Spectroscopic ellipsometry of amorphous Se superlattices

Superlattice structures have a variety of electrical and optical properties that allow for interesting applications like quantum cascade lasers and ultrasensitive photo-detectors. However, such structures require high-tech fabrication methods like molecular beam epitaxy, and this technology barrier means that these promising devices are not in widespread use. Using the simple method of rotational evaporation, we fabricated films with alternating multi-nanolayers of amorphous selenium (Se) and arsenic selenide (As2Se3). We investigated the optical properties of the individual materials, and the resulting multi-layer structure using spectroscopic ellipsometry. The results were modeled using Cody-Lorentz oscillators to obtain the refractive index (n) and extinction coefficient (k). The models showed the optical band gaps of Se and As2Se3 to be 1.97 and 1.69 eV, respectively. The absorption coefficient (alpha) of the multi-layer structure showed a series of five 'steps' in energy at 1.72, 1.82, 1.89, 1.97, and 2.04 eV. These are confirmed to stem from the transitions between confined quantum well levels due to the superlattice structure. In this way, the optical measurement using spectroscopic ellipsometry confirms the possibility of fabricating good quality nanostructutres using amorphous materials and rotational evaporation.

Automated summary

Superlattice structures have unique electrical and optical properties suitable for applications like quantum cascade lasers and ultra-sensitive photo-detectors, but their fabrication requires specialized techniques like molecular beam epitaxy. Using rotational evaporation, films with alternating layers of amorphous selenium and arsenic selenide were successfully fabricated and their optical properties were investigated using spectroscopic ellipsometry. The models showed distinct absorption energy levels in the multi-layer structure, confirming the transitions between quantum well levels due to the superlattice structure.