Deep levels induced by InAs/GaAs quantum dots

Self-organised InAs/GaAs quantum dots (QDs) were formed by molecular beam epitaxy using the Stranski-Krastanov growth mode. Deep-level transient spectroscopy as well as secondary ion mass spectrometry have been used to characterise structures containing the QDs. DLTS depth profiling procedures indicate that deep level-related defects are localised in GaAs in the vicinity of the QD plane. For the first time, we report the presence of a deep level-related trap with an extremely high thermal activation energy of E-c - 1.03 eV. An electron trap at E-c - 0.78 eV can be identified as the well-known level related to the EL2 family. We conclude that a third trap revealed at E-c -0.57 eV is the familiar PL killer related to the intrinsic point defect-oxygen complex. The latter is confirmed by results of the SIMS study, which indicates that the amount of oxygen accumulated at the InAs/GaAs heterointerface is increased. This paper demonstrates that the EL2 and oxygen-related deep-level centers occur by the presence of InAs/GaAs QDs. We present the hypothesis that deep states could be a factor limiting the efficiency of QD-based devices. (c) 2005 Elsevier B.V. All rights reserved.