InAs/InGaAs quantum dots confined by InAlAs barriers for enhanced room temperature light emission: Photoelectric properties and deep levels

Abstract InAs/InGaAs heterostructures with quantum dots (QDs) have been studied for quite some time for light-emitting diodes operating from the near to the far infrared range. However, the room temperature QD emission is rather low, thus it is needed to look for improved structure designs allowing efficient enhancement of luminescence. In this work, we study the modification of photo- and thermo-electrical properties of InAs/In0.15Ga0.85As QD heterostructure, when introducing wide-bandgap In0.15Al0.85As confining barriers (CBs) at one or both sides of the QD layer. The structures demonstrate interband QD photoluminescence (PL) peaked at 1.2 μm measured from room temperature down to 10 K. The introduction of CBs allows to enhance the PL intensity by more than four orders of magnitude. The reason is a strong decrease of the thermal escape of both charge carriers confined in QDs and wetting layer, leading to a highly increased radiative recombination. The changes in optical transitions, involving quantum confinement states and defect-related levels, are studied by photocurrent (PC) measurements, also showing the expectable quenching of PC in the structures with CBs. The existing deep levels of defects are determined by thermally stimulated current spectroscopy. Having the same defect spectrum in all the studied structures, an increase in the defect density was detected near CBs at the QD layer. At low temperatures, defect traps in vicinity of the QDs layer caused the Coulomb screening of conductivity channel, that is studied by kinetics measurements in view of the CB introduction. The PC decrement under the constant illumination is theoretically explained by the screening. We confidently show that, despite of a slight increase in defects and PL blueshift in the QD structure with In0.15Al0.85As CBs, they can serve as improved active elements for energy-efficient QD lasers, single-photon emitters and optical amplifiers.