QD VCSELs with InAs/InGaAs short period superlattice QW injector

Abstract

Structures with tunnel-coupled pairs consisting of InGaAs quantum wells (QWs) grown on top of self-assembled InAs quantum dots (QDs) were used previously as a gain medium for vertical cavity surface emitting lasers (VCSELs) to eliminate problems with QD-limited maximum saturated gain. Conventional molecular beam epitaxy of tunnel-coupled QDs with slow InAs growth rate and InGaAs solid solution QW injector with high InAs growth rate required a long delay in growth process for changing indium source temperature/flux. This leads to non-intentional doping of tunnel barrier and reproducibility issues. To overcome these problems, structures of tunnel-coupled QDs-QW pairs consisting of InAs/InGaAs short period superlattice (SPSL) QW injector with compatible slow InAs growth rate (QDs-SPSL) were developed and compared with traditional InAs-InGaAs (QDs-InGaAs). Photoluminescence (PL) and electroluminescence were used to study the properties of the well-on-dots active medium with InAs/InGaAs SPSL QW and with InGaAs QW. The optimized tunnel triple pair QDs-SPSL structure with 2x reduction of growth time has demonstrated a 2x enhanced PL efficiency as compared with traditional QDs-InGaAs structures. A novel tunnel-coupled triple QDs InAs-SPSL was successfully employed as a gain medium of VCSELs with doped all-epitaxial distributed Bragg reflectors (DBRs). Room temperature CW lasing wavelengths in the range from 1100 nm to 1150 nm were measured in VCSELs with attuned DBRs. These QDs-SPSL VCSELs demonstrated minimum threshold current value Ith = 0.85 mA and maximum differential efficiency of 0.16 W/A.