Most modern IR photodetectors based on Hg_1-xCd_xTe narrow-gap semiconductors are manufactured from LPE- and MBE-films grown on CdTe and Cd_1-yZn_yTe substrates. The energy gap of these ternary compounds is a function of the cadmium atomic concentration x. Precise determination of the composition grading is extremely essential for monitoring the material quality and predicting the photoelectrical properties of Hg_1-xCd_xTe-based infrared detectors.
The Hg_1-xCd_xTe epilayers (12-25 mkm thickness) with different Cd concentrations x, p- and n-type conductivity were investigated. The thickness of the layers was determined, using high-resolution light microscope and interference optical methods. The temperature dependence of the minority carrier lifetime were measured. To determine the value of x, the composition profile x and the calculation of the cutoff wavelength at 80 K were carried out the experimental and theoretical studying of the optical transmission spectra at room temperature by two different methods. In the case of MBE-layers the composition grading is absent, but in LPE-layers case there is non-linear composition grading. This data were confirmed by independent SIMS - measurements of the LPE and MBE films. The photocurrent investigations of the photoresistors prepared on the Hg_1-xCd_xTe epilayers confirmed that cutoff wavelength corresponds to the composition, measured by the optical methods.

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