Raman characterization of Hg1−xCdxTe and related materials

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Abstract
We report Raman scattering (RS) measurements from Hg1−xCdxTe (x≊0.2) and related materials HgTe, Hg1−xMnxTe (x≊0.1 and band gap ∼100 meV at 77 ° K) at 77 °K and Br/methanol polished 〈100〉 CdTe at 300 °K. Polarization dependent RS from the three principal faces, i.e., 〈100〉, 〈11̄0〉, and 〈111〉 of Hg1−xCdxTe and HgTe was studied and the symmetries of the various spectral features were identified. All measurements were made in the back-scattering geometry using the 5145 Å line of the Ar+ laser. In addition to the q=0 transverse and longitudinal optical (TO and LO) phonon features in HgTe, Hg1−xCdxTe and Hg1−xMnxTe (mixed-mode behavior in alloys) we observed several features that indicate surface quality (S– mode) and deviations from ideal crystallinity (‘‘defect mode’’, ‘‘clustering mode’’, and symmetry forbidden TO mode). The extremely surface sensitive S– feature observed at 132 cm−1 in p-Hg0.8Cd0.2Te is assigned to a coupled LO phonon-intersubband excitation. A 108 cm−1 feature present in HgTe and some samples of Hg0.8Cd0.2Te was confirmed to possess TO symmetry and may originate in antisite defects. The strong peak observed at 135 cm−1, displaying Γ1 symmetry, from all Hg1−xCdxTe samples may arise from clustering of the cations or vacancies; a weak feature observed at 132 cm−1 from Hg1−xMnxTe may also originate from clustering effects. The presence of a symmetry forbidden TO feature in 〈100〉 HgTe as well as 〈100〉 Hg0.8Cd0.2Te may be due to surface morphology or built in strains in the crystals. The HgTe RS contained a broad feature with an atomic displacement LO symmetry at 133 cm−1, slightly below the LO peak (139 cm−1), probably as a result of a screened LO mode. The Br/methanol treated 〈100〉 CdTe was found to have a thin (∼10 Å) surface layer of Te that could be removed by a rinse in 1 N KOH/methanol.

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