CdTe is widely used for fabrication of solar cells, X-ray and gamma-ray detectors. All these applications are based on the manipulation with incoherent carriers (i.e., carriers that do not have any definite phase relationship among themselves). Recently, however, also the coherent regime in semiconductors attracts a lot of attention due to the envisioned applications in the fields of quantum computing and spintronics. Here we report on the measurements of the carrier dephasing (i.e., loss of orbital coherence) using a self-diffraction technique of the ultrafast laser spectroscopy. The samples were thin platelets prepared from undoped bulk CdTe. We concentrated on the measurements in two samples that differ only in the preparation procedure - one was mechanically polished and the other was polished and also chemically etched. The etching leads to removal of several micrometers of CdTe from the polished surface and, consequently, to considerably lower concentration of preparation induced dislocations. The thickness of both samples was about 1 μm. We observed that the increased concentration of defects leads to a pronounced acceleration of carrier dephasing. The characteristic time constants describing the decay of the measured signal in the etched sample at 10 K are 1.3 ps for excitons and 0.34 ps for free carriers while these time constants are shorter than the time resolution of our experiment (0.08 ps) in the polished sample. The dephasing time of free carriers in the etched sample is a non-monotonous function of the lattice temperature, and above 100 K it is dominated by an interaction with optical phonons. We also observed that the dephasing of spin coherence is considerably slower than that of orbital coherence - the characteristic decay times are 60 ps for excitons and 150 ps for electrons in the etched sample at 10 K. This shows that the spin coherence is rather appealing for applications where long coherence times are essential.

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