We investigated the effects of SiNx interlayers on the structural and electrical properties of nonpolar a-plane (11-20) GaN grown on r-plane (1-102) sapphire substrates by metal–organic chemical vapor deposition (MOCVD). The Nomarski optical microscope images showed that the deposition conditions of the SiNx layer could strongly affect the a-plane GaN surface morphology due to the different SiNx coverage. Basal-plane stacking faults (BSFs) and threading dislocation (TD) densities were reduced in the a-plane GaN samples with high SiNx coverage and multiple SiNx-treated GaN interlayers. These results indicate that TD reduction is associated with an increase in the 3D growth step and with the blocking of TD propagation. From on-axis (11-20) X-ray rocking curve (XRC) measurements, the anisotropy of full width at half maximum (FWHM) can be attributed to the crystal mosaicity due to insertion of different SiNx interlayers. The anisotropy of sheet resistance between the c-and m-axis was also clearly seen in a-plane GaN samples with a high density of defects, which was attributed to the BSFs as scattering centers.
All-optical logic gate based on MMI (Multi-Mode Interference) is proposed in this paper. Different from other methods, MMI efffect is utilized for the logic functions including AND, OR, NOR, and XOR. All-optical logic function is realized at specific output waveguides in accordance with the control signal condition.
The refractive index and the film thickness were measured by the prism coupler, and GeO2 and P2O5 concentration were analyzed by EPMA (Electron Probe Micro Analysis) according to the torch inclination angle and the distance between torch and substrate. As the torch angle was steeper, the thickness and the GeO2 concentration were increased, and the P2O5 concentration was decreased for the angle greater than 45o.