Effect of Mn concentration on the polar optical phonons frequencies in Cd1− xMnxTe thin films

Abstract

Cd1−xMnxTe (CMT) is a wide bandgap semiconductor that stands out among the ternary compounds in several industrial applications, such as optoelectronic and solar cell devices. Therefore, it is worth understanding the mechanisms of light interaction with CMT produced by growth techniques. In this work, we investigate the room temperature Raman scattering by longitudinal optical phonon modes CdTe-like (LO1) and MnTe-like (LO2) in CMT thin films grown on Si(111) by molecular-beam epitaxy. The well-known linear dependence of LO1 and LO2 frequencies on x is observed in Raman spectra when the excitation photon energy is above the bandgap energy. As expected, for the excitation energy of the incident laser line near the fundamental gap of CMT, the resonance becomes evident in the Raman results. However, for a specific resonance condition due to tuning of the bandgap energy dependence on Mn concentration, the frequencies of the LO1 and LO2 phonon modes remain constant as the average manganese concentration increases to values x≳ 0.30. From micro-photoluminescence spectroscopy investigations, we concluded that for Mn concentration above 0.3, a broad range of optical transitions provides the required conditions for a resonant Raman scattering selected by the incident photon energy. It introduces a resonant selectivity of regions where the incident excitation energy coincides with a bandgap energy associated with a specific value of x, even for samples with nominally different compositions. The results show the sensitivity of resonant Raman to express diagnostics of ternary compound growth.