Study On The Mosaic Structure And Luminescence Properties Of GaN Films

Gallium Nitride (GaN) as the representative of the third generation of semiconductor material for its outstanding properities in recent years become a research hotspot. It was widely used in anti-radiation, high-frequency, high-power and high-density integrated electronic devices and a variety of light-emitting and light detecting device. With the help of previous growth experience, We got a mature two-step growth process of GaN/Al2O3thin film on Thomas Swan MOCVD system, after a amount of exploration. The films all have a roughness surface, and the dislocation density is108cm-2orders of magnitude. We observed a significantly layered distribution after wet etching, and that indicated the film was already into a two-dimensional layered growth process, which was also confirmed by the AFM surface morphology characterization.We measure the (0002) plane and the (2021) plane of different thickness GaN films grown on C-plane sapphire by high resolution x-ray diffraction. The half peak width of the rocking curve of the crystal plane show that the existence of dislocation density in the film and the edge dislocation density is an order of magnitude more than the screw dislocation density. We found that the film thickness increases, making a significantly reduction in the dislocation density of the films, and the screw dislocation density decrease faster than the edge dislocation density. Ayers fitting of the dislocation density show the transformation from the mix of two-dimensional and three-dimensional to the two-dimensional growth stage. The rate of reduction of the dislocation density declines sharply, and finally tends to ease.Meticulous research is taken on mosaic structure with thickness variation, with the Pseudo-Voigt function fitting method and the Williamson-Hall method. Found that with increasing thickness consistent regularity of the mosaic structure is getting better and better. For example, the in-plane rotation angle is getting smaller, and the out-plane tilt angle is getting smaller, and the lateral correlation length becomes larger. That several aspects of the change speed is gradually reduced, This shows when it reaches a certain thickness, increasing the thickness of films has a weaker influence on mosaic structure.Absorption spectrum and the PL spectrum of different thickness GaN films were tested to obtain the optical properties. The peaks are all3.38eV. The thickness has no impact on the well-grown epitaxial wafer. Because of multiple internal reflections, Fabry-Perot interference fringes appear in the transmittance spectrum and the PL spectrum, which can be used to roughly calculate the thickness of the film. The yellow band is not observed in the PL spectrum, on the contrary, With the film thickness increases, the peak position of blue band is blue-shifted, and the luminous intensity also increased. We believe that a large number of oxygen impurity were brought in during the epitaxy growth, and the positively On donor and the negatively VGa acceptor can easily form the VGa-On complex. The energy level of the VGa-ON complex is gradually pulled down with the increasing thickness. Frontside spectra and backside spectra of one sample are tested. Yellow band becomes obvious, and has a high light intensity in the backside spectra, suggesting a large number of defects in the GaN buffer layer between the film and the substrate.