Size dependence of small-aperture thin-oxide VCSEL´s

We report on the aperture-width dependence of modal size and wavelength for thin-oxide VCSEL´s. The modal characteristics differ significantly from those of thick-oxide devices. The three main types of oxidized apertures that are used for current and light confinement in VCSELs are quarter-wave-thick, tapered, and thin oxides. The thick oxides require the least complicated epitaxial structure, since one must only increase the aluminum content in one or more of the Al/sub x/Ga/sub 1-/As quarter-wave layers of the distributed Bragg reflector (DBR), for example, from 92% to 98%. The tapered and thin-oxide devices require a more complicated DBR structure that incorporates a thin epitaxial layer with increased aluminum content. The extra effort is justified because of the lower optical-scattering losses, and hence lower thresholds, that can be obtained.