Z. Golacki

Secondary phase segregation in heavily transition metal implanted ZnO

With micro-Raman spectroscopy and x-ray diffraction (XRD), we studied ZnO crystals implanted with Mn, Fe, Co, and Ni, respectively, with implantation concentrations from 4 up to 16 at. %. Using thermal treatments in air up to 700 °C, we analyzed the annealing effect on the ZnO crystal lattice as well as the onset of secondary phases and their microstructure on the sample surface. While the 500 °C treatment induces a considerable annealing, secondary phases are observed for transition metal (TM) concentrations ≥8 at. % after the treatment at 700 °C. Their microstructure strongly depends on the TM species. Various stoichiometric and nonstoichiometric TM oxide precipitates as well as elemental TM clusters are identified by their Raman and XRD signatures and their possible magnetic impact is discussed.

Transport and magnetic properties of dilute rare-earth–PbSe alloys

Polycrystalline alloys of PbSe with rare-earth elements (Ce, Pr, Nd, Eu, Gd, and Yb) have been prepared and their magnetic susceptibility (from 4 to 120 K), galvanomagnetic and thermomagnetic transport (from 80 to 380 K) properties have been measured. Most samples are paramagnetic, and the concentration of rare-earth atoms in the PbSe lattice is deduced from fitting a Curie-Weiss law. The electrical conductivity, Hall, Seebeck, and transverse Nernst-Ettingshausen effects are interpreted in terms of the carrier density and mobility, the density of states effective mass, and the scattering exponent. In summary, Pb1−xEuxSe is a semiconductor with a wider gap than PbSe, but the carrier density is unaffected by the presence of Eu. The other rare earths, which are essentially trivalent atoms, act as donors, with a doping efficiency close to unity in the case of Ce and Nd, but much less for Gd and Yb. The mechanisms that govern the observed decrease in mobility are also discussed.

Non-linear optical effects and transport phenomena of magnetic semiconductors Pb1−xPrxTe near the semiconductor–metal phase transformation

Measurements of transport and non-linear optical (NLO) properties of the new, synthesized semiconductor Pb0.9835Pr0.0165Te in the vicinity of low-temperature metal–semiconductor phase transformations were performed. A correlation between the temperature behaviour of transport properties near the phase transition and NLO susceptibilities of second- and third-order was observed. FTIR spectra show the substantial role played by the Pr3+ localized levels in the observed anomalies.Among the transport properties, the resistivity, Seebeck coefficient and specific heat were measured. The presence of the minimum at about in the temperature dependence of the resistivity ρ(T) is due to the metal–semiconductor transition in Pb1−xPrxTe and the low-temperature upturn observed in the resistivity is well fitted by the Mott law. Substitution of PbTe by other rare earths shows the crucial role played by Pr in the observed dependences.Experimental temperature measurements using photo-induced NLO (pumped by a UV-laser as well as by second harmonics of the YAG–Nd lasers) and a probing YAG–Nd (at λ = 1.06 µm) laser, show the existence of two maxima in the photo-induced second harmonic generation (PISHG) at temperatures 17 and 30 K, the behaviours of which substantially depend on the wavelength of the pump beam. At the same time the third-order two-photon absorption possesses maxima near 50 K, i.e. at about . Such discrepancies in the positions of the temperature maxima are caused by the difference in contributions of the photo-induced anharmonic phonons near the surfaces PISHG and the bulk. Varying the penetration depth of the photo-inducing light one can operate with the output NLO properties.

Mn2+ intra-shell recombination in bulk and quantum dots of II-VI compounds

Origin of a fast component of the photoluminescence (PL) decay of Mn 2+ intra-shell 4T1 ? 6A 1 transition in bulk and quantum dot structures is discussed based on the results of PL, PL kinetics and ...

Horizontal unseeded vapour phase growth of CdTe

Abstract Cadmium telluride crystals with mirror-like surfaces have been obtained by horizontal unseeded vapour phase growth method. The surfaces of the crystals were usually Te (111) planes, sometimes (110) planes perpendicular to the (111) planes were observed. The rocking curves of the (111) reflection were measured.

Vapour phase growth and properties of Pb1-xSnxTe single crystals

Abstract High quality Pb 1- x Sn x Te crystals of desired orientation having a diameter of 20 mm and weights up to 100 g were obtained using the vapour phase method. The crystals were grown in sealed quartz ampoules, on cylindrical BaF 2 pedestals, without contact with the tube walls. Such contactless conditions cause low dislocation density and are favourable for obtaining less contaminated crystals. In this method, contrary to other vapour phase growth methods, even a relatively large excess of tellurium does not affect noticeably the quality of the crystals. The composition along and across the crystals was examined using electron beam microprobe analysis. The results of measurements of conductivity and Hall effect in as-grown and annealed samples are presented. Some data concerning preparation of the source material are also included.

Vapour phase growth of large crystals of PbTe and Pb1−xSnxTe

Abstract Large crystals of PbTe and Pb 1− x Sn x Te up to 25 g were obtained in sealed tubes by vapour phase growth on oriented BaF 2 sticks. The crystals were grown without contact with the tube wall. Details of the growth technique, growth rate and thermal conditions of the processes are described. An X-ray reflection topogramme of one of the crystals is presented.

CdSxTe1-x: bulk vapour growth, twin formation and the electrical activity of twin boundaries

CdSxTe1-x has been used as a model substance to investigate crystal growth from the vapour, twinning phenomena and the electrical properties of grain boundaries. A self-selecting vapour growth method produced solid solutions of CdSxTe1-x (x?0.067) with compositional uniformity of <2{%} of x (i.e.?<0.0013) as determined by x-ray diffraction and photoluminescence spectroscopy. The CdSxTe1-x crystals were highly twinned. Statistical tests showed that the twin boundaries are spatially correlated. A model for twin formation based on nucleation and grain size development is proposed. Band bending at grain and twin boundaries in CdTe and in CdSxTe1-x was measured using the scanning electron microscope remote electron beam induced current technique. Boundaries in CdTe have downward band bending, but those in CdSxTe1-x have upward band bending. Decoration of grain boundaries with Te inclusions reduced the band bending effect in CdTe. It is postulated that the grain boundary passivation in CdTe/CdS solar cells is partly caused by enrichment of the grain boundaries in CdTe with CdSxTe1-x, and partly by the Te enrichment that occurs during processing.

Recycled Crystallisation of ZnTe by Evaporation‐Condensation

ZnTe crystals have been grown by self-selecting vapour growth SSVG in a vertical, modified system, which reduces contact of the crystallised material with foreign materials to the minimum possible. Geometrical stability of the growth system is increased. The obtained crystals are of the sizes slightly below 10 mm and the rocking curve measurement results in the value of 36 arc sec. Distinct purification effect appears. The lattice constant of ZnTe is equal to 0.61036 nm.

Growth of CdTe single crystals by vapour condensation on the surface of polycrystalline source material

Abstract A method of crystal growth from the vapour phase, which had been worked out for A IV B VI compounds, has been applied to CdTe. Single crystals shaped with (110) and (111) planes of approximately 10 mm size have been obtained. A high level of structure perfection has been confirmed by means of X-ray rocking curve measurements resulting in half-width values down to approximately 15″. The suitability for production of homogeneous CdTe-based A IV B VI solid solution crystals is discussed.