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The “double Dirac cone” 2D topological interface states found on the (001) faces of topological crystalline insulators such as Pb1–xSnxSe feature degeneracies located away from time reversal invariant momenta and are a manifestation of both mirror symmetry protection and valley interactions. Similar shifted degeneracies in 1D interface states have been highlighted as a potential basis for a topological transistor, but realizing such a device will require a detailed understanding of the intervalley physics involved. In addition, the operation of this or similar devices outside of ultrahigh vacuum will require encapsulation, and the consequences of this for the topological interface state must be understood. Here we address both topics for the case of 2D surface states using angle-resolved photoemission spectroscopy. We examine bulk Pb1–xSnxSe(001) crystals overgrown with PbSe, realizing trivial/topological heterostructures. We demonstrate that the valley interaction that splits the two Dirac cones at each X̅is extremely sensitive to atomic-scale details of the surface, exhibiting non-monotonic changes as PbSe deposition proceeds. This includes an apparent total collapse of the splitting for sub-monolayer coverage, eliminating the Lifshitz transition. For a large overlayer thickness we observe quantized PbSe states, possibly reflecting a symmetry confinement mechanism at the buried topological interface.

Step edges of topological crystalline insulators can be viewed as predecessors of higher-order topology, as they embody one-dimensional edge channels embedded in an effective three-dimensional electronic vacuum emanating from the topological crystalline insulator. Using scanning tunneling microscopy and spectroscopy, we investigate the behavior of such edge channels in Pb1–xSnxSe under doping. Once the energy position of the step edge is brought close to the Fermi level, we observe the opening of a correlation gap. The experimental results are rationalized in terms of interaction effects which are enhanced since the electronic density is collapsed to a one-dimensional channel. This constitutes a unique system to study how topology and many-body electronic effects intertwine, which we model theoretically through a Hartree–Fock analysis.

Atomic layer epitaxy (ALE) of ZnO on a GaN template was performed in a low-pressure gas flow system using ZnCl2 and O2 precursors, and the evidence of monocrystallinity of an ALE-grown ZnO film is presented. The growth is achieved under the pressure of about 5 mbar with 480 °C substrate temperature and the ZnCl2-source temperature of 390 °C. According to the AFM analyses, the film surface exhibits a low roughness value of 0.45 nm RMS, which fulfills the expectations with respect to high morphological quality of the ALE products. The structural properties of the produced ZnO are characterized by means of X-ray diffraction methods based on wide range 2θ/ω scans and high-resolution studies of 00.2 and 11.4 reciprocal lattice points. Lattice parameters for ALE-grown ZnO layer are a = 0.3253(1) nm and c = 0.52060(5) nm, as derived from the high-resolution data. The mosaicity level of the GaN template layer is reproduced in the grown ZnO film.

The core‐level S 2p and Pb 5d spectra of galena (natural PbS) single crystals have been investigated using synchrotron radiation. Comparison between a synthetic PbS and a mineral galena has been made and the former gave broader S 2p lines than the latter. In both samples a strong broadening of the line was observed when the temperature was increased. Also, the surface core‐level shift (SCLS) was slightly smaller for the synthetic sample. No shift was found for the Pb 5d lines. The atomic force microscopy (AFM) study of the mineral (100) surface showed that only one type of atom (most likely sulphur) is visible, in agreement with Heinzelmann et al.(Z. Phys. B1992; 88:321). Copyright © 2002 John Wiley & Sons, Ltd.

CdS_xTe_1-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 CdS_xTe_1-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 CdS_xTe_1-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 CdS_xTe_1-x was measured using the scanning electron microscope remote electron beam induced current technique. Boundaries in CdTe have downward band bending, but those in CdS_xTe_1-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 CdS_xTe_1-x, and partly by the Te enrichment that occurs during processing.

The surface electronic structure of a PbS sample, cleaved in ultra-high-vacuum environment, has been studied with surface differential reflectivity (SDR) and angle-resolved photoelectron spectroscopy (ARUPS). The ARUPS spectra show the presence of two surface (resonance) states along the two angular directions [001] and [011]. SDR shows the existence of a gap of approximately 2.1 eV and two more optical transitions at energies of 2.7 and 3.1 eV. These transitions have been, tentatively, assigned to different points in the surface Brillouin zone.

Monocrystals of sphalerite‐type CdTe1‐xSexwere grown by self‐selecting vapour growth SSVG in the horizontal configuration. As measured on a series of points of a (110) split plane, the “rocking curve” half‐width was below 30 arcsec, while the lattice parameter measurements demonstrated the molar fraction x varying within 0.0024 (0.24 %). The values of x obtained from photoluminescence spectra taken from samples of different quality were in the ranges of 0.0034 (0.34 %) and 0.0047 (0.47 %). On the basis of the photoluminescence measurements, the maximum difference in x within the crystallised material was estimated to be 0.01 (1 %).

Photovoltaicp-n junctions inn-type Pb1-xMnxSx?0.04, have been made by sulphur diffusion. Current-voltage and resistance-voltage characteristics have been examined at various temperatures. The spectral responses of the diodes have been measured within the temperature range from 5 to 300 K at a zero bias. From these measurements the energy band gap of Pb1-xMnxS solid solution has been determined as a function of temperature and manganese content. A phenomenological expression describing the variation of the energy gap of Pb1-xMnxS with temperature and alloy composition has been proposed.

Logarithmic anomalies in the temperature-dependent resistivity in the vicinity of the ferroelectric phase transition of Pb1−xGexTe crystals have been measured. We associate these anomalies with the local movements of the off-centre Ge2+ions.

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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.

Evaporation-condensation driven in a closed system by a small temperature difference has demonstrated its ability to deliver semiconducting IV-VI and II-VI solid solution crystals of highest compositional uniformity. Geometrical aspects of solution component distribution emerging in the crystals grown in the near equilibrium evaporation/condensation systems are considered in this paper. The conclusion is drawn that no increase in the range of compositional variations with increase in the crystal size is to be anticipated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Perpendicular transport through single- and double-barrier eterostructures made up of ferromagnetic EuS layers embedded into a PbS matrix was investigated. Both resonant tunneling and probably spin filtering through EuS barrier were observed.

SQUID magnetometry is applied to study the temperature and magnetic field dependence of magnetization M(T, H) of semiconductor EuS–PbS ferromagnetic multilayers grown on insulating KCl(100) and conducting n-PbS(100) monocrystalline substrates. For low external magnetic fields (of the order of 10 Oe) and PbS spacer layers thinner than about 2 nm, we observe in EuS–PbS–EuS trilayers the strongly nonmonotonic temperature dependence of magnetization with almost zero total magnetic moment below the Curie temperature. The application of the magnetic field of the order of 100 Oe restores the regular monotonic increase of magnetization with decreasing temperature. To explain this M(T,H) dependence we present a model that considers the competition of three (temperature dependent) contributions to the total magnetic energy of the trilayer: the antiferromagnetic interlayer interaction energy, the Zeeman energy, and the energy of in-plane magnetocrystalline anisotropy.

Self-selecting vapor growth (SSVG) allows the achievement of uniform composition with structural perfection of solid solution crystals. Proven usefulness of this process for IV−VI semiconducting compounds and their solid solutions is presently extended to the II−VI wide-gap semiconductors.

Monocrystalline films of sphalerite-type (Cd,Zn)S were grown on GaAs by atomic layer epitaxy in a gas flow system. Structural properties were determined and compositional uniformity confirmed by means of X-ray diffraction and photoluminescence.