Microhardness studies on some compound semiconductors

Vickers microhardness studies on some III–V and II–VI compound semiconductors have been made. The results showed that ZnS has the highest microhardness value. These results are compared with other properties of the crystals such as melting point, ionicity etc. Variation of microhardness with load was also studied on all the crystals. The results indicated that the hardness value increases at low loads. These results have been analysed by using resistance pressure model and interpreted.     

Vacancy formation enthalpies in AIBIIIC chalcopyrite semiconductors

Formation enthalpies ΔH_v of single vacancies in all A^IB^IIIC₂^VI chalcopyrite structure compounds are estimated using the macroscopic cavity model. A comparison with atomic sublimation enthalpies ΔH_sub of the B^III and C^VI atoms derived from existing partial vapour pressure data shows that within the accuracy of this data and the theoretical calculations the relation ΔH_v ⪆ ΔH_sub is fulfilled as expected from general considerations.     

Melting temperature and debye temperature of ternary chalcopyrite semiconductors

Band state concept has been used for the first time to explain the Melting temperature and Debye temperature of ternary chalcopyrite semiconductors. The experimental results agree quite well with those evaluated from this model. Finally we derive a correlation between the two termperatures.     

Adiabatic bond charge model for lattice dynamics of ternary chalcopyrite semiconductors

The adiabatic bond charge model of Rustagi and Weber is extended to study lattice dynamical properties of ternary chalcopyrite semiconductors AgGaS₂, AgGaSe₂, CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂, CuAlS₂ and CuAlSe₂. The new model calculations agree well with the results of Raman/IR and neutron measurements of Brillouin zone center phonon frequencies for both low and high frequency modes which was difficult for other phenomenological lattice dynamical models. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and structural characteristics of the chalcopyrite semiconductor CuInSe2

The growth and structural characteristics of chalcopyrite semiconductor CuInSe₂ have been investigated with particular emphasis on the photovoltaic behaviour of the CdS/CuInSe₂ thin film heterojunction. It has been found that the structural phase of the CuInSe₂ has an important bearing on the photovoltaic behaviour of the heterojunction. Thus the heterojunctions having the sphalerite type cubic CuInSe₂ as one of its component have been found to possess better conversion effciency than those employing the chalcopyrite type tetragonal form of CuInSe₂. Evidences and argument have been put forward to show that the better efficiency with sphalerite phase arises due to smaller lattice mismatch with CdS base. In addition to the type of structural phase, the state of order of CuInSe₂ phase has been found to affect the performance of heterojunctions. The heterojunctions having the disordered sphalerite type CuInSe₂ structure exhibits a much lower efficiency than those embodying the ordered CuInSe₂ phase.     

III-V compound semiconductors: Growth and structures

The semiconductors formed from group 13 metals and from group 15 anions, referred to as the III-V semiconductors, have found use in a broad range of technologies. Their versatility arises from the wide range of optical and electronic properties accessed through the formation of multi-component alloys. These alloys can be synthesized using the epitaxial growth techniques for devices consisting of several-to-hundreds of highly controlled individual layers monolithically formed into a nearly defect-free structure. This ability to design and fabricate such detailed structures, whose dimensions can be at the nanometer scale, has been driven by an understanding of the crystal growth and materials technology. The paper introduces key features of these materials, their materials science and crystal growth.     

Growth of some urinary crystals and studies on inhibitors and promoters. II. X-ray studies and inhibitory or promotery role of some substances

Best conditions were established for the gel growth of three urinary crystals viz., calcium oxalate monohydrate, calcium hydrogen phosphate dihydrate and ammonium magnesium phosphate hexahydrate. The crystals grown were characterized using single crystal X-ray diffraction techniques and density measurements. Crystal growth experiments were carried out by incorporating the extracts or juices of some natural products in the gel media. By carefully observing the changes in the growth of crystals (compared to control experiments carried out at the same conditions), results about the inhibitory or promotery role of the substance incorporated were obtained. It was found that the extracts or juices of many of the naturally occurring substances have interesting inhibitory or promotery effects. These results may have useful applications in the treatment of recurrent stone patients.     

First principles studies on In-related nitride semiconductors

In-related nitride semiconductors exhibit characteristic behavior which can be ascribed to the large difference in the covalent radius between In and N atoms. We consider atomic and electronic structures of N mono-vacancies (V_N) in InGaN in detail by the first principles calculations. We find that the second nearest neighbor In–In interactions, which are not important in conventional semiconductors such as Si and InAs, are as crucial as the nearest neighbor In–N interaction in In-related nitride semiconductors. Moreover, we clearly show that the strong second nearest neighbor In–In interactions in InN are the physical origin of the unusually narrow band gap of InN.     

Defect studies in CuBIIIC chalcopyrite compounds using the ion channeling technique

Based on simple approximations the backscattering minimum yield is estimated for axial ion channeling in perfect crystals of six CuB^IIIC chalcopyrite compounds. The results obtained for CuInSe₂ are compared with experimental channeling spectra. Point defect concentrations up to about 10²¹ cm⁻³ are estimated for CuInSe₂ single crystals grown by the vertical Bridgman method. A simple power law is found for the fluence dependence of the damage density in oxygen implanted CuInSe₂ single crystals.     

Growth of gallium antimonide epitaxial layers on indium arsenide substrates

In the present work the possibility is demonstrated of growing gallium antimonide epitaxial layers on indium arsenide substrates using the liquid phase epitaxial (LPE) method. The influence is nivestigated of the growth conditions on the morphology of the surface and interface of the epitaxial structures InAs GaSb. The optimum technological regimes for growth of heterostructures in the system InAs GaSb are found.     

Growth and microstructural features of laser ablated LiCoO2 thin films

Thin films of LiCoO₂ were prepared by pulsed laser deposition technique and the properties were studied in relation to the deposition parameters. The films deposited from a sintered composite target (LiCoO₂+Li₂O) in an oxygen partial pressure of 100 mTorr and at a substrate temperature of 300 °C exhibited preferred c-axis (0 0 3) orientation perpendicular to the substrate surface. The AFM data demonstrated that the films are composed of uniform distribution of fine grains with an average grain size of 80 nm. The grain size increased with an increase in substrate temperature. The (0 0 3) orientation decreased with increase in (1 0 4) orientation for the films deposited at higher substrate temperatures (>500 °C) indicating that the films’ growth is parallel to the substrate surface. The composition of the experimental films was analyzed using X-ray photoelectron spectroscopy (XPS). The binding energy peaks of Co(2p_3/2) and Co(2p_1/2) are, respectively, observed at 779.3 and 794.4 eV, which can be attributed to the Co³⁺ bonding state of LiCoO₂. The electrochemical measurements were carried out on Li//LiCoO₂ cells with a lithium metal foil as anode and LiCoO₂ film as cathode of 1.5 cm² active area using a Teflon home-made cell hardware. The Li//LiCoO₂ cells were tested in the potential range 2.6-4.2 V. Specific capacity as high as 205 mC/cm² μm was measured for the film grown at 700 °C. The growth of LiCoO₂ films were studied in relation to the deposition parameters for their effective utilization as cathode materials in solid-state microbattery application.     

Growth and characterization of the chalcopyrite LiGaTe2: A highly non-linear birefringent optical crystal for the mid-infrared

LiGaTe₂ crystals have been grown by the Bridgman–Stockbarger technique. The clear transparency range of LiGaTe₂ extends from 2.5 to 12 μm and its band-gap at room temperature is at 2.41 eV (515 nm). LiGaTe₂ is a positive uniaxial crystal which possesses sufficient birefringence for phase-matching. Its non-linear coefficient d₃₆ estimated by phase-matched second harmonic generation is 43 pm/V ± 10% at 4.5 μm. The properties of LiGaTe₂ are compared to those of other mid-IR chalcopyrite non-linear optical crystals with special emphasis on the frequency doubling potential for CO₂ lasers operating at 10.6 μm.     

Growth and defect studies of CdTe particles

The paper reports the epitaxial growth of cadmium telluride (CdTe) particles by thermal deposition on cleaved planes of (001)NaCl and (001)KBr. Using high resolution transmission electron microscopy and electron diffraction it was shown that CdTe particles could have different orientation and phase (cubic or hexagonal) depending on the substrate temperature. Their most common defects are twins and stacking faults.     

Computer simulation, thermodynamic and microstructural studies of benzamide–benzoic acid eutectic system

Phase diagram of benzamide–benzoic acid system has been studied by the thaw–melt method. Linear velocities of crystallization of the components and the eutectic mixture were determined at different undercoolings. Values of the heat of fusion were obtained from DSC studies. Excess Gibbs free energy, excess enthalpy and excess entropy of mixing were calculated. In order to know the nature of interaction between the two components, FT-IR spectral analyses were done. In addition to these studies, computer simulation has been done to obtain an idea about the interaction energy and the optimized geometry of the eutectic mixture. Microstructural studies showed the formation of an irregular structure in the eutectic mixture, which changed with aging and on addition of impurities.     

Growth and some properties of lanthanum sulphate enneahydrate single crystals

A technique for the growth of single crystals of Lanthanum Sulphate Enneahydrate from saturated aqueous solution by slow program-heating under different growing conditions has been developed. Polarized Raman spectrum and vibrational assignments of an oriented single crystal are reported.     

Growth and some properties of cerium sulphate enneahydrate single crystals

Colorless single crystals of cerium sulphate enneahydrate were grown from aqueous solutions under carefully controlled conditions of temperature and supersaturation. Polarized Raman spectra and vibrational assignments of oriented single crystals are reported. Several physical properties (density, refractive indices, dielectric constants, coefficient of linear expansion, specific heat, microhardness) are also listed.     

Electrical and photoelectrical properties of chalcopyrite n-AgInS2 crystals

The chalcopyrite n-type crystals have been grown from AgInS₂ material having stoichiomtric Ag excess. The temperature dependence of the Hall effect in these crystals have been studied. The ionization energies of donors have been determined. The dependence of the photoconduction on the photon energy, the light intensity and the temperature in the n-AgInS₂ crystals have been measured. The recombination model of photoconductor with one class of recombination centres has been proposed for explanation of the photoelectrical results.     

Growth,spectral and thermal studies of ibuprofen crystals

RS ‐Ibuprofen was crystallized for the first time in silica gel under suitable pH conditions by reduction of solubility method. The grown crystals were characterized by single crystal X‐ray diffraction and density measurement. The functional groups present in the crystal were identified using Fourier transform infrared spectroscopy. Optical bandgap energy of ibuprofen was estimated as 3.19(3) eV from UV‐Vis spectrum. Thermogravimetric analysis revealed that ibuprofen is thermally stable upto 102.9 °C and the initial loss of mass was due to evaporation only. Morphological study showed that the growth is prominent along b‐axis and the prominent face is {100}. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)