Optical and Electrical Spectroscopy of Zinc Oxide Crystals Simultaneously Doped with Copper and Donors

In Cu‐doped ZnO crystals the Fermi level is varied by additional donor doping (In or H) in the energy range 0 to 250 meV below the bottom of the conduction band. The results of optical absorption and electrical conductivity measurements carried out in these crystals can be explained by using the model in which Cu acts as an acceptor with an energy spacing of E CA = 190 meV from the bottom of the conduction band. Moreover oscillator strengths of inner transitions of the Cu 2+ ‐ion are presented.