Improving low-temperature performance of infrared thin-film interference filters utilizing temperature dependence of refractive index of Pb 1-x Ge x Te

Abstract

Pb 1-x Ge x Te is a pseudobinary alloy of IV-VI narrow-gap semiconductor PbTe and GeTe, 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. A simple Fabry-Perot type narrow-bandpass filter was fabricated, in which Pb 0.94 Ge 0.06 Te was substituted for PbTe. It was found that the low-temperature stability of the filter is obviously improved: in the temperature range of 80-300 K, the shift of center wavelength with temperature is reduced from 0.48 nm.K -1 to 0.23 nm.K -1 ; furthermore, the peak transmittance of filter fabricated with Pb 0.94 Ge 0.06 Te is ~3% over that fabricated with PbTe.