Optical second harmonic imaging of zinc oxide thin films grown by metal organic chemical vapour deposition (MOCVD)

Abstract

We demonstrate optical second harmonic (SH) imaging using femtosecond laser pulses (80 fs, 1.59 eV, 80 MHz) as a suitable probe to spatially investigate the structural homogeneity of zinc oxide (ZnO) thin films grown by metal organic chemical vapour deposition (MOCVD). We find that, despite obvious differences in crystalline structure as well as lattice mismatch, ZnO films grown on the three different substrates Si(100), GaAs(100) and amorphous glass under equal growth conditions show a very similar crystalline structure, which appears to be of polycrystalline nature. Our study on films of different thickness reveals that initially micro-crystallites are deposited randomly on the substrate and possibly act as seeds for the further growth process. Furthermore, SH images of ZnO films grown on GaAs show sample regions (20–50 μm in size), where the SH response vanishes, indicating that the strong SH signal generated in the underlying substrate material is suppressed. We attribute these regions to presumably amorphous particles deposited during the growth process, which have light absorbing properties and suppress the SH generation process. Hence SH imaging is an applicable method to obtain detailed information about some aspects of the film deposition process. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)