Tunnel quantum dot/well InAs/InGaAs structures as active medium for laser diodes

Structures of tunnel pairs consisting of InGaAs quantum well (QW) and self-assembled InAs quantum dots (QDs) were employed to improve gain medium in laser diodes. Photoluminescence, transmission electron microscopy and electroluminescence were used to study the influence of the relative position of ground states (GS) energies of QW and QDs as well as structure design on the properties of tunnel structures and the characteristics of multi-layer lasers. QDs on QW structures with different GS relative separation were grown by variation of In concentration in QWs with fixed growth process of QDs. An 1160 nm edge-emitting lasers with 4 pairs of QDs-on-QW as active medium showed higher (than in a similar multilayer QD lasers) maximum saturated gain, 26 cm(-1), with low minimum threshold current density J(th) = 95 A/cm(2). First attempt of a triple-pair tunnel QW-on-QDs laser emitting at 1125 nm exhibited a saturated modal gain more than 50 cm-1. These lasers demonstrated broad multi-peak emission spectra with minimum threshold current density J(th) = 255 A/cm(2) and with lasing from intermediate states between QDs and QW GS transitions. RF small signal modulation characteristics of the 3x(QW-on-QDs) lasers were measured. From the damping factor and resonance frequency dependence, maximum possible 3dB cut-off frequency for this QW-on-QD media can be estimated as 13 GHz.