Production of three-dimensional quantum dot lattice of Ge/Si core–shell quantum dots and Si/Ge layers in an alumina glass matrix

Abstract

Abstract. We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al 2 O 3 /Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells.

Ge/Si core/shell quantum dots in alumina: tuning the optical absorption by the core and shell size

“…The very recent calculations show that the effective band-gap and exciton binding energy are strongly dependent on the size of the core and shell [12,13]. Our recent studies demonstrated the possibility to produce Ge/Si core/shell QDs [14]. It is also shown that these materials indeed have specific absorption properties that significantly differ from the absorption of either Ge or Si QDs.…”

“…Finally, Ge/Si core/shell materials are more stable at higher temperatures. Ge QDs in alumina disintegrate at temperatures above 700°C, whereas in the core/shell system this limit is shifted to values above 800°C [14]. Optical properties, especially absorption, are important for potential solar cell materials.…”

“…The deposition conditions were chosen to ensure the selfassembled growth of QDs and their internal core/shell structure [14]. The thin films were deposited on glass and Si(100) substrates at the temperature of 300°C.…”

“…For the analysis, it was assumed that QDs are arranged in a 3D paracrystal body centered tetragonal (BCT) lattice and that they have a core/ shell internal structure, with the center of the core shifted from the shell center (see Figures 1 and 3). It was shown that this model was necessary for a reliable interpretation of GISAXS intensity distributions [14]. .…”

“…Ellipsometric analysis was carried out by considering each multilayer structure as a single homogenous film with a thickness equal to the total multilayer thickness and effective optical constants modeled using a flexible multiple-oscillator model [14]. Taking into account that the Al 2 O 3 matrix is transparent in the considered spectral range, all the absorption was associated with the presence of Ge/Si QDs.…”