M Benyoucef

Raman mapping of epitaxial lateral overgrown GaN: Stress at the coalescence boundary

Using micro-Raman scattering spectroscopy we have investigated stress fields in epitaxial lateral overgrown (ELO) GaN fabricated by metalorganic vapor phase epitaxy using a two-step growth method. The presence of an increased compressive stress at the coalescence boundary of two adjacent wings of ELO GaN was identified. From changes in the E2 (high) phonon frequency we estimate the magnitude of the stress concentration at the coalescence boundary to be on the order of ≈0.07 GPa with respect to the ELO GaN wing. Mechanisms for the stress concentration at the coalescence boundary were studied. Differences in stress and crystalline quality between wing and window regions of ELO GaN were also investigated.

Raman mapping, photoluminescence investigations, and finite element analysis of epitaxial lateral overgrown GaN on silicon substrates

Epitaxial lateral overgrown (ELO) GaN grown by metalorganic vapor phase epitaxy on Si substrates was characterized using Raman mapping, photoluminescence (PL) experiments and finite element (FE) analysis. Stress in the structures was determined from the E2 phonon frequency and compared to FE results. Low temperature PL spectra are dominated by donor bound exciton (DBE) emission at (3.457–3.459) eV. PL spectra reveal a peak at ∼3.404 eV in window regions attributed to structural defects in the GaN. Differences in crystalline quality between window and overgrown regions of ELO GaN were investigated.

Raman scattering and photoluminescence studies on Si/SiO2 superlattices

Photoluminescence and Raman scattering experiments were performed on Si/SiO2 superlattices grown by radio frequency magnetron sputtering on Si, quartz and glass substrates. Increasing the Si layer thickness in the Si/SiO2 superlattice gave rise to an increased photoluminescence signal and a Raman signature for nanocrystalline Si. Annealing the superlattice at 1000 °C in nitrogen atmosphere also resulted in a significantly increased photoluminescence intensity that correlated with the formation of nanocrystalline Si in the Si/SiO2 superlattice. Relationships between the emergence of nanocrystalline Si and changes in the photoluminescence properties of Si/SiO2 superlattices are discussed.

Nano‐Fabrication of GaN Pillars Using Focused Ion Beam Etching

Focused ion beam etching was used for the nano-fabrication of GaN. GaN pillars as small as 20 to 30 nm in diameter were fabricated. Using secondary electron imaging, the quality of the GaN pillars was investigated as function of the gallium ion beam current used for the etching. Gallium ion beam currents as low as 1 to 4 pA are needed to fabricate nanometer-size GaN structures.

Finite element analysis of epitaxial lateral overgrown GaN: Voids at the coalescence boundary

We report on the finite element analysis of stress distribution at the coalescence boundary in epitaxial lateral overgrown (ELO) GaN related to voids. Different void geometries were considered in our model to investigate the influence of their size/shape on the stress distribution. Large compressive stress is localized in the vicinity of the voids, also an increased tensile stress is present at the corners of the SiN mask. Confocal micro-Raman mapping experiments confirm the presence of increased stress at the coalescence boundary of ELO GaN.

Raman mapping investigations and finite element analysis of double epitaxial lateral overgrown GaN on sapphire substrates

Double epitaxial lateral overgrown (D–ELO) GaN grown by metalorganic vapor phase epitaxy on sapphire substrates was characterized using Raman mapping and finite element analysis. Reductions in stress variations at the D–ELO top surface with respect to single ELO GaN were achieved. Stress near the top surface was mainly attributed to the presence of voids on top of the upper dielectric mask.

Raman scattering, photoluminescence and X-ray diffraction studies of GaN layers grown on misoriented sapphire substrates

Abstract Photoluminescence, Raman scattering and X-ray diffraction experiments were performed on GaN films grown by metalorganic chemical vapor deposition on misoriented sapphire substrates. Sapphire substrates misoriented up to 6° from the a-plane were used in this study. An increased photoluminescence intensity was observed for layers grown on substrates having miscut angles of ∼3° indicating improvements in the crystalline quality, supported by X-ray diffraction and Raman scattering results. The GaN layers also show a minimum in compressive stress when grown on ∼3° misoriented sapphire substrates.

Stress at the Coalescence Boundary of Epitaxial Lateral Overgrown GaN

We have investigated stress fields in epitaxial lateral overgrown (ELO) GaN fabricated by metalorganic vapor phase epitaxy. An increased compressive stress was found at the coalescence boundary of two adjacent wings of ELO GaN using confocal micro-Raman spectroscopy. Voids present at the coalescence boundary were identified as major source for this stress concentration. Stress concentration in the vicinity of voids was illustrated using finite element analysis. Differences in stress and crystalline quality between wing and window areas of ELO GaN were also investigated.

Focused Ion Beam Etching of Nanometer-Size GaN/AlGaN Device Structures and their Optical Characterization by Micro-Photoluminescence/Raman Mapping

The authors report on the nano-fabrication of GaN/AlGaN device structures using focused ion beam (FIB) etching, illustrated on a GaN/AlGaN heterostructure field effect transistor (HFET). Pillars as small as 20nm to 300nm in diameter were fabricated from the GaN/AlGaN HFET. Micro-photoluminescence and UV micro-Raman maps were recorded from the FIB-etched pattern to assess its material quality. Photoluminescence was detected from 300nm-size GaN/AlGaN HFET pillars, i.e., from the AlGaN as well as the GaN layers in the device structure, despite the induced etch damage. Properties of the GaN and the AlGaN layers in the FIB-etched areas were mapped using UV Micro-Raman spectroscopy. Damage introduced by FIB-etching was assessed. The fabricated nanometer-size GaN/AlGaN structures were found to be of good quality. The results demonstrate the potential of FIB-etching for the nano-fabrication of III-V nitride devices.