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.     

Trends in the thermal expansion coefficients of the AIBIIIC2VI and AIIBIVC2V chalcopyrite compounds

Empirical relations are derived for the average linear thermal expansion coefficient α_L and the linear thermal expansion coefficients α_a and α_c of the lattice parameters a and c, respectively, of the A^IB^IIIC₂^IV and A^IIB^IVC₂^V compounds. It is shown that the thermal expansion coefficients of all tetrahedrally coordinated compounds can be described within the same model. The anisotropy of the thermal expansion coefficients depends essentially on the lattice constant ratio c/a. There exists a critical c/a value below of which α_c becomes negative.     

Interatomic force constants in AIIBIVCV2 chalcopyrite compounds

Force constants of the A^II C^V and B^IV C^V bonds in the A^IIB^IVC^V₂ compounds with chalcopyrite structure are estimated from experimental lattice vibration data using a simplified version of the Keating model. It is shown that the force constants depend exponentially on the bond length. The parameters of this relation are practically the same as those found for the A^IV A^IV, A^III B^V and A^II B^VI bonds in the elemental semiconductors and binary compounds and for the B^III C^VI bond in the A^IB^IIIC^VI₂ semiconductors.     

Heat capacity and lattice anharmonicity in CdBIVC chalcopyrite compounds

The heat capacity at constant pressure of CdSiP₂, CdGeP₂, CdSnP₂ and CdGeAs₂ is measured in the temperature range from 300 to 500 K. The anharmonic contribution to the heat capacity is evaluated and it is shown that the degree of lattice anharmonicity decreases with increasing atomic weight of the constituent atoms of the compounds. Comparing the temperature variation of the heat capacity and of the thermal expansion coefficient some conclusions are made regarding the interatomic potential in the A^IIB^IVC compounds.     

Microhardness scaling and bulk modulus-microhardness relationship in AIIBIVC chalcopyrite compounds

An analysis of experimental microhardness data shows that the microhardness of the A^IIB^IVC compounds can be described by a simple scaling law which depends only on the unit cell volume and the melting temperature. On the basis of this result a simple bulk modulus — microhardness relationship is proposed and used to estimate the bulk moduli of the compounds. The results are compared with existing literature data.     

Thermal expansion anisotropy and individual bond expansion coefficients in ternary chalcopyrite compounds

The individual bond expansion coefficients of the A^IIB^IVC and A^IB^IIIC₂^VI chalcopyrite compounds are calculated from the principal linear thermal expansion coefficients of the lattice parameters using the regular B C tetrahedron model and a model with a temperature independent free parameter of the lattice. It is shown that the bond expansion coefficients derived from the latter model are in better agreement with the trends found for the interatomic forces in the chalcopyrite compounds and observed for the thermal expansion coefficients in the binary AC, A^IIC and BC compounds.     

Estimation of the debye temperature of diamond-like semiconducting compounds from bulk modul and microhardness

The reliability of estimation of Debye temperature θ_D evaluated from bulk modul and microhardness is proved for semiconductors with diamond, sphalerite, and chalcopyrite structure. The known linear relations available from the literature do not yield a reasonable agreement between experimental and calculated Debye temperatures. As in the case of the Lindemann rule a better approximation is obtained by use of a more general relation θ_D = a₁x + a₂. The constants a₁ and a₂ are calculated for the substances under consideration. Unknown Debye temperatures are calculated.     

Depth profile of the microhardness in helium implanted GaP

Depth profiles of the damage density and the microhardness are measured in GaP single crystals implanted with 1 MeV helium ions. From an analysis of the experimental data it follows that the microhardness increases up to a damage density of about 16% due to point defect hardening. At higher damage densities the microhardness decreases rapidly, probably due to the formation of extended defects.     

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.     

On the microhardness of some organic molecular solids

Microhardness measurements have been carried out on the (001) cleavage surfaces of anthracene, Phenanthrene and benzoic acid single crystals. The variation of the Vicker's Hardness Number (VHN) with load (P) shows a decrease in hardness with increasing load. Plots of load (P) vs the square of the diagonal (d²) and logarithm of load (log P) vs logarithm of diagonal (log d) are found to be linear. These observations are being explained in terms of the geometrical packing of molecules in these crystals which play an important role in causing slip.     

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.     

Magnetostimulated changes of microhardness in potassium acid phthalate crystals

A decrease in microhardness along the (010) cleavage in potassium acid phthalate single crystals by 15–18% after the application of a permanent magnetic field is revealed for the first time. It is shown that the effect revealed is of the volume character. The role of interlayer water in the processes stimulated by a magnetic field is studied. Interlayer water does not cause the observed changes; it only plays the part of an indicator of these changes in potassium acid phthalate crystals in a magnetic field. It is established that microhardness in the (100) plane of the crystal in an applied a magnetic field first increases by 12–15% and then remains constant in time within the accuracy of the experiment. The possibility of varying the crystal structure of potassium acid phthalate crystals by applying magnetic fields inducing rearrangement in the system of hydrogen bonds or in the defect structure is discussed.     

Ion implantation effects on the microhardness and microstructure of GaN

We study the effect of N⁺ and O⁺ implantation on the microhardness and the microstructure of epitaxially grown GaN. The microhardness is measured using a Knoop diamond indenter while information on the effect of implantation on the surface morphology, microstructure and electronic structure is provided by atomic force microscopy, cross-section transmission electron microscopy and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. It is demonstrated that implantation increases the surface microhardness. A possible mechanism for the surface hardening effect is based on the formation of N interstitials that pin the dislocations and prohibit the plastic deformation. In addition to the hardening effect, the implantation induced N interstitials introduce a characteristic resonance in the NEXAFS spectra, at 1.4 eV below the absorption edge.     

Diffusion induced segregation in the case of the ternary system sphalerite,chalcopyrite and cubanite

A mathematical model for describing natural and experimental diffusion induced segregation (DIS) in the case of a (Zn,Fe)S single crystal with three coexisting phases is derived. As main result, a new and quite general segregation principle for ternary systems is discovered where one phase has a flat free energy density and serves as catalyst for the segregation of the other two phases. The model includes also a stochastic noise term to represent fluctuations of the copper concentration. Numerical simulations in 2‐d underline the physical significance of the model and allow to make quantitative predictions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of divalent impurity state on the microhardness of NaCl crystals

The microhardness and bulk density variations with annealing temperature have been measured in NaCl crystals doped with Ca²⁺, Cd²⁺, Ni²⁺, and Pb²⁺. Both characteristics are not affected by coherent metastable precipitation while incoherent precipitation produces either hardening or softening depending on the impurity phase type (stable or metastable). The results support the suggestion that aggregates and coherent precipitates are cut through by dislocations whereas incoherent precipitates are by-passed via the Orowan looping mechanism.     

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.