ANALYSIS OF THE EFFECTS OF DOPING AND BARRIER DESIGN ON THE SMALL-SIGNAL MODULATION CHARACTERISTICS OF LONG-WAVELENGTH MULTIPLE-QUANTUM-WELL LASERS

This theoretical work has modelled the small signal response of InGaAs P and InGaAlAs multiple quantum well (MQW) lasers based on an ambipola r carrier transport model. The MQW parameters such as barrier bandgap, barrier width and the number of quantum wells have been optimized for high-speed modulation. The effect of the p-type doping and the strain of the InGaAs well have also been investigated. For the InGaAsP-based system, the optimization for maximum 3 dB bandwidth shows that the op timum width is about 5 nm for 1.1 mu m barriers and 7 nm for 1.2 mu m barriers. The optimum barrier bandgap wavelength is about 1.1 mu m for the barrier width of 6 nm, about 1.15 mu m for 8 nm and 10 nm barrier s. The p-doped MQW exhibits a higher modulation bandwidth because of i ts high differential gain and improved carrier distribution among the MQWs. The compressively strained InGaAs quantum well system has the po tential for a higher modulation bandwidth. For the InGaAlAs-based syst em, the optimization for maximum 3 dB bandwidth shows that the optimum width is about 4 nm for a barrier wavelength of 1.10 mu m, and 6 nm f or 1.2 mu m. The optimum barrier bandgap wavelength is about 1.1 mu m for a barrier width of 4 nm, and about 1.2 mu m for 6, 8 and 10 nm.