Analysis of the performance of 1.55-μm InGaAs-InP tensile strained quantum-well lasers

We fabricated 1.55-μm tensile strained InGaAs quantum-well (QW) lasers into broad-area and ridge waveguide lasers, and their performance was analyzed and compared with compressive strained and lattice-matched QW lasers. It is seen that the limitation on the tensile strain to a value less than 0.7%, which is required to prevent the emission wavelength being shorter than 1.55 μm, imposes restrictions on the performance enhancement in several aspects. Broad-area InGaAs QW lasers with a tensile strain of 0.7% show a larger gain coefficient and smaller transparency current density per well than those with InGaAsP QW lasers with a compressive strain of 1.0%. However, the internal quantum efficiency is much smaller than that for compressive ones and the internal optical loss increases rapidly as the number of QW´s increases. These are thought to be caused by a smaller conduction band offset and the onset of dislocation generation at the well-barrier interfaces with the number of QW´s, respectively. Ridge waveguide lasers with two QW´s with tensile strain of 0.7%, which is designed not to exceed the critical thickness for dislocation generation, show smaller modal gain coefficients and inferior temperature characteristics as compared to those with six 0.7% compressive strained QW´s and those with three lattice matched InGaAs QW´s. However, the modulation bandwidth is measured to be larger than that for one that is compressively strained. It is believed to originate from the small effective capture time of the carriers due to thicker wells