AlGaAsSb/AlGaInAs Type-Ⅱ Superlattices for Tuning Regions in Tunable Laser Diodes

摘要

Tunable laser diodes exploiting the free-carrier plasma-effect are renown for their large tuning range. To control the emission wavelength, carriers are injected into a tuning region inducing a refractive index change. Typically, the material system GaInAsP/InP is used for tuning regions. Since this material shows strong recombination, a large current has to be applied while tuning. Unfortunately, the tuning current causes a parasitic temperature increase of the device acting negatively in a twofold way. Firstly, the index change due to the temperature increase works directly against the index change that is brought about by the plasma-effect. Secondly, many parameters of the laser device depend critically on temperature. Therefore, a reduction of the current consumption would instantly improve all relevant device parameters. In this paper we propose a type-Ⅱ superlattice consisting of Al_(0.30)Ga_(0.17)In_(0.53)As/Al_(0.50)Ga_(0.50)As_(0.56)Sb_(0.44) as a tuning region. The staggered band alignment leads to a spatial separation of the electrons and holes. As a result, the recombination rate can be significantly reduced by over one order of magnitude, which in turn leads to an increase of the carrier density as a function of the current. An analysis shows that type-Ⅱ superlattices can provide an equal tuning range with a reduced current consumption by a factor of six compared to conventional heterostructures.