| A study on the design of 1.55-mum InGaAlAs/InP quantum-well laser (QWL) is conducted to investigate the effect of various design parameters on the laser's performance and to design an improved laser structure. The study is separated into stages; it begins with an extensive review on InGaAlAs/InP, followed by the analysis on InGaAlAs/InP material system, and completed with the investigation on the design of QWL. Numerical analysis is employed in the study. A consistent set of InGaAlAs/InP material parameters had been determined and the laser's light-current performance was compared against experimental result to ensure the accuracy of the results. Along this process, a convenient band-gap interpolation technique and an improved band line-up model for InGaAlAs on InP were proposed. They are less complex in nature and offer better accuracy as compared to other existing models. The study on the confinement structure design shows that it is not necessary to grow a high number of graded-index layers to improve the threshold and efficiency performance, but an optimum number was deduced. It is found that the choice of grading range of material composition for the graded-index separate confinement heterostructure involves the trade-off between slope efficiency and electron leakage current. To circumvent this, a novel non-symmetrical separate confinement heterostructure (NS-SCH) is developed and tested. Simulation results show that QWL with NS-SCH is superior to QWL with electron stopper layer, and the maximum output power and threshold current obtained are 43% and 25% better than the respective figures of the reference device. On top of these, investigation on the QW gain spectra reveals that the tensile strained QWs exhibit better gain-to-temperature stability as compared to the compressively strained QWs. With a complete analysis performed on the active region, which involves the adjustment of material composition of QW/barrier, the strain on the QW, and the number of QW, an optimized QW design had been deduced. Simulation of an improved laser structure consisting of this optimized active region and the proposed NS-SCH gave rise to promising results; the threshold current, slope efficiency, and maximum output power obtained are one-fourth, twice, and four-fold of those of the reference device, respectively. It has a high characteristic temperature of 110 K and an excellent maximum operating temperature of 160 °C. |
