Investigation of InAs quantum dashes for 1.45-2.1 μm vertical external cavity surface emitting laser active regions

摘要

Lasers with emission wavelength around 2 _m have been traditionally based on InGaSb quantum wells grown on GaSb. An alternative is to use self assembled InAs Quantum Dashes grown on InP by the Stranski-Krastanov growth mode. More speci_cally, InAs quantum dashes embedded in strained GaInAs quantum wells, grown in InAlGaAs waveguides lattice matched to InP substrates have been successfully used as active medium in edge emitting lasers with wavelengths in the range from 1.45 _m to 2.1 _m. Advantages of this material system compared to the GaSb based system include easier lattice matching; i.e. only one group V element is involved. Many optoelectronic properties of the InAs/InP quantum dash material system are similar to those of InAs quantum dots grown on GaAs substrates. The latter material system has been very successfully used for VECSELs in the wavelength region around 1 _m, leading to the highest power VECSEL at this wavelength, mode locking, wide range tunability as well as intra cavity SHG to generate red light. A challenge in the material system based on InP substrates is to fabricate a DBR. A lattice-matched DBR can consist of GaAsSb/AlAsSb. Alternatively one can grow a metamorphic DBR based on either GaAs/AlAs or GaSb/AlSb. The latter requires the DBR to be grown after the active region. The resultant VECSEL is then a bottom emitter, where the substrate has to be removed. This can be achieved by introducing an etch stop layer between substrate and active region. Lastly, the DBR can be grown separately and subsequently wafer bonded to the active region. This paper will discuss details of these technologies and present results.