Microstructure of Nonpolar a-Plane GaN Grown on (1120) 4H-SiC Investigated by TEM (original) (raw)
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Prismatic defects in GaN grown on 6H-SiC by molecular beam epitaxy
Materials Science and Engineering: B, 1997
The atomic structure of the prismatic defects in GaN layers grown on 6H-SiC by electron cyclotron assisted MBE has been determined. High resolution images have been matched to Drum's model, which, along the [OOOI] projection, corresponds to 8 and 4 atoms cycles. The i (1101) fault vector is parallel to the fault plane. 0 1997 Elsevier Science S.A.
Physical Review B, 2005
Conventional and high-resolution electron microscopy have been applied for studying lattice defects in nonpolar a-plane GaN grown on a 4H-SiC substrate with an AlN buffer layer. Samples in plan-view and cross-sectional configurations have been investigated. Basal and prismatic stacking faults together with Frank and Shockley partial dislocations were found to be the main defects in the GaN layers. High-resolution electron microscopy in combination with image simulation supported Drum's model for the prismatic stacking faults. The density of basal stacking faults was measured to be ϳ1.6ϫ 10 6 cm −1. The densities of partial dislocations terminating I 1 and I 2 types of intrinsic basal stacking faults were ϳ4.0ϫ 10 10 cm −2 and ϳ0.4ϫ 10 10 cm −2 , respectively. The energy of the I 2 stacking fault in GaN was estimated to be ͑40± 4͒ erg/ cm 2 based on the separation of Shockley partial dislocations.
Influence of 4H-SiC substrate miscut on the epitaxy and microstructure of AlGaN/GaN heterostructures
Materials Science in Semiconductor Processing, 2019
AlGaN/GaN heterostructures were grown on "on-axis" and 2° off (0001) 4H-SiC substrates by metalorganic vapor phase epitaxy (MOVPE). Structural characterization was performed by transmission electron microscopy. The dislocation density, being greater in the on-axis case, is gradually reduced in the GaN layer and is forming dislocation loops in the lower region. Steps aligned along [11 ̅ 00] in the off-axis case give rise to simultaneous defect formation. In the onaxis case, an almost zero density of steps is observed, with the main origin of defects probably being the orientation mismatch at the grain boundaries between the small not fully coalesced AlN grains. V-shaped formations are observed in the AlN nucleation layer, but are more frequent in the off-axis case, probably enhanced by the presence of steps. These V-shaped formations are completely overgrown by the GaN layer, during the subsequent deposition, presenting AlGaN areas in the walls of the defect, indicating an inter-diffusion between the layers. Finally, at the AlGaN/GaN heterostructure surface in the on-axis case, V-shapes are observed, with the AlGaN (21% Al) thickness exceeding the critical for relaxation thickness. On the other hand, no relaxation in the form of V-shape creation is observed in the off-axis case, probably due to the smaller AlGaN thickness (less than 21% Al). The AlN spacer layer, grown in between the heterostructure, presents a uniform thickness and clear interfaces.
The volume expansion of the {112̄0} planar defect in 2H–GaN/6H–SiC (0001)Si grown by MBE
Thin Solid Films, 1998
Ä 4 In an attempt to complete the determination of the atomic structure of the 1120 planar defects which are found systematically in the Ž. interfacial area of 2H GaN-AlNr6H-SiC, high resolution electron microscopy and atomistic calculations were used and an adequate ² :Ä 4 model was chosen. It is found that the atomic structure corresponds to the ideal 1r2 1101 1120 stacking fault model, with no volume expansion.
TEM Study of the Morphology Of GaN/SiC (0001) Grown at Various Temperatures by MBE
MRS Proceedings, 1999
GaN films grown on SiC (0001) by MBE at various substrate temperatures (600° - 750° C) were characterized by RHEED, STM, x-ray diffraction, AFM and TEM. This work focuses on the TEM analysis of the films' features, such as stacking faults and dislocations, which are related to the substrate temperature. There are several basal plane stacking faults in the form of cubic inclusions for samples grown at low temperatures compared to those grown at high temperatures. The dislocation density is greatest for the film grown at 600°C, and it steadily decreases with increasing growth temperatures. Despite the presence of various defects, x-ray analysis shows that the GaN films are of high quality. The double crystal rocking curve full width at half maximum (FWHM) for the GaN (0002) peak is less than 2 arc-minutes for all of the films we measured and it decreases with increasing growth temperature.
Studies of Defect Structure in Epitaxial AlN/GaN Films Grown on (111) 3C-SiC
Nanomaterials
Several aspects such as the growth relation between the layers of the GaN/AlN/SiC heterostructure, the consistency of the interfaces, and elemental diffusion are achieved by High Resolution Transmission Electron Microscopy (HR-TEM). In addition, the dislocation densities together with the defect correlation lengths are investigated via High-Resolution X-ray Diffraction (HR-XRD) and the characteristic positron diffusion length is achieved by Doppler Broadening Spectroscopy (DBS). Moreover, a comparative analysis with our previous work (i.e., GaN/AlN/Si and GaN/AlN/Al2O3) has been carried out. Within the epitaxial GaN layer defined by the relationship F4¯3m (111) 3C-SiC || P63mc (0002) AlN || P63mc (0002) GaN, the total dislocation density has been assessed as being 1.47 × 1010 cm−2. Compared with previously investigated heterostructures (on Si and Al2O3 substrates), the obtained dislocation correlation lengths (Le = 171 nm and Ls =288 nm) and the mean distance between two dislocation...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1995
Transmission electron microscopy was used for the characterization of GaN epitaxial layers grown by molecular-beam epitaxy on two different substrates: sapphire ͑Al 2 O 3 ͒ and 6H-SiC. GaN layers grown on both substrates crystallize with the wurtzite structure. Despite the very different lattice mismatch associated with their two substrates, similar types of defects were formed in the GaN layer; only their density differed. In addition to small-angle subgrain boundaries two other types of defects were seen in cross-sectioned samples: defects parallel to the growth surface and microtwins with a width of about 8 -10 nm perpendicular to the growth surface. The parallel defects were identified as stacking faults leading to a local fcc atom arrangement in the layer and are believed to be growth defects. The density of these faults decreased with layer thickness. However, the density of the vertical microtwins remained constant through the layer. Slight local lattice twists between the microtwins and surrounding areas or differences of stoichiometry are suggested as an explanation for the observed contrast of the high-resolution images.
Mosaic Defects of AlN Buffer Layers in GaN/AlN/4H-SiC Epitaxial Structure
Politeknik Dergisi, 2020
Structural properties of AlN buffer layers, grown by Metal Organic Chemical Vapor Deposition (MOCVD) on 4H-SiC substrate with thicknesses of 61.34, 116.88, 129.46 and 131.50 nm, are investigated by High Resolution X-Ray Diffraction (HR-XRD) technique. Interfacial roughness of AlN buffer layer was determined by XRR technique. The interface roughness value of 131.50 nm thick sample is determined as 0.50 nm. Mosaic defects, tilt angle, vertical and lateral coherence lengths are characterized by HR-XRD technique. The edge and screw dislocations of the 131.50 nm thick sample are found as 2.98x1010 and 8.86x108 cm-2 respectively. The results indicate that 131.50 nm thick AlN buffer layer should be used in order to gain high performance in optoelectronic terms in this study. Thus, optimization of AlN buffer layer thickness is extremely important in device performance.
The structure of GaN layers grown on SiC and sapphire by molecular beam epitaxy
Materials Science and Engineering: B, 1997
A comparative study of the defects at the interfaces and inside the layers was carried out in GaN/AlN epitaxial layers on SiC and sapphire. Whereas surface cleaning of the sapphire substrates is rather standardised now, the SiC substrates cleaning is still to optimise conditions, as the high densities of defects inside the epitaxial layers cannot be explained solely by the 3.54% lattice mismatch. The investigated specimens were grown by molecular beam epitaxy (MBE), either assisted by electron cyclotron resonance or an NH 3 gas source system to provide atomic nitrogen. Assuming that MBE is a growth technique more or less close to equilibrium, the observed defects are interpreted and a growth mechanism, for GaN layers on the stepped (0001) SiC and sapphire surfaces, is proposed. © 1997 Elsevier Science S.A.