Toward high temperature active region intermixing in VCL structures

Vast improvements in VCL efficiencies at low-output powers have been made possible by reducing the device size without sacrificing slope efficiencies. However, for a 6 μm diameter device, the threshold current is twice the value expected from extrapolation of the broad-area threshold current density even after current spreading above the active region is suppressed. The additional current is due to lateral carrier diffusion in the active region away from its center, the effect of which becomes even worse at smaller diameters. The motivation for this work stems from a desire to use selective intermixing techniques to provide lateral carrier confinement (LCL) while maintaining the current and optical confinement of buried apertures in VCL´s. However, at the high temperatures required to intermix, issues such as dopant diffusion, compositional intermixing of adjacent epitaxial layers, and anomalous degradation mechanisms need to be addressed. In particular, the oxide formed by steam oxidation of high aluminum content AlGaAs layers, which will hereafter be referred to as oxide, is responsible for a perplexing degradation mechanism during a high temperature anneal