In0.68Ga0.32As∕Al0.64In0.36As∕InP 4.5μm quantum cascade lasers grown by solid phosphorus molecular beam epitaxy

The authors report the growth and fabrication of 4.5μm quantum cascade lasers based on strain balanced In0.68Ga0.32As∕Al0.64In0.36As heterostructures by molecular beam epitaxy. A device with 12.5μm waveguide width and 2.25mm cavity length has a threshold current density of 5kA∕cm2 and can deliver power from one facet of about 90mW at room temperature under pulse mode. The characteristic temperature is 124K. The measured waveguide losses at room temperature are 11.5 and 13.2cm−1 with ridge width of 14 and 11μm, respectively. The temperature dependence of the waveguide loss is correlated with the change of the carrier mobility.