Abstract
Zinc selenide (ZnSe) is a promising mid-infrared waveguide material with a high refractive index and wide transparency. Optical quality ZnSe thin films were deposited on silicon substrates by RF sputtering and thermal evaporation, and characterized and compared for material and optical properties. Evaporated films were found to be denser and smoother than sputtered films. Rib waveguides were fabricated from these films and evaporated films exhibited losses as low as 0.6 dB/cm at wavelengths between 2.5 µm and 3.7 µm. The films were also used as isolation/lower cladding layers on Si with GeTe4 as the waveguide core and propagation losses were determined in this wavelength range.
Highlights
Zinc selenide (ZnSe) is a chemically stable and non-hygroscopic group II-VI metal chalcogenide which possesses many useful semiconducting and optical properties, making it an important optoelectronic material
Low-loss waveguides have been realized in ZnSe substrates by methods such as diamond dicing [6], laser writing [7], proton implantation [8] and a macroscopic Fourier transform infrared-attenuated total reflection (FTIR-ATR) waveguide element has been used for the detection of DNA hybridization [9]
Studies of the microstructure of thin ZnSe films deposited on Si [13], of the influence of substrate heating on structural, optical and electronic properties of the ZnSe film deposited on Si [12,14,15], of UV to IR ellipsometry of ZnSe films deposited on Si [16] and of epitaxial film of ZnSe deposited on Si by MBE [17] have been reported
Summary
Zinc selenide (ZnSe) is a chemically stable and non-hygroscopic group II-VI metal chalcogenide which possesses many useful semiconducting and optical properties, making it an important optoelectronic material. In this paper, we report the deposition of ZnSe films of thicknesses between 1.9 and 4.5 μm on Si substrates by thermal evaporation and sputtering. The ZnSe film is used as a waveguide core on oxidized silicon and as a lower cladding layer on Si, with GeTe4 as the waveguide core for the MIR. The optical quality of evaporated and sputtered ZnSe was tested as a waveguide core and as a lower cladding/isolation layer on Si with a higher refractive index (GeTe4, n~3.3) core. In order to keep the chamber pressure below 5x10-5, the deposition was performed in steps, depositing 1 μm thick film at a time and leaving the samples inside the chamber at 250°C for approximately one hour to allow the pressure to fall again, before starting the deposition step This is equivalent to vacuum annealing of the samples to release thermal stresses built during the formation of the film. Sputtered ZnSe film samples cracked after annealing under similar annealing conditions to evaporated samples (See Appendix 1.1) and so the annealing step was omitted for sputtered samples
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