ABSTRACTZinc oxide (ZnO) single crystals are grown by the traditional chemical vapor reaction method and ZnO crystal pairs with a single boundary are successfully obtained. The obtained specimens with one ZnO–ZnO boundary (ZnO homojunction) show nonlinear current-voltage (I–V) characteristics without the addition of Bi2O3, CoO, MnO2, and/or rare earth metal oxides. A specimen with higher breakdown voltage shows superior nonlinearity with negative resistivity in its I–V characteristics. Electrical characterization of the ZnO homojunction is conducted and extremely slow response with the current (or voltage) stress is confirmed. The phenomenon had never been observed in commercial ZnO varistors. The surface temperature of the ZnO homojunction is enhanced by larger applied current. The effect of the Joule heat on the nonlinearity in the I–V curves of the ZnO homojunction is discussed.
