Semitransparent and conductive CaSi2 films for silicon device applications

• Published in: Japanese Journal of Applied Physics 2020-04, Vol.59, p.1
• Main Authors: Galkin, Nikolay G, Galkin, Konstantin N, Tupkalo, Andrei V, Chusovitin, Evgenii A, Goroshko, Dmitrii L, Fogarassi, Z, Pecz, B
• Format: Article
• Language: English
• Subjects: Carrier density; Electrical properties; Electrical resistivity; Epitaxial growth; Nanocrystals; Optical properties; Photodiodes; Photons; Photovoltaic cells; Silicides; Silicon; Silicon devices; Silicon substrates; Solar cells
• ISSN: 0021-4922; 1347-4065
• DOI: 10.35848/1347-4065/ab6b75

The purpose of this work was to comparatively analyze the structural, optical and electrical properties of calcium silicides (CaSi, and CaSi2) on silicon in the form of epitaxial and nanocrystalline films grown on Si(001) and Si(111) substrates and to determine the field of use. An analysis of the structure of the grown films showed the presence of contributions from amorphous, nanocrystalline and crystalline phases (Ca2Si, CaSi and CaSi2) with an increase of the Si substrate temperature from 190 °C to 500 °C. It has been established that transparency in the photon energy range 0.2–1.3 eV in CaSi2 films is associated with a low density of states at the Fermi level, and high conductivity is determined by the concentration of free carriers up to 1021 cm–3 at T = 7–300 K. The latter provide high electrical conductivity up to 1200 (Ω cm)−1, low sheet resistance (26–40 Ω/square) and high reflection (80%–90%) at photon energies below 0.4 eV. The unique properties of CaSi2 films are promising for the creation of transparent conductive pads for silicon-based solar cells and the development of infrared photodiodes with a Schottky barrier on p-type silicon.