Vacuum coating machine manufacturers introduce the wavelength of coating control mode
Vacuum coating machine, the manufacturer of vacuum coating machine introduced that the film material we use is SiNO series material. Figure 1 shows the experimental results obtained by coating SiN film. Curve 1 is the reflectance spectrum of the epitaxial wafer before coating. Curves 2 and 3 correspond to the case where the film thickness is 95 nm and 135 nm, respectively. The film thickness is measured by ellipsometer. It can be seen from curve 1 that the e-lh peak of the film is at 840 nm, the e-hh peak is at 848 nm, and the position of the mode wavelength is at 832 nm. For normally-on modulators, the position of the mode wavelength should be in the long wavelength direction of the e￣hh peak; for normally-off devices, the position of the mode wavelength should be near the e-hh peak, and the top must be coated with an anti-reflection coating, otherwise the device It will work in the saturation region, reducing the modulation characteristics of the device. Due to the inappropriate position of the mode wavelength, the method of coating SiNO anti-reflection film was used to shift the mode wavelength.
Vacuum coating machine, vacuum coating machine manufacturer introduction It can be seen from the reflection spectrum of curve 2 with a thickness of 95 nm that the mode wavelength has shifted, but due to the decrease of the surface reflectivity, the resonance absorption of the ASFP cavity is weaker than the exciton absorption. , so no obvious mode wavelength position can be seen on the curve. Measured by ellipsometer, it can be seen that the refractive index of the film is about 1.8, and the theoretical calculation shows that the mode wavelength is shifted by about 10 nm and is about 842 nm. After coating, the reflectivity at the e-hh peak is significantly reduced. At this time, although the mode wavelength is not at the e-hh peak position, the reflectivity near the e-hh peak is greatly reduced because the mode wavelength is relatively close to the exciton peak.
According to the reflection spectrum of curve 3 with a film thickness of 135 nm, compared with the mode wavelength before coating, the mode wavelength after coating is reduced instead, from the original 832 nm to 820 nm. The refractive index of the film layer is 1.8. From the above theoretical analysis, when the refractive index is 1.8 and the film thickness increases to 135 nm, the mode wavelength will drop by about 10 nm. Curve 3 should belong to this situation.
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