Systematic study on the confinement structure design of 1.5-μm InGaAlAs/InP multiple-quantum-well lasers

An in-dept analysis on the separate confinement heterostructure (SCH) design parameters of 1.5-μm InGaAlAs/InP multiple quantum-well (MQW) lasers is reported. Theoretical calculations show a drastic enhancement on threshold current and slope efficiency from step-index SCH (STEP-SCH) to graded-index SCH (GRIN-SCH) design, but the effect ceases beyond a critical number of grading steps. This finding implies ease of the growth process and reduction in cost. The overall GRIN-SCH’s thickness is found to exert great influence over the achievable laser’s threshold current and slope efficiency. An average of 27 mA threshold current reduction and more than 32% of slope efficiency increment were achieved by optimizing the GRIN-SCH thickness. Increasing the grading energy range of the GRIN-SCH decreases the slope efficiency, but is found to effectively reduce carrier leakage at elevated temperature leading to a less temperature-sensitive threshold current MQW ridge lasers were fabricated and characterized out of two laser materials, one with a reference STEP-SCH and another with a proposed optimized GRIN-SCH profile. The laser with optimised SCH design has shown a 36% reduction in room temperature threshold current as compared to that with the STEP-SCH design, which is in good agreement to the theoretical simulation. In addition, a record high characteristic temperature (T ₀) of 105 K was obtained on the GRIN-SCH laser structure, which is more than three fold increment as compared to the STEP-SCH design.