ENERGY-LEVELS OF A AND B EXCITONS IN WURTZITE-TYPE SEMICONDUCTORS WITH ACCOUNT OF ELECTRON-HOLE EXCHANGE INTERACTION EFFECTS

The effect of both the complexity of the two upper valence bands as well as the electron–hole exchange interaction on the exciton binding energies in wurtzite‐type semiconductors is studied. The energy level scheme and explicit expressions for the lowest exciton states of both A and B series are given. Using recent very accurate experimental data on exciton energies in CdS, the averaged B band hole mass is estimated to 1.6mo, and the position of the n = 1 B(Γ2) exciton level to about 0.2 meV below the transverse B(γ5) level. The longitudinal–transverse splitting of γ5 excitons is calculated from a microscopic approach in excellent agreement with experimental data taking into account an interband momentum matrix element P cv2 = 21 eV screened by a background dielectric constant ε' = 8. The exchange parameters introduced by Cho are determined for CdS to 3j0 ≈ 1 meV and 9j1 ≈ 2.1 meV. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA