Supporting Information for Using Visible Laser Based Raman Spectroscopy to Identify the Surface Polarity of Silicon Carbide Submitted by Yi-Chuan Tseng, a Yu-Chia Cheng, a Yang-Chun Lee, a Dai-Liang Ma, b Bang-Ying Yu b, Bo-Cheng Lin b, and Hsuen-Li Chen* a a Department of Materials Science and Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan b Materials and Electro-Optics Research Division, National Chung-Shan Institute of Science and Technology, P.O. Box 90008-8-1, Lungtan, Taoyuan 32599, Taiwan *Corresponding author E-mail: hsuenlichen@ntu.edu.tw Telephone: +886-2-3366-3240 S1
Contents 1. Measurements of more positions on SiC wafers 2. The determination of the intensity of the two FTA doublet modes 3. Identification of the surface polarity of SiC by using a Raman system having a 473 nm excitation laser S2
Measurements of more positions on SiC wafers To clearly prove that we can identify the surface polarity of SiC by visible light based Raman spectroscopy, we also measured the Raman signals from many positions on different 4H-SiC wafers. Figure S1 displays the photographs of the 4H-SiC wafers, named sample A to sample C. The grid points, numbers, and letters represent the measured positions. Figure S2 presents the Raman peak intensity ratios of the signals at 210 and 203 cm 1 obtained from the C and Si faces at the each position of the three 4H-SiC wafers. Obviously, we found that the peak intensity ratio of the signals at 210 and 203 cm 1 was always higher when measured on Si face than on the C face, for all positions on the three different SiC wafers. Therefore, the result provides clear and convincing evidence that we can identify the surface polarity of SiC by using visible laser based Raman spectroscopy. S3
Figure S1. Photographs of the 4H-SiC wafers measured in this study. S4
Peak intensity ratio(arb. unit) Peak intensity ratio(arb. unit) Peak intensity ratio (arb. unit) 10 9 8 7 6 bright dark Si C 1%-sample A 210/203 cm -1 5 4 3 11 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 a Position b c d 11 10 9 8 7 6 5 4 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Position bright 15 16 17 18 dark 1%-sample B 210/203 cm -1 a b c d Si C e f 10 9 8 7 6 bright dark Si C 1%-sample C 210/203 cm -1 5 4 3 1 2 3 4 5 6 7 8 9 10 11 12 Position 13 14 15 16 17 18 a b c Figure S2. The Raman intensity ratios of the signals at 210 and 203 cm 1 on the Si. S5
The determination of the intensity of the two FTA doublet modes As shown in Figure 5a and 5c, the Raman spectra of two FTA doublet modes do not display flat backgrounds. Therefore we took a simple baseline removal method (Figure S3) to determine the intensity of the two FTA doublet modes. Similar approach to determine the intensities of peaks was used in previous literature. S1 1. Take the Raman spectra in Figure 5c as an example, we first linearly fitted the Raman spectra of the background signals at both sides of the two FTA doublet modes, as the blue lines shown in Figure S3. 2. Then, we connected two close endpoints of blue lines to estimate a baseline, as the green line shown in Figure S3. 3. After the above operation, we can calculate the Raman intensities of the peaks at 203 and 210 cm -1 by subtracting an estimated baseline, as shown in Figure S3. REFERENCES (S1) Jiang, J. L.; Wang, Q.; Huang, H.; Zhang, X.; Wang, Y. B.; Geng, Q. F. Microstructure Evolution Induced by Ultraviolet Light Irradiation in Ti-Si Codoped Diamond-like Carbon films. J. Inorg. Mater. 2014, 29, 941-946. S6
Intensity(counts) excitation wavelength @ 532 nm, power = 1 % 16000 FTA 14000 (1) (3) (2) 12000 180 190 200 210 220 230 Raman shift (cm -1 ) Figure S3. The baseline removal method we adopted in this study to determine the intensities of the two FTA doublet modes. S7
Identification of the surface polarity of SiC by using a Raman system having a 473 nm excitation laser To confirm the idea of using visible laser to identify the surface polarity of SiC, we further employed another micro Raman system using a 473 nm excitation laser to confirm the measured results. Micro-Raman spectra of the SiC wafer were measured using a commercial micro-raman microscope (UniRAM, UniNanoTech) equipped with a monochromator having a focal length of 30 cm. The wavelength of the excitation laser line was fixed at 473 nm. The laser beam was focused by a 50 objective having a numerical aperture of 0.55. The power of the excitation laser was fixed at 100 mw. The spot size of the excitation laser was approximately 0.86 μm 2 ; the integration time was 75 s. Figure S4 displays a photograph of the micro-raman system having a 473 nm excitation laser. Figure S5 displays a Raman spectrum of 4H-SiC (sample A, position 1, Si face) obtained from an excitation laser having a wavelength of 473 nm with an attenuated intensity of 1%. The Raman spectrum also appeared two optical phonon peaks at 203 and 778 cm 1, corresponding to the FTA and FTO vibration modes of 4H-SiC, respectively. Figure S6 displays the FTA mode of a 4H-SiC wafer excited by a 473-nm laser with an attenuated intensity of 1%. Notably, the signal of the FTA mode still appeared of a doublet, with a sharp peak at 203 cm 1 and a weaker peak at S8
194 cm 1. To identify the surface polarity of SiC, we measured the Raman spectra of 18 positions in bright region and 4 positions in dark region, as displayed in the photograph of the 4H-SiC (sample A) in Figure S1. We observed and calculated the peak intensity ratios between the signals at 203 and 194 cm 1 at various positions, as displayed in Figure S7. We noted that the peak intensity ratios of the signals at 203 and 194 cm 1 were always higher when measured on Si face than on the C face, for all 22 positions (1 18 in bright region, a d in dark region). This feature is the same as the experimental result that we demonstrated by using an excitation laser having a wavelength of 532 nm. Figure S4. The photograph of the micro-raman system having a 473 nm excitation laser used to characterize the SiC wafers. S9
Intensity (count) 26000 24000 22000 20000 Si-face sample A position 1 FTO 18000 16000 FTA 14000 200 400 600 800 Wavenumber (cm -1 ) Figure S5. The Raman spectrum of 4H-SiC (sample A, position 1, Si face). S10
Intensity (count) 19000 18000 Si-face sample A position 1 17000 FTA 16000 15000 160 170 180 190 200 210 220 230 240 Wavenumber (cm -1 ) Figure S6. The FTA mode of a 4H-SiC wafer excited by a 473-nm laser. S11
Peal intensity ratio (a. u.) 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 dark Si face C face sample A 203 / 194 cm -1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 a b c d -- Position bright Figure S7. The Raman peak intensity ratios of the signals at 203 and 194 cm 1 obtained from the C and Si faces at the each position of the 4H-SiC wafer (sample A). S12