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The interface properties between nonpolar ZnO and sapphire have been studied using high resolution transmission electron microscopy. Two nonpolar orientations are investigated: a- and m-orientations corresponding to [1120] and [1010] crystallographic directions. After the definition of the epitaxial relationships and the resulting initial lattice mismatch, we show that nonpolar ZnO can be grown on sapphire with perfectly flat interfaces. Geometrical misfit dislocations are observed at the interface ZnO/sapphire and their density gives the residual strain in the layer. A strong anisotropy in the strain relaxation is found along the two perpendicular in-plane directions. This anisotropy may be explained in terms of initial anisotropic mismatch yielding different relaxation processes. A domain matching epitaxy is observed in m- and a-oriented layers for mismatches larger than 9% while a lattice matching epitaxy, in which the relaxation is driven by nucleation and glide of dislocations, is observed in a-oriented ZnO along the [0001] in-plane direction. In order to explain the observed relaxation the activated slip systems are calculated for both nonpolar orientations as a function of the in-plane stress due to the anisotropic mismatch. There is a major difference from the polar orientations. Low energy prismatic slip systems can be effective for plastic relaxation in the nonpolar orientations because they are no longer parallel to the growth direction, which is the case of c-oriented layers, nor to the applied stress. Our results can be directly extended to other nonpolar wurtzite structures such as III-nitrides. [ABSTRACT FROM AUTHOR]

CdO(110) layers with a self-organized surface structure have been grown on (1010) sapphire (m Plane) substrates by metal-organic vapor phase epitaxy. The epitaxial relationships between layer and substrate have been determined and a crystallographic model that accounts for the CdO in-plane orientation, which results in a reduced lattice mismatch when the CdO[001] direction is perpendicular to the sapphire c axis, has been proposed. Although the measured lattice parameters indicate that the layers are almost fully relaxed, an anisotropic mosaicity is detected with symmetrical rocking curves attaining minimum values when measured along the CdO[110] direction. The layer morphology consists of a regular ridge-and-valley structure which defines, again, a preferential in-plane direction. The grooves run parallel to the CdO[001] axis and exhibit lateral surfaces sloped at 28° with respect to the (110) surface. The influence of growth temperature and VI/II molar ratio on the anisotropic mosaicity and morphology has been analyzed. [ABSTRACT FROM AUTHOR]

Presents a study which investigated by high-resolution x-ray diffraction, temperature-dependent photoluminescence (PL) and reflectivity spectroscopies, and low-temperature selective-photoluminescence spectroscopy ZnSe single crystals grown by solid-phase recrystallization. Sample preparation and experimental procedure; Details on x-ray characterization; PL properties of the SPR-grown ZnSe single crystals.

Non polar ZnO and (Zn, Co)O layers were successfully grown on (11̄02) sapphire (R-plane sapphire). The growth process was shown to directly influence the surface morphology as well as the strain state in (112̄0) ZnO (A-plane ZnO). The dominant defect lines seen in photoluminescence were due to basal stacking faults as demonstrated by means of selective photoluminescence and transmission electron microscopy. We present a novel method for growing high quality A-plane ZnO by inserting a (Zn, Co)O thin buffer layer, which strongly reduced the surface roughness. Finally (Zn, Mg)O/ZnO quantum well structures were grown on such a buffer layer. These quantum wells exhibited no intrinsic quantum confined Stark effect. [ABSTRACT FROM AUTHOR]

The article reports that III-V nitride arsenide materials have attracted a great deal of attention in the last years, in particular for their ability to realise long wavelength lasers on GaAs substrates. These compounds are also good candidates for solar cell applications, but unlike the (Ga,In)(N,As)--based laser case, the research activity on this topic is restricted to only a few groups. The samples were processed using standard photolithography and etching steps. AuGe was evaporated to form the backside contact on the n-GaAs substrate and AuZn was deposited to realise the grid on the p-GaAs contact layer.

We investigate the dependence on Mg content of the lattice parameters and the surface morphology of nonpolar [formula] Zn1-xMgxO (x≤0.55) grown by molecular beam epitaxy. The anisotropy of the lattice parameters gives rise to an unusual in-plane strain state in the ZnO QWs: tensile strain along [1100] and compressive strain along [0001]. For a Zn0.6Mg0.4O barrier, the strain in a ZnO QW reaches -1.3% along [0001] and +0.3% along [1100]. This induces a strong blueshift of the excitonic transitions, in addition to the confinement effects, which we observe in photoluminescence excitation experiments. [ABSTRACT FROM AUTHOR]

We report the growth of highly reflective distributed Bragg reflectors (DBRs) in the UV region using the Al0.85In0.15N/Al0.2Ga0.8N lattice-matched system. The DBRs were deposited on nearly strain-free Al0.2Ga0.8N templates to avoid strain-induced structural degradations. The appearance of cracks was then completely suppressed. The DBRs exhibit a reflectivity higher than 99% at a wavelength as short as ∼340 nm and a stop band width of 215 meV (20 nm). [ABSTRACT FROM AUTHOR]

We report the growth over 2 in. sapphire substrates of crack-free fully epitaxial nitride-based microcavities using two highly reflective lattice-matched AlInN/GaN distributed Bragg reflectors (DBRs). The optical cavity is formed by an empty 3λ/2 GaN cavity surrounded by AlInN/GaN DBRs with reflectivities close to 99%. Reflectivity and transmission measurements were carried out on these structures, which exhibit a stopband of 28 nm. The cavity mode is clearly resolved with a linewidth of 2.3 nm. These results demonstrate that the AlInN/GaN system is very promising for the achievement of strong light–matter interaction and the fabrication of nitride-based vertical cavity surface emitting lasers. [ABSTRACT FROM AUTHOR]

Waveguiding GaN epitaxial layers have been grown by low-pressure metalorganic vapor phase epitaxy on Si(111) substrates using AlN/GaN short period-superlattice (SPS) buffer layer systems. The AlN/GaN SPS has been studied by x-ray diffraction where it appears as pseudoternary Al[sub x]Ga[sub 1-x]N alloy. Using elastic theory an effective Al content of 44% is calculated. This value is confirmed by the average Al content calculated from the AlN:GaN layer thickness ratio measured in cross-section transmission electron microscopy. The GaN waveguiding properties have been assessed using the prism coupling method. They sensibly improve with the total thickness of the underlying AlN/GaN superlattice as well as if an additional AlN/GaN SPS is grown atop the GaN waveguiding layer. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate that a careful optimization of the molecular-beam-epitaxy growth conditions allows us to obtain high-quality GaInNAs/GaAs quantum-well (QW) heterostructures exhibiting a perfect two-dimensional microstructure at high In and N contents. Room-temperature emission is achieved up to 1.61 and 1.51 µm for as-grown and annealed samples, respectively. High-resolution x-ray diffraction and transmission electron microscopy reveal that post-growth annealing does not affect the QW composition and width. This confirms that the GaInNAs semiconducting material is well suited for emission in the telecommunication wavelength range near 1.55 µm. [ABSTRACT FROM AUTHOR]