Light-matter coupling in semiconductor microcavities has been intensively investigated over the past twenty years. Microcavities containing quantum dots (QDs) or quantum wells (QWs), led to the achievement of various devices for optoelectronics such as vertical cavity surface emitting lasers (VCSELs) [1] or resonant cavity light emitting diodes (RCLEDs) [2]. Etched pillar microcavities containing QDs allow controlling spatial, energetic and temporal properties of light emission [3,4]. The coherent coupling between light and matter in such structures is of great interest for quantum information processing. Compared to III-V compounds, the stronger carrier confinement and more robust excitonic states exhibited by II-VI compounds is expected to extend the fundamental investigations on light matter coupling and the functionalization of the devices to higher temperatures [5]. In addition, II-VI compounds based emitters are good candidates to answer the problem of the low efficiency of III-V based emitters in the green yellow range [6].
The fabrication of high quality microcavities relies on opposite constrains: lattice matching of the layers with different refractive index (crystalline quality) and high refractive index contrast (optical quality, photon confinement efficiency within the cavity). The additional question of the implementation of efficient light emitters in the cavity dedicated to the desired application (spectrally narrow tunable light emitter, VCSEL, investigation of the photon-exciton strong coupling) makes the successful realization of II-VI based microcavities a real challenge.
In this work, we present three groups of microcavities: based on selenide compounds, based on telluride compounds, and structures based on mixed selenide and telluride compounds. We focus on their possible applications in the field of optoelectronic devices and fundamental physics (VCSELs, narrow range light sources, studies of photon-exciton coupling).
Selenide based microcavities built on (Zn,Mg)Se and (Zn,Cd)Se layers containing CdSe quantum dots present the advantage of exhibiting a relatively short wavelength absorption (near or under 520 nm). In addition, CdSe / ZnSe quantum dots are known to be good light emitters and good candidates for room temperature emission. However, we show that the relatively low refractive index contrast reachable limits the light confinement and the quality factor. As a resultmicrocavities based on these compounds could be used to build narrow range emitters in the green – yellow range since the quality factor of the cavity plays a secondary role for these devices. Telluride based microcavities allowed us to reach a higher refractive index contrast which resulted in the growth of a fully lattice matched structure containing (Cd,Zn)Te QWs [7]. Here we present the observation of the photon-exciton strong coupling for such structures with a single QW. However, the lower band gap of telluride based materials restrains the applications of such structures to the spectral range over 650 nm. Good candidates for a wide range of practical applications and fundamental studies are found to be selenide-telluride based structures [8,9] exhibiting a high refractive index contrast and lower absorption edge wavelength. We show that the cavity mode can be obtained for wavelength as short as 560 nm. We present results obtained with structures (planar and pillar microcavities) lattice matched to ZnTe for yellow optoelectronics applications and prospects for novel structures based on Zn(Se,Te) and (Cd,Zn,Mg)Se layers.
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[7] J.-G. Rousset et al., ArXiv, 1210.1933 (2012).
[8] W. Pacuski et al., Appl. Phys. Lett., 94, 191108 (2009).
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