Spectral characteristics of single InAs/InGaAs quantum dots in a quantum well

Abstract

Self assembled InAs quantum dots embedded in an InGaAs quantum well were grown by molecular beam epitaxy. At room temperature these dots in a well (DWELLS) have an emission wavelength of 1.3 µm. Small mesas with lateral sizes down to 200 × 200 nm 2 were fabricated by electron beam lithography and etching techniques. By photoluminescence spectroscopy at low temperatures we observe narrow lines, which we attribute to excitons and excitonic molecules. Biexciton binding energies ranging between 3.5-5 meV are found.1 Introduction There has been considerable interest in the development of gain material with layers of self assembled quantum dots emitting at telecommunication wavelength windows (1.3 and 1.55 µm) [1 -2]. For emission at 1.3 µm the InAs dots are usually embedded in In x Ga 1-x As layers, according to the dot in a well (DWELL) concept [3]. Up to now most investigations of DWELLs are related to semiconductor lasers or to the optical properties of dot ensembles. In contrast, there exists no information on the spectral characteristics of single dots.We have grown self assembled InAs quantum dots embedded in the center of an In 0.15 Ga 0.85 As quantum well by molecular beam epitaxy. Using electron beam lithography and wet etching techniques small mesas with only a few quantum dots were fabricated. At room temperature the quantum dots have an emission wavelength of 1.3 µm. By photoluminescence spectroscopy at low temperatures, we observe the emission lines of excitons and biexcitons in single dots. The assignment of exciton and biexciton recombination is based on the dependence of these states on the characteristic excitation power intensity. Biexciton binding energies ranging from 3.5 -5 meV are obtained for the present dots. Our studies demonstrate that single quantum dot spectroscopy can be carried out far beyond the Si CCD sensitivity range using InGaAs array detectors. This extends the number of systems accessible for single dot studies considerably, permitting, e.g., the study of single InAs/InAlGaAs/InP dashes or GaSb dots.