SANDiE Partner P15

Universidade de Aveiro, Portugal

Multilayers of Ge have been deposited on (001)Si at low temperatures (250 and 300°C) and investigated by several complementary techniques. AFM measurements suggested that QDs could be formed for the deposition of 10 ML of Ge or more. The X-ray reciprocal space maps showed that a pseudomorphic growth was achieved. In the PL, only Ge QWs were observed for low Ge covering.

The formation of Ge QDs grown on an ultrathin interlayer of SiO2 on top of a (001)Si substrate has been investigated as a function of the thicknesses of the SiO2 interlayer (0.5, 0.75 or 1 monolayer) and the Ge layer (0.3, 0.6 or 0.9 nm). The structural characterization was performed by Rutherford backscattering spectroscopy (RBS). PL studies were done to characterize the optical behavior of all samples. The results suggest the formation of Ge nanoislands for the sample with 1 ML of SiO2 and 0.9 nm of Ge, and exclude their formation for samples with lower SiO2 and Ge layer thicknesses. We also observed an influence of the SiO2 interlayer thickness in the QD formation.

A set of samples incorporating multiple layers of Ge QDs grown on Si at 700°C via the Stranski-Krastanow mechanism has been investigated. Using RBS/channeling we determined the multilayer periodicity; a tetragonal distortion of (1.8 ± 0.2)% was calculated for the first Ge layer, indicating a possible relaxation process. The RBS simulation shows that the topmost Ge layer is strongly mixed with Si.

(001)Silicon has been co-implanted with Mn and As ions and subjected to an annealing. The samples have been investigated by means of the SQUID magnetometry, ferromagnetic resonance (FMR), RBS, HRTEM, electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS) in the TEM. HRTEM has shown the formation of two types of crystalline nanoclusters: small ones with a diameter of 10-20 nm and larger ones with a diameter of ca. 100 nm. According to TEM-EDS data, the former consist of Mn and As, whereas the latter of Mn only. The FMR spectra reveal the existence of magnetic particles with the hard magnetization axis oriented along the four <111> axes of the Si crystal and a smaller anisotropy in the perpendicular plane. The SQUID measurements prove the existence of ferromagnetism with the Curie temperature well above the maximum measurement temperature of 380 K.

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last update: 28 February 2019, A. Weber