Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction (original) (raw)
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Strain Modification of GaN in AlGaN/GaN Epitaxial Films
Japanese Journal of Applied Physics, 1999
We investigated AlGaN/GaN heterostructures grown by metal-organic vapor-phase epitaxy on sapphire by calorimetric absorption, transmission and reflection spectroscopy (CAS/CTS/CRS) at 47 mK. The AlGaN film on a 2-µm-thick GaN layer introduces additional compressive strain into the GaN layer. A blue shift of the A-and B-exciton line positions is directly proportional to the AlN molar fraction in the films. The amount of strain in the GaN layers is quantified by micro-Raman experiments. We can explain the results by taking into account the elastic properties of GaN and AlGaN.
Mapping strain gradients in the FIB-structured InGaN/GaN multilayered films with 3D X-ray microbeam
This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence (-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation of complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent.
physica status solidi (a), 2006
Intrinsic stresses due to lattice mismatch, high densities of threading dislocations, and extrinsic stresses resulting from the mismatch in the coefficients of thermal expansion, are present in almost all III-Nitride heterostructures. Stress relaxation in the GaN layers occurs in conventional, cantilever (CE) and in pendeo-epitaxial (PE) films via the formation of additional misfit dislocations, domain boundaries, elastic strain and wing tilt. Polychromatic X-ray microdiffraction, high resolution monochromatic X-ray diffraction and SEM analysis have been used to determine the crystallographic properties, misfit dislocations distribution and crystallographic tilts in uncoalesced GaN layers grown by PE and CE. The crystallographic tilt between the GaN(0001) and Si(111) planes was detected in the CE grown samples on Si(111). In contrast there was no tilt between GaN(0001) and SiC(0001) planes in PE grown samples. The wings are tilted upward for both the PE and CE grown uncoalesced GaN layers.
Grazing-incidence x-ray diffraction from GaN epitaxial layers with threading dislocations
Applied Physics Letters, 2011
We used high-resolution x-ray reciprocal space mapping in noncoplanar grazing-incidence geometry for the determination of the density of edge threading dislocations in c-oriented GaN epitaxial layers and we compared the measured intensity distributions with results of numerical Monte Carlo simulations of diffuse scattering. We demonstrated that a combination of diffraction data taken in coplanar symmetric and noncoplanar grazing-incidence geometries makes it possible to obtain the densities of screw and edge threading dislocations.
High resolution X-ray diffraction and X-ray topography study of GaN on sapphire
Materials Science and Engineering: B, 1999
High resolution X-ray diffraction and X-ray topography study of GaN thin films, grown on sapphire (11.0) substrate by reduced pressure metalorganic vapor phase epitaxy (MOVPE) under various conditions, were performed. The strained lattice parameters, stress, misorientation and dislocation density of GaN films were estimated. The experimental stress compares well with the theoretical stress obtained from the difference in the thermal expansion coefficient between the film and substrate. The dislocation density was found to be highest in the thinner GaN film. It was also higher in the film without any buffer layer. For the same carrier concentration, the mobility of one of the film was lower than the other which could be due to the presence of higher dislocation density. Slip lines associated with dislocations, stacking faults, cellular structure of dislocations and double positioning boundaries were found in the X-ray topography from the GaN films.
Current Applied Physics, 2009
In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(1 1 1) substrates by metal-organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(1 1 1) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(1 1 1) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 lm. Secondly, the effect of in situ substrate nitridation and the insertion of an Si x N y intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the Si x N y layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without Si x N y layer) and B (with Si x N y layer on ). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0 0 0 2) diffraction from the GaN epilayer of the sample B in x-scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a Si x N y intermediate layer significantly improved the optical and structural properties. In sample C (with Si x N y layer on Al 0.11 Ga 0.89 N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties.
Materials Science in Semiconductor Processing, 2013
The strain analysis of GaN film on nitridated Si(111) substrate with different growth times between 0 and 660 s via metal organic chemical vapor deposition (MOCVD) was conducted based on the precise measurement of the lattice parameters by using highresolution X-ray diffraction (HR-XRD). The nitridation time (NT) was changed at a fixed growth condition. The a-and c-lattice parameters were measured, followed by the in-plane and out-of-plane strains. Then, the biaxial and hydrostatic components were extracted from the total strain values obtained, and were then discussed in the present study as functions of the NT. The biaxial strain and stress are also strongly affected by the non-uniformity of the SiN x buffer layer thickness.