Semiconductors which exhibit a very rapid transition from opacity to transparency at the intrinsic edge are particularly
useful in making excellent absorption filters. In this paper, we report the investigation on composition dependence of
absorption edges in the evaporated Pb1-xGexTe thin films, which will be of a potentiality to fabricate a single-layer
infrared short-wavelength cutoff filter by means of controlling the composition and processes. It is revealed that for
thin films with an identical Te concentration, the absorption edges will shift towards short-wavelength with the increase
of Ge concentration x in films; whereas, for those with a similar Ge concentration within a small range of deviation, the
edges will also shift towards the short-wavelength with Te concentration approach to stoichiometry.ÿÿ
PbTe based semiconductors are well-known narrow gap IV-VI compounds, which are of interest due to potential application in the fabrication of photo-detectors in the mid- and far infrared spectral range. Among them, Pbl−xGexTe is known to have wider band gap than PbTe, which has been used to fabricate photo-detectors with shorter wavelength (λ<6.7 μm). However, the homogeneity of composition in evaporated Pbl−xGexTe thin films directly from bulk alloys has not been investigated. In the paper, we report the investigation that the homogeneity of composition on the surface was studied using energy-dispersive X-ray analysis (EDAX), and the compositional depth profiles was investigated using Auger electron spectroscopy (AES) in combination with argon ion sputtering. ASE depth profiling and characterization of details in the Ge concentration gradient is demonstrated.
The degeneration of performance of an optical thin-film interference filter associated with the change of temperature is not acceptable. In this letter, we report a new progress in improving low-temperature performance of infrared narrow-band filters by using Pb1-xGexTe initial bulk alloy with appropriate Ge concentration x. It can be found that there exists a critical temperature for the investigated narrow-band filter, at which the temperature coefficient of filter is exactly zero. Therefore, by means of controlling the composition in (Pb1-xGex)1-yTey layers, the temperature coefficient of filter can be tunable at the designated low-temperature. In our present investigation, when temperature varies from 300 to 85 K, a shift of peak wavelength of 0.05935 nm.K-1 has been achieved.
Pb1-xGexTe 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 Pb0.94Ge0.06Te 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 Pb0.94Ge0.06Te is ~3% over that fabricated with PbTe.
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