For the development of information technology, more and more memory arrays are needed. Recently, memristors have been the most promising candidates for the creation of modern universal memory. The possibility of light stimulated resistive switching (RS) is promising for creating optical computers, technical vision and neuron networks. The studied SixGeyOz solid alloys films (~50-65 nm) were obtained by simultaneous evaporation of GeO2 and SiO2 (or SiO) powders in high vacuum (10-8 Torr) and deposition onto n+-type, p+-type Si(001), and on Al/SiO2/Si(001) heated up to 100°C. The transparent indium tin oxide (ITO) contacts were used as top electrode. It was found, that as-deposited GeOx[SiO](1-x) films contain amorphous Ge (a-Ge) nanoclusters. The furnace annealing at temperature 500 °C lead to further forming of a-Ge clusters in both types of the films. Reversible (up to several thousand cycles) RS from high resistance state (HRS) to low resistance state (LRS) (memristor effect) were observed for the semiconductor-dielectric-metal structures, namely p+-Si (or n+-Si)/ GeO[SiO2] (or GeO[SiO]) /ITO structures (MIS structures) in air atmosphere. Both negative and positive photoconductivity was observed in the annealed MIS structure when both negative/positive voltage biases were applied to the top ITO electrode. This is possibly due to light-stimulated recharging of holes from a-Ge nanoclusters, which act as deep traps. The effects of light-induced RS was observed for annealed MIS structures based on GeO[SiO] films with a-Ge nanoclusters. These results are promising for creation of photomemristors and optoelectronic devices combining the properties of a memristor.
The processes involved in picosecond infrared pulsed laser annealing of multylayer structures consisting of alternating thin films of amorphous silicon and germanium were investigated. The films were fabricated by plasma-chemical deposition on Si(001) and glass substrates. An analysis of structural transformation of Ge/Si multi-nanolayers was performed using Raman spectroscopy. Regimes of annealing were found when the Ge layers are partially crystallized while the Si layers remain amorphous without noticeable intermixing of Ge and Si. The developed approach can be used for creation of GeSi solid alloys (which can be used in memristors on not refractive substrates) and also for creation of Si based p-i-n structures on non-refractory substrates with Ge nanoclusters in i-layer, that can enhance the efficiency of thin film solar cells.
Silicon nanocrystals and germanium nanolayers and nanocrystals were created into i-layers of p–i–n structures based on thin hydrogenated amorphous silicon films. The nanocrystals were formed using pulsed laser annealing with an excimer XeCl laser generating pulses with the wavelength of 308 nm and the duration of 15 ns. The laser fluence was varied from 100 (that is below the melting threshold) to 250 mJ/cm2 (above the threshold). The laser treatment allowed the formation of the nanoscrystals with the average size from 2 to 5 nm, depending on the laser-annealing parameters. The size of nanocrystals (in Si and Ge layers) and their Si-Ge composition (in GeSi alloy structures) was estimated through Raman spectra analysis. The structural parameters of Si, Ge and GeSi nanocrystals were also studied using electron microscopy and atomic force microscopy. Current–voltage measurements showed that the p–i–n structures exhibit diode characteristics. The diodes with Si nanocrystals produced the electroluminescence peak in the infrared range (0.9–1.0 eV), which spectral position was dependent on the laser annealing conditions. It was suggested that radiative transitions are related to the nanocrystal/amorphous silicon matrix interface states. The proposed approach can be used for producing of solar cells or light-emitting diodes on non-refractory substrates.
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