Influence of the lattice mismatch strain on the surface morphology of ZnMgTe/ZnTe/ZnMgTe electro-optical waveguide structure

ZnMgTe/ZnTe waveguide is a high potential electro-optical device. Thick and high Mg composition cladding layers are required for high optical performance waveguides. However, adding Mg would increase the lattice mismatch between ZnMgTe and ZnTe which would cause dislocation defects and generate asperities at interfaces. In this article, influence of the lattice mismatch strain to the waveguide surface morphology was studied. Waveguide structures were prepared by molecular beam epitaxy. The surface morphologies were observed using atomic force microscope and propagation loss of the waveguides were studied. Total of 0.5-0.7μm asperities were observed on the surface of waveguides with 20% of Mg composition and 1.2μm of the total cladding layer thickness. The asperities on the surface became larger (1.0-1.2μm) when the Mg composition increased to 40%. The propagation loss of the waveguide was suppressed to 7dB by tuning the growth parameters and the resulting interface roughness.