Electrical characterization of ZnO, including analysis of surface conductivity
Most of the ZnO semiconductor device applications are currently hampered by the lack of control over the electrical conductivity. As-grown ZnO usually exhibits n-type conductivity, and the cause for this residual doping is heavily debated. We have performed temperature dependent Hall measurements and materials characterization by secondary ion mass spectroscopy (SIMS) on nominally undoped bulk ZnO crystals as well as on material doped with potential candidates for p-conductivity in order to explore the cause of the background doping and to study the impact of possible candidates for p-doping of ZnO. Also, this paper gives an overview about surface conductivity of high-resistivity ZnO bulk material and discusses how this property might impact the difficult search for p-type ZnO. For the first time we will demonstrate this effect on homoeptiaxial MgZnO layers grown by liquid phase epitaxy (LPE). The visibility of a surface conducting channel on an epi sample proofs the extremely high structural quality and low background doping of these layers.
Schmidt, O. ; Kiesel, P. ; Ehrentraut, D.; Geis, A. W. ; Fukuda, T.; Johnson, N. M. Electrical characterization of ZnO, including analysis of surface conductivity. Applied Physics A. 2007 July; 88 (1): 71-75.