“…In the framework of the two‐band model, the general formula reduces to the form (see Refs. for details) Here, the dimensionless integration variable x corresponds to the energy difference between bands measured in the energy gap units, , the z and b parameters correspond to the dimensionless photon energy, , and the broadening parameter, . The function presents an integral of the Fermi occupation factors over the ‐vector component perpendicular to ‐vector, …”