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InSb nanowires (NWs) show an important application in topological quantum computing owing to their high electron mobility, strong spin–orbit interaction, and large g factor. Particularly, ultra-thin InSb NWs are expected to be used to solve the problem of multiple sub-band occupation for the detection of Majorana fermions. However, it is still difficult to epitaxially grow ultra-thin InSb NWs due to the surfactant effect of Sb. Here, we develop an in-plane self-assembled technique to grow catalyst-free ultra-thin InSb NWs on Ge(001) substrates by molecular-beam epitaxy. It is found that ultra-thin InSb NWs with a diameter as small as 17 nm can be obtained by this growth manner. More importantly, these NWs have aspect ratios of 40–100. We also find that the in-plane InSb NWs always grow along the [110] and [ 1 1 ¯ 0 ] directions, and they have the same {111} facets, which are caused by the lowest-surface energy of {111} crystal planes for NWs grown with a high Sb/In ratio. Detailed structural studies confirm that InSb NWs are high-quality zinc blende crystals, and there is a strict epitaxial relationship between the InSb NW and the Ge substrate. The in-plane InSb NWs have a similar Raman spectral linewidth compared with that of the single-crystal InSb substrate, further confirming their high crystal quality. Our work provides useful insights into the controlled growth of in-plane catalyst-free III–V NWs. [ABSTRACT FROM AUTHOR]

We have examined the origins of polytype selection during metal-mediated molecular-beam epitaxy of GaN nanowires (NWs). High-angle annular dark-field scanning transmission electron microscopy reveals [111]-oriented zinc blende (ZB) NWs and [0001]-oriented wurtzite (WZ) NWs, with SixNy at the interface between individual NWs and the Si (001) substrate. Quantitative energy dispersive x-ray spectroscopy reveals a notably higher Si concentration of 7.0% ± 2.3% in zinc blende (ZB) NWs than 2.3% ± 1.2% in wurtzite (WZ) NWs. Meanwhile, density functional theory calculations show that incorporation of 8 at. % Si on the Ga sublattice inverts the difference in formation energies between WZ and ZB GaN, such that the ZB polytype of GaN is stabilized. This identification of Si and other ZB polytype stabilizers will enable the development of polytype heterostructures in a wide variety of WZ-preferring compounds. [ABSTRACT FROM AUTHOR]

Spin-polarized photoemission from wurtzite and zinc blende gallium nitride (GaN) photocathodes has been observed and measured. The p-doped GaN photocathodes were epitaxially grown and activated to negative electron affinity with a cesium monolayer deposited on their surfaces. A field-retarding Mott polarimeter was used to measure the spin polarization of electrons photoemitted from the top of the valence band. A spectral scan with a tunable optical parametric amplifier constructed to provide low-bandwidth light revealed peak spin polarizations of 17% and 29% in the wurtzite and zinc blende photocathodes, respectively. Zinc blende GaN results are analyzed with a spin polarization model accounting for experimental parameters used in the measurements, while possible mechanisms influencing the obtained spin polarization values of wurtzite GaN are discussed. [ABSTRACT FROM AUTHOR]

Traditional zinc blende semiconductor materials of groups II–VI and III–V exhibit excellent electrical properties, yet suffer from oversized lattice thermal conductivity, causing poor thermoelectric performance. Herein, we have explored an alternative metastable phase of those materials, namely, porous phase. Compared with the stable zinc blende structure, which has simple crystal structure with nearly isotropic bonding feature, porous compounds exhibit complex bonding hierarchy and softened acoustic phonon modes with strong anharmonicity, reducing the lattice thermal conductivity by nearly two orders of magnitude. As an outstanding representative of porous compound family, the suppressed thermal conductivity [∼0.76 W / (m K) at room temperature] combined with enhanced Seebeck coefficient makes porous MgTe a high-performance thermoelectric material with figure of merit above unity at n-type doping and high temperature. This work highlights the important role of intrinsic porosity in design of high-performance thermoelectric materials with low lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

Structural and optical properties of a green-emitting cubic (i.e., zinc blende) GaN/In0.16Ga0.84N/GaN single quantum well structure are reported. The active layer is grown on a phase-pure (i.e., 100%) cubic GaN enabled on a 1 × 1 cm2 U-grooved silicon (100) through aspect ratio phase trapping. Energy dispersive x-ray spectroscopy combined with room temperature cathodoluminescence reveals 522 nm green light emission at room temperature with only 16.0% ± 1.6% of indium content, which is ∼30% less than the amount of indium needed in a traditional green-emitting hexagonal (i.e., wurtzite) well. Temperature-dependent behavior of the green emission, such as activation energy, s-shaped peak energy shift, and linewidth, is reported. Cathodoluminescence at 8 and 300 K reveals an internal quantum efficiency of 32.0% ± 0.6%, which is higher than any reported value for cubic wells. Overall, phase-pure cubic active layers on phase transition cubic GaN are shown to be promising for green and longer wavelength emitters. [ABSTRACT FROM AUTHOR]

Ferroelectric materials have been explored for a long time for easy integration with state-of-the-art semiconductor technologies. Doped wurtzite nitrides have been reported as promising candidates due to their high stability, compatibility, and scalability. We investigate doping effects on ferroelectric properties of Sc-doped AlN (AlScN) and B-doped AlN (AlBN) by first-principles methods. The energy barrier against polarization switching is observed to decrease with increasing doping concentration at low concentration ranges, which is the origin of the emerging ferroelectricity in doped AlN. Further increasing the doping concentration to a critical value, the ferroelectric wurtzite phase transforms into paraelectric phases (a rock salt phase for AlScN and a zinc blende phase for AlBN), making it invalid to decrease the coercivity by increasing the doping concentration. Furthermore, it is revealed that different nonpolar structures (a hexagonal phase for AlScN and a β -BeO phase for AlBN) appear in the ferroelectric switching pathway, generating different switching features in doped AlN. Our results give a microscopic understanding of the ferroelectricity in doped wurtzite materials and broaden the route to improve their ferroelectric properties. [ABSTRACT FROM AUTHOR]

We report the effects of antimony (Sb) surfactant on the growth and correlated structural and optical properties of non-catalytic GaAs nanowires (NW) grown by selective area epitaxy on silicon. Strong enhancements in the axial growth with very high aspect ratio up to 50 are observed by the addition of small traces of Sb (1%–2%), contrasting the commonly reported growth limiting behavior of Sb in GaAs(Sb) NWs. The Sb surfactant effect modifies the growth facet structure from a pyramidal-shaped growth front terminated by {1–1–0} planes to a flat (111)B growth plane, that is even further improved by the presence of Si co-dopants. Additional benefits are seen by the substantial change in microstructure, from a heavily defected layer stacking in Sb-free GaAs NWs to a twinned phase-pure zinc blende structure in Sb-mediated GaAs(Sb) NWs. We directly confirm the impact of the altered microstructure on the optical emission and carrier recombination dynamics via observation of long, few-ns carrier lifetimes in the GaAs(Sb) NWs using steady-state and time-resolved photoluminescence spectroscopy. [ABSTRACT FROM AUTHOR]

Colloidal zinc blende II–VI semiconductor nanoplatelets (NPLs) demonstrate as a promising class of materials for optoelectronic devices due to their unique excitonic characteristics, narrow emission linewidth, and quantum well-structure. Adopting heterostructures for these nanocrystals allows tuning of their optical features and enhances their photostability, photoluminescence (PL), quantum yield (QY), and color purity for further device integration. Exchanging of carboxylate capping ligands on top and bottom [001] facets of CdSe NPLs with halide ligands is an alternative to achieve the aims of spectral tunability and improve surface passivation, but to date there have been no reports on integrating the advantages of halide ligand exchanged CdSe NPLs for device fabrication. In this work, we demonstrate green electroluminescence (EL) of bromide ligand-capped CdSe NPLs as active emitters in an electrically driven light emitting diode (LED) with a low turn-on voltage of 3.0 V. We observed EL emission at 533.1 nm with a narrow linewidth of 19.4 nm, a maximum luminance of 1276 cd/m2, and the highest external quantum efficiency (EQE) of 0.803%. These results highlight the ability of halide ligand exchange in tuning the EL properties of CdSe NPL-LEDs and potential of bromide ligand-capped CdSe NPLs in contributing to the green emission region of NPL-LEDs, demonstrating its potential for future device integration and contribution to a high color rendering index of future NPL displays. [ABSTRACT FROM AUTHOR]

Electron–phonon interaction (EPI) is ubiquitous in condensed matter and materials physics, and nowadays, it is possible to calculate many materials properties related to the EPI from first-principles. Here, we review the EPI effect on electrical transports of thermoelectric (TE)/electronic materials from our recent works. By using the constant EPI, such as the deformation potential approximation, we carried out high-throughput electrical transport calculations in TE chalcogenides and ABX2 compounds with diamond-like structures and effectively screened some high-performance TE materials; besides, the mobility in hybrid organic–inorganic perovskite CH3NH3PbI3 was also studied, which included the effect of temperature-induced structural fluctuation. Then, the phonon scattering mechanism for the electrical transports in two-dimensional Dirac sheets and chalcogenides ZnX (X = S, Se) with a zinc blende structure was further discussed by full accurate evaluation of the EPI. It is found that the scatterings from optical phonons and inter-bands are strong and should not be neglected in contrast to the common wisdom. Finally, we perspective the EPI effect on more aspects such as the band structure and thermal transport. [ABSTRACT FROM AUTHOR]

Drawing upon a collection of electron transport results, coupled with a variety of other material parameters, we set expectations on the upper limits to device performance of zinc blende boron-nitride-based electron devices. We examine how the device performance varies with the device length-scale, noting that a diversity of physical regimes are experienced as the device length-scale reduces from that corresponding to a long electron device, i.e., 100 μm, to the sub-micron level. Results corresponding to zinc blende boron nitride are contrasted with those associated with germanium, silicon, gallium arsenide, the 4H-phase of silicon carbide, wurtzite gallium nitride, and diamond. The electron device performance metrics that we focus upon for the purposes of this analysis include the effective mobility, accounting for the transition between the ballistic and the collision-dominated electron transport regimes, and the cutoff frequency. [ABSTRACT FROM AUTHOR]

The interface between wurtzite and zinc blende InP has been identified as type-II, where electrons gather on the zinc blende side and holes on the wurtzite side of the interface. The photoluminescence resulting from recombination across the interface is expected to be long-lived and to exhibit non-exponential decay of emission intensity after pulsed excitation. We verify this prediction using time-resolved photoluminescence spectroscopy on nanowires containing a single heterostructure between a single segment of wurtzite and zinc blende. We find that a significant intensity of type-II emission remains even more than 30 ns after excitation. The decay of the emission intensity is also non-exponential and considerably longer than the exponential decay of the wurtzite InP segment (260 ps). Our results are consistent with the expected photoluminescence characteristics of a type-II interface between the two polytypes. We also find that the lifetime becomes shorter if we create an electron gas at the interface by n-type doping the entire wurtzite segment of the nanowire. This is expected since there are many electrons that a given hole can recombine with, in contrast to the undoped case. [ABSTRACT FROM AUTHOR]

For zinc blende semiconductors, such as InP, the Raman selection rules for a backscattering configuration from the (001) surface forbid the transversal optical (TO) phonon mode, whereas the longitudinal optical mode is allowed. However, when InP is highly doped with Si atoms, InP-Si clusters with the reduced C 3 v symmetry allow TO modes in the Raman spectrum with the backscattering configuration. Here, we demonstrate that the amplitude of the TO modes can be modulated spatially by using a highly doped InP grating. By exciting the sample with a laser linearly polarized parallel and perpendicular to the grating grooves, we observe a change in amplitude of the phonon optical response for the TO mode. [ABSTRACT FROM AUTHOR]

We have examined the influence of Ga surface saturation on gallium nitride (GaN) nanowire (NW) polytype selection during molecular-beam epitaxy. The Ga surface saturation in the absence and presence of nitrogen determines the GaN polytype and morphology (i.e., films vs NW) selection, respectively. We discuss the interplay between surface and step-edge diffusion barriers governing the NW-to-film-transition and the influence of SixNy interlayer formation on zinc blende (ZB) vs wurtzite (WZ) polytype selection of GaN. In addition, distinct exciton emissions associated with ZB and WZ GaN are observed, suggesting a type-I WZ/ZB GaN band-offset. This work provides a crucial step toward the realization of polarization-free, CMOS-compatible GaN-based optoelectronics. [ABSTRACT FROM AUTHOR]

ScxAl1−xN (x = 0.18–0.40) thin films of ∼28 nm thickness grown on metal polar GaN substrates by molecular beam epitaxy are found to exhibit smooth morphology with less than 0.5 nm roughness and predominantly single-phase wurtzite crystal structure throughout the composition range. Measurement of the piezoelectric d33 coefficient shows a 150% increase for lattice-matched Sc0.18Al0.82N relative to pure aluminum nitride, whereas higher Sc contents exhibit lower piezoelectric coefficients. The electromechanical response of the epitaxial films correlates with the crystal quality and the presence of zinc blende inclusions, as observed by high-resolution electron microscopy. It is further found that the polarity of the epitaxial ScxAl1−xN layers is locked to the underlying substrate. The measured electromechanical properties of epitaxial ScxAl1−xN, their relation to the atomic crystal structure and defects, and its crystal polarity provide useful guidance toward the applications of this material. [ABSTRACT FROM AUTHOR]

In this paper, the structural, electronic, and magnetic properties of Ga 1 − x V x Sb compounds with various vanadium (V) contents (x) ranging from dilute doping to the extreme doping limit were systematically investigated by first-principles calculations. The results show that V atoms prefer to substitute for gallium (Ga) atoms, and the formation energy is lower under Sb-rich growth conditions than under Ga-rich growth conditions. Meanwhile, the Sb Ga antisite defects effectively decrease the energy barrier of the substitution process from 0.85 to 0.53 eV. The diffusion of V atoms in the GaSb lattice occurs through metastable interstitial sites with an energy barrier of 0.6 eV. At a low V concentration (x = 0.0625), V atoms prefer a homogeneous distribution with antiferromagnetic coupling among the V atoms. However, when x increases above 0.5, the magnetic coupling among V atoms changes to ferromagnetic coupling due to the enhanced superexchange interaction between the eg and t 2 g states of neighboring V atoms. At the extreme doping limit of x = 1.00, zinc blende VSb along with its analogs VAs and VP is an intrinsic ferromagnetic semiconductor that exhibits a large change in light absorption at the Curie temperature. The results indicate that Ga 1 − x V x Sb compounds provide a platform to design next-generation electronic, spintronic, and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Since the first-principles calculations were reported, which indicate that zinc blende boron arsenide (BAs) has an unusually high room-temperature thermal conductivity, close to that of diamond, extensive theoretical and experimental effort has been dedicated to research on BAs. Although great achievements have been made recently in growing large single crystals demonstrating room-temperature thermal conductivity reaching 1300 W m−1 K−1, further optimization of the crystal quality has been stunted because of the purity of the boron source and contamination of the quartz tube. Here, we focus on the effects of different boron sources on the final BAs products synthesized via the chemical vapor transport method. We find that, compared to the reported methods that produce good BAs crystals from high-purity boron, using BAs crystals as the source material may contribute to further improvement. We believe that the current research can provide crucial support for further development of the BAs single-crystal growth techniques. [ABSTRACT FROM AUTHOR]

InP nanowires are an important material for nanoscale electronic and optical devices. However, the crystal phase mixing and stacking faults severely degrade the device's performance. Here, we demonstrate high performance field-effect transistors and photodetectors based on high-quality InP nanowires. The ⟨110⟩-oriented InP nanowires, which are formed by spontaneous kinking from the original ⟨111⟩ nanowire roots, exhibit a stacking-faults-free zinc blende crystal structure. Based on the high-quality nanowire, the field-effect transistor exhibits a high electron mobility of 1438 cm2 V−1 s−1, much higher than that with stacking faults. A high responsivity of 5495 A/W is obtained from the photodetector, among the highest values reported for InP nanowire photodetectors. Moreover, the response/recovery time of the device is only 0.6/2.2 ms, 2–3 orders of magnitude shorter than other InP nanowire photodetectors. The high crystal quality and excellent electrical and optical properties make the zinc blende ⟨110⟩ InP nanowire a promising candidate for high performance electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

The surface structures of ionic zinc-blende CdTe (001), (110), (111), and (211) surfaces are systematically studied by first-principles density functional calculations. Based on the surface structures and surface energies, we identify the detrimental twinning appearing in molecular beam epitaxy (MBE) growth of II-VI compounds as the (111) lamellar twin boundaries. To avoid the appearance of twinning in MBE growth, we propose the following selection rules for choosing optimal substrate orientations: (1) the surface should be nonpolar so that there is no large surface reconstructions that could act as a nucleation center and promote the formation of twins; (2) the surface structure should have low symmetry so that there are no multiple equivalent directions for growth. These straightforward rules, in consistent with experimental observations, provide guidelines for selecting proper substrates for high-quality MBE growth of II-VI compounds. [ABSTRACT FROM AUTHOR]

Recent calculations predict a super-thermal-conductivity of ~2000 Wm-1 K-1, comparable to that of diamond, in cubic boron arsenide (BAs) crystals, which may offer inexpensive insulators with super-thermal-conductivity for microelectronic device applications. We have synthesized and characterized single crystals of BAs with a zinc blende cubic structure and lattice parameters of a = 4.7830(7) Å. A relatively high thermal conductivity of ~200Wm-1 K-1 is obtained, close to those of best non-carbon crystal insulators, such as SiC, although still an order of magnitude smaller than the value predicted. Based on our XPS, X-ray single crystal diffraction, and Raman scattering results, steps to achieve the predicted super-thermal conductivity in BAs are proposed. [ABSTRACT FROM AUTHOR]

MnAs nanoclusters in GaAs were investigated with cross-sectional scanning tunneling microscopy. The topographic images reveal that the small clusters have the same zinc-blende crystal structure as the host material, while the larger clusters grow in a hexagonal crystal phase. The initial Mn concentration during molecular beam epitaxy growth has a strong influence on the size of the clusters that form during the annealing step. The local band structure of a single MnAs cluster is probed with scanning tunneling spectroscopy, revealing a Coulomb blockade effect that correlates with the size of the cluster. With a spin-sensitive tip, for the smaller clusters, superparamagnetic switching between two distinct states is observed at T = 77 K. The larger clusters do not change their magnetic state at this temperature, i.e., they are superferromagnetic, confirming that they are responsible for the ferromagnetic behavior of this material at room-temperature. [ABSTRACT FROM AUTHOR]

We study by microphotoluminescence the optical properties of single zinc-blende GaN/AlN quantum dots grown by droplet epitaxy. We show evidences of both excitonic and multiexcitonic recombinations in individual quantum dots with radiative lifetimes shorter than 287 6 8 ps. Owing to large band offsets and a large exciton binding energy, the excitonic recombinations of single zinc-blende GaN/AlN quantum dots can be observed up to 300 K. [ABSTRACT FROM AUTHOR]

We report on (112̅2) oriented Al1−xInxN grown by low pressure metal organic vapor phase epitaxy on (112̅2) GaN templates on patterned r-plane sapphire. The indium incorporation efficiency as well as the growth rate of (112̅2) oriented layers are similar to c-plane oriented Al1−xInxN layers. Deposition of thick Al1−xInxN layers does not lead to additional roughening like in case of c-plane oriented Al1−xInxN . Independent of the thickness, the degree of relaxation of layers lattice matched in m-direction is in the range of 33%-45% in [112̅3̅]-direction. Associated with the relaxation in [112̅3̅]-direction, there is a tilt of the Al1−xInxN layers around the [11̅00] axis due to slip of threading dislocations on the basal (0001)-plane. Relaxation in m-direction is not observable for layers lattice matched in [112̅3̅] direction. The possibility to adjust the lattice parameter of AlInN in [112̅3̅] direction without changing the lattice parameter in m-direction by anisotropic strain relaxation opens up opportunities for subsequent growth of optically active structures. One possibility is to form relaxed buffer layers for GaInN quantum well structures. [ABSTRACT FROM AUTHOR]

We present a phononic and electronic study of SiSn in the zinc-blende phase. A detailed description of the longitudinal optical (LO) phonon decay in a three-phonon process is presented together with the corresponding lifetime. The necessity to go beyond the zone center phonon approximation in this case is highlighted as it reveals a steep dependence of the lifetime on the initial phonon wavenumber, which differs from usual semiconductors. The electronic band structure is calculated within the GW formalism and shows a small direct band gap. It is shown that the LO-phonon resulting from electron cooling has a lifetime four to eight orders of magnitude above all the known value in semiconductors for this process. We finally show the suitability of SiSn for hot-carrier solar cells, as it is endowed with ultra-slow cooling of hot carriers. [ABSTRACT FROM AUTHOR]

We consider theoretically the electronic structure of quasi-two and quasi-one-dimensional heterostructures comprised of III-V and II-VI semiconductors such as InAs/GaInSb and HgCdTe. We show that not only a Dirac-like dispersion exists in these materials when the energy gap approaches zero but also the states with opposite momentum are orthogonal (i.e., can be described by a pseudo-spin), which suppresses backscattering and thereby enhances the electron mobility, by analogy with the case of graphene. However, unlike in graphene, a quasi-one-dimensional quantum wire with zero gap can be realized, which should eliminate most of the scattering processes and lead to long coherence lengths required for both conventional and ballistic electronic devices. [ABSTRACT FROM AUTHOR]

We demonstrate in this work controllable synthesis of cubic InN nanocrystals` through Mn doping. We show that the pristine nanocrystal has the wurtzite structure, but can be converted into the zinc-blende (ZB) structure when it is doped with Mn. Our first-principles calculations show that the phase transition is caused by the stronger p-d coupling between the host p valence state and the impurity d level in the ZB structure, which makes the hole generation in the ZB structure easier. Quantum confinement in the nanocrystals further enhanced this effect. This observation lays an important foundation for defects control of crystal phases. [ABSTRACT FROM AUTHOR]

It is demonstrated that the growth direction of InP nanowires grown on (001)-oriented silicon substrate strongly depends on the diameter of the gold catalyst droplets. Small droplets with diameter less than about 15 nm lead to the formation of nanowires leaning on the {111} planes of the zinc blende InP seeds formed in the early stages of growth. Larger droplets lead to the formation of twins in the InP seeds and to the formation of nanowires leaning on the {111} planes of these twinned InP variants, inducing growth directions corresponding to the <115> directions of the silicon substrate. [ABSTRACT FROM AUTHOR]

We report four probe measurements of the low field magnetoresistance (MR) in single core/shell GaAs/MnAs nanowires (NWs) synthesized by molecular beam epitaxy, demonstrating clear signatures of anisotropic magnetoresistance that track the field-dependent magnetization. A comparison with micromagnetic simulations reveals that the principal characteristics of the magnetoresistance data can be unambiguously attributed to the nanowire segments with a zinc blende GaAs core. The direct correlation between magnetoresistance, magnetization, and crystal structure provides a powerful means of characterizing individual hybrid ferromagnet/semiconductor nanostructures. [ABSTRACT FROM AUTHOR]

ZnO crystallizes in various crystallographic forms. While, the zinc blende (zb) and the rock salt (rs) structure of ZnO occur at high pressure, wurtzite (w) ZnO is the observed structure under ambient conditions. Interestingly, the high pressure polymorph of ZnO, cubic rs-ZnO oxide is presented on MgO (200) substrate at ordinary condition of temperature and pressure. The lattice constant of rs-ZnO is observed to be 4.203 Å identical to that for MgO. The possible configurational path for the hexagonal to cubic transformation is proposed. The compression of w-ZnO along c-axis, movement of Zn or O sub-lattice along [[formula]] direction and (110) plane appears to drive the transition. It has also been observed that rs-ZnO on MgO substrate is stable for certain maximum thickness (150 nm). It may be possible to stabilize the cubic phase at lower temperature and smaller thickness level. [ABSTRACT FROM AUTHOR]

Optical transmittance measurements on epitaxial, phase-pure, wurtzite-structure ScxGa1-xN films with ≤ x ≤ 0.26 showed that their direct optical band gaps increased from 3.33 eV to 3.89 eV with increasing x, in agreement with theory. These films contained I1- and I2-type stacking faults. However, the direct optical band gaps decreased from 3.37 eV to 3.26 eV for ScxGa1-xN films, which additionally contained nanoscale lamellar inclusions of the zinc-blende phase, as revealed by aberration-corrected scanning transmission electron microscopy. Therefore, we conclude that the apparent reduction in ScxGa1-xN band gaps with increasing x is an artefact resulting from the presence of nanoscale zinc-blende inclusions. [ABSTRACT FROM AUTHOR]

ZnSnP2, an absorber material for solar cells, transitions from an ordered chalcopyrite to a disordered sphalerite structure at high temperatures. We investigate the electronic structure of both phases, combining a screened hybrid density functional with the special quasi-random structure method. We predict a bandgap reduction of 0.95 eV between the ordered and fully disordered materials. Experimental reports are consistent with partial disorder. Tuning of the order parameter would lead to a family of ZnSnP2 phases with bandgaps ranging from 0.75 eV to 1.70 eV, thus providing graded solar cell absorbers from a single material system. [ABSTRACT FROM AUTHOR]

We report electron transmission and Raman spectroscopy study of InAs nanowires. We demonstrate that the temperature dependent behavior of optical phonon energies can be used to determine the relative wurtzite fraction in the InAs nanowires. Furthermore, we propose that the interfacial strain between zincblende and wurtzite phases along the length of the wires manifests in the temperature-evolution of the phonon linewidths. From these studies, temperature-dependent Raman measurements emerge as a non-invasive method to study polytypism in such nanowires. [ABSTRACT FROM AUTHOR]

We studied the magnetization of zinc blende Mn1-xCrxS films embedded between diamagnetic ZnSe layers grown by molecular beam epitaxy with chromium mole fractions x ≤ 0.7. These ternary semiconductors exhibit an increasing ferromagnetic contribution with increasing x caused by competing antiferromagnetic and ferromagnetic coupling. As a result, whereas MnS in the zinc blende phase is a pure antiferromagnet, it was found that with increasing x zinc blende Mn1-xCrxS became a ferromagnet. The ferromagnetic phase transition dominates in case of x greater than about 0.5. Hence, we conclude that metastable zinc blende CrS will be a ferromagnetic material with half-metallic character in contrast to the analogous stable NiAs-structure which exhibits an antiferromagnetic phase transition. [ABSTRACT FROM AUTHOR]

We report the sulfur vacancies-related d0 ferromagnetism in undoped sphalerite ZnS nanoparticles. Systematically tune of sulfur deficiency in ZnS nanoparticles was done by selecting different synthesized temperatures and varying the ratio of hydrogen and argon in post-annealing processes. Our study suggests that such sulfur vacancies can induce the room temperature ferromagnetism. Importantly, the ferromagnetism can be modulated by changing the concentration of sulfur vacancies in the samples. This finding should be the focus of future electronic and spintronic devices. [ABSTRACT FROM AUTHOR]

Here we show the high-temperature thermoelectric (TE) properties of Cu2Ga4Te7 with the defect zinc-blende structure in which one-seventh of the cation sites are structural vacancies. Cu2Ga4Te7 exhibited relatively low electrical resistivity (ρ) and thermal conductivity (κ) and moderate positive Seebeck coefficient (S) at high temperatures, making this compound a promising high-performance p-type TE material. At 940 K, the S, ρ, and κ were +215 μV K-1, 10.1×10-5 Ω m, and 0.67 Wm-1 K-1, respectively, which resulted in the maximum dimensionless figure of merit ZT (=S2T/ρ/κ, where T is the absolute temperature) of 0.64. [ABSTRACT FROM AUTHOR]

The InxGa1-xN alloys present levels as a result of the intentional (doped) or unintentional (contamination) introduction of C atoms into the host semiconductor. The III-V nitride semiconductors and their alloys usually crystallize in the wurtzite structure although the zinc blende structure has also been grown. We obtained the InxGa1-xN:C ionization energies from first-principles calculations of the two ordered wurtzite and zinc blende structures using different exchange and correlation terms. In accordance with the experimental results, the ionization levels could give rise, on some occasions, to a metallic impurity band. [ABSTRACT FROM AUTHOR]

GaAs/MnAs core/shell nanowire heterostructures were synthesized by catalyst-free molecular beam epitaxy. Transmission electron microscopy (TEM) reveals that the GaAs core predominantly grows with the zinc-blende crystal structure with a [111] growth direction. In a small population of wires, the crystal structure transitions from zinc blende to wurtzite with a [001] growth direction. Cross-sectional TEM shows that the MnAs grows epitaxially on the GaAs core in the NiAs prototype structure with an epitaxial relation of [formula] MnAs∥[111]GaAs and (0110) MnAs∥GaAs (110). When the GaAs core is in the wurtzite structure, the epitaxial relation between the GaAs and MnAs changes to [0001] MnAs∥[0001]GaAs and (1210) MnAs∥(1210)GaAs. [ABSTRACT FROM AUTHOR]

Using contactless electroreflectance, we determined the band gap of the two known phases of epitaxial ZnSnP2. Induced by small changes in Sn/Zn flux ratio during epitaxy, the order-disordered transition between the chalcopyrite and sphalerite phases reduces the band gap by 300 meV. The chalcopyrite ordered phase, unambiguously identified from x-ray diffraction, exhibits a band gap of 1.683 eV at 293 K. The band gap of the disordered sphalerite phase is 1.383 eV. Using the volume-averaged order parameter measured on the chalcopyrite sample, we find that its morphology is best described by the presence of perfectly ordered domains inside a disordered matrix. [ABSTRACT FROM AUTHOR]

Using contactless electroreflectance, we determined the band gap of the two known phases of epitaxial ZnSnP2. Induced by small changes in Sn/Zn flux ratio during epitaxy, the order-disordered transition between the chalcopyrite and sphalerite phases reduces the band gap by 300 meV. The chalcopyrite ordered phase, unambiguously identified from x-ray diffraction, exhibits a band gap of 1.683 eV at 293 K. The band gap of the disordered sphalerite phase is 1.383 eV. Using the volume-averaged order parameter measured on the chalcopyrite sample, we find that its morphology is best described by the presence of perfectly ordered domains inside a disordered matrix. [ABSTRACT FROM AUTHOR]

We use laser diffraction microscopy to visualize in real time the motion of partial dislocations in thin colloidal crystals confined in flat capillaries. The results show that the formation of partial dislocation loops with their associated stacking faults is an energetically preferred strain-relaxation channel for colloidal crystals. The local residual stress in the crystal can be estimated by measuring the velocity of the dislocations. Two types of interactions between the dislocations are observed, namely, that between two dislocations in two intersecting slide planes and that between two dislocations in two parallel slide planes. [ABSTRACT FROM AUTHOR]

GaN nanorods with a wurtzite/zinc-blende (WZ/ZB) heterostructure are synthesized by chemical vapor deposition. They have a triangular cross section and grow along the WZ [formula] direction. The WZ and ZB phases appear alternately along the nanorod’s transverse direction, forming a type-II superlattice structure. Two ultraviolet emission peaks dominate the photoluminescence spectra of the GaN nanorods. One originates from excitonic transitions within the WZ regions. The other shows an anomalous “S-shaped” energy shift with increasing temperature, and is attributed to radiative recombinations of carriers localized at potential fluctuations in ZB regions. The carrier localization also results in high luminescent efficiency of the GaN nanorods. [ABSTRACT FROM AUTHOR]

Using the full-potential linearized augmented plane wave method, we study the magnetism and electronic structures of C-doped ZnS (zinc-blende structure). Calculations indicate that C can induce stable ferromagnetic ground state in ZnS hosts. The magnetic moment of the 64-atom supercell (containing one CS defect) is 2.00μB. Low formation energy implies ZnS0.96 875C0.03 125 can be fabricated experimentally. Electronic structures show C-doped ZnS is p-type half-metallic ferromagnetic semiconductor and hole-mediated double exchange is responsible for the ferromagnetism. Relative shallow acceptor levels indicate C-doped ZnS is ionized easily at working temperatures. Several doped configurations calculations suggest ferromagnetic couplings exist between the doped carbon atoms. [ABSTRACT FROM AUTHOR]

Microphotoluminescence measurements are used to investigate the optical properties of single wurtzite GaAs nanowires grown by molecular beam epitaxy. The wurtzite GaAs nanowires exhibit a photoluminescence emission peak at 1.544 eV, 29 meV higher than the zinc blende GaAs free exciton energy. Temperature dependent photoluminescence measurements (4.4–70 K) show indications of defect and impurity related emissions at lower energies (1.53–1.54 eV) and the presence of nonradiative defects. High resolution transmission electron microscopy images show a low density of short zinc blende segments sandwiched in between a dominating wurtzite structure and weak photoluminescence emission related to such zinc blende segments is also observed. [ABSTRACT FROM AUTHOR]

We report on the electron transport in zinc blende InN simulated by the ensemble Monte Carlo method. To obtain the relevant band structure parameters, ab initio calculations have been carried out. Then, Monte Carlo transport simulations at room temperature and over a wide range of carrier concentrations have been performed. We obtain a steady-state peak drift velocity around 3.3×107 cm/s at an electric field of 55 kV/cm. For low-doped material, a room-temperature low-field mobility of about 6000 cm2/V s is calculated. A comparison with wurtzite InN does not reveal an advantage for the zinc blende InN phase regarding the electron transport. [ABSTRACT FROM AUTHOR]

Using quasiparticle band structures based on modern electronic-structure theory, we calculate the branch-point energies for zinc blende (GaN, InN), rocksalt (MgO, CdO), wurtzite (AlN, GaN, InN, ZnO), and rhombohedral crystals (In2O3). For InN, CdO, ZnO, and also In2O3 the branch-point energies are located within the lowest conduction band. These predictions are in agreement with observations of surface electron accumulation (InN, CdO) or conducting behavior of the oxides (ZnO, In2O3). The results are used to predict natural band offsets for the materials investigated. [ABSTRACT FROM AUTHOR]

In this study, we in situ employed low-temperature x-ray diffraction to investigate phase separation in GaN nanowires. Our observations showed that a distinct phase separation developed below 260 K, the zinc-blende phase, which is related to short range ordering. The correlation lengths of the zinc-blende phase reached their maximum at 140 K but correlation length was still revealed at around 23 nm. Our results may be understood using the finite size model and support the conclusion that the phase separation was reversible and occurred through the interaction of the characteristic size of the ordered domain of the GaN nanowires. [ABSTRACT FROM AUTHOR]

Electron microscopy studies are carried out to determine the structure of GaMnN films grown on 6H-SiC(0001) and MgO(111) substrates by plasma-assisted molecular beam epitaxy. For the Mn/GaN multilayer growth, cubic zinc blende GaMnN is observed in the nominal Mn/GaN multilayer region and surface microprotrusions, indicative of high Mn mobility. In contrast, for the H-assisted growth of Mn-doped GaN, single phase hexagonal wurtzite GaMnN is obtained, but with columnar structure, indicative of reduced Mn mobility during growth. [ABSTRACT FROM AUTHOR]

We use polarization-resolved and temperature-dependent photoluminescence of single zincblende (ZB) (cubic) and wurtzite (WZ) (hexagonal) InP nanowires to probe differences in selection rules and bandgaps between these two semiconductor nanostructures. The WZ nanowires exhibit a bandgap 80 meV higher in energy than the ZB nanowires. The temperature dependence of the PL is similar but not identical for the WZ and ZB nanowires. We find that ZB nanowires exhibit strong polarization parallel to the nanowire axis, while the WZ nanowires exhibit polarized emission perpendicular to the nanowire axis. This behavior is interpreted in terms of the different selection rules for WZ and ZB crystal structures. [ABSTRACT FROM AUTHOR]

The stable crystal structure of magnesium sulfide (MgS) is rocksalt. However, the metastable zinc-blende structure is obtained when MgS is deposited by molecular beam epitaxy (MBE) on (001) zinc-blende substrates with a relatively small misfit. In the present work, the zinc blende to rocksalt phase transition is analyzed in MgS/ZnSe/GaAs multilayer samples grown by MBE with different MgS layer thicknesses. By x-ray diffraction and transmission electron microscopy methods, a partial nucleation of MgS rocksalt is evidenced and correlated to the presence of stacking faults at the bottom interface. The unexpected coexistence of both rocksalt and zinc-blende MgS structural phases is discussed. [ABSTRACT FROM AUTHOR]

First-principles calculations are employed to study the structural and magnetic properties of SrC and BaC in four different phases: rocksalt, CsCl, zinc blende, and NiAs. The obtained results indicate that both compounds show half-metallic behavior in all phases except the CsCl-type structure. Among them the rocksalt structure is found to be the most stable one with a robust half-metallic characteristic with respect to the lattice compression and expansion. The magnetic phase transition temperature Tc of the rocksalt phase is calculated employing both the mean-field approximation and the random-phase approximation. The predicted Tc values of both compounds are considerably above room temperature. [ABSTRACT FROM AUTHOR]

Tunneling-assisted carrier transfer in coupled double InGaN/GaN quantum wells (QWs) has been studied by temperature-dependent photoluminescence (PL) at varied excitation density. It is found that the carriers captured by the wide (“deep”) well are efficiently transferred to the adjacent narrow (“shallow”) one by resonant tunneling, which results in anomalous temperature dependence of PL intensity and significantly enhanced luminescent efficiency for the narrow well. This is disparate from those conventional tunneling-assisted behaviors in coupled double QWs constructed by zinc-blende materials without polarization effect, where the carriers are always tunneling from the narrow (“shallow”) well to the wide (“deep”) one. [ABSTRACT FROM AUTHOR]