Codeposition Of Ge Research Articles

Multiple Exciton Generation in 3D-Ordered Networks of Ge Quantum Wires in Alumina Matrix.

Thin films containing 3D-ordered semiconductor quantum wires offer a great tool to improve the properties of photosensitive devices. In the present work, we investigate the photo-generated current in thin films consisting of an interconnected 3D-ordered network of Ge quantum wires in an alumina matrix. The films are prepared using nitrogen-assisted magnetron sputtering co-deposition of Ge and Al2O3. We demonstrate a strong photocurrent generation in the films, much stronger than in similar films containing Ge quantum dots. The enhanced photocurrent generation is the consequence of the multiple exciton generation and the films’ specific structure that allows for efficient carrier transport. Thin film with the largest nitrogen content showed enhanced performance compared to other thin films with 1.6 excitons created after absorption of a single photon at an energy nearly equal to the double bandgap value. The bandgap value depends on the geometrical properties of the quantum wires, and it is close to the maximum of the solar irradiance in this case. In addition, we show that the multiple exciton generation is the most pronounced at the photon energy values equal to multiple values of the thin film bandgap.

Photo-sensitive Ge nanocrystal based films controlled by substrate deposition temperature

Lowering the temperature of crystallization by deposition of thin films on a heated substrate represents the easiest way to find new means to develop and improve new working devices based on nanocrystals embedded in thin films. The improvements are strongly related with the increasing of operation speed, substantially decreasing the energy consumption and reducing unit fabrication costs of the respective semiconductor devices. This approach avoids major problems, such as those related to diffusion or difficulties in controlling nanocrystallites size, which appear during thermal treatments at high temperatures after deposition. This article reports on a significant progress given by structuring Ge nanocrystals (Ge-NCs) embedded in silicon dioxide (SiO2) thin films by heating the substrate at 400 °C during co-deposition of Ge and SiO2 by magnetron sputtering. As a proof-of-concept, a Si/Ge-NCs:SiO2 photo-sensitive structure was fabricated thereof and characterized. The structure shows superior performance on broad operation bandwidth from visible to near-infrared, as strong rectification properties in dark, significant current rise in the inversion mode when illuminated, high responsivity, high photo-detectivity of 1014 Jones, quick response and significant conversion efficiency with peak value reaching 850% at −1 V and about 1000 nm. This simple preparation approach brings an important contribution to the effort of structuring Ge nanocrystallites in SiO2 thin films at a lower temperature for the purpose of using these materials for devices in optoelectronics, solar cells and electronics on flexible substrates.

Induced Co-Deposition of Cu-Ge Alloys

It is well known that some elements cannot be electrodeposited in pure form from aqueous solutions, but could instead be co-deposited with transition metals, forming alloys [1]. The codeposition of Fe, Ni, or Co with P, B, W, Mo and most recently Re have been reported and in most cases mechanisms have been proposed [2-5]. The induced codeposition of Ge however has been reviewed by Brenner in 1963 [1], but so far it has not been investigated in detail. Due to the potential importance of Cu-Ge alloys as candidate materials for next-generation interconnects, we have studied in detail their electrodeposition process from an alkaline tartrate-complexed electrolyte [6], and proposed an induced codeposition mechanism. Electrochemical processes occurring during the reduction of pure Cu, pure Ge and Cu-Ge alloys were studied by means of cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM) and electrochemical impedance spectroscopy (EIS) techniques. Cu reduction was found to be strongly inhibited at low overpotential by the addition of Ge in solution, due to the Ge4+ reduction to GeOH, which is adsorbed at the electrode. At higher overpotentials, GeOH is reduced to GeH [7], which could be dissociated by surface Cu, forming a Cu-Ge alloy. Cu-Ge thin films were grown under potential control and their composition, phase, morphology and microstructure were investigated. Ge fraction in the alloys increases with the applied overpotential up to ~ 30 at%, resulting in a phase transition from face-centered cubic solid solutions (a-phase) to an ordered orthorhombic Cu3Ge intermetallic compound (ɛ-phase). The dependence of resistivity on Ge content was also examined, showing a non-monotonic behavior. A minimum value was found for stoichiometric ɛ-Cu3Ge, displaying a resistivity of 7.5 μΩ cm-1 (~50 nm thickness) or 25 μΩ cm-1 (~1 μm thickness). The resistivity increase was linked to the slow but progressive incorporation of O into the films.

Formation and Optical Properties of Thin Mg<sub>2</sub>Ge Films on Si(001) Substrate

Thin Mg2Ge films were grown using two methods: a co-deposition of Ge and Mg on Si substrate kept at room temperature followed by annealing at 200 °C (solid phase epitaxy – SPE) and reactive deposition epitaxy (RDE) of Ge and Mg on Si at 200 °C. Optical properties of these structures were investigated in the photon energy range of 0.02–6.2 eV. Based on optical functions calculation, it was shown that SPE growth results in formation of a crystalline layer of Mg2Si, which exhibits a strong optical phonon originated from the substrate-film interface. In the case of RDE growth, the amount of Mg2Si is sufficiently lower, but Mg‑Si-Ge compound phonon appears. The estimate of a fundamental indirect transition value in the film is 0.72 eV for SPE growth method and 0.56 eV for RDE due to the ternary compound Mg-Ge-Si at the film-substrate interface.

Electrochemical Deposition of Germanium Sulfide from Room-Temperature Ionic Liquids and Subsequent Ag Doping in an Aqueous Solution

A facile room-temperature electrochemical deposition process for germanium sulfide (GeS(x)) has been developed with the use of an ionic liquid as an electrolyte. The electrodeposition mechanism follows the induced codeposition of Ge and S precursors in ionic liquids generating GeS(x) films. The electrodeposited GeS(x) films were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and Raman and X-ray photoelectron spectroscopy (XPS). An aqueous-based Ag doping method was used to dope electrochemically grown GeS(x) films with controlled doping compared to the conventional process, which can be used in next-generation solid-state memory devices.

Formation of void lattice after annealing of Ge quantum dot lattice in alumina matrix

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.

Formation of Ge-nanocrystals in SiO 2 matrix by magnetron sputtering and post-deposition thermal treatment

Germanium Quantum Dots (Ge QDs) were formed in SiO 2 by RT magnetron sputtering co-deposition of Ge and SiO 2 and subsequent annealing. Films were deposited in the form of alternating (Ge+SiO 2) layers (40:60 molar ratio) and pure SiO 2 layers, serving as spacers. Grazing incidence small angle x-ray scattering (GISAXS) was applied for structural characterization of the QDs synthesized in the SiO 2 amorphous matrix. The chemical composition and phase of the QDs were determined by Raman spectroscopy, and the spatial distribution and concentration of the Ge atoms by Rutherford Backscattering. The 2D GISAXS patterns, besides giving information on the layered structure, were used to reveal the onset of the synthesis of Ge QDs in SiO 2 and to determine the average size and shape of QDs. It has been shown that the insertion of spacer SiO 2 layers between (Ge+SiO 2) layers transforms the 3D growth of Ge QDs into a preferentially 2D growth, within each 7 nm thick (Ge+SiO 2) layer. This resulted in a considerably smaller average size of Ge QDs in the layered films. The synthesis of well crystallized, moderately sized, spherical Ge QDs was achieved by post-deposition annealing in the 700–800 ∘C range.

Epitaxial growth of ultrahigh density Ge1−xSnx quantum dots on Si (111) substrates by codeposition of Ge and Sn on ultrathin SiO2 films

A method to form epitaxial Ge1−xSnx quantum dots (QDs) on Si (111) substrates has been developed by codeposition of Ge and Sn on ultrathin SiO2 films with predeposited Ge nuclei. Hemispherical Ge1−xSnx QDs with an ultrahigh density (∼1012 cm−2) were epitaxially grown in the nanometer-size range. The QD size was controlled by changing the GeSn deposition amount. High-resolution transmission electron microscopy observations revealed that the main formed Ge1−xSnx QDs had less strain and no misfit dislocations.

Germanium nanoclusters in silica thin films

We have characterized the properties of Ge nanoclusters in silica films. The films are grown by physical vapor deposition (PVD) or ion-beam-assisted deposition (IBAD): by co-deposition of Ge and SiO 2 with and without the presence of an argon ion beam. The IBAD process affects the development and ultimate morphology of the nanoclusters. Rutherford backscattering (RBS) and index of refraction measurements give the volume fraction of Ge nanoclusters in the silica films and quantify the effects of sputtering on the ultimate film composition. At a Ge/SiO 2 arrival rate greater than or equal to 0.8, SiO 2 is preferentially sputtered; at lower arrival rates Ge is preferentially sputtered. Absorption measurements are used to deduce the effective band gap of the Ge nanoclusters and the growth of the nanoclusters with annealing. X-ray diffraction studies and transmission electron microscopy confirm that the IBAD processing accelerates the growth of the Ge nanoclusters at low annealing temperatures and inhibits the ultimate size of the nanoclusters, as compared to clusters in those films grown by PVD. Photoluminescence of the Ge-silica films is examined for the IBAD and PVD cases.

Alkali–germanium surface compound formation on a Ge(100)-(2×1) surface

Alkali–germanium surface compound formation and decomposition has been studied by means of temperature-programmed desorption (TPD), AES and EELS measurements using alkali metal and germanium codeposition on a Ge(100)-(2×1) surface at room temperature. At a sodium coverage ( ϴ Na) of one monolayer on a Ge(100) surface, the codeposition of Ge does not change the multipeak structure in the Na TPD spectra as compared to Na adsorption on bare Ge(100). A clear peak appears in the Na TPD spectra at around 490 K after Ge codeposition when ϴ Na>1 ML. Well pronounced EELS peaks situated at 5.5, 13 and 30 eV develop in the EELS spectra after Ge codeposition on sodium-covered Ge(100) surface, and are attributed to a Na–Ge compound. Two cycles consisting of K deposition followed by Ge deposition were carried out. Decomposition of a thus prepared K–Ge surface compound shows the same peak at 550 K in the K TPD spectra as in the Na–Ge case.

Characterization of termination layer of SiGe system through signatures of SiO and GeO species

In this paper, we describe a novel method of employing the phenomenon of oxygen chemisorption for surface atom identification on a SiGe surface. On a clean Si(100), dosing 100 L O 2 (1 Langmuir = 1 s at 1 × 10 −6 Torr) at room temperature gives rise to peaks at 7 and 10.2 eV in ultraviolet photoelectron spectroscopy with He I excitation (HeI UPS) and O 1s is observed at 532.3 eV in X-ray photoelectron spectroscopy (XPS). Corresponding spectra for Ge(100) are a single peak at 5.2 eV in HeI UPS and O 1s at 531.3 eV. These signature spectra of SiO and GeO species have been effectively employed for unambiguous characterization of the termination layer of SiGe surfaces. Upon dosing at room temperature, on a sample prepared by depositing 5 Å Ge on Si(100) at 550°C, oxygen bonds with Ge atoms are forming GeO, exclusively. This indicates surface termination entirely by Ge atoms. Oxygen adsorption at room temperature, on a sample prepared by codeposition of Ge and Si (total 5 Å) onto Si(100) at 550°C, forms a mixed oxide suggesting a surface termination by both Ge and Si atoms.

Oxygen chemisorption as a tool for atom discrimination in the SiGe termination layer

This Letter describes a novel method of employing the phenomenon of oxygen chemisorption for atom discrimination in the SiGe surface termination layer. Formation of SiO species on clean Si(100) gives rise to peaks at 7 and 10.2 eV in He I UPS and a peak at 532.3 eV in O 1s XPS. Whereas GeO species on a Ge(100) surface exhibits a single peak at 5.2 eV in He I UPS and a peak at 531.3 eV in O 1s XPS. These signature spectra of SiO and GeO species have been effectively employed for atom discrimination in the termination layer of SiGe surfaces. Upon dosing at room temperature, on a sample prepared by depositing 5ÅGe on Si(100) at 550°C, oxygen bonds with Ge atoms forming GeO, exclusively. This indicates termination entirely by Ge atoms. Oxygen adsorption at room temperature, on a sample prepared by codeposition of Ge and Si (total 5Å) onto Si(100) at 550°C, forms a mixture of SiO and GeO species suggesting a surface termination by both Ge and Si atoms.