Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 31: Poster II

HL 31.36: Poster

Dienstag, 26. Februar 2008, 16:30–19:00, Poster D

Cd-loss of CdSe quantum dots in ZnSe during MBE growth — •Utz Bass, Jean Geurts, Fabian Eschenbach, Suddhasatta Mahapatra, and Karl Brunner — Universität Würzburg, Physikalisches Institut, Experimentelle Physik III, Am Hubland, 97074 Würzburg

CdSe quantum dots (QD) on ZnSe grown by a special MBE technique are distinct QDs with lateral sizes up to 50 nm in AFM, a necessary property for application as single photon sources. In contrast, those QDs when capped with ZnSe appear significantly smaller in TEM-Images, indicating a severe segregation of Cd during overgrowth. This behaviour was analyzed by X-ray diffraction and Raman spectroscopy.

A detailed analysis by X-Ray interferometry for a series of samples with 0<d_CdSe<3 ML reveals an increasing loss of Cd (Δ d_CdSe) up to 0.7 ML for d_CdSe of 2.6 ML within the Cd(Zn)Se layer.

The segregation of Cd into the ZnSe layer was also evaluated by Raman spectroscopy. The frequency shift of the ZnSe LO phonon amounts to 3 cm⁻¹ for Δ d_CdSe= 0.7 ML, corresponding to a Cd content of 20%. This result indicates a strongly inhomogeneous segregation, resulting in Cd-rich regions above the QDs, which contribute predominantly under our nearly resonant Raman excitation conditions.

The combined analysis gives a congruent picture of Cd segregation in the ZnSe capping layer.