Study of temperature effects on loss mechanisms in 1.55 μm laser diodes with In0.81Ga0.19P electron stopper layer

The importance of the electron loss from the separate confinement layer (SCL) to the p-cladding in 1.5 mu m lasers is analysed comparing two structures. One is a regular structure with strained InGaAsP quantum wells and a 1.15 mu m emitting InGaAsP SCL and the second one incorporates an additional In0.81Ga0.19P electron stopper layer (about 50 meV high) at the interface between the p-cladding and the SCL. The results are analysed using comprehensive simulation software. It is shown that the current leakage at the SCL p-cladding interface is not the dominant loss phenomenon at room temperature. Instead, the inhomogeneity of the carrier injection over the QWs is identified as being mainly responsible for the non-unit internal quantum efficiency. The inhomogeneity increases above threshold with the current injection and produces increasing carrier recombination losses. However, at higher temperature (above 60 degrees C) the additional In0.81Ga0.19P electron stopper layer is efficient to decrease the electron leakage from the SCL to the p-cladding. It is also shown that besides the beneficial effect of improving the internal quantum efficiency at high temperature the electron stopper layer also slightly increases the threshold current by increasing the carrier density and the absorption loss in the SCL. Finally, our measurements show that above a critical temperature (97 degrees C in this case) the SCL absorption loss increases dramatically.