Biaxial strain effect of spin dependent tunneling in MgO magnetic tunnel junctions Appl. Phys. Lett. 101, 042407 (2012) Magnetotransport anisotropy in lattice-misfit-strained ultrathin La2/3Ca1/3MnO3 films epitaxially grown on (110)-oriented SrTiO3 and LaAlO3 substrates J. Appl. Phys. 112, 013907 (2012) Tunnel electroresistance in junctions with ultrathin ferroelectric Pb(Zr0.2Ti0.8)O3 barriers Appl. Phys. Lett. 100, 232902 (2012) Transport and switching behaviors in magnetic tunnel junctions consisting of CoFeB/FeNiSiB hybrid free layers

Existence of Zn-As and Ga-Se interfacial layers were suggested by transmission electron microscopy in Zn treated and Se treated or reacted ZnSe/GaAs interfaces, respectively. High densities of As precipitates and Shockley partials were introduced in films with Zn treatment on a c(4×4) As-rich GaAs surface. In addition, high densities of vacancies and Shockley partials were obtained in samples with a Se-reacted ZnSe/GaAs interface. Formation of the Shockley partials may originate from the stacking errors induced by disordering of Zn- or Ga-interstitials on the GaAs surface.

A systematic dependence of the density and type of stacking fault defects with substrate surface chemistry and film growth mode was observed in ZnSe-based films grown on GaAs substrates. Namely, the density of Frank-type stacking faults is very large for films grown on Ga-rich surfaces, but is very low for films grown on As-stabilized surfaces exposed to Zn prior to the growth of the film. In contrast, the density of Shockley-type stacking faults increases for films grown by 3D growth mode at the initial stages of growth, but decreases greatly if the films are grown by the layer-by-layer growth mode. Films with stacking fault densities as low as 104/cm2 were obtained by growing the films by the layer-by-layer growth on GaAs epilayers with As-stabilized surfaces that were exposed to Zn for 1–2 min prior to the growth of the films.

Epitaxial ferromagnet/semiconductor/ferromagnet sandwiches with the nominal structure δ Mn60Ga40/GaAs/δ Mn54Ga46 have been grown on GaAs(001) by molecular beam epitaxy, with spacer layer thicknesses ranging from 2 to 19 monolayers (ML) GaAs nominally. A strong antiferromagnetic coupling field μ0Hs=−12 to −39 mT at room temperature is observed for spacer layers of 4–14 ML GaAs nominally, a weaker ferromagnetic coupling of +1 to +7 mT exists outside of this thickness region. Magnetic contamination of the spacer layer and the inclusion of antiferromagnetic Mn2As cannot be ruled out.

We study the growth of pseudomorphic ZnSSe layers on GaAs. The dependence of the epilayer quality on Zn exposure to the GaAs surface is investigated. Zn treatment prior to the ZnSe buffer growth on the As-rich GaAs surface results in the lowest defect density. Transmission electron microscopy studies show that an atomic scale smooth interface is formed. Based on the etch pit density and photoluminescence image analysis, ZnSSe layers with defect density ≤1×104 cm−2 can be reproducibly obtained.

Refractive index measurements of ZnSe-based ternary epitaxial layers grown by molecular-beam epitaxy on GaAs (100)Transmission electron microscopy is used to investigate the structure of the crystalline defects in degraded and undegraded ZnSe-based films/GaAs heterostructures. In degraded areas, dark line defects ͑DLDs͒ originate from the preexisting or grown-in defects ͑i.e., stacking faults and misfit dislocations͒ during device operation and make the laser diode fail. From our observation, the nucleation of DLDs is based on the initial emission of a mobile faulted defect from the preexisting grown-in defects. Along the trace of the faulted defects, ͓100͔ dark line defects form. We also investigated the origins and mechanisms for the generation of stacking faults and misfit dislocations. The generation of stacking faults is strongly related to the doping concentration, substrate surface stoichiometry, and growth mode of the films. The vacancy contained Ga-Se interfacial layers are thought to be sources for the generation of Frank-type stacking faults. In addition, Shockley partial dislocations form due to island coalescence of the ZnS x Se 1Ϫx /ZnSe epilayers on GaAs substrates. In situ electron beam heating studies were carried out to realize the mechanism of strain relaxation and formation of 60°-type misfit dislocations in the II-VI/GaAs interface from the dissociation of Frank-type partial dislocations. The generation of screw-type interfacial dislocations was also observed. This takes place by gliding the threading segments of the Shockley partial dislocations toward the ZnS x Se 1Ϫx /GaAs interface on ͕111͖-type planes.

We have observed that undoped ZnSe films grown on GaAs substrates by molecular beam epitaxy show an irregular array of interfacial 60° misfit dislocations. However, N and Cl doping of the ZnSe thin films changes the interfacial dislocation structure. p-type ZnSe with N concentrations of ∼1018/cm3 shows a regular array of interfacial 60° misfit dislocations and a lower (∼1×106/cm2) density of threading dislocations compared to undoped films. However, samples with doping levels higher than 1019/cm3 show a density of threading dislocations of ∼108/cm2. These differences are explained in terms of Frank partial dislocations observed only in doped ZnSe. The Frank partial dislocations act as nucleation sites for the misfit dislocations. Thus, different mechanisms for the formation of misfit dislocations in doped and undoped films occur in this system.

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