Fabrication and analysis of highly-reflective metal-dielectric mirrors for high-performance semiconductor laser applications

The device performance improvement of ridge waveguide (RWG) laser diodes (LDs), operating at a wavelength (λ) of ∼960 nm, with a metal-dielectric high-reflection (HR) mirror consisting of Au/Ti–SiO2 layers on the back facet was demonstrated. To determine the optimum thickness of each layer, optical reflection calculations were performed using a rigorous coupled-wave analysis method, which leads to the resultant Au (80 nm)/Ti (5 nm)–SiO2 (164 nm) layers. The layers exhibited a broad high reflection band of >91% over a wavelength range of 920–1000 nm, indicating the reflectivity of ∼91.2% at λ ∼ 960 nm. For 2 mm-cavity RWG LDs with the Au/Ti–SiO2 HR mirror, an enhanced maximum output power (Pmax) of 499.3 mW at an injection current of 3000 mA and a decreased threshold current (Ith) of 516 mA (i.e., Pmax = 259.4 mW and Ith = 650 mA for the uncoated LDs) were obtained, showing an increased slope efficiency percentage of 82%. The external differential quantum efficiency was also increased from ∼17.1 to ∼31.1%. Also, the full widths at half maximum values of beam divergences of the device were 38° (vertical direction) and 4° (horizontal direction).