Synthesis of light emitting Ge nanocrystals by reactive RF sputtering

摘要

In this work we report the results of the synthesis, structural and optical characterization of SiO_2/Ge/SiO_2 heterostructures by reactive RF sputtering. The SiO_2 films were grown by reactive sputtering employing a plasma mixture of oxygen and argon. The Ge layer was grown employing an Ar atmosphere. The samples were prepared on p-type Si (111) substrates by reactive sputtering. The effect of the partial pressure of oxygen on the electronic properties of the heterostructure is reported[1]. Structural characterization was carried out by grazing angle X-ray difraction. Surface roughness was quantified by atomic force microscopy. The presence of Ge nanocrystals (Ge-NCs) was evidenced by X-ray diffraction. The vibrational properties were studied by Raman spectroscopy. The Raman spectra showed modes associated to germanium indicating the formation of low dimensionality germanium particles embedded within a SiO_2 matrix. Photoluminescence emission is observed around ～1.7 eV and it is associated to the quantum confinement of carriers in Ge-NCs. Ohmic contacts were deposited using a van der Pauw geometry employing an a AuSb alloy for the contacts. Temperature dependent Hall (T-Hall) measurements were done between 35 K and 150 K, using the van der Pauw method. The results indicated low resistivity values that could be explained due to some variable range hopping conduction mechanism.