Pulsed Low-energy Ion-beam Induced Nucleation and Growth of Ge Nanocrystals on SiO 2
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1020-GG06-11
Pulsed Low-energy Ion-beam Induced Nucleation and Growth of Ge Nanocrystals on SiO2 Anatoly Dvurechenskii1, Nataly Stepina1, Pavel Novikov1, Vladislav Armbrister1, Valery Kesler1, Anton Gutakovskii1, Victor Kirienko1, Zhanna Smagina1, and Reiner Groetzschel2 1 Siberian Branch of Russian Academy of Sciences, Institute of Semiconductor Physics, Novosibirsk, 630090, Russian Federation 2 Forschungszentrum Rossendorf, Dresden, D-01314, Germany ABSTRACT Pulsed low-energy (200 eV) ion-beam-induced nucleation during Ge deposition on thin SiO2 film was used to form dense homogeneous arrays of Ge nanocrystals. The ion-beam action is shown to stimulate the nucleation of Ge nanocrystals when being applied after thin Ge layer deposition. Temperature and flux variation was used to optimize the nanocrystal size and array density required for memory device. Kinetic Monte Carlo simulation shows that ion impacts open an additional channel of atom displacement from a nanocrystal onto SiO2 surface. This results both in decrease of the average nanocrystal size and in increase of nanocrystal density.
INTRODUCTION The use of nanocrystals (NCs) embedded in a dielectric matrix has been widely studied for diverse applications for a good number of years. Non-volatile memories are one of the attractive areas of applicability for semiconductor NCs. An advantage of the nano-floating gate memory over the continuous floating gate is its improved endurance due to preventing lateral charge transport. Faster writing/erasing time, lower operating voltage and longer retention time have been demonstrated in memory device based on Si NCs embedded in SiO2 [1,2]. Many research activities have been carried out on NC Si and Ge films grown on SiO2 substrates using, for example, molecular beam epitaxy (MBE) [3], chemical vapor deposition (CVD) [4], and
Figure 1. ESCA spectra for Ge deposition at 300°C with usual MBD (1) and ion-assisted MBD for "capped SiO2" (2) and "uncapped SiO2" (3) regimes. Left - peak of 2p Si, right peak of 2p Ge.
pulsed-laser deposition [5]. Various methods were used for fabrication of Si and Ge NCs embedded in dielectric matrix, such as ion beam synthesis [6], oxidation and reduction of Ge/Si NCs [7], rapid thermal annealing of cosputtered layers [8]. Recently King showed that Ge has
Figure 2. HREM image (upper part - cross-section, lower part - plan view) of nanocrystals on SiO2 JGe=0.08 ML/s, T=250°C.
the superior properties over Si as a charging nodes in a single-electron memory device (SEMD) in terms of the writing/erasing time and the operating voltage [4]. However, space distribution of NCs within dielectric obtained by most of these techniques is random. To suppress an undesirable effects resulted from the tunneling distance fluctuation, one should form in-plane arrangement of NCs. Another requirements that can be beyond the control are the size of NCs, their density and homogeneity in growth plane. That is the challenge for most of abovementioned growth methods. Our preliminary results [9] showed the stimula
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