this paper the fabrication of CuInSe 2 chalcopyrite single crystals by the vertical Bridgman technique using non-stoichiometric In 2Se 3-rich congruent composition and a novel ampoule design is describe. Furthermore the growth of CuInSe 2 crystals by the travelling heater method (THM) using an In solvent was investigated. The elemental composition of as-grown CuInSe 2 semiconducting compounds and their electrical properties are discussed and correlated with predictions made by an intrinsic chemistry model.

Horizontal travelling heater method growth of Hg 1−xCd xTe with crucible rotation

A horizontal travelling heater method (THM) for growing cylindrical cyrstals from a partially filled solution zone has been investigated for the first time. By applying ampoule rotation, the whole cross section of the crystal is successively brought into contact with the liquid solution, which is effectively stirred by forced convection. This approach was used to grow single-crystalline Hg 1− x Cd x Te ingots from a Te-rich solution zone. The structural perfection and metallurgical homogeneity are equivalent to vertically-grown THM material.

Crystal growth of AgGaS2 by the Bridgman-Stockbarger and travelling heater methods

Single crystals of AgGaS2 were grown by the Bridgman-Stockbarger technique in two-zone furnaces and by the travelling heater method in ellipsoid mirror furnaces. PbCl2 and AgBr were proved to be novel solvents for the high temperature solution growth of AgGaS2. Melt grown AgGaS2 crystals show weak transparency. Optically clear AgGaS2 crystals could be obtained after annealing them in the presence of Ag2S. Flux grown AgGaS2 crystals are transparent without annealing, but show microscopically small inclusions originated from the solvents.

A new model for the absorption coefficient of narrow-gap (Hg,Cd)Te that simultaneously considers band tails and band filling

A semiempirical model is presented that correlates the broadening of the absorption edge with both transitions below the energy gap and with transitions by the Kane band model. This model correctly fits both the absorption and luminescence spectra of narrow-gap (Hg,Cd)Te samples that have been grown by the traveling heater method as well as by molecular-beam epitaxy. The accuracy of the band-gap determination is enhanced by this model.

Optical and electrical characterization of Al xGa 1− xSb crystals grown by the travelling heater method

Bulk Al xGa 1−xSb single crystals with various AlSb solid compositions were grown by the travelling heater method (THM) on GaSb substrates. The crystals were grown with a Ga-rich as well as on an Sb-rich solution zone (undoped or doped with Te). We report in this investigation on results obtained by electrical characterization (DLTS, Hall effect) and optical spectroscopy (photoluminescence). Deep centres (DX centre) and shallow centres ( ⌈ and X conduction band derived donors) were investigated.

TEM investigation of precipitates in Hg0.8Cd0.2Te grown by the travelling heater method

Transmission electron microscopy investigations of Hg 0.8 Cd 0.2 Te crystals grown by the travelling heater method are presented. In as-grown material mercury vacancy loops are found at a density of about 1 x 10 15 cm -3 . These defects completely disappear by annealing under mercury saturated conditions. Peculiarities of the defect formation are analyzed.

Growth of ZnTe by physical vapor transport and traveling heater method

ZnTe crystals were grown by horizontal physical vapor transport (PVT) and a Te-solution vertical traveling heater method (THM). The grown crystals were examined by X-ray Laue diffraction technique and Hall measurements to determine the growth orientation and the electrical properties of the crystals. They were also characterized by low temperature infrared (IR) absorption measurements. Several sets of distinct peaks were observed in the IR absorption spectra for the THM samples and were identified as resulting from CU(2+) impurities. Similar measurements on vapor grown ZnTe showed featureless absorption spectra. Chemical analyses were carried out to measure the impurity content in various ZnTe samples and synchrotron radiation topography was used to Study crystalline microstructure of the (111) ZnTe single crystals grown by PVT.

Hg vacancy diffusion in mercury cadmium telluride

In Hg 0.8 Cd 0.2 Te crystals grown by the travelling heater method (THM), a significant increase in carrier concentration in the last solidified part is observed. The carriers can be identified with mercury vacancies. The observed longitudinal vacancy concentration profiles can be quantitatively described by a model that takes into account the thermal history of the different parts of the crystal along its length and a concentration dependent Hg vacancy diffusion coefficient

THM growth of Al xGa 1− xSb bulk crystals

Single crystals of Al xGa 1−xSb with a diameter up to 24 mm and length of more than 28 mm have been successfully grown with the travelling heater method (THM). The AlSb solid composition x ranges from 0.06 to 0.65. The material was grown in quartz glass ampoules with Ga-rich as well as Sb-rich solution zones. The crystals were undoped for p-type and doped with Te for n-type conductivity.

The growth of a cubic, single phase, Cd0.6Mn0.4Te single crystal by the vertical gradient freeze method

The growth of CdMnTe single crystals faces some difficulties due to the phase transition in the solid state at high temperatures, just after solidification. To overcome this problem, it has been suggested to grow the crystals from a Te-rich solution by the traveling heater method at a lower temperature than that of growth from the melt, or alternatively to grow the crystal from the melt at high axial thermal gradient near the interface. In this paper, we present for the first time the growth of cubic, single phase, Cd x Mn 1− x Te single crystals by the vertical gradient freeze technique under a very low axial thermal gradient in the melt (3°C/cm) and high manganese content ( x ≈ 40%). The solidification stage is characterized by a rapid cooling of the crystal through the phase transition temperature region, followed by annealing at about 800°C. The crystal exhibits a very high crystalline perfection, as measured by the double-crystal X-ray rocking curves with a full width at half maximum of 30 arc sec and low optical losses of about 1 dB/mm between 650 and 820 nm with λ-cutoff at 630 nm. Further magneto-optical properties are currently examined for a possible application in devices.

Single Crystal Growth of Cu–III–VI2 Semiconductors by THM

The traveling heater method (THM) has been applied to the single crystal growth of Cu–III–VI2 chalcopyrite semiconductors. Up to this time, bulk single crystals of CuGaS2, CuGaSe2, CuInS2 and CuInSe2 ternary compounds have been obtained by the THM technique using In solvent. The THM growth of bulk single crystals of CuGa0.6In0.4S2 quaternary alloy, which is lattice-matched to ZnS, has been investigated. By the use of In-solution zones containing 60 mol% CuGa0.37In0.63S2 solute, single crystals with a uniform composition of CuGa0.6In0.4S2 were obtained.

Crystallization method providing composition autocontrol in situ (CAM-S)

A novel approach to crystal growth from a molten solution zone (MSZ) is presented. There are five variants of CAM-S, which is a modification of the travelling heater method (THM), which can solve crystal growth problems as THM does, especially synthesis, repeated creation of the MSZ, zoning operations with vibrational stirring, and perform all these operations in situ. The combination of CAM-S with calculation method of optimal molten-solution composition (COM-S) has been applied to the growth of bulk crystals of the ternary solid solutions Ga x In 1− x Sb. Extreme constancy of the lattice parameter throughout the crystalline length has been achieved. Both methods are based on the knowledge of phase diagrams.

CdTe detectors responses to pulsed X-rays : comparison of different materials

ABSTRACTThe goal of this work is to compare and analyze the transient responses to X-ray pulses of different cadmium telluride detectors:- CdTe: Cl grown by the vertical Bridgman method (B.).- CdTe: Cl grown by the Travelling Heater Method (T.H.M.).- Cd0,8 Zn0,2 Te grown by the High Pressure Bridgman method (H.P.B.).Photoconductive detectors were subjected to very short (20 ns) 100 keV X-ray pulses and short (4 µs) 2 MeV pulses. The transient response of the photoconductors CdTe: Cl and CdZnTe under high X-ray energy beam were characterized in terms of sensitivity, linearity and dynamic range vs different parameters such as bias voltage and X-ray beam fluence. Bridgman and T.H.M. detectors show similar behaviors while H.P.B. detectors which are highly resistance show shorter transient behavior after the 20 ns pulses irradiations and larger afterglow after the 4 µs pulses irradiations.

High quality CdTe and its application to radiation detectors

CdTe crystal growth by the travelling heater method and the characteristics of its radiation detectors are described. A CdTe polycrystalline ingot is synthesized from purified 99.99999% Cd and Te metals and crystals of 32 mm in diameter are grown at temperaturesof 700°C–900°C with a growth speed of 2–5 mm per day. A high resistivity of more than 10 9Ω cm is obtained at a Cl concentration of 1.5 ppm with electron and hole lifetimes of 1.0 and 0.5 μs respectively. The pulse count mode detectors are fabricated using wafers cut from the ingots. For practical application to medical diagnostics, 90-element array detectors with an element size of 1.8 mm × 2 mm × 1.2 mm are developed. The averaged FWHM is 4.0 keV and the count rate variation is less than 4% for a 60 keV γ-ray source. For dosimetry use, detectors as large as 10 mm × 10 mm × 2 mm and 25 mm diameter × 2 mm thickness volumes are fabricated. Environmental and high temperature acceleration tests have been systematically conducted. Mean time to failure is estimated to be 10 9h at 25°C.

Twinning Effects in Hg1−xCdxTe (x∼0.2) Grown by Thm in The <111> Direction

ABSTRACTHg1−xCdxTe crystals with x∼0.2 were grown by the traveling heater method (THM), in either the [111]A or [111]B directions, using oriented CdTe seeds. Twins are sometimes formed during the growth of these crystals. In crystals grown in the [11]A direction the twins, of orientation [511]B, are constantly growing at the expense of the original [111]A oriented grain. Growth in the [111]B direction, on the other hand, suppresses the growth of the twin domain. Photodiodes and capacitors realized on the (111)A plane are markedly superior to those on the twin plane, (511)B. The difference is due to higher fixed charge and larger fast surface state densities in the case of the (511)B plane. These effects are explained by the lattice structures in the {111} and {511} planes and their possible influence on surface reactivity.

Crystal growth under reduced gravity

During the German Spacelab mission D1 various Crystal Growth Experiments have been successfully performed. The aim of this article is to review those growth studies which have been carried out in ellipsoidal mirror furnace systems. A Floating Zone Technique has been applied to Si whereas GaSb, InP, CdTe and (Pb, Sn) Te have been grown in quartz ampoules by the Travelling Heater Method (THM). One CdTe-growth run used a vapour zone instead of a metallic solution zone. As a main result of all experiments it could be demonstrated that semiconductor crystals may be grown under reduced gravity conditions in a nearly diffusive growth regime.

Positron trapping at native vacancies in CdTe crystals: In doping effect

Positron lifetime measurements give evidence on vacancies in n-type CdTe crystals. The crystals are either nominally undoped or In doped and grown by the travelling-heater method (THM) or the Bridgman technique. In THM CdTe(In) crystals grown using Te as the solvent, the concentration of vacancies correlates with the concentration of In and electrons. This correlation is in aggreement with the model of self-compensation where the In donors are compensated by In-vacancy complexes. In addition to (V Cd−In) − complexes, it is found that positrons are trapped by negative ions.

Carbon and silicon in travelling heater method grown semi-insulating CdTe

Carbon- and silicon-doped CdTe have been studied by charged particle activation heavy ion induced X-ray emission and secondary ion mass spectroscopy to determine the impurities present at low concentrations. Electrical characteristics have been investigated by thermally stimulated current and the Van der Pauw resistivity measurements, in order to correlate the impurity concentrations and electrical behaviours.

THM growth and properties of CuInSe 2 single crystals

Growth of bulk CuInSe 2 single crystals by the traveling heater method (THM) using In solvent has been investigated. The THM growth was performed at about 750°C, where the CuInSe 2 crystals with chalcopyrite structure grow without solid state phase transformation at 810°C, and where the In solution of CuInSe 2 is a single liquid phase. The obtained ingots have a stoichiometric composition of CuInSe 2 throughout the entire crystal. The as-grown crystals are of n-type conductivity, and have an emission band peaking at 0.95 eV in photoluminescence spectra at 77 K.