Carrier dynamics and lasing behavior of InAs/GaAs quantum dot lasers with short cavity lengths

The modulation p-doping technique has emerged as an effective way to optimize the carrier dynamics process of quantum dot (QD) structures. Here, the laser structures based on the 1.3μm multiple-layer InAs/GaAs QD were fabricated with and without modulation p-doping. The carrier relaxation rate was increased after modulation p-doping, as demonstrated by transient absorption spectroscopy. The higher relaxation rate in p-doped QDs could be explained by more rapid carrier-carrier scattering process originating from increasing of the hole quasi-Fermi-level movement that increases the probability of occupancy of the valence states. In addition, the lasing behavior of Fabry-Perot lasers with and without modulation p-doping was investigated and compared. It was found that the ground state (GS) lasing in the absence of facet coating was successfully achieved in a p-doped laser diode with short cavity length (400μm), which can be attributed to the higher GS saturation gain caused by p-doping. With assistance of a designed TiO₂/SiO₂facet coating whose central wavelength (∼1480 nm) is far beyond the lasing wavelength of 1310 nm, the GS lasing could be realized in a laser diode with short cavity lengths (300μm) under continuous wave operation at room temperature, implying great potential for the development of low-cost and high-speed directly modulated lasers.