Pb1-xGexTe is a pseudobinary alloy of IV–VI narrow-gap semiconductor, of which maximum refractive index corresponds to the ferroelectric phase transition. Since the temperature coefficient of refractive index can be tunable from negative to positive by changing the Ge composition, it is possible to utilize the intrinsic property in the fabrication of infrared thin-film interference filters. In this letter, we report a narrow-bandpass filter, in which Pb0.94Ge0.06Te was substituted for PbTe. It found that the low-temperature stability of the filter is obviously improved: in the temperature range of 80-300K, the shift of center wavelength with temperature is reduced from 0.48nm. K-1 to 0.23nm K-1; furthermore, the peak transmittance of filter fabricated with Pb0.94Ge0.06Te is ~3% over that fabricated with PbTe.
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