High-performance small vertical-cavity lasers: a comparison of measured improvements in optical and current confinement in devices using tapered apertures

Comparison of optical VCSEL models on the simulation of oxide-confined devices

“…This excess loss is mainly due to scattering losses at the oxide aperture. It has been observed that this quantity scales roughly as [14], [29], which is confirmed by most of the models in the log-log plot of Fig. 12.…”

Scaling quantum-dot light-emitting diodes to submicrometer sizes

“…Second, if a currentblocking layer is used to define a current aperture near the active region ͑e.g., Al 2 O 3 obtained by selective oxidation of AlGaAs in VCSELs͒, current spreading between the blocking layer and the active region can increase the effective active diameter by several micrometers. [6][7][8] Finally, carrier diffusion in the active region ͓usually quantum wells ͑QWs͔͒ increases the effective radius by the diffusion length, typically, 1-2 m. While current spreading can be minimized by proper design of the injection region, carrier diffusion can be suppressed only by applying a lateral carrier confinement in the active region. Several approaches have been reported, such as QW interdiffusion, 9 segmented QWs, 10 and selfassembled QDs, 11 although with limited success, probably due to the need to combine strong carrier confinement and good radiative properties of the active material.…”

Modeling of the polarization behavior of elliptical surface-relief VCSELs

“…In the second case, the modal gain for the fundamental mode can be enhanced by adjusting the current injection profile (Unold et al 2001) or by restricting lateral diffusion (Naone et al 1998). The optical losses can be made radially dependent by implementing saturable absorbers to act as a variable optical aperture (Unold et al 2001), by applying externally a graded-index lens (Koch et al 1997), a curved micromirror (Nikolajeff et al 1999) or a Fabry-Perot etalon (Chen et al 1999). Furthermore, the p-contact can be used as an additional mode filter (Ueki et al 1999) or the reflectivity of the top Bragg mirror can be varied spatially, for example by etching shallow local structures Milster et al 1998;Martinsson et al 1999).…”

“…The general ideas are either to reduce (or even overcompensate) the transverse optical waveguiding or to introduce additional mode-selective losses for higher-order modes (Unold et al 2001). In first instance, either the thickness of the AlAs layer intended for oxidation is much reduced (to as little as 15-20 nm) or made tapered (Hegblom et al 1999); or it is placed in a node of the standing wave pattern of the VCSEL cavity (Demeulenaere et al 1999). In the second case, the modal gain for the fundamental mode can be enhanced by adjusting the current injection profile (Unold et al 2001) or by restricting lateral diffusion (Naone et al 1998).…”