Technical Insight
Selectively etched VCSEL apertures (Research Review)
VCSELs operating in the 1.31.55 m range can be obtained using wafer fusion or metamorphic growth of AlGaAs DBR mirrors (see ). The AlGaAsSb/AlAsSb materials system also offers an attractive option for InP-based monolithic VCSELs, due to the high refractive index of the AlGaAsSb mirrors. However, forming oxide apertures in these devices is difficult due to the slow oxidation rate of AlAsSb. E Hall and colleagues from UCSB describe the selective etching of AlAsSb DBRs and strained AlGaInAs QWs that make up the active region (Phot. Tech. Lett. 2001 13(2) 97). Citric acid and hydrogen peroxide was used to attack the active region, leaving the mirrors untouched and forming regions that confine the current and optical mode in the same manner as oxide apertures. VCSELs with 50 m apertures were produced with an emission centered on 1540 nm. Etching experiments showed that reducing the aperture size improved the external quantum efficiency from 9 to 13%. The threshold current was reduced to 13 mA for a 33 m diameter device (50 m pillar and 8 m undercut).
