Tunable laser diodes with type II superlattice in the tuning region

Type II superlattices as tuning regions in continuously tunable laser diodes are investigated. They are used to create an artificial indirect semiconductor by spatially separating electrons and holes from each other. At a given current the mean electron density is increased and therefore a larger tuning range and efficiency are achieved. The type II superlattice can be prepared in different ways, e.g. by a superlattice consisting of two different semiconductors, by a doping superlattice, by alternately strained layers or by combining these effects. In the case of a tuning region with 1.3 μm wavelength lattice matched to an InP substrate one may use an unstrained InGaAsP/lnGaAsSb superlattice with an estimated band offset of 302 meV. This enhances the tuning by a factor of 160 in the low-current limit. At high tuning currents this factor decreases, but it is still considerable.