Zinc Blende MgS Research Articles

Molecular beam epitaxial growth of zinc blende MgS on GaAs (2 1 1)B substrates

This paper reports the growth of zinc blende (ZB) MgS on GaAs (2 1 1)B substrates by molecular beam epitaxy. Initial growths of (2 1 1)B ZnSe were performed at 240 °C and showed to be of comparable quality to (1 0 0) ZnSe grown at the same temperature. Samples of MgS deposited on ZnSe buffers showed good quality 2D growth. Subsequently, multilayer structures of ZnSe and ZnCdSe were deposited on (2 1 1)B MgS layers for structural and optical examination before and after epitaxial lift off (ELO). Photoluminescence (PL) spectroscopy showed strong emission before and after ELO and X-ray spectra demonstrated the presence of a single continuous zinc blende phase.

Theoretical Investigation of Half-metallic Ferromagnetism in Mg 0 . 7 5 Ti 0 . 2 5 Y (Y = S, Se, Te) Alloys by Using DFT-mBJ Studies

The full-potential linear-augmented-plane-waves plus local-orbitals (FP-LAPW + lo) method has been employed to explore the mechanical and half-metallic ferromagnetic properties of Ti-doped ordered zinc-blende MgS, MgSe, and MgTe semiconductors. Ductile and partial ionic natures of subjected compounds are investigated in terms of Poisson’s and Pough ratios, while the anisotropy value is evaluated to affirm the preferred orientation properties of these materials. Two different formalism of exchange and correlation (XC) effects have been applied in the form of generalized gradient approximation (GGA) and orbital independent modified Becke-Johnson potential combined with local density approximation (mBJLDA). Enthalpy of formation and energetic comparison has been used to establish the stability of ferromagnetic (FM). Premeditated electronic properties divulge that the Ti-doping induces ferromagnetism in MgS, MgSe, and MgTe which appear to show half-metallic (HM) gap at Fermi level (E F). In addition, the calculated electronic properties are analyzed in terms of the s−d and p−d exchange constants (N 0 α and N 0 β) that are found to be comparable with typical magneto optical experiment.

Epitaxial growth of zinc blende MgS directly on GaAs (0 0 1) substrates

We report the epitaxial growth of zinc blende MgS directly on GaAs (0 0 1) substrates without the use of any II–VI buffer layer. MgS layers up to 35 nm thick were grown before conversion to the rocksalt phase is observed. The layers were grown by molecular beam epitaxy using significantly lower Mg fluxes than previously used and over a narrow temperature range of 230–255 °C. Analysis of the layers during and after growth shows very little difference between these and layers deposited conventionally on ZnSe buffers. In particular,the low Mg flux does not significantly alter the growth rate or residual Zn content. This point is discussed with respect to previous models of MgS growth.

Control of surface defects in zinc blende MgS grown by MBE

The growth by molecular beam epitaxy of thick zinc blende (ZB) MgS on ZnSe buffer layers has been investigated by atomic force microscopy, X-Ray Diffraction and RHEED for samples grown at 240°C. Two different populations of pits are observed on these samples, neither of which have been observed previously on samples grown at 270°C. Type A pits are found on samples grown using the largest Mg fluxes. They are as deep as the MgS layer and appear to nucleate at the underlying surface. Reducing the Mg flux eliminates the type A pits and produces shallow type B pits which are possibly caused by rocksalt phase inclusions. Samples grown with the low Mg flux do not have an increased residual zinc incorporation, which is in agreement with a previously suggested model of the MgS growth mechanism. Single MgS ZB layers up to 64nm thick can be produced using a low Mg flux before conversion to the rocksalt phase is observed. This thickness is increased using a ZnSe/MgS buffer layer. Optimizing the buffer layer thickness, allows 200nm thick layers of ZB MgS to be produced.

Growth and stability of zinc blende MgS on GaAs, GaP, and InP substrates

The molecular beam epitaxial growth of zinc blende (ZB) MgS on GaAs, GaP, and InP substrates has been investigated by X-ray diffraction and RHEED, with MgS layer strain varying between 3.1% compressive strain (GaP) and 4.4% tensile strain (InP). ZB MgS could be grown on all three substrates. X-ray diffraction showed substantial MgS relaxation during growth before conversion to the rock salt phase. Results are compared with predictions that stable growth on GaP is unlikely and relaxed ZB MgS does not grow in layers over a few Å thick. Our results imply growth of ZB MgS is truly metastable.

On the structural properties of MgS-rich II–VI-based microcavities

II–VI-based microcavities grown by molecular beam epitaxy designed for emission in the blue spectral region have been comprehensively characterized by transmission electron microscopy in bright field, dark field and scanning mode. These complex structures contain a high amount of MgS, which is correlated with the occurrence of a certain kind of defect. Typical V-shaped stacking faults caused by the metastability of zinc-blende and rocksalt MgS along different (111) glideplanes have been identified. Optimized growth conditions have been found where this defect type can be suppressed to a large extend. Results obtained by x-ray diffraction measurements are consistent with the microscopy findings.

Metastable zinc-blende MgS structure: Combined experimental and theoretical study

MgS/ZnSe/GaAs multilayers with the MgS thickness ranging from 20 to 140 nm were grown at $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ by molecular-beam epitaxy on [001] GaAs substrates. The samples were studied by using several x-ray methods and transmission electron microscopy. The coexistence of metastable zinc-blende (ZB) and rocksalt MgS structural phases was evidenced and discussed. The analysis of reciprocal space maps of the x-ray intensity distribution around asymmetrical reciprocal-lattice nodes allowed us to determine the strain status of the MgS layers and to show that the ZB-MgS phase was pseudomorphic also in the case of the thickest film. The lattice parameter of the pure Ζ\ensuremath{\mathrm{B}}-MgS phase ranging between $0.563\text{ }33<{a}_{\text{MgS}}<0.563\text{ }67\text{ }\text{nm}$ was obtained by extrapolation from x-ray diffraction data and predicted ab initio elastic constants, taking into account that there was a Zn incorporation during the MgS growth estimated in the range $0.005\ensuremath{\le}{x}_{\text{Zn}}\ensuremath{\le}0.02$.

MBE Growth and Characterization of MgS-Rich Zinc-Blende ZnxMg1-xS1-ySey Alloys

Samples containing ZnMgSSe alloy were grown by using molecular beam epitaxy at 240 C and were analyzed by using X-ray interference. The alloy composition was found to be Zn0.20Mg0.80S0.64Se0.36. The surfaces of these layers were found to be extremely flat, unlike MgS layers of similar thickness grown under identical conditions, which show pronounced ridges. Structures with Zn0.20Mg0.80S0.64Se0.36 barriers were grown with ZnSe quantum wells and showed good quantum confinement with a sharp PL peak. Calculations of the phase stability of ZnMgSSe alloys suggest that an alloy of this composition should phase separate. However, samples with this composition are demonstrably single phase, and the discrepancy with the calculation can be removed if the enthalpy of formation of zinc-blende MgS is reduced by less than 2 % to 231 kJ mol 1 .

Surface Reconstructions of Zincblende MgS (100) Observed by Using RHEED

Surface Reconstructions of Zincblende MgS (100) Observed by Using RHEED

MBE growth of MgS nanowires characterized using AFM

The surface morphology of zinc blende MgS layers grown on ZnSe buffer layers has been investigated by atomic force microscopy (AFM). Under certain growth conditions, 1D nanowires form on the surface and both their dimensions and distribution are sensitive to the growth parameters used. We have investigated the nanowire formation as a function of flux ratio and MgS layer thickness. In thin MgS layers, the nanowires form bunches with atomically flat regions between them. In thicker MgS layers, the wires increase in size and density with the elimination of the flat regions between bunches of wires. This method of wire formation is consistent with an anisotropic relaxation of the MgS layer by mismatch dislocations leading to a surface instability by the Asaro–Tiller–Grinfield mechanism.

Direct experimental evidence of metastable epitaxial zinc-blende MgS

High resolution transmission electron microscopy has provided direct experimental evidence of monocrystalline, single-phase zinc-blende MgS. The authors report the first high resolution images of a metastable β-MgS epilayer. This material naturally has rocksalt crystalline structure, but β-MgS was grown in this work by molecular beam epitaxy on a ZnSe∕MgS multilayer buffered GaAs (001) substrate using Mg and ZnS sources, following a simple procedure. A metastable β-MgS layer of up to 125nm thick has been examined using this technique. Embedded stacking faults are observed in the β-MgS thick epilayer.

Development of surface structures in MBE grown MgS and the origin of the phase instability

MgS is an excellent barrier material for wide-gap II–VI quantum structures due to its large band gap of ∼5 eV. Although its stable crystal structure is rocksalt we have demonstrated the growth of zinc blende (ZB) MgS lattice matched to GaAs substrates [1]. MgS layers up to a critical thickness of 130 nm can be grown in the metastable ZB phase before the compound reverts to the stable rocksalt structure. In this paper we describe the changes in the surface morphology which occur during the growth of MgS in the stages leading up to the collapse of the ZB crystal structure. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Mechanical, elastic and anharmonic properties of zinc blende MgS compound

AbstractThe mechanical, elastic and anharmonic properties of zinc blende MgS compound have been investigated using a three‐body force potential arising from the charge transfer effects due to the deformation of the electronic shell of overlapping ions. The agreement between the results for elastic constants and bulk modulus and the available data is generally satisfactory. Values for the zone center LO phonon frequency, Debye temperature and specific heat at constant volume have also been obtained. In the case of anharmonic properties, such as third‐order elastic constants, physically significant and systematic values have been obtained similar to other compounds of the zinc blende structure.

Growth of zinc blende MgS and MgS/ZnSe quantum wells by MBE using ZnS as a sulphur source

We have grown MgS by MBE in the zinc blende crystal structure on GaAs (1 0 0) substrates using a novel technique where the sources are Mg and ZnS. Layers up to 134 nm thick have been grown without any degradation in the crystal structure. The lattice constant was found to be 0.5619±0.0001 nm and Poisson's ratio was estimated to be 0.425. PL and reflection spectra obtained from ZnSe quantum wells showed sharp signals indicating less than 1 ML fluctuations on the well widths. A binding energy of 43.9 meV has been obtained from excitons confined in a 5 nm wide ZnSe well.

Growth of zinc blende MgS/ZnSe single quantum wells by molecular-beam epitaxy using ZnS as a sulphur source

Zinc blende MgS has been grown on GaAs by molecular beam epitaxy using a novel method where the sources were Mg and ZnS. A reaction at the surface results in the formation of MgS layers with a Zn content estimated by secondary ion mass spectrometry and Auger spectroscopy to be between 0.5% and 2%. Double crystal x-ray rocking curve measurements of ZnSe/MgS/ZnSe layers show layers with good crystallinity. Using this growth technique layers up to 67 nm thick have been grown. Photoluminescence measurements of MgS/ZnSe/MgS single-quantum-well structures show that the confinement of the heavy hole excitons can be as large as 430 meV for a 1.7 nm well.

Excitonic properties of zinc-blende ZnSe/MgS superlattices studied by reflection spectroscopy

Excitonic properties of newly developed zinc-blende ZnSe/MgS superlattices (SL's) were measured by reflection spectroscopy. The modification of the excitonic peaks by the multiple reflection in the SL films was treated theoretically and a fitting method to estimate the exciton absorption peak positions and exciton linewidths was developed. Although zinc-blende MgS did not exist before, excellent optical properties were observed in the ZnSe/MgS SL"s. Excitonic structures were clearly observed from 13 K up to the measured room temperature. In spite of strong ionicity of MgS barrier layers in the ZnSe/MgS SL's, the reduction of exciton--LO-phonon coupling was clearly observed in narrower wells. This indicates that the quantum confinement effect on excitons is large due to the large band offsets and it overcomes the enhancement of exciton--LO-phonon scattering due to high ionicity in barrier layers.

Growth of zincblende [formula omitted] superlattices and their heterointerface properties

MgS naturally forms the rocksalt structure, but zincblende MgSZnSe superlattices were grown with atmospheric-pressure MOVPE. The lattice constant of zincblende MgS was determined to be 5.59 Å from a series of X-ray measurements. The purging effect during the growth of MgSZnSe heterointerfaces was studied. While purging with a Se precursor resulted in the formation of an extra MgSe-related interface layer, purging with a Zn precursor improved the abruptness of the heterointerfaces.

Epitaxial growth of zinc-blende ZnSe/MgS superlattices on (001) GaAs

We report the growth of zinc-blende ZnSe/MgS superlattices (SLs) on GaAs (001) substrates. The SLs were grown with metalorganic vapor phase epitaxy by selecting appropriate precursors for Mg and S. MgS naturally forms rocksalt structures, but zinc-blende MgS layers were grown. The lattice constant of MgS was estimated to be 5.59 Å. X-ray diffraction measurements show that the ZnSe/MgS SLs are grown coherently to the GaAs substrates up to the total thicknesses of ∼3000 Å.