New concepts for ZnTe-based microcavities

Wojciech Pacuski 1,2Carsten Kruse 1Stephan Figge 1Kristian Frank 1Marco Schowalter 1Andreas Rosenauer 1Matthias Florian 1Frank Jahnke 1Tomasz Jakubczyk 2Jan A. Gaj 2Mihai Stoica 3Mariuca Gartner 3Detlef Hommel 1

1. University of Bremen, Institute of Solid State Physics, P.O. Box 330440, Bremen 28334, Germany
2. University of Warsaw, Institute of Experimental Physics (IFDUW), Hoża 69, Warsaw 00-681, Poland
3. Instituite of Physical Chemsitry (ICF), Splaiul Independentei 202, Bucharest 060021, Romania

Abstract

We report on the realization and a detailed characterization of photonic structures based on II-VI compounds and designed for ZnTe substrates. Our motivation is to enhance CdTe quantum dots (QDs) emission using cavity effects. Distributed Bragg reflectors (DBRs) lattice matched to ZnTe were developed in order to create a microcavity and to confine light in direction perpendicular to the sample plane [1]. Micropillars were etched using a focused ion beam (FIB) in order to confine light in the sample plane by internal reflection. Inside the microcavity, a sheet of CdTe QDs was introduced. Our structures were grown using molecular beam epitaxy (MBE) on GaAs substrate followed by a 1 μm thick fully relaxed ZnTe buffer layer. The requirements of the lattice matching and of a high refractive index step are fulfilled using a novel method. Instead of using ternary or quaternary compounds, the low refractive index layer is made of a short period triple superlattice based only on the binary compounds: ZnTe, MgTe, and MgSe. Layer thicknesses in the superlattice are chosen to balance strain and fit to ZnTe. The high refractive index layer is ZnTe. Pseudomorphic growth of the structure on the ZnTe buffer was confirmed using high resolution X-ray diffraction (HRXRD). Images of the main components of the structure, i.e. cavity, QDs, and DBR pairs with triple supperlattice were obtained using scanning transmission electron microscopy (STEM). The reflectivity spectrum reveals a large width of the stopband (over 60 nm) and a cavity mode at about 620 nm with a linewidth corresponding to Q factor of 1000. Ellipsometry studies were performed separately for all materials used in the structure in order to determine both real and imaginary part of refractive indices. The determined parameters are used for calculation of optical properties of photonic structures.
[1] W. Pacuski, C. Kruse, S. Figge, D. Hommel, Appl. Phys. Lett. 94, 191108 (2009).

 

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Presentation: Invited oral at E-MRS Fall Meeting 2009, Symposium C, by Wojciech Pacuski
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-25 18:14
Revised:   2009-06-15 15:06