Optimizing InAs/InP (113) B quantum dot lasers with considering mutual effects of coverage factor and cavity length on two-state lasing

While the first quantum-dot (QD) laser was developed about 20 years ago, the performance of QD lasers have improved significantly. Currently, compared to the conventional quantum-well (QW) lasers, QD lasers have shown extremely low threshold current, high internal efficiency, and superior characteristic temperature [i]?[vi]. However, the high-speed modulation performance of QD lasers is generally poorer compared to that of QW lasers due to several factors, such as the low carrier capture/relaxation rate and the closely spaced hole energy states in the QDs. Semiconductor lasers with QD based active regions have generated a huge amount of interest for applications including communications networks due to their anticipated superior physical properties due to three dimensional carrier confinement. For example, the threshold current of ideal quantum dots is predicted to be temperature insensitive [vii]. Intensive attention should be paid to investigate the carrier dynamics in QD laser active regions. The carriers injected into the wetting layer (WL) are captured by QD ES with a relatively fast capture time of about several picoseconds. Then carriers relax into QD GS through some complicated dynamical processes. Especially, how the inter-level relaxation affects QD laser performance is very important for device design. Due to the photon bottleneck effect [viii], [ix], which is much slower than 0.1?1 ps in QWs [x]. This effect will have significant impact on the stimulated emission in QD lasers [xi]. Most investigations reported in the literature deal with In(Ga)As QDs grown on GaAs substrates [xii],[xiii]. In order to reach the standards of long-haul transmissions, 1.55 μm InAs QD lasers on InP substrate have been developed. Recent experimental studies conducted on these devices have shown that a second laser peak appears in the laser spectrum as the injection power increased. The double laser emission is a common property found independently by different research groups for In(Ga)As/GaAs as well as for InAs/InP (113)B systems [xiv]? [xv]. Many studies have been done on the simulation of spectral behavior and dynamic characteristics of self-assembled QD lasers [xvii]?[xxi].