The growth optimization and mechanism of N-polar GaN films with an in situ porous SiNx interlayer

Abstract

In this paper, N-polar GaN films were grown on vicinal C-face SiC substrates by metal–organic chemical vapor deposition. In situ porous SiN_x interlayers with different deposition times of 0 s to 120 s were adopted in the growth processes of N-polar GaN films. We find that the crystalline quality, such as surface morphology and structural characteristics, of N-polar GaN films can be controlled by changing the deposition time of the SiN_x interlayers. The N-polar GaN film with a SiN_x deposition time of 60 s exhibits the best crystallinity. Based on the observed porous feature of the SiN_x interlayer from the phase image obtained using an atomic force microscope, we propose a model to illustrate the epitaxial growth mechanism of N-polar GaN films grown on the top of the porous SiN_x interlayer. In this model, we reveal that the SiN_x deposition time determines the SiN_x coverage and the nucleated island density of overgrown GaN, which markedly affects the structural characteristics of the N-polar GaN films. This model can also be used to analyze the influence of SiN_x deposition times on the stress states in N-polar GaN films. Additionally, the threading dislocation propagation behaviors were observed experimentally from the cross-sectional transmission electron microscopy image of N-polar GaN with a SiN_x interlayer, which demonstrates the reasonability of this model. It is reasonably believed that this work provide a valuable information to obtain high-quality GaN films that can be used to the fabrication of N-polar GaN-based optoelectronic devices.