The valence and conduction bands of a 1D semiconductor are given by Ev (k) = A + B cos(ka) and Ec (k) = C + D cos(ka), where A = -0.6 eV, B = 0.6 eV, C = 3.5 eV, D = 1.1 eV, and a = 5.2 . The dielectric constant of this material is = 10 and the electron scattering time is 10 fs. a) Evaluate the donor ionization energy. b) If this semiconductor is doped with 10 19 cm-3 donors, what is the electrical conductivity? Assume all donors atoms are fully ionized. c) What is the longest photon wavelength that can be absorbed by this material?