Deep level defects in ZnO

The current understanding on intrinsic and extrinsic defects in ZnO is briefly reviewed. Special attention is given to defects defining the doping asymmetry as well as to approaches and theoretical predictions to control the conductivity of zinc oxide. Silver doping is considered a promising way to achieve hole conductivity in bulk ZnO. Results of defect spectroscopic studies on hydrothermally grown single ZnO crystals with an electron concentration of ≈1017cm−3 and ≈1014cm−3 are presented. Besides several other deep level centers in higher doped materials the Zni related level at Ec– (341±2) meV was found to be the dominating donor level in low doped ZnO. Further thermal post-treatments under inert and oxygen ambient conditions result in electrical intrinsic properties. First experiments on ZnO:Ag gave no hints for a detectable electrical activity of silver.