Analysis of strain in GaN and SiC films by Raman-scattering spectroscopy

• Main Authors: Pei-Chun Chung, 鍾佩君
• Other Authors: Hsiang-Lin Liu
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/12394676326439502290

碩士 === 國立臺灣師範大學 === 物理學系 === 100 === We present Raman-scattering studies of structural phases in GaN and 3C-SiC films. Cross-sectional Raman spectra are also used to detect the depth dependence of residual strain in both films. First, the Raman spectrum of 7.6 micrometre-thick GaN film shows two phonon modes at about 569 cm-1 and 739 cm-1, corresponding to E2(high) and A1(LO) symmetries. While the cross-sectional spectrum exhibits five first-order Raman modes at about 143 cm-1, 531 cm-1, 558 cm-1, 567 cm-1 and 740 cm-1 having symmetries E2(low), A1(TO), E1(TO), E2(high) and E1(LO). These results reflect the characteristics of wurtzite phase of GaN film. The TO and LO phonon modes are observed at about 796.1 cm-1 and 970.5 cm-1 in different configurations of 5.0 micrometre-thick 3C-SiC film, indicating its cubic structure. Second, we found that the peak positions of E2(high) and TO phonon modes exhibit a blueshift as one probes deeper from the surface into the sample toward the substrate in 7.6 micrometre-thick GaN film and 5.0 micrometre-thick 3C-SiC film, respectively. In contrast, the E2(high) phonon mode shows a redshift in 4.0 micrometre-thick GaN film and other Si-doped GaN films. The above data indicate two implications: (i) the blueshift observed in E2(high) phonon mode of GaN film is mainly due to the effect of lattice mismatch between film and substrate, while the redshift arises from the effect of thermal coefficient; (ii) the blueshift observed in TO phonon mode of 3C-SiC film is likely associated with different deposition conditions of the films. Finally, the values of strain on the interface between GaN film and sapphire substrate are ranging from 8.0 × 10-4 to 1.16 × 10-3. In the case of 3C-SiC film, it is about 1.78 × 10-4.