Optical and structural analysis of Ge quantum dots embedded in strained Si quantum wells grown on patterned substrates
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Optical and structural analysis of Ge quantum dots embedded in strained Si quantum wells grown on patterned substrates A. Beyer, E. Müller, H. Sigg, S. Stutz, C. David, D. Grützmacher and K. Ensslin1 Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen-PSI, Switzerland 1 Solid State Physics Laboratory, Swiss Federal Institute of Technology Zurich, CH-8093 Zürich, Switzerland
ABSTRACT Germanium quantum dots embedded in silicon have been used in the past to improve the opto-electronic properties of Si based materials. The idea is to overcome the limitation of the indirect band gap of Si by a strong localization of the carriers in quantum dots. However, the Ge quantum dots provide a strong carrier confinement only for the holes, the electrons are only weakly confined in the Si. In this study we embedded the Ge quantum dots in strained Si quantum wells grown on relaxed SiGe buffer layers. The strained Si quantum wells provide a confinement of the electrons in the vicinity of the Ge dots. The structures were deposited on planar as well as on patterned substrates by molecular beam epitaxy. The structural and optical properties of the samples were analyzed using high resolution cross sectional transmission electron microscopy (TEM) as well as low temperature photoluminescence. The size of the mesa structures have been used as experimental parameter. Relaxed buffer layers grown on line shaped mesa structures show a strongly reduced dislocation density. Consequently the deep luminescence attributed to dislocations in the buffer layers is strongly reduced and pronounced photoluminescence of the quantum structures grown on top of the buffer layers can be observed.
INTRODUCTION A promising way in the development of an silicon based light emitting device is to localize the charge carriers. The localization enhances the uncertainty of the momentum, which allows optical transitions without the use of phonons in an indirect bandgap material like silicon. Germanium islands embedded in silicon are known to improve the opto-electronic properties of silicon based materials [1,2]. These islands provide a strong confinement unfortunately only for the holes. The electrons are only weakly confined in the surrounding strained silicon. Recently it has been shown that this can be improved in vertically stacked germanium islands due to the strain induced into the silicon layer above the germanium dots [3]. Here we used a strained silicon quantum well grown on a relaxed SiGe buffer layer with the intent to improve the electron confinement. This quantum well will confine the electrons. We have embedded the germanium islands in the quantum well to establish an large wavefunction overlap between the electrons in the quantum well and the holes in the islands.
F14.8.1Mat. Res. Soc. Symp. Proc. Vol. 633 © 2001 Materials Research Society
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