Optical and structural properties of AlN thin films deposited on different faces of sapphire substrates

Abstract

We report the comprehensive spectroscopic results of AlN thin films deposited on the A-, R- and C-surfaces of sapphire substrates by radio frequency magnetron sputtering. The optical and structural properties of the epitaxial-grown AlN films were characterized using various techniques of high-resolution x-ray diffraction spectroscopy, x-ray photoelectron spectroscopy, Raman scattering spectroscopy, spectroscopic ellipsometry and associated analytical tools. Our large number of measurement results clearly show that sapphire substrates of different polarities have effects on the surface roughness, dislocation density, grain size, microstrain, and surface oxygen binding capacity of the film grown on its surface. The results obtained from Ellipsometry measurements show that the thickness, band gap and roughness of AlN films grown on C-plane sapphire are the smallest among the three samples. After careful analyses of the variable temperature Raman spectra, as the temperature rises from 80 K to 800 K, the AlN film has always exhibited tensile stress. In the same temperature range, the tensile stress of the AlN film grown on the C-plane sapphire has the greatest effect with temperature. The lifetime of E2 (high) phonons gradually decays with the increase of temperature.

A comparative investigation of the optical properties of polar and semipolar GaN epi-films grown by metalorganic chemical vapor deposition

“…Figure 14 shows varying-temperature Raman spectra of GaN samples 4c and 4m in a measurement temperature range of 80-800 K [37,38] and wavelength range of 500-800 cm −1 . Excitation wavelength used is 532 nm.…”

“…Excitation wavelength used is 532 nm. Sum of the half-widths of E 2 (high) Raman modes is used to evaluate grain size and residual strain [38]. With increased temperature, the E 2 (high) vibrational mode gradually shifts to a lower wave number and the FWHM value gradually increases [40,41].…”

“…Spreading phenomenon of the scattering peak is caused by a combination of phonon attenuation and impurities and defects. Variation in Raman spectra and peak-shift ω(T) changes with the temperature ω(T) can be fitted by equation ( 9) [38]:…”

Angle-Resolved Intensity of Polarized Micro-Raman Spectroscopy for 4H-SiC

“…The polarization states of O light and E light in the crystal are expressed in Equation (8). Because the basis vectors are e 1 = (100), e 2 = (010), and e 3 = (001) in the sample coordinate system X-Y-Z, the crystal Jones matrix is inferred in the sample coordinate system X-Y-Z [18], as shown in Equation (9).…”

“…Due to its nondestructive, noncontact, in situ, and highly sensitive characteristics, Raman spectroscopy has been successfully applied to the field of semiconductor materials and two-dimensional materials [4][5][6]. The Raman spectra of semiconductor crystals contain structural and physical information, including crystal orientation [7], doping [8], grain size [9], stress/strain [10], and electron mobility [11]. Therefore, these properties can be characterized by quantitative analysis of the intensity, wavenumber, full width at half maximum (FWHM), and symmetry through the Raman spectra of the samples.…”