CdSe quantum dots and their application in surface emitters and micropillars: A comparison to analogous nitride structures

Detlef Hommel 1Carsten Kruse 1Arne Gust 1Tomohiro Yamaguchi 1Stephan Figge 1Kai Otte 1Henning Lohmeyer 1Kathrin Sebald 1Jürgen Gutowski 1Roland Kröger 1Angelika Pretorius 1Andreas Rosenauer 1Jan Wiersig 2Norman Bär 2Frank Jahnke 2

1. University of Bremen, Institute of Solid State Physics, Kufsteiner Strasse 1, Bremen 28359, Germany
2. University of Bremen, Institute of Theoretical Physics, Bremen 28359, Germany

Abstract

The growth of CdSe quantum dots (QDs) embedded in a ZnMgSSe matrix will be discussed. Laser diodes with CdSe/ZnSSe quantum dot stacks show a superior stability compared to conventional LDs with a quantum well as optically active region. For low power applications CdSe QDs as active region can be a real alternative to other semiconductor materials for the green spectral region. Approaches to reach a single photon emitter at room temperature will be presented. The monolithic growth of a vertical cavity surface emitting laser (VCSEL) requires a reflectivity well above 99%. This can be realized by stacks of distributed Bragg reflectors (DBR). For the low index DBR a short period superlattice ZnCdSSe/MgSe is used. The stop-band can be tuned over the whole visible spectral region. Optically pumped lasing of such a monolithic VCSEL has been obtained. Using a focused ion beam (FIB) for nano-structuring, air gap micropillars can be realized with a very high aspect ratio. The dependence of the optical modes on pillar diameter will be presented including theoretical modelling. First results on CdSe QDs in micropillars show the Purcell effect (enhancement of emission) when such a QD comes in resonance with the cavity mode.
InGaN quantum dots can be easily realized on open surfaces but are highly unstable when overgrown by GaN. Using a novel growth procedure the problems can be overcome and evidence for single quantum dot emission was obtained. Such InGaN quantum dots show a high T-stability up to 150 K which make them, in connection with their low density of mid 108 cm-2, a good candidate for single photon emitters. The approach developed for II-VI has been used for nitrides as well to obtain high reflectivity DBRs for VCSELs. One problem here is the cracking due to a strong thermal mismatch of the materials (AlN-GaN). Nevertheless, first microcavities containing InGaN quantum wells could be realized showing the characteristic optical modes.

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Presentation: Invited oral at E-MRS Fall Meeting 2006, Symposium F, by Detlef Hommel
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-06-14 11:48
Revised:   2009-06-07 00:44
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