Nanocomposites and nanomaterials

InAs/InGaAs Quantum Dots Confined by InAlAs Barriers: Photoelectric Study and Deep Levels
Datsenko O.I.1, Golovynskyi S.2, Seravalli L.3, Trevisi G.3, Frigeri P.3, Li Baikui2, Qu Junle2
1 Department of Physics, Taras Shevchenko National University of Kyiv, Kyiv 01601, Ukraine.
E-mail: lesoto8g@gmail.com
2 College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, People’s Republic of China
3 Institute of Materials for Electronics and Magnetism, CNR-IMEM, I-43124 Parma, Italy.

The modification of photo- and thermo-electrical properties of InAs/In0.15Ga0.85As quantum dot (QD) heterostructure is studied, 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. Introduction of the upper and lower CBs (UB and LB) allows to enhance the PL intensity by more than four orders of magnitude due to 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 are studied by photocurrent (PC) measurements, showing the expectable quenching of PC in the structures with CBs. 
The existing deep levels of defects are found 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.
Particular study of the structures with single barriers shows that UB or LB cause trap-like defects on both sides of the QD layer, but they have different effect on the photoelectric properties. So, the introduction of UB causes a creation of trap-like defects near the InAs nanolayer, resulting in a delayed kinetics of PC increase. The LB creates various point defect traps below the QD layer and extended defects near the QD array. Simultaneously, LB inhibits the manifestation of deep levels in activation of the dark conductivity and keeps the long increase PC kinetics.