Microstructure and optical response optimization of Ge/Si quantum dots transformed from the sputtering-grown Ge thin film by manipulating the thermal annealing

Abstract

A series of zero-dimensional Ge/Si quantum dots (QDs) samples are fabricated by inducing the transformation from the two-dimensional Ge thin film, which is grown by the traditional direct current (DC) magnetron sputtering, via regulating the annealing process. The QD density increases sharply after the post rapid thermal annealing (PRTA). The observations of atomic force microscopy (AFM) and Raman spectroscopy suggest that the good morphology of Ge QDs results from an appropriate thermodynamics and kinetics surrounding shaped by the cooperative interaction of the Ge-Si lattice mismatch, the film's surface temperature, and the difference in thermal expansion coefficients between Ge and Si. The photoluminescence (PL) peaks of Ge QDs are detected in monolayer Ge QDs with ultrahigh density at 17 K. The Metal-Ge/Si QDs-Metal (MGM) photodetector fabricated from the ultrahigh-density QDs sample exhibits a relatively high current gain, absolute photoelectric responsivity, and internal quantum efficiency (IQE). Our results demonstrate that the high-quality Ge QDs with strong light absorption and quantum confinement effect can be realized by modulating DC magnetron sputtering and the PRTA process. This paves the way for realizing silicon-based optoelectronic devices with high performance by the traditional, relatively low-cost, and large-scale production nanomaterial fabricating method.

Morphology and structure evolution of multilayered Ge/Si quantum dots grown by magnetron sputtering

“…As Figure 5 shows, the Raman spectra of samples M 550 , M 650 , and M 750 , a strong characteristic peak stem from Ge-Ge transverse optical vibration was observed at around 300 cm −1 in each sample. The symmetrical shape and low FWHM (full width at half maximum) of the Ge-Ge peak indicated that the deposited Ge layers have good crystallinity, which was consistent with our previous work [15] in which Ge has a high crystallization while the growth temperature > 550 • C. The broad peak near 400 cm −1 shown in each sample was caused by the vibration of the Ge-Si intermixed atoms, the increase of the peak intensity and the decrease of the peak width as the growth temperature rose from 550 • C to 750 • C meant the Ge-Si intermixing intensified with the accelerated diffusion of atoms, which confirmed the inference from Figures 3 and 4 that the growth and evolution of QDs in samples M 550 , M 650 , and M 750 was accompanied by the process of mutual mixing of atoms.…”

“…In recent years, fruitful research [11][12][13][14] of fabricating QDs by magnetron sputtering have negated the preexisting preconception that the high kinetic energy of particles and the high deposition rate of magnetron ion beam sputtering might induce drastic growth that leads to the formation of polycrystalline islands and the inhibition of the formation of self assembled QDs. Magnetron sputtering is gradually developing into an emerging QD growth technique even though its relevant literatures are still few, and the corresponding obtained evolution mechanism of QDs are still focused on the single-layer structure.…”

“…Magnetron sputtering is gradually developing into an emerging QD growth technique even though its relevant literatures are still few, and the corresponding obtained evolution mechanism of QDs are still focused on the single-layer structure. Under such circumstances, on the basis of the empirical parameters obtained from single-layer Ge/Si QDs fabricated by magnetron sputtering in our previous work [13,14], magnetron sputtering was proposed to study the growth of multilayered Ge/Si QDs to explore a new approach with both high growth e ciency and low operating cost.…”

“…In recent years, fruitful research [13][14][15][16] of fabricating QDs by magnetron sputtering have negated the preexisting preconception that the high kinetic energy of particles and the high deposition rate of magnetron ion beam sputtering might induce drastic growth that leads to the formation of polycrystalline islands and the inhibition of the formation of self-assembled QDs. The latest typical work on the growth of multilayer Ge/Si structures by magnetron sputtering was carried out by Peng et al [16], which involved the study of boron-doped Si 1-x Ge x films with multilayer structure of five periods, the work focused on the effects of post annealing on the structure of the samples and the influence of doped atoms on the thermoelectric properties of the samples.…”

High Curie Temperature Achieved in the Ferromagnetic MnxGe1−x/Si Quantum Dots Grown by Ion Beam Co-Sputtering

“…These evolutions agreed with that of their counterparts grown by MBE [10]. Furthermore, similar density-decrease and sizeincrease behaviors found in the pure Ge QDs, which experienced the post-annealing process, were attributed to the diffusion of Ge adatom and the Ostwald ripening growth of Ge islands [26,27]. It suggested that the bonding amount of Mn-Ge during the initial stage of nucleation formation can enhance the diffusion of Ge adatom and favor ripening growth.…”