Controlling the formation of quantum dot pairs using nanohole templates
Résumé
Modifying the shape of nanoholes formed by arsenic debt epitaxy by the overgrowth of a thin GaAs buffer is shown to provide a simple and robust method to grow low density lateral In(Ga)As quantum dot pairs (QDPs). We present here a systematic study of the effect of GaAs buffer thickness. InAs deposition amount, substrate temperature and arsenic overpressure on dot nucleation and QDP formation. A (10-30) nm GaAs buffer over nanoholes initially similar to 10.5 nm deep, (60-80) nm wide results in up to 80% of the nanoholes containing QDPs. The QD pairs are aligned along the [1101 direction and have centre-to-centre separation of similar to 38 nm. These QDPs form following InAs deposition between 1.3 ML and 1.6 ML at 490 degrees C under an arsenic arrival flux of 0.6 ML/s. From the infilling of the hole prior to QD formation, we estimate a net indium surface flux towards the hole of similar to 7 times the incident flux. The substrate temperature does not significantly alter the dot distribution over the range (470-510) degrees C. However, the QDP formation is very sensitive to the arsenic overpressure over the range (0.6-1.2) ML/s because of a partial collapse of the nanohole, due to mass transport as the substrate passes through the (2 x 4) to c(4 x 4) surface reconstruction around 500 degrees C. (C) 2011 Elsevier B.V. All rights reserved.