In this work we report on a self-assembled growth of a Ge quantum dot lattice in a single 600-nm-thick Ge+ Al 2 O 3 layer during magnetron sputtering deposition of a Ge+ Al 2 O 3 mixture at an elevated substrate temperature. The self-assembly results in the formation of a well-ordered three-dimensional body-centered tetragonal quantum dot lattice within the whole deposited volume. The quantum dots formed are very small in size ͑less than 4.0 nm͒, have a narrow size distribution and a large packing density. The parameters of the quantum dot lattice can be tuned by changing the deposition parameters. The self-ordering of the quantum dots is explained by diffusion-mediated nucleation and surface-morphology effects and simulated by a kinetic Monte Carlo model.

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We report on the formation of a regularly ordered void lattice with a void size of about 4 nm in an alumina matrix. The voids were formed by thermal treatment of a well-ordered three-dimensional Ge quantum dot lattice formed earlier by self-assembled growth in an alumina matrix during magnetron sputtering codeposition of Ge+Al2O3. During the subsequent annealing the germanium atoms were lost from the film and so voids were produced. The positions of the voids are ordered in the same way as the Ge quantum dots that were present before annealing, while their sizes can be controlled by the deposition parameters.

In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C.

Ge NCs have attracted considerable attention because of their potential applications in nonvolatile memory and integrated optoelectronics. A number of groups have already proposed integrate flash memories based on Ge NCs embedded SiO 2 matrix [1]. Since Al 2 O 3 presents a high dielectric constant comparatively to SiO 2 , it is a good candidate to replace silica in flash memory systems, and therefore improve their performances [2]. Moreover, Al 2 O 3 presents good mechanical properties, and supports high temperature, which leads it to be an ideal material for Si processing conditions. However, a few studies have been reported on Ge NCs embedded in Al 2 O 3 matrix [3].In this work, Ge NCs embedded in Al 2 O 3 were grown on a commercial RF magnetron Alcatel SCM 650 apparatus using a conventional co-sputtering method. Two materials, Al 2 O 3 (99,99%) and polycrystalline Ge (99,99%), were simultaneously used as target to produce the doped films. Low electrical resistivity (3-6 Ω cm) n-type Si(111) 2 inches wafers were used as substrates. Prior to sputtering, a pressure of at least 1x10 -6 mbar was reached inside the chamber and in situ argon plasma treatment of target and substrates was performed in order to clean the surface and remove any impurities. More details of the samples preparation can be found in pervious works [4,5]. The as grown films were annealed at 800 ºC and 900 ºC, during one hour, under air pressure at 1,0x10 -6 and 1,0x10 -3 mbar, in order to improve the cristallinity of the Ge phase and to achieve control over the NCs size. With the aim to study the cristallinity and distribution of the Ge NCs size Raman spectroscopy, X-ray, and high resolution transmission electron microscopy (HRTEM) techniques were used. X-ray diffraction in conventional θ−2θ geometry (Philips PW1710) was performed towards the crystallographic structure investigation, using Cu K α radiation. The identification of the crystalline phases was made using the JCPDS (Joint Committee of Powder Diffraction) data base. Raman scattering spectra were obtained using a Jobin-Yvon T64000 system with an optical microanalysis system and a CCD detector, in a backscattering geometry. Raman spectroscopy was performed at room temperature using 514.5 nm and 488.0 nm line of an argon laser at a power of 50 μW focus on an area of the sample ~1 μm 2 . After preparing cross-section specimens by standard procedures the structure of the samples was examined using HRTEM.XRD diffraction shows the characteristic peaks of Ge diamond structure, which confirms the high cristallinity of our samples. Figure 1 illustrates the XRD diffraction of an as grown sample and after annealing. It is clear that the post grown annealing treatment leads to sharp peaks and a therefore better cristallinity. The average size of Ge NCs was estimated using the Debye-Scherrer equation [6]. Using Lorentzian functions to fit each XRD peak of the samples, we obtained mean diameter values of 3.0 nm and 5.3 nm for sample B (see table) before and after annealing, respectively. Figure 2 ...