Performance characteristics of low threshold current 1.25-{\mu}m type-II GaInAs/GaAsSb W-lasers for optical communications

Type-II W-lasers have made an important contribution to the development of mid-infrared laser diodes. In this paper, we show that a similar approach can yield high performance lasers in the optical communications wavelength range. (GaIn)As/Ga(AsSb) type-II W structures emitting at 1255 nm have been realised on a GaAs substrate and exhibit low room temperature threshold current densities of 200-300 Acm$^{-2}$, pulsed output powers exceeding 1 W for 100 ${\mu}$m wide stripes, and a characteristic temperature T${_0}$${\approx}$90 K around room temperature. Optical gain studies indicate a high modal gain around 15-23 cm$^{-1}$ at 200-300 Acm$^{-2}$ and low optical losses of 8 ${\pm}$ 3 cm$^{-1}$. Analysis of the spontaneous emission indicates that at room temperature, up to 24% of the threshold current is due to radiative recombination, with the remaining current due to other thermally activated non-radiative processes. The observed decrease in differential quantum efficiency with increasing temperature suggests that this is primarily due to a carrier leakage process. The impact of these processes is discussed in terms of the potential for further device optimisation. Our results present strong figures of merit for near-infrared type-II laser diodes and indicate significant potential for their applications in optical communications.