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

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