Modulation-doped multi-quantum well (MD-MQW) lasers. I, Theory

A number of important parameters, such as gain, modulation response and threshold current in modulation-doped multi-quantum-well (MD-MQW) lasers are theoretically investigated. The analytical results indicate that the relaxation oscillation frequency of p-type MD-MQW lasers is enhanced by a factor of 4 compared with DH lasers, and that the linewidth enhancement factor of p-type MD-MQW lasers is reduced to 1/4 that of undoped MQW lasers. The threshold current density of n-type MD-MQW lasers is reduced to 1/2∼1/4 that of undoped MQW lasers. The improvements in these properties basically result from the unsatisfied charge neutrality due to the modulation doped effect and from asymmetry in density of states between conduction band and valence bands in III-V materials.