Optical absorption in array of Ge/Al-shell nanoparticles in an Alumina matrix

Abstract

The absorption spectra in array of Ge, Al and Ge/Al-shell nanoparticles immersed in alumina (Al 2 o 3) matrix is calculated in framework of ab initio macroscopic dielectric model. It is demonstrated that absorption is strongly enhanced when germanium nanospheres are encapsulated by Al-shell. Two absorption peaks, appearing in the spectra, correspond to low energy ω + and high energy ω − plasmons which lie in visible and ultraviolet frequency range, respectively. It is demonstrated that in Ge/Al-shell composite the ω + plasmon exists only because quantum confinement effect which provides larger Ge band gap (Δ ~ 1.5 eV) and thus prevent decay of ω + plasmon to continuum of interband electron-hole excitation in semiconducting core. Absorption in visible frequency range enhances additional 3 times when alumina is replaced by large dielectric constant insulator, such as SiC, and additional 6 times when Ge core is replaced by wide band-gap insulator, such as Si 3 n 4. Strong enhancement of optical absorption in visible frequency range make this composites suitable for optoelectronic application, such as solar cells or light emitting devices. The simulated plasmon peaks are brought in connection with peaks appearing in ellipsometry measurements.

Ge Quantum Dots Coated with Metal Shells (Al, Ta, and Ti) Embedded in Alumina Thin Films for Solar Energy Conversion

“…The films from the first class (Al3, Ta2, Ta3, and Ti3), all have interconnected metal shells (as visible from the icons of the QD structure in Figure a–c). The interconnected shells cause the appearance of this peak, as theoretically predicted in ref (Figure ). The films with isolated core–shell QDs do not show absorption in that energy range, which is in accordance with the theory.…”

“…On the other hand, too thick shells provide a smaller enhancement. The increased field enhancement in the core is a consequence of the low-energy bonding mode excited at the core–shell nanoparticle (Figure f–h), which shifts to longer wavelengths and decreases its intensity as the shell-to-core ratio increases. , Additionally, a too thick shell may hamper efficient extraction of photo-generated carriers from the semiconductor core.…”

“…Very recent theoretical studies have shown a great potential of Ge-core Alshell nanoparticles. 27 The systems analyzed there show a variety of different phenomena that enable a strong manipulation of the material dielectric properties. Although there are many reports about metal-core semiconductor-shell QDs and several reports about semiconductor-core metal-shell structures, 28 there is no experimental realization yet of a Gecore metal-shell system that should support the theoretical predictions.…”

“…Germanium (Ge) QDs embedded in oxide matrices were extensively studied both theoretically and experimentally due to their strong confinement effects and compatibility with the modern nanotechnology. − The production of more complex Ge-based QDs having Ge-core Si-shell internal structure and their properties recently intrigued researchers. − The core–shell geometry with a size of only a few nanometers causes specific confinement effects in semiconductors, resulting in charge separation in space, significant reduction of recombination rates, strong enhancement of absorption, and tunability of the absorption curve. Very recent theoretical studies have shown a great potential of Ge-core Al-shell nanoparticles . The systems analyzed there show a variety of different phenomena that enable a strong manipulation of the material dielectric properties.…”

Ge/Al and Ge/Si3N4/Al Core/Shell Quantum Dot Lattices in Alumina: Boosting the Spectral Response by Tensile Strain

“…Semiconductor core-, metal-shell QDs nowadays draw strong attention due to their specific properties, leading to different nanotechnology applications [18]. In this structure, an additional manipulation of the material's properties, besides the confinement effects, is possible due to the shell properties.…”