M. Nemoz

Comparative study of the role of the nucleation stage on the final crystalline quality of (111) and (100) silicon carbide films deposited on silicon substrates.

We study the impact of the nucleation step on the final crystalline quality of 3C-SiC heteroepitaxial films grown on (111) and (100) oriented silicon substrates by low pressure chemical vapor deposition. The evolution of both the structural and morphological properties of 3C-SiC epilayers in dependence on the only nucleation parameters (propane flow rate and duration of the process) are investigated by means of x-ray diffraction, scanning electron, atomic force, and optical microscopies. At first, we show how the formation of interfacial voids is controlled by the experimental parameters, as previously reported, and we correlate the density of voids with the substrate sealing by using an analytical model developed by V. Cimalla et al. [Mater. Sci. Eng., B 46, 190 (1997)]. We show that the nucleation stage produces a more dense buffer layer in case of (111) substrates. Further, we investigate the impact of the nucleation parameters on the crystalline quality of 3C-SiC epilayers. Within our experimental set...

Semipolar GaN films on patterned r-plane sapphire obtained by wet chemical etching

It is shown that (112¯2)-oriented GaN films can be achieved from r-sapphire patterned by chemical etching. Growth first occurs selectively from the inclined c-facet of sapphire, leading finally to a fully coalesced layer with (112¯2) orientation. The structural and optical quality of these layers was assessed by x-ray diffraction, cathodoluminescence and photoluminescence measurements. The results clearly show that the quality of (112¯2) GaN on patterned r-sapphire is markedly improved in comparison with (112¯2) GaN on m-sapphire.

Improved semipolar (112¯2) GaN quality using asymmetric lateral epitaxy

Semipolar (112¯2) GaN films were obtained by epitaxial lateral overgrowth from (112¯2) GaN templates patterned with SiO2 stripes 7 μm wide with 3 μm spacing, oriented along the [11¯00] GaN in-plane direction. The growth conditions were optimized in order to promote a fast growth rate along the +c [0001] direction. The crystal expands both laterally and vertically until a situation where it overgrows the adjacent crystal, thus stopping the propagation of stacking faults and threading dislocations. The growth anisotropy and filtering of defects is observed by cross-sectional scanning electron microscopy and cathodoluminescence. The lowering of defect density is confirmed by x-ray diffraction measurements. The photoluminescence spectrum of the coalesced epitaxial lateral overgrowth of the (112¯2) epilayers exhibits a strong band edge emission and a low emission band at 3.41 eV, assigned to the remaining stacking faults.

Indium incorporation dynamics into AlInN ternary alloys for laser structures lattice matched to GaN

Al1−xInxN ternary alloys with solid phase indium compositions between x=0.15 and 0.28 have been grown by metal organic chemical vapor deposition under indium rich conditions within the growth temperature range of 750–810 °C. A thermally activated process with activation energy of 1.05±0.05eV is found to compete with indium incorporation. Smooth epitaxial layers with root mean-squares surface roughness of 0.3–0.8nm are obtained. (Al,In)N films lattice matched to GaN have been introduced into laser diode structures for optical confinement. Optical gain is observed.

Built-in electric field in ZnO based semipolar quantum wells grown on (101¯2) ZnO substrates

We report on the properties of semipolar (Zn,Mg)O/ZnO quantum wells homoepitaxially grown by molecular beam epitaxy on (101¯2) R-plane ZnO substrates. We demonstrate that atomically flat interfaces can be achieved with fully relaxed quantum wells because the mismatch between (Zn,Mg)O and ZnO is minimal for this growth orientation. The photoluminescence properties evidence a quantum confined Stark effect with an internal electric field estimated to 430 kV/cm for a 17% Mg content in the barriers. The quantum well emission is strongly polarized along the [1¯21¯0] direction and a comparison with the semipolar bulk ZnO luminescence polarization points to the effect of the confinement.

Blue Light-Emitting Diodes Grown on ZnO Substrates

Blue light-emitting diodes (LEDs) grown on ZnO substrates were fabricated owing to the monolithic integration of an entire nitride-based LED structure including a GaN p–n junction and an (In,Ga)N/GaN multiple quantum well active region. The surface preparation of the ZnO substrate, as well as the GaN nucleation process, was developed to grow the structures and limit the inter diffusion of O from the substrate, which are the key points for the fabrication of a light-emitting device on ZnO. LEDs with a clear rectification behavior and electroluminescence over the blue range, from 415 to 450 nm, were demonstrated.

Filtering of Defects in Semipolar (11−22) GaN Using 2-Steps Lateral Epitaxial Overgrowth

Good-quality (11−22) semipolar GaN sample was obtained using epitaxial lateral overgrowth. The growth conditions were chosen to enhance the growth rate along the [0001] inclined direction. Thus, the coalescence boundaries stop the propagation of basal stacking faults. The faults filtering and the improvement of the crystalline quality were attested by transmission electron microscopy and low temperature photoluminescence. The temperature dependence of the luminescence polarization under normal incidence was also studied.

Structural and Morphological Characterization of 3C-SiC Films Grown on (111), (211) and (100) Silicon Substrates

The structural and morphological modifications induced by the carbonization stage upon 3C-SiC heteroepitaxial films grown on (111) and (100) oriented silicon substrates have been investigated. The crystalline quality of the films is strongly dependent on the carbonization parameters (propane flow rate and duration of carbonization). The (111) heteroepitaxial films coalesce more rapidly and present a lower dependence on the carbonization conditions than (100) films. By comparing the evolution of the interfacial defects (voids) density with existing models, we show that this is related to the initial mechanisms occurring during the carbonization stage. The twin defects densities on (111), (100) and (211) films are also investigated and the role of the only carbonization stage on their formation is studied.

Role of Substrate Misorientation in Relaxation of 3C-SiC Layers on Silicon

We analyze in detail the evolution of curvature of 3C-SiC layers grown on vicinal silicon substrates. A common feature of (100) and (111) oriented layers is a strongly asymmetric wafer bending that may suggest an anisotropic stress relaxation within the layer. A comparative study of the curvature, lattice parameter, surface morphology and structural defects for the off-angles ranging from 0.5° to 6° is performed in order to confirm or disprove this hypothesis. We find a homogeneous, tensile in-plane lattice deformation. We also show the correlation of the orientation of the high and low curvature axes with the morphology and defect pattern of the layer.

Optical properties of a-plane (Al, Ga)N/GaN multiple quantum wells grown on strain engineered Zn1−xMgxO layers by molecular beam epitaxy

Nonpolar (112¯0) Al0.2Ga0.8N/GaN multiple quantum wells (MQWs) have been grown by molecular beam epitaxy on (112¯0) Zn0.74Mg0.26O templates on r-plane sapphire substrates. The quantum wells exhibit well-resolved photoluminescence peaks in the ultra-violet region, and no sign of quantum confined Stark effect is observed in the complete multiple quantum well series. The results agree well with flat band quantum well calculations. Furthermore, we show that the MQW structures are strongly polarized along the [0001] direction. The origin of the polarization is discussed in terms of the strain anisotropy dependence of the exciton optical oscillator strengths.