Infrared Attenuation Spectrum of Bulk High-Resistivity CdZnTe Single Crystal in Transparent Wavelength Region Between Electronic and Lattice Absorptions

Abstract

We report measurement of the internal attenuation coefficient, $$\alpha _{att}$$ , of a bulk high-resistivity cadmium zinc telluride (CdZnTe) single crystal at wavelength, $$\lambda$$ = 0.84–26 $$\mu$$ m, to the unprecedentedly low level of $$\alpha _{att}$$ $$\sim$$ 0.001 cm $$^{-1}$$ . This measurement reveals the spectral behavior for small attenuation in the infrared transparent region between the electronic and lattice absorptions. This result is essential for application of CdZnTe as an infrared transmitting material. Comparing the attenuation spectrum with model spectra obtained on the basis of Mie theory, we find that sub-micrometer-sized Te particles (inclusions) with a number density of approximately 10 $$^{7.5-9}$$ cm $$^{-3}$$ are the principal source of the small attenuation observed at $$\lambda$$ = 0.9–13 $$\mu$$ m. In addition, we determine $$\alpha _{att}$$ = $$(7.7 \pm 1.9) \times 10^{-4}$$ cm $$^{-1}$$ at $$\lambda$$ = 10.6 $$\mu$$ m, which is valuable for CO $$_2$$ laser applications. Higher transparency can be achieved by reducing the number of inclusions rather than the number of precipitates. This study also demonstrates that high-accuracy measurement of CdZnTe infrared transmittance is a useful approach to investigating the number density of sub-micrometer-sized Te particles that cannot be identified via infrared microscopy.