Rapid Research Note Radiative Recombination in Type II GaSb/GaAs Quantum Dots

The type II band alignment of GaSb quantum dots (QDs) in a GaAs matrix leads to peculiar optical and electronic properties [1–4]. Such type II QDs provide an about twice as large hole confinement as comparable type I InAs/GaAs QDs, whereas the electrons are delocalized in the surrounding barrier. However, the Coulomb interaction provides for bound exciton states. The spatial separation of the electron and the hole reduces the overlap of the wavefunctions reducing the oscillator strength compared to type I structures. The disparate electron and hole localization is reflected in many-particle effects being dominated by hole–hole interaction. [4] In this paper we report time-resolved photoluminescence (TRPL) measurements of self-orga-nized GaSb/GaAs QDs. Previous investigations [1, 5] have been performed on samples with addi-tional AlGaAs barriers, which artificially enhance the electron–hole overlap. Here we report on the intrinsic radiative lifetime of isolated type II QDs, which will be much longer than the previously reported 5 ns. The investigated sample was grown by me-tal organic vapor phase deposition (MOCVD) using the Stranski-Krastanov mode. The is-land density is 3 1010 cm–2 and atomic force microscopy (AFM) measurements of a comparable uncapped sample suggest a lateral width of 25 nm and a height of 2–4 nm. More details of the growth are reported else-where [6]. The sample was cooled to 2 K in a He-im-mersion cryostat and excited at 2.18 eV by a pulsed dye laser with a repetition rate of 3.8 MHz. The emission was dispersed by a 0.35 m subtractive double monochromator and detected with a multi-channel-plate photomultiplier with a S1 cathode. Using sin-gle photon counting a time resolution of 30 p