Photoluminescence from InGaAs/GaAs Quantum Dots in a High Electric Field

Abstract

Growing interest in semiconductor quantum dots (QDs) results both from their peculiar properties and their prospective applications in optoelectronics. Semiconductor laser devices with QDs have been shown to have lower threshold current density, higher differential gain, and higher thermal stability as compared to their quantum well-based counterparts [1–2]. The 3 dimensional confinement of electronic motion in QDs results in a S-like density of states, which is crucial to QD properties [3]. The energy distribution of these levels depends on the size of a particular dot. Therefore the QD photoluminescence (PL) spectra obtained under a non-resonant excitation, which influences a large ensemble of QDs, have the form of Gaussian peak with a broadening factor depending on the size distribution of the QDs [4–5]. With a decrease of the number of excited QDs, well reproducible individual peaks of ground states can be observed in the PL spectrum. The most successful way of fabricating QDs makes use of the Stranski-Krastanow mode of growth. Deposition of a mismatched material layer (such as InGaAs on GaAs) proceeds in two steps: first a very thin layer of highly strained material is grown, forming the so called wetting layer (WL), then the StranskiKrastanow growth mode transition takes place, resulting in the formation of 3dimensional highly strained islands [6–8]. The areal density and shape strongly depends on the substrate orientation and growth conditions.