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Extensive studies on the impact of bismuth incorporation into the (Ga,Mn)As prototype dilute ferromagnetic semiconductor (DFS) on its structural, magnetic and magnetotransport properties are summarized in this review. Thin epitaxial layers of the quaternary (Ga,Mn)(Bi,As) compound, containing up to 1% Bi and 6% Mn atoms, and the reference ternary (Ga,Mn)As compound, have been grown under either a compressive or tensile biaxial misfit strain by the low-temperature molecular-beam epitaxy technique with precisely optimized growth conditions. The high-resolution X-ray diffractometry measurements and transmission electron microscopy imaging of cross-sections across the sample interfaces have evidenced for high structural perfection of the DFS layers and sharp interfaces with the substrate. An addition of bismuth into the layers causes a small decrease in their ferromagnetic Curie temperature and a distinct increase in the coercive fields, as revealed by the superconducting quantum interference device magnetometry investigations. Most of all, the incorporation of a small atomic fraction of heavy Bi atoms, substituting As atoms in the layer, predominantly enhances the spin-orbit coupling strength in its valence band, considerably affecting electromagnetic properties of the layers. Investigations of magnetotransport properties of the DFS layers, performed on micro-Hall-bars prepared from the layers using electron-beam lithography patterning, reveal, as a result of Bi addition to the layers, significantly enhanced magnitudes of magnetoresistance, anomalous and planar Hall effects as well as the spin-orbit torque effect. The latter effect is of special interest for applications to the next generation non-volatile data storage and logic spintronic devices, utilizing electrically controlled magnetization reversal., Comment: 22 pages, 7 figures

Pulsed current-induced magnetization reversal is investigated in the layer of (Ga,Mn)(Bi,As) dilute ferromagnetic semiconductor (DFS) epitaxially grown under tensile misfit strain causing perpendicular magnetic anisotropy in the layer. The magnetization reversal, recorded through measurements of the anomalous Hall effect, appearing under assistance of a static magnetic field parallel to the current, is interpreted in terms of the spin-orbit torque mechanism. Our results demonstrate that an addition of a small fraction of heavy Bi atoms, substituting As atoms in the prototype DFS (Ga,Mn)As and increasing the strength of spin-orbit coupling in the DFS valence band, significantly enhances the efficiency of current-induced magnetization reversal thus reducing considerably the threshold current density necessary for the reversal. Our findings are of technological importance for applications to spin-orbit torque-driven nonvolatile memory and logic elements., Comment: 8 pages, 5 figures

Structural defects in the p-ZnTe/i-CdTe/n-CdTe single-crystalline heterojunctions designed for photovoltaic applications have been investigated by transmission electron microscopy (TEM) and deep-level transient spectroscopy (DLTS). Lattice parameters and misfit strain in the undoped CdTe absorber layers of the heterojunctions, grown by the molecular-beam epitaxy technique on two different substrates, GaAs and CdTe, have been determined with high-resolution X-ray diffractometry. A dense network of misfit dislocations at the lattice-mismatched CdTe/GaAs and ZnTe/CdTe interfaces and numerous threading dislocations and stacking faults have been shown by the cross-sectional TEM imaging of the heterojunctions. The DLTS measurements revealed five deep-level traps in the heterojunctions grown on the GaAs substrates and only three of them in the heterojunctions grown on CdTe. One of the traps, showing the exponential capture kinetics of charge carriers, has been identified as associated with the double acceptor level of Cd vacancies in the CdTe absorber layers. All the other traps have been attributed to the electronic states of extended defects, presumably dislocations, on the grounds of their logarithmic capture kinetics. Two of these traps, displaying the largest values of their capture cross-section and the properties characteristic of bandlike electronic states, have been ascribed to the core states of dislocations. It is argued that they are most likely responsible for decreased lifetime of photo-excited carriers resulting in a low energy conversion efficiency of solar cells based on similarly grown heterojunctions.