Metalorganic Vapor Phase Deposition Research Articles

Elastic and inelastic strain in submicron-thick ZnO epilayers grown on r-sapphire substrates by metal-organic vapour phase deposition.

A significant part of the present and future of optoelectronic devices lies on thin multilayer heterostructures. Their optical properties depend strongly on strain, being essential to the knowledge of the stress level to optimize the growth process. Here the structural and microstructural characteristics of sub-micron a-ZnO epilayers (12 to 770 nm) grown on r-sapphire by metal-organic chemical vapour deposition are studied. Morphological and structural studies have been made using scanning electron microscopy and high-resolution X-ray diffraction. Plastic unit-cell distortion and corresponding strain have been determined as a function of film thickness. A critical thickness has been observed as separating the non-elastic/elastic states with an experimental value of 150-200 nm. This behaviour has been confirmed from ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy measurements. An equation that gives the balance of strains is proposed as an interesting method to experimentally determine this critical thickness. It is concluded that in the thinnest films an elongation of the Zn-O bond takes place and that the plastic strained ZnO films relax through nucleation of misfit dislocations, which is a consequence of three-dimensional surface morphology.

Simulation study on the diversity and characteristics of twin structures in GaN

Gallium nitride (GaN) is a promising material for high-frequency and high-power electronics owing to its high thermal stability, wide bandgap, and high breakdown voltage. Monocrystalline GaN films are usually produced by metal organic chemical vapor phase deposition using Si, SiC, or Al 2 O 3 as the substrate. However, the difference in lattice constants and thermal expansion coefficients causes many defects in GaN epilayers . In particular, the formation of twins will strongly influence the electronic properties of GaN-based devices. In this study, the solidification process of GaN was simulated by molecular dynamics at a cooling rate of 10 12 K/s, and the twin structures in GaN were discussed. The results of this simulation showed two types of twins, including coherent twin and rotating twin, which were analyzed by visualization technology. The formation of twins was related to the coexistence of zinc blende and wurtzite phases. Furthermore, the types of twins were closely associated to the stacking ways of zinc blende and wurtzite structures. In general, it is essential to study the microstructure and the structural evolution of twin GaN, in order to give references to experiments about the growth and characteristics of twins. • Zinc blende and wurtzite nucleated randomly and formed lots of complex structures at the beginning of crystallization. • Coherent and rotating twins were formed according to different stacking methods of zinc blende and wurtzite structures. • The rules for the combination of twin structures in GaN crystals have been summarized and it can be generalized. • An error in the stacking sequence can cause the metastable phase c-GaN to start seeding the h-GaN phase.

Identification of Star Defects in Gallium Nitride with HREBSD and ECCI.

This paper characterizes novel “star” defects in GaN films grown with metal–organic vapor phase deposition (MOVPE) on GaN substrates with electron channeling contrast imaging (ECCI) and high-resolution electron backscatter diffraction (HREBSD). These defects are hundreds of microns in size and tend to aggregate threading dislocations at their centers. They are the intersection of six nearly ideal low-angle tilt boundaries composed of $\langle a\rangle$-type pyramidal edge dislocations, each on a unique slip system.

Heat Dissipation in Flexible Nitride Nanowire Light-Emitting Diodes.

We analyze the thermal behavior of a flexible nanowire (NW) light-emitting diode (LED) operated under different injection conditions. The LED is based on metal–organic vapor-phase deposition (MOCVD)-grown self-assembled InGaN/GaN NWs in a polydimethylsiloxane (PDMS) matrix. Despite the poor thermal conductivity of the polymer, active nitride NWs effectively dissipate heat to the substrate. Therefore, the flexible LED mounted on a copper heat sink can operate under high injection without significant overheating, while the device mounted on a plastic holder showed a 25% higher temperature for the same injected current. The efficiency of the heat dissipation by nitride NWs was further confirmed with finite-element modeling of the temperature distribution in a NW/polymer composite membrane.

Van Der Waals Growth of III-V Semiconductors on Graphene

Recent discovery of graphene and its unique properties has attracted a great deal of interest in implementing this material in a variety of new devices, targeting applications in ultra-fast electronics, quantum information, carbon-free energy conversion, optoelectronics, and bio-integrated technologies [1,2]. However, graphene lacks a controlled non-zero bandgap, which prevents its large-scale application in electronic and energy conversion devices. To overcome this limitation, we exploit direct integration of III-V semiconductors on graphene through van der Waals epitaxy. Known for their efficient light emission and high charge carrier mobilities, III-V semiconductors are at the core of numerous technologies including high-efficiency solar cells, lasers, light emitting diodes, and ultra-fast transistors, to name a few [3].Due to lack of dangling bonds on graphene’s surface, in epitaxial growth of III-V semiconductors on graphene the crystals follow the order of graphene lattice through van der Waals forces. Initially, two nucleation and growth processes were suggested for such van der Waals epitaxy: (1) nucleation starts at defect sites on graphene [4], and (2) nucleation starts on specific sites on graphene lattice, which are the favorable adsorption sites for III/V adatoms [5]. The latter growth mechanism limits the epitaxial growth of the III-V crystals in four different relative orientations (with different strain values) [5]. Recently, density functional theory calculations followed by homoepitaxial growth of InP, GaP, and GaAs through several layers of graphene suggested another determining factor in van der Waals epitaxial growth: long-range interaction between the III-V substrate under graphene and the III-V structures grown on graphene [6].In this talk, we demonstrate the low-pressure metal-organic vapor phase deposition (MOCVD) of InAs, GaAs, InP, and GaP islands on single layer graphene sheets grown on copper foils and transferred on SiO2/Si (100), as well as graphene sheets directly grown on Ge (100), (110), and (111) substrates. We show that regardless of the nature of the substrate under graphene, III-V crystals grow mostly on graphene defect sites and their morphology can be somewhat controlled through controlling the growth parameters. We then show the effect of long-range forces between Ge and III-V structures on growth morphology, which results in significant coalescence and growth of tens of micron large islands on graphene/Ge as opposed to parasitic crystals grown on graphene/SiO2. In what follows, we provide a brief summary of our observations in both systems.All III-V semiconductors grown on graphene/SiO2/Si showed very similar growth morphology and crystal structure. Plan-view and cross-sectional scanning electron microscopy (SEM), micro-Raman spectroscopy, powder and high-resolution X-ray diffraction (XRD), along with cross-sectional transmission electron microscopy (TEM) and nanoscale cathodoluminescence analysis revealed formation of 1D, 2D, and 3D structures in zinc-blende, wurtzite, and polytypic (mixed zinc-blende/wurtzite) phases. We have recently demonstrated that polytypic InP crystals form a type II homojunction with potential applications in optoelectronic devices [7]. XRD analysis of the growth time evolution of texture, as well as growth rate and crystal size evolution analysis of the crystals using atomic force microscopy (AFM) suggested a growth mechanism similar to selected area MOCVD growth [7], which is widely used to grow nanostructures and devices. This enabled us to have some degree of control over the growth morphology (single crystals, polycrystals, nanowires) through controlling the growth parameters such as growth temperature, rate and time.Similar 1D, 2D, and 3D structure were grown on graphene/Ge (100), (110), (111). However, the size and crystalline quality of the islands have significantly improved for growth on Ge substrates. Moreover, two-step growth (nucleation at low temperature (450 °C) and growth at higher temperature (600 °C)) lead to coalescence of the crystals and formation of tens of microns large islands with smooth surface (roughness ~ 1nm from AFM data) on graphene/Ge, while no significant improvement in growth morphology was observed for growth on graphene/SiO2. These observations suggest a strong sensitivity of the morphology of the deposited films on the nature of the substrate below the graphene monolayers. This provides insight to control the properties of such hybrid systems and will pave the path to engineering a new class of electronic and optoelectronic devices by combining the advantages of semiconductors and graphene.

High-frequency surface acoustic wave devices based on epitaxial Z-LiNbO3 layers on sapphire

Filter market demands push the development of new piezoelectric materials to address the modern telecommunication challenges. Combining composite wafers with an epitaxial piezoelectric layer and a said high velocity and acoustic quality substrate is a promising way to answer those demands. However, the fabrication of high-quality LiNbO3 films with reproducible physical properties is complicated by the difficulty in controlling volatile Li2O incorporation into the film and of measuring its composition. So far, large-scale production of films with physical properties suitable for the targeted applications is not available. In this paper, lithium niobate films with controlled nonstoichiometry were deposited by means of pulsed injection metalorganic vapor phase deposition. We have demonstrated a high acoustical performance for surface acoustic wave devices operating in the frequency range of 3.7 GHz up to 5.3 GHz and based on grown epitaxial Z-axis oriented LiNbO3 films on sapphire. An electromechanical coupling of 8% for the Rayleigh wave at 5.3 GHz was demonstrated experimentally.

Wafer‐Scale Epitaxial 1T′, 1T′–2H Mixed, and 2H Phases MoTe2 Thin Films Grown by Metal–Organic Chemical Vapor Deposition

Abstract2D materials beyond molybdenum disulfide such as molybdenum ditelluride (MoTe2) have attracted increasing attention because of their distinctive properties, such as phase‐engineered, relatively narrow direct bandgap of 1.0–1.1 eV and superior carrier transport. However, a wafer‐scale synthesis process is required for achieving practical applications in next‐generation electronic devices using MoTe2 thin films. Herein, the direct growth of atomically thin 1T′, 1T′–2H mixed, and 2H phases MoTe2 films on a 4 in. SiO2/Si wafer with high spatial uniformity (≈96%) via metal–organic vapor phase deposition is reported. Furthermore, the wafer‐scale phase engineering of few‐layer MoTe2 film is investigated by controlling the H2 molar flow rate. While the use of a low H2 molar flow rate results in 1T′ and 1T′–2H mixed phase MoTe2 films, 2H phase MoTe2 films are obtained at a high H2 molar flow rate. Field‐effect transistors fabricated with the prepared 2H and 1T′ phases MoTe2 channels reveal p‐type semiconductor and semimetal properties, respectively. This work demonstrates the potential for reliable wafer‐scale production of 1T′ and 2H phases MoTe2 thin films employing the H2 molar flow rate‐controlled phase tunable method for practical applications in next‐generation electronic devices as a p‐type semiconductor and Wyle semimetal.

Control of Wigner localization and electron cavity effects in near-field emission spectra of In(Ga)P/GaInP quantum-dot structures

Structural and emission properties of few-electron In(Ga)P/GaInP quantum dots (QDs) representing natural Wigner molecules (WM) and whispering gallery mode (WGM) electron ($e$) cavities have been investigated. QD structures were grown using self-organized metal-organic vapor phase epitaxy and deposition from $\ensuremath{\sim}3$ to 7 monolayers of InP at $700{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Using atomic force microscopy, transmission electron microscopy, near-field scanning optical microscopy (NSOM), and $\ensuremath{\mu}$-photoluminescence ($\ensuremath{\mu}$-PL) spectra we obtained In(Ga)P/GaInP QDs having lateral size 80--180 nm, height 5--30 nm, Ga content 0.0--0.4, density $2\ensuremath{-}10\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{\ensuremath{-}2}$, and electron population up to 20 and demonstrated control of their density and size distribution. Using high-spatial-resolution low-temperature PL spectra, NSOM imaging, and calculations of charge density distributions we observed Wigner localization and $e$-cavity effects for a series of dots having quantum confinement $\ensuremath{\hbar}{\ensuremath{\omega}}_{0}=0.5\ensuremath{-}6\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$. We used these data together with time-resolved PL measurements to clarify the effect of Coulomb interaction and WM formation on emission spectra of few-electron QDs. We present direct observation of $2e$, $6e$, and $9e$ WMs; $2e$ and $4e$ WGMs; and Fabry-Perot $e$ modes and establish conditions of $e$-WGM-cavity formation in these QDs.

Defect formation and optical activation of Tb implanted AlxGa1−xN films using channeled implantation at different temperatures

AlxGa1−xN (x = 0.20, 0.50, 0.63) films grown on (0001) sapphire substrates by metal organic chemical vapor phase deposition were implanted with Tb ions at 150 keV and a fluence of 7 × 1014 Tb cm−2. The implantation was carried out with the beam aligned with the c-axis and the implantation temperature was varied from room temperature (RT) to 550 °C. Additionally, post-implantation rapid thermal annealing was performed at 1200 °C during 120 s. The impact of implantation temperature on the damage accumulation is investigated. Rutherford backscattering spectrometry/channeling (RBS/C) measurements show that two damage regions are forming and the damage is not decreasing monotonically with the increase of implantation temperature. Bulk damage follows the same trend for all AlxGa1−xN compositions, increasing when the temperature is raised up to ~100 °C, and then decreasing for higher temperatures. A good agreement is observed between the damage accumulation obtained from RBS/C and the strain profile derived from symmetric (0002) 2θ-ω X-ray diffraction scans. Transmission electron microscopy results show the suppression of basal stacking faults after implantation at 550 °C. Tb lattice site location studies revealed two preferential sites: the substitutional cation site and a site displaced from that by 0.2 Å along the c-axis. A higher substitutional fraction of Tb ions is obtained for implantation temperature of 550 °C. The optical activity investigated by photoluminescence showed that after thermal annealing, the 5D4 → 7FJ intra-4f8 transition is detected in all the samples.

Modeling and analysis of smoothly diffused vertical cavity surface emitting lasers

Inter-diffusion in a 850 nm AlGaAs/GaAs top-emitting oxide-confined vertical-cavity surface-emitting laser (VCSEL) has been modeled and analyzed. Some important VCSEL parameters such as, the threshold gain, relative confinement factor, and the effective cavity length have been derived as a function of diffusion length and were found to reliably describe intermixing in VCSELs. It has been shown that inter-diffusion in VCSELs during typical molecular beam epitaxy (MBE) and metal-organic vapor-phase deposition (MOCVD) growth conditions is negligible and has no effect on a various range of VCSEL parameters. The model reveled that the VCSEL reflectivity spectra remains roughly unchanged for diffusion lengths of up to 16 nm, however, it is associated with a very small resonance shift and a decrease in the band width. The VCSEL threshold gain was found to increase noticeably at small diffusion lengths. The error-function solution to the diffusion equation as presented in the model could be adapted as a new compositional grading scheme in VCSELs. This newly proposed compositional grading scheme could be controlled during VCSELs growth and/or by post-growth thermal treatment.

Manganese phosphide thin films and nanorods grown on gallium phosphide and on glass substrates

We report a simple and fast route to grow ferromagnetic manganese phosphide polycrystalline films and nanorods on GaP and on glass substrates using metalorganic vapor phase deposition. Increasing the growth temperature (≥600°C) and growth time (≥30min) results in nucleation of secondary MnP crystals on the primary grains. The secondary crystals grow faster along a specific direction of orthorhombic MnP (c-axis) and form long rods (up to ~10μm) whose diameters are in the nanoscale (20–100nm). The nanorods can be easily detached from the glass substrate. The films exhibit ferromagnetic behavior with a range of transition temperatures, depending on the growth conditions.

Tri-gate InGaAs-OI junctionless FETs with PE-ALD Al2O3 gate dielectric and H2/Ar anneal

We present a tri-gate In0.53Ga0.47As-on-insulator (InGaAs-OI) junctionless field-effect transistor (JLFET) architecture. The fabricated devices feature a 20-nm-thick n-In0.53Ga0.47As channel doped to 1018/cm3 obtained by metal organic chemical vapor phase deposition and direct wafer bonding along with a 3.5-nm-thick Al2O3 gate dielectric deposited by plasma-enhanced atomic layer deposition (PE-ALD). The PE-ALD Al2O3 presents a bandgap of 7.0eV, a k-value of 8.1 and a breakdown field of 8–10.5MV/cm. A post-fabrication H2/Ar anneal applied to the PE-ALD Al2O3/In0.53Ga0.47As-OI gate stack yielded a low density of interface traps (Dit) of 7×1011/cm2eV at Ec−E=−0.1eV along with lower border trap density values than recently reported PE-ALD bi-layer Al2O3/HfO2 and thermal ALD HfO2 gate stacks deposited on In0.53Ga0.47As. The H2/Ar anneal also improved the subthreshold performance of the tri-gate InGaAs-OI JLFETs. After H2/Ar anneal, the long-channel (10μm) device featured a threshold voltage (VT) of 0.25V, a subthreshold swing (SS) of 88mV/dec and a drain-induced barrier lowering (DIBL) of 65mV/V, while the short-channel (160nm) device exhibited a VT of 0.1V, a SS of 127mV/dec and a DIBL of 218mV/V. Overall, the tri-gate InGaAs-OI JLFETs showed the best compromise in terms of VT, SS and DIBL compared to the other III–V JLFET architectures reported to date. However, a 15× increase in access resistance was observed after H2/Ar anneal, significantly degrading the maximum drain current of the tri-gate InGaAs-OI JLFETs.

Growth of GaN Film on Graphene by HVPE

A method to grow gallium nitride (GaN) films directly on the graphene layers by hydride vapor phase epitaxy (HVPE) method is reported in this work. We used a chemical vapor deposition (CVD) method to grow graphene on a copper foil, and the test results showed the presence of monolayer graphene at most regions. GaN films were grown on the graphene/MO-GaN substrate (GaN which was grown by metal organic vapor phase deposition) and MO-GaN template by HVPE method. Raman Spectroscopy, Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD) were adopted for characterization. By comparing with the MO-GaN substrate, the crystalline quality of the GaN films were both increased. However, the crystalline quality of the HVPE-GaN with graphene interlayer is slightly lower than that directly grown on MO-GaN.

GaN BASED 3D CORE-SHELL LEDS

As a promising novel route towards highly efficient optoelectronic devices, GaN based 3D core-shell light emitting diodes (LEDs) have attracted increased attention in recent years. In comparison to conventional 2D thin film LED, the 3D LED systems using a core-shell geometry with high aspect ratio are a breakthrough in technology with lots of advantages. In this paper, we review our developed growth strategies of these LED systems on Si and sapphire substrates. A catalyst free selective area growth of GaN 3D core-shell LED systems was realized using patterned substrates by metal organic vapor phase deposition in a convenient continuous-flux growth mode. We have recently suggested that the surface polarity plays a crucial role for the morphology of GaN 3D structure growth. In order to analyze the surface polarity of 3D submicron or micron structures, Kelvin probe force microscopy and selective etching techniques have been developed. During the growth of GaN submicron rods and micron columns on patterned SiOx /sapphire templates, mixed polarity effects could be detected. A new "truncated pyramid + column" growth method was developed to effectively avoid the formation of mixed polarity and realize single N-polar GaN 3D devices. Transmission electron microscopy and spatially and spectrally resolved cathodoluminescence measurements evidently prove the core-shell structure of 3D LED systems.

When Fewer Photons Do More: A Comparative O2Photoadsorption Study on Vapor-Deposited TiO2and ZrO2Nanocrystal Ensembles

The charge separation properties of TiO2 and ZrO2 nanocrystal powders which were produced by metal organic chemical vapor phase deposition were compared by means of O2 photoadsorption. Prior to the UV excitation experiments, we carefully explored the structure and morphology as well as the spectroscopic properties of the dehydroxylated nanoparticles in controlled gas atmospheres using UV diffuse reflectance, FT-IR, and electron paramagnetic resonance spectroscopy. On the basis of this information, we utilized the photogeneration of surface-adsorbed O2− radicals and their detection by EPR spectroscopy to quantify the concentration of separated charges and to relate these figures to the number of oxide particles that were exposed to known numbers of UV photons with defined energies. The results presented in this study reveal that upon band-gap excitation, ZrO2 nanoparticles are by 2 orders of magnitude more efficient in oxygen-assisted charge separation than TiO2. The dramatically diminished charge separation yield in TiO2 is attributed to the existence of deep trap states which persistently stabilize paramagnetic holes and at the same time act as recombination centers. Their absence in ZrO2 nanocrystals gives rise to a comparable performance in terms of photoadsorbed O2 and essentially compensates for the significantly wider optical band gap in relation to TiO2.

MOCVD를 이용한 BiSbTe3박막성장 및 열전소자 제작

Bismuth-antimony-telluride based thermoelectric thin film materials were prepared by metal organic vapor phase deposition using trimethylbismuth, triethylantimony and diisopropyltelluride as metal organic sources. A planar type thermoelectric device has been fabricated using p-type and n-type thin films. Firstly, the p-type thermoelectric element was patterned after growth of thickness of layer. Again n-type film was grown onto the patterned p-type thermoelectric film and n-type strips are formed by using selective chemical etchant for . The top electrical connector was formed by thermally deposited metal film. The generator consists of 20 pairs of p- and n-type legs. We demonstrate complex structures of different conduction types of thermoelectric element on same substrate by two separate runs of MOCVD with etch-stop layer and selective etchant for n-type thermoelectric material. Device performance was evaluated on a number of thermoelectric devices. To demonstrate power generation, one side of the device was heated by heating block and the voltage output was measured. The highest estimated power of 1.3 is obtained at the temperature difference of 45 K.

Fabrication of Bismuth Telluride-Based Alloy Thin Film Thermoelectric Devices Grown by Metal Organic Chemical Vapor Deposition

Bismuth-antimony-telluride based thin film materials were grown by metal organic vapor phase deposition (MOCVD). A planar-type thermoelectric device was fabricated with p-type Bi 0.4 Sb 1.6 Te 3 and n-type Bi 2 Te 3 thin films. The generator consisted of 20 pairs of p-type and n-type legs. We demonstrated complex structures of different conduction types of thermoelectric elements on the same substrate using two separate deposition runs of p-type and n-type thermoelectric materials. To demonstrate power generation, we heated one side of the sample with a heating block and measured the voltage output. An estimated power of 1.3 μW was obtained for the temperature difference of 45 K. We provide a promising procedure for fabricating thin film thermoelectric generators by using MOCVD grown thermoelectric materials that may have a nanostructure with high thermoelectric properties.

Characterization of Non-Polar ZnO Layers with Positron Annihilation Spectroscopy

We applied positron annihilation spectroscopy to study the effect of growth polarity on the vacancy defects in ZnO grown by metal-organic vapor phase deposition on sapphire. Both c-plane and a-plane ZnO layers were measured, and Zn vacancies were identified as the dominant defects detected by positrons. The results are qualitatively similar to those of earlier experiments in GaN. The Zn vacancy concentration decreases in c-plane ZnO by almost one order of magnitude (from high 10 cm−3 to low 10 cm−3) when the layer thickness is increased from 0.5 to 2 μm. Interestingly, in a-plane ZnO the Zn vacancy concentration is constant at a level of about 2×10 cm−3 in all the samples with thicknesses varying from 0.6 to 2.4 μm. The anisotropy of the Doppler broadening of the annihilation radiation parallel and perpendicular to the hexagonal c-axis was also measured.

Composition analysis of ternary semiconductors by combined application of conventional TEM and HRTEM

AbstractThe chemical composition of ternary material systems can be determined by a combined analysis of dark‐field imaging and quantitative high‐resolution transmission electron microscopy (qHRTEM). This method is restricted to material systems where on the one hand chemically sensitive reflections occur and on the other hand the material surrounding the nanostructure contains only those atomic species which are also present in the nanostructure. In the developed procedure the dark‐field image intensity is calculated as a function of chemical composition. Additionally, it is taken into consideration that the strained state of the system leads to a change of the symmetry. For analysing the chemically sensitive dark‐field images the composition must be normalized by a known concentration value. The method will be demonstrated for the following system: GaSbxAs1–x quantum dots (QDs) grown by metal‐organic chemical vapour phase deposition (MOCVD) on GaAs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mosaicity and stress effects on luminescence properties of GaN

AbstractHigh‐resolution X‐ray diffraction (HRXRD) of several GaN layers grown on Si/N treated c ‐plane sapphire substrate by metal‐organic chemical vapour phase deposition (MOCVD) were investigated. Photoluminescence (PL) measurements were carried out at 13 K. GaN mosaicity was studied at different growth stage with a thickness varying from 0.1 to 4.5 µm. Rocking curves of symmetric and asymmetric plane reflections were investigated to determine respectively the tilt and twist mosaic. Using PL spectra and HRXRD scattering a correlation were found between the intensity and the full width at half maximum (FWHM) of the bound exciton neutral donor (I2) with the GaN mosaicity. The I2 intensity increased significantly with increasing the interaction parameter (m) between tilt and twist mosaic, whereas the FWHM of I2 decreased with increasing m. The evolution of the compressive stress with thickness is extracted from HRXRD and correlated with PL measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)