| In order to exploit the versatility of colloidal nanocrystals e.g. in the fabrication of devices, one has to accomplish the challenging task of incorporating them into high quality epitaxial thin films, which are compatible with molecular beam epitaxy (MBE) growth. Based on methods reported by our group in its first stage of development, we here present an optimized hybrid colloidal-epitaxial technique for deposition and incorporation of CdSe nanocrystals in high quality ZnSe epilayers. Structural characterizations show that the whole MBE grown structure is epitaxial and fully strained to the GaAs(001) substrate and furthermore exhibits a high crystalline quality. The successful integration of optically active nanocrystals enabled us to conduct a detailed study of the photoluminescence of different sorts of CNCs and the temperature dependence of their emission. The hybrid colloidal-epitaxial technique was also employed to study an additional aspect of matrix-host interaction, namely the enhancement of charge transfer from the epitaxial matrix into the incorporated CNCs by designing a graded energy gap structure. For this study, core nanocrystals, which typically suffer from lower PL efficiency and robustness towards processing conditions, were incorporated in matrices of either ZnSe or ZnMgSe (core-in-matrix) as well as into a single ZnSe quantum well within a ZnMgSe matrix (core-in-well). While almost no PL was detected from the core-in-matrix samples, the core-in-well samples' emission was clearly observed. This investigation suggests some guidelines for the potential integration of semiconductor nanocrystals as active building blocks in epitaxial optoelectronic devices. |
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