Epitaxial Structure Design of a Long-Wavelength InAlGaAs/InP Transistor Laser

The threshold condition in long-wavelength InAlGaAs/InP transistor lasers is theoretically and numerically investigated. The optical gain in the In_0.58Ga_0.42As/In(Al_0.4Ga_0.6)As strained quantum well is calculated using a simplified k-selection model while intervalence band absorption is considered as the major intrinsic optical loss in the transistor lasers. It is found that room-temperature lasing of an N-InP/p-In(Al_0.4Ga_0.6)As/N-InP double heterostructure transistor laser is achieved only when the base thickness and doping level are within a specific narrow range. However, the selectable range is significantly expanded by means of facet coating, structure engineering, and quantum well design. By using a more compressively-strained or thicker quantum well as the active region in a separate confinement heterostructure transistor laser, it is possible to obtain a threshold current density as low as sub-100 A/cm².