Exciton Structure and Zeeman Effects in Cadmium Selenide

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Abstract
A semi‐empirical theory of exciton structure in the presence of an external magnetic field developed from Dresselhaus' effective mass approximation [G. Dresselhaus, J. Phys. Chem. Solids 1, 15 (1956)] has been used to obtain the band parameters at K=0, 0, 0 of CdSe from observed exciton spectra. The theory has been approximated to the case of uniaxial crystals of small anisotropy by the assumption that the effective mass tensor for both the hole and the electron is diagonal, the remaininganisotropy is cylindrical and small and that the anisotropy in the dielectric constant is also cylindrical and small. The exciton spectra of CdSe has been observed and identified by optical reflection, absorption, and Zeeman structure at 1.8°K. The reflection and absorption spectra indicate the presence of two nonoverlapping exciton series. From observed optical selection rules, the conduction band is identified as having Γ7 symmetry. The two series correspond to the Γ9−Γ7 valence band crystal field splitting of approximately 200 cm−1. A third series, at higher energies, has been observed in absorption corresponding to a Γ7 valence band state split by spin‐orbit effects from the other two states by approximately 3490 cm−1. The n1 = 1, 2, 3, and 4 states of the first, Γ9, series, the n2 = 1 and 2 states of the second (first Γ7) series, and the n3 = 1 state of the third (second Γ7) series have been observed and identified in absorption. The series limit of the first series, corresponding to the band gap, has been measured to be 14 850 cm−1. The band parameters have been obtained by comparing theory and experiment. The effect of the finite photon momentum has been observed through changes in the Zeeman structure of the n1 = 2, P states upon 180° rotation of the magnetic field in the plane perpendicular to the crystal C axis.

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