Molecular beam epitaxial growth of vertical cavity surface emitting lasers with digital alloys and digital gradings

Abstract

Electrical resistance through vertical cavity surface emitting lasers (VCSELs) grown by molecular beam epitaxy is generally higher than in VCSELs grown by metalorganic chemical vapor deposition (MOCVD). The better performance of MOCVD-grown material is attributed to the fact that MOCVD can continuously grade the composition between the high index (narrow band gap) and low index (wide band gap) materials that constitute the Bragg mirror stack. This leads to a lower resistance for the charge to traverse through the mirror stack. In addition, the oxidation of VCSEL apertures dramatically reduces threshold current Ith; however, the oxidation process requires a low index layer with a high aluminum mole fraction for reasonable oxidation rates and for good material stability. The MOCVD process benefits from its ability to tailor the high mole fraction AlGaAs material that is crucial for creating the oxide apertures. The majority of these problems can be alleviated using digital alloys and digital grades.