Photoinduced effects in ZnO films deposited on MgO substrates

A large effective second-order optical susceptibility equal to about 52 pm/V for ZnO films with thickness about several μm deposited on MgO substrate by molecular epitaxial method was achieved using a bicolour coherent treatment by a pulsed 1.32 μm Nd-YAG laser and its second harmonic at λ = 0.66 μm. The written grating was stable during 24 days and its optical susceptibility decreased not more than 26% with respect to the initially written one after interruption of optical treatment. The same measurements performed for the ZnO films deposited by metaloorganic chemical vapor deposition, pulsed laser ablation and spray pyrolysis have shown that the output optical susceptibility is at least half order less. The temperature dependences of the second order susceptibilities have shown that it achieves a maximum near a temperature of 261 K. Other methods do not show substantial temperature dependences. We have found that maximal second harmonic generation signal was achieved for the films with thickness of about 2.75 μm.