Tunnel QW-QDs InGaAs-InAs High Gain Medium for All-Epitaxial VCSELs

Abstract

ABSTRACTStructures of tunnel-coupled pairs consisting of InGaAs (In composition was varied from 29 to 36%) quantum wells (QW) grown on top of shape-engineered self-assembled InAs quantum dots (QW-on-QDs) were employed to increase the maximum saturated gain of QD-based laser active medium. Room temperature optical properties of tunnel-coupled well-on-dots structures at low excitation were found to be sensitive to energy separation between GS energies of QDs and QW. The spectra also show that QD-related photoluminescence (PL) tends to peak at discrete energy separations from the QW peak, in this case multiples of ∼ 35meV (LO phonon energy). The optimized GS energy separation between QW and QDs was found to be close to the energy of the LO phonon. This structure demonstrated narrowing of the QD PL line down to 21.6 meV at T=77K, indicating efficient resonant tunneling of carriers from QW into QD ensemble states. All-epitaxial vertical cavity surface emitting lasers (VCSELs) with triple-pair tunnel QW-on-QDs as active medium demonstrated continuous wave mode lasing. Tunnel QDs-QW VCSELs exhibited 1.8 mA (Jth ∼ 800 A/cm2) minimum threshold current at QD GS emission wavelength, 1135 nm, with 0.7mW optical power and 12% light-current efficiency.