The thermophysical properties of liquid Te, namely, density, electrical conductivity, and viscosity, were determined using the pycnometric and transient torque methods from the melting point of Te (723 K) to approximately 1150 K. A maximum was observed in the density of liquid Te as the temperature was increased. The electrical conductivity of liquid Te increased to a constant value of 2.89 x 10(exp 5 OMEGA-1m-1) as the temperature was raised above 1000 K. The viscosity decreased rapidly upon heating the liquid to elevated temperatures. The anomalous behaviors of the measured properties are explained as caused by the structural transitions in the liquid and discussed in terms of Eyring's and Bachiskii's predicted behaviors for homogeneous liquids. The Properties were also measured as a function of time after the liquid was coded from approximately 1173 or 1123 to 823 K. No relaxation phenomena were observed in the properties after the temperature of liquid Te was decreased to 823 K, in contrast to the relaxation behavior observed for some of the Te compounds.

Thermophysical Properties of Liquid Te: Density, Electrical Conductivity, and Viscosity

Horizontal casting for the growth of Hg1-xCdxTe by solid state recrystallization

The stability regions of Te-rich p-conducting Hg1-xCdxTe with x=0.20, 0.28 and 0.38 were investigated by means of high-temperature in situ Hall and conductivity measurements. The Te-rich limits of the p-side stability regions, measured in situ, correspond to higher electrically active native point defect concentrations than reported in the literature for quenched samples. In the temperature range 300<or=T<or=900 K, there is a linear relationship between the reciprocal temperature and the logarithm of electrically active native acceptor concentrations. The authors conclude that only one predominant kind of native point defect exists probably the mercury vacancy VHg. Its defect formation energies are calculated. The assumption of Hg vacancies as the predominant kind of defects is supported by precision measurements of lattice parameters, which decrease with increasing defect concentration. From these investigations the authors conclude that a considerably greater number of defects exist than are electrically measurable, especially at higher Cd contents.

Native point defects in Te-rich p-type Hg1-xCdxTe

Magnetotransport measurements in pulsed fields up to 15 T have been performed on mercury cadmium telluride (Hg1−xCdxTe, x∼0.2) bulk as well as liquid phase epitaxially grown samples to obtain the resistivity and conductivity tensors in the temperature range 220–300 K. Mobilities and densities of various carriers participating in conduction have been extracted using both conventional multicarrier fitting (MCF) and mobility spectrum analysis. The fits to experimental data, particularly at the highest magnetic fields, were substantially improved when MCF is applied to minimize errors simultaneously on both resistivity and conductivity tensors. The semiclassical Boltzmann transport equation has been solved without using adjustable parameters by incorporating the following scattering mechanisms to fit the mobility: ionized impurity, polar and nonpolar optical phonons, acoustic deformation potential, and alloy disorder. Compared to previous estimates based on the relaxation time approximation with outscattering only, polar optical scattering and ionized impurity scattering limited mobilities are shown to be larger due to the correct incorporation of the inscattering term taking into account the overlap integrals in the valence band.

Multicarrier conduction and Boltzmann transport analysis of heavy hole mobility in HgCdTe near room temperature

The field of narrow bandgap II-VI semiconductors is dominated by the compound Hg1−xCdxTe (MCT), although some Hg-based alternatives to this ternary have also been suggested. The fact that MCT is still the preeminent infrared (IR) material stems, in part, from the fact that by varying the x value material can be made to cover all the IR regions of interest. In addition, the direct band transitions are responsible for large values of absorption coefficients, allowing quantum efficiencies to approach 100%. Long minority carrier lifetimes result in low thermal noise allowing high-performance detectors to be made at the highest operating temperatures of comparable wavelengths. This chapter covers the growth of MCT by various bulk growth techniques, used mainly for first-generation infrared detectors; by liquid phase epitaxy, used mainly for second-generation infrared detectors; and by metal-organic vapor phase and molecular beam epitaxies, used mainly for third-generation infrared detectors.

Narrow-Bandgap II-VI Semiconductors: Growth

A stoichiometric annealing treatment is proposed for removing the tellurium precipitates from Hg0.8Cd0.2Te crystals grown by solid state recrystallisation. The fact that the chemical potential of tellurium decreases with increasing x in Hg saturated Hg1−xCdxTe is high-lighted and utilized in evolving the treatment. An Hg–Hg0.7Cd0.3Te source is used for annealing the bulk grown Hg0.8Cd0.2Te wafers. The annealing was carried out isothermally first at 420 °C and subsequently at 260 °C. Because of the retrograde solubility of Te in MCT the Te microprecipitates are partly dissolved back into the matrix at 420 °C and the remaining excess of Te is driven out into the ambient under the chemical potential gradient provided by the source. The proposed treatment almost completely eliminates the wafer-to-wafer and batch-to-batch variation in electrical properties of the low-temperature annealed Hg0.8Cd0.2Te crystals.



Es wird ein stoichiometrisches Temperverfahren vorgeschlagen zur Beseitigung von Te-Prazipitaten in Hg0.8Cd0.2Te-Kristallen, die durch Festkorper-Rekristallisation hergestellt worden sind. Die Abnahme des chemischen Potentials des Tellurs mit wachsendem x in Hg-gesattigtem Hg1−x · CdxTe wird zur Optimierung des Verfahrens genutzt. Verwendet wird eine Hg-Hg0,7Cd0,3Te-Quelle zur Temperung der Hg0,8Cd0,2Te-Proben. Die Temperung erfolgt isothermisch zunachst bei 420 °C und danach bei 260 °C. Wegen der rucklaufigen Loslichkeit des Te in MCT werden die Te-Prazipitate bei 420 °C wieder partiell in der Matrix gelost, und der verbleibende Te-Uberschus wird durch den chemischen Potentialgradienten, der durch die Quelle aufrecht erhalten wird, in die Umgebung herausgetrieben. Das vorgeschlagene Verfahren eliminiert fast vollstandig die Schwankungen von Scheibe zu Scheibe und von Charge zu Charge in den elektrischen Eigenschaften der bei tiefen Temperaturen getemperten Hg0,8Cd0,2Te-Kristalle.

V. K. Singh

Papers

Horizontal casting for the growth of Hg1-xCdxTe by solid state recrystallization

Stoichiometric annealing and electrical properties of Hg0.8Cd0.2Te grown by solid state recrystallization