HIGH Mg content wurtzite phase Mg_xZn_(1-x)O epitaxial film grown via pulsed-metal organic chemical vapor deposition (PMOCVD)

摘要

We report on high quality, wurtzite Mg_xZn_(1-x)O (MgZnO) epitaxial films grown via the PMOCVD method with a record high Mg content up to 51 %. A series of MgZnO films with various Mg content were grown on ZnO (～30 nm)/Al_2O_3(0001) and ZnO (～30 nm)/AlN (～25 nm)/Al_2O_3(0001) substrates. The band gap for the films estimated using UV-visible transmission spectroscopy ranges from 3.24 - 4.50 eV, corresponding to the fraction of Mg between x=0.0 to x=0.51, as determined by Rutherford backscattering spectroscopy (RBS). The cathodoluminescence (CL) measurement showed a blue shift in the spectral peak position of MgZnO, indicating an increase in Mg content. No multi-absorption edges and CL band splitting were observed, suggesting the absence of phase segregation in the as grown films. The phase purity and crystal structure of the films were further confirmed by XRD. The absence of phase separation is attributed to the fast periodic transition steps in the PMOCVD, creating a non-equilibrium system where radicals that are formed will have insufficient time to reach their energy minimum. AFM analysis of the films had decreasing surface roughness with increasing Mg content. MSM photodetector was fabricated from the films to characterize the spectral response. The devices exhibit peak response ranging between 276 - 383 ran, covering a large portion of the solar blind spectral window. Moreover, the Schottky barrier was enhanced by treating the MgZnO surface with H_2O_2, reducing the device's dark current.