Near Infrared InAs/GaAsSb Quantum Dot Light Emitting Diodes

A series of light-emitting diodes (LEDs) with active layers based on InAs quantum dots (QDs) covered by GaAsSb capping layers is presented. Varying the Sb content in the capping layer from
${\sim}{2}$
to
${\sim}28\%$
, room temperature electroluminescence (EL) from 1.15 to 1.5
$\mu{\rm m}$
is obtained. The external efficiency of the devices,
$\eta_{\rm ext}$
, increases as the Sb is increased up to
${\sim}{15\%}$
and then decreases for higher Sb contents, consistently with the reported increase of QD height with the Sb content up to
${\sim}{15\%}$
and the band alignment transition from type I to type II above
${\sim}{15\%}$
Sb. An analysis of the EL and photocurrent spectra shows that the emission from type I LEDs originates from the recombination between electrons and holes confined in the QDs. On the other hand, the EL from the type II devices is the combination of two different processes. First, recombination between electrons confined in the QDs and holes at the capping layer. Second, a type I-like recombination of electrons from the QDs and holes residing in extended levels of the quantum well composed by the capping layer and the QDs. The mechanisms responsible for the thermal quenching of the EL are also studied. Escape of holes from the QD to the capping layer is identified as the dominant mechanism for the type I devices, whereas in type II structures it is the escape of electrons from QD excited levels to the barrier which dominates.