Micro-Raman scattering in laterally epitaxial overgrown GaN

Abstract

In this study, micro-Raman spectroscopy has been used to investigate the vibrational properties of laterally epitaxial overgrown ͑LEO͒ GaN. The LEO GaN films were grown by metal organic chemical vapor deposition on a 2 in. sapphire substrate with SiN mask. Photoluminescence and polarized Raman scattering measurements have been performed in the two regions of GaN growth ͑wing and window regions͒. Raman scattering results are consistent with the lateral growth of GaN in the overgrown region. We have observed second-order Raman scattering in the wing and window regions of GaN. The observations of longitudinal optical phonon plasmon modes in the overgrown region demonstrate that LEO GaN is doped. We have carried out micro-Raman mapping of the local strain and free carrier concentration in the LEO GaN. Anharmonicity due to temperature in LEO GaN has also been investigated. The anharmonicity was found to increase with increasing temperature, and such temperature-induced anharmonicity introduces changes in the linewidth and line center position of the Raman active phonons. The phonon lifetimes in GaN are estimated in the LEO region as well as in the coherently grown region ͑window region͒.

Dislocation Reduction and Stress Relaxation of GaN and InGaN Multiple Quantum Wells with Improved Performance via Serpentine Channel Patterned Mask

“…Figure f shows the fluorescent microscopy image of the as-grown GaN surface. In contrast to the dark blue colored wing and window regions, light blue colored sharp and parallel lines are located in coalescent fronts, which are caused by the defect-related yellow band emission …”

“…Moreover, the wavelength of NBE peak gets shorter in the vicinity of the right and left edges of the top mask opening, while that in the middle of the top opening is longer and remains unchanged. The fact that NBE emission is shifted to higher energy can be explained by the Burstein–Moss effect, caused by the increased concentration of free carriers near the Si 3 N 4 and SiO 2 mask. ,, The CL line scanning from channel upward to surface, was employed to study the optical properties and residual strain. As clearly shown in Figure c, d, the fwhm of NBE peak becomes narrower and the intensity keeps increasing as GaN grows along the c -axis direction, while the (e–h) plasma and DAP peaks gradually disappear.…”

Structural modifications of GaN after cerium implantation

“…) point to the level of implantation‐induced damages. The increase in Raman line width also means the shortening of phonon life time, which indicates that probability of phonon scattering has been increased in GaN after implantation …”

Structural and optical properties of nearly stress-free m-plane ZnO film on (100) γ-LiAlO2 with a GaN buffer layer by metal-organic chemical vapor deposition

“…And the two peaks located at 534.6 cm À1 and 572.4 cm À1 in curve A are attributed to the A 1 (TO) and E 2 (high) modes of GaN, respectively [17]. For crystals with wurtzite structure like ZnO, the induced stress can be estimated by calculating the frequency shift of the E 2 (high) mode [20]. Using the pressure coefficient (5.2 Â 10 À9 cm À1 Pa À1 ) determined by Mitra et al [21], we calculated that the epitaxial ZnO film was under slight tensile stress, about 5.77 Â 10 7 Pa, which was much smaller than those of ZnO epilayers deposited on other substrates [22,23].…”