Raman scattering study of GaN nanostructures obtained by bottom-up and top-down approaches

Abstract

GaN nanocolumnar structures were grown by plasma-assisted molecular beam epitaxy (PAMBE) and also fabricated by electron cyclotron resonance reactive ion etching (ECR-RIE) of a compact GaN film parallel to the [111] direction of the Si(111) substrates. Scanning electron microscopy shows that the nanocolumns fabricated by PAMBE have a length of about 300-500 nm with diameters ranging from 20 to 150 nm while nanowhiskers formed by RIE have diameters of 40-80 nm and a height between 1.4 and 1.7 µm. A comparative study of the vibrational spectrum (including optical and interface phonons) of the nanostructures using conventional macro-Raman and micro-Raman scattering as well as surface-enhanced Raman scattering is presented.

Chemical Vapor Deposition of Diamond Films on Patterned GaN Substrates via a Thin Silicon Nitride Protective Layer

“…For the substrate, a Raman peak located at about 570 cm -1 was observed, which is assigned to E 2 (high) mode of GaN. 26,27 The full-width at half-maximum (fwhm) of the peak is about 4.2 cm -1 . After diamond deposition via different approaches, that is, nanodiamond (spectrum I) and microcrystalline diamond (spectrum II) film deposition using two-step process with an initial rapid growth stage, and the nanodiamond film deposition with addition of nitrogen in hydrogen-based plasma (spectrum III) and in Ar-based plasma (spectrum IV), the peak location and fwhm are almost identical to that before diamond deposition, indicating that the GaN underlayers are maintained intact after diamond deposition with our approaches.…”

Highly polarized Raman scattering anisotropy in single GaN nanowires

“…Details of the growth mechanism as well as optical and electrical characterization have been discussed elsewhere. 7,8,[19][20][21][22][23][24][25][26][27][28][29][30] The nanowires are single crystalline, 50-90 nm in diameter and up to 2 m in length. Raman spectra of the as grown samples, i.e., ensembles of GaN NWs, were measured in backscattering geometry using a laser wavelength of 514 nm and an excitation power of 25 mW.…”

Reactive plasma sputtering deposition of polycrystalline GaN thin films on silicon substrates at room temperature

“…The peaks of the A1(LO) mode at ~ 711 cm -1 are weak and deviate drastically with respect to the reference values of GaN at 735 cm -1 . Although the A1(LO) mode is allowed, literature suggests that a quantitative analysis with this peak is hardly possible unless an epitaxial GaN layer is deposited 38 . The blue shift of both the E2(high) and the A1(LO) mode from a typical crystalline GaN layer may be attributed to numerous factors such as the strain, inhomogeneity in the chemical composition and structural defects 39 .…”