Search

We report on the near-infrared (NIR) photoresponse of a micropatterned Ge/Si quantum dot (QD) pin photodiode at different angles of radiation incidence. The photon-trapping hole array was etched through the n+-type top contact layer to reach the buried QDs. The normal-incidence responsivity was observed to be resonantly increased at wavelengths of 1.4, 1.7, and 1.9 μ m by factors of 40, 33, and 30, respectively, compared with the reference detector without holes. As the incident angle θ increases, the resonance peaks are disappeared and at θ > 40 ∘ a new resonance with a 25 × enhancement arises at a wavelength of 1.8 μ m. Simulation of the near-field intensity, Poynting vector distribution and wave polarization showed that at small θ , the strong electric field is primarily localized under the air holes (1.4 μ m, TM mode) or between the holes (1.7 and 1.9 μ m, TE modes) inside the region occupied by QDs, resulting in the strong NIR photocurrent. At large θ , the dominant resonance detected at 1.8 μ m is the result of coupling between the TE and TM modes and formation of a mixed near-field state. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental studies and analysis of the dynamics (changes in characteristics) of the photoluminescence (PL) spectrum of a SiNx/SiO2 dielectric heterostructure with a change in the energy of exciting photons in the range of comparable and smaller values of the band gap of SiNx and SiO2 layers. The experimental dependences of the peak energy of the PL spectra, the PL intensity of the corresponding peak energy, and the Stokes shift on the excitation photon energy are found. The existence of two regions of excitation photon energies, in which these dependences have a fundamentally different character: monotonic (linear or exponential) or nonmonotonic, is found. We have concluded that small-radius excitons and hot electron–hole pairs are mainly PL emitting centers. They are localized in the interface layer, and their radii do not exceed the size of the crystalline cells of silicon dioxide and silicon nitride. The dynamics of the PL spectrum is due to the evolution of their state during multiphonon interaction with crystal lattice nodes. The conclusions obtained are of a general nature for dielectric heterogeneous layered nanostructures. The exciton masses and binding energies, which determine the PL and its dynamics, were calculated specifically for the superlattice under study. Types of excitons excited in the a SiNx/SiO2 superlattice in region their interface Spatially indirect 2DIX and 3DIX excitons with an electron in SiNx and a hole in SiO2; 2D excitons in the both layers SiO2 and SiO2; 2DBLX excitons in the area of the border between the layers; 3D excitons. The arrows indicate the direction of excitons travel. [ABSTRACT FROM AUTHOR]

The radiation-induced phenomena of CaSi2 crystal growth were investigated, both directly during the epitaxial CaF2 growth on Si (111) and film irradiation with fast electrons on Si (111) after its formation, while maintaining the specified film thickness, substrate temperature and radiation dose. Irradiation in the process of the epitaxial CaF2 film growth leads to the formation of CaSi2 nanowhiskers with an average size of 5 µm oriented along the direction <110>. The electron irradiation of the formed film, under similar conditions, leads to the homogeneous nucleation of CaSi2 crystals and their proliferation as inclusions in the CaF2 film. It is shown that both approaches lead to the formation of CaSi2 crystals of the 3R polymorph in the irradiated region of a 10 nm thick CaF2 layer. [ABSTRACT FROM AUTHOR]

Large-area periodical pattern on Si(100) was fabricated using combination of nanoimprint lithography and ion irradiation through mask. Ordered structures with grooves and ridges were prepared by the selective etching of regions amorphized by ion irradiation. Laterally ordered chains of Ge nanoislands were grown by molecular beam epitaxy of Ge on the pre-patterned Si substrates. It was shown, that the location of subsequently grown Ge nanoislands depends upon the sidewall inclination in grooves. The effect is ascribed to strain induced by Ge interstitials under the groove's bottom. Our proposal was confirmed by molecular dynamics calculations that allowed the determination of strain in grooves as dependent on the groove's shape. [ABSTRACT FROM AUTHOR]

Electron states in Ge/Si heterostructures with nanodisc shaped quantum dots (QDs) were studied using the electron spin resonance (ESR) method. Three ESR signals were observed under light illumination of the samples. The analysis of the angular dependences of the ESR spectra allows one performing signal assignment. Two ESR signals observed in the dark, as well as under illumination, are related to the electrons localized due to the strain at the top edges and base edges of the nanodiscs, while the third ESR signal observed only under illumination is related to the electrons localized in the Si layer above (or under) the central parts of the nanodiscs due to the Coulomb interaction with photoholes. A comparison with ESR results obtained for structures with lens-shaped QDs was performed. It was found that the nanodisc shape is crucial for the simultaneous localization of three electrons with different g values on the same QD. In the case of lens shaped QDs, only two ESR signals corresponding to the electrons localized at the QD top and base edges of QDs were observed. [ABSTRACT FROM AUTHOR]