p -doped 1.3μm InAs∕GaAs quantum-dot laser with a low threshold current density and high differential efficiency

A modification of the thickness of the low-growth-temperature component of the GaAs spacer layers in multilayer $1.3\mu \mathrm{m}$ $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum-dot (QD) lasers has been used to significantly improve device performance. For a $p$ -doped seven-layer device, a reduction in the thickness of this component from $15\text{to}2\mathrm{nm}$ results in a reduced reverse bias leakage current and an increase in the intensity of the spontaneous emission. In addition, a significant reduction of the threshold current density and an increase of the external differential efficiency at room temperature are obtained. These improvements indicate a reduced defect density, most probably a combination of the selective elimination of a very low density of dislocated dots and a smaller number of defects in the thinner low-growth-temperature component of the GaAs spacer layer.