Extending the spectral range of CdSe/ZnSe quantum wells by strain engineering

Abstract

We demonstrate efficient room-temperature photoluminescence and spectral tuning of epitaxially grown ZnSe/CdSe quantum well structures almost over the whole visible spectrum (470-600 nm wavelength). The key element to achieve the observed high quantum efficiency and enormous tuning range was the implementation of a special strain engineering technique, which allows us to suppress substantial lattice relaxation of CdSe on ZnSe. Previous studies indicated that a CdSe coverage exceeding 3 ML on ZnSe results in the formation of extensive lattice defects and complete quenching of the photoluminescence at low and room temperature. In contrast, our approach of strain engineering enables the deposition of planar CdSe quantum wells with a thickness ranging from 1 to 6 ML with excellent optical properties. We attribute the observed experimental features to a controllable strain compensation effect that is present in an alternating system of tensile and compressively strained epitaxial layers and supported this model by calculations of the transition energies of the ZnSe/CdSe quantum wells. PACS number(s): 85.60.−q, 71.20.Mq, 78.55.−m, 78.67.−n 1098-0121/2015/91(3)/035409(8) 035409-1

Optical properties of strain-compensated CdSe/ZnSe/(Zn,Mg)Se quantum well microdisks

“…The real QW widths were derived from reflection high energy electron diffraction (RHEED) measurements. Further details on the growth and properties of such samples are described elsewhere [19].…”

“…The luminescence of the two thickest QW samples with 4.7 ML and 5.6 ML CdSe is further red-shifted to ∼ 2.3 eV and ∼ 2.05 eV, respectively. It should be noted, that these QW thicknesses cannot be realized on standard (001)-GaAs substrates without the strain engineering technique [19], as the strain in the CdSe (e.g. lattice mismatch ∼ 6.7 % to GaAs) causes the formation of quantum dots for CdSe layers exceeding 2.1 ML [24,25].…”

“…waveguide-coupled microdisks) fabricated from the same sample chip, longer emission wavelength would be preferred to reduce the relatively strong photon re-absorption probability in the ZnSe host crystal starting in the blue spectral range. In this context we have recently established so called "strain-engineered" CdSe/ZnSe/(Zn,Mg)Se QWs grown on (In,Ga)As substrates: Here efficient room-and low-temperature photoluminescence and spectral tunability almost over the whole visible range (470 − 600 nm wavelength) was achieved just by the variation of the CdSe well width between 1 − 6 monolayer (ML) [19] .…”

Free‐Standing ZnSe‐Based Microdisk Resonators: Influence of Edge Roughness on the Optical Quality and Reducing Degradation with Supported Geometry

“…[1,2] ZnSe-based structures have the additional advantage of being nearly lattice-matched to GaAs which allows for a high quality (i.e., low defect and dislocation densities) of epitaxially grown structures on this widely used substrate. [3][4][5][6] Microdisk resonators offer a small mode volume combined with high optical quality because total internal reflection contains light in constructively interfering whispering gallery modes (WGMs) inside these structures. These properties make microdisks interesting candidates for the study of strong light-matter interaction [7] as well as for the emission of single photons utilizing the cavities' high Purcell factors.…”

“…[ 1,2 ] ZnSe‐based structures have the additional advantage of being nearly lattice‐matched to GaAs which allows for a high quality (i.e., low defect and dislocation densities) of epitaxially grown structures on this widely used substrate. [ 3–6 ]…”