Amorphous semiconductors

Amorphous semiconductors are non-crystalline solids with semiconductor properties .

Like other amorphous materials , they only have a short-range but no long-range order . Like semiconductors, they have a band gap with fully occupied valence bands and empty conduction bands that is smaller than that of non-conductors . Semiconductor components can be manufactured from amorphous semiconductors.

Physical Properties

Due to the lack of long-range order of amorphous solids, no theory is available that comes close to that of solid-state physics of crystalline substances. In particular, the Bloch theorem does not apply because there is no periodic potential, so the wave functions of the electrons are not Bloch functions . The optical properties mainly depend on the short-range order. The high absorption of photons with energies just above the optical band gap of the material is particularly important for use in solar cells.

Tetrahedral amorphous semiconductors

If the semiconductor materials silicon and germanium are vaporized on substrates that are not too hot, thin, amorphous layers are deposited on them. The pure amorphous semiconductors have a high density of localized states in the region of the band gap, which are caused by structural defects. The most important structural defect is the unsaturated bonds . The incorporation of hydrogen saturates these bonds and the density of the localized states decreases by orders of magnitude, more in the case of silicon than in the case of germanium. This group includes amorphous silicon and amorphous germanium ; with incorporation of hydrogen they are referred to as a-Si: H or a-Ge: H for short.

Chalcogenide semiconductors

Due to the divalent nature of the chalcogenides, chalcogenide semiconductors form chains and rings of atoms that are only bound to one another by van der Waals forces . This strongly favors the formation of amorphous structures. Its most important representative is selenium . The electrons not involved in the bonds represent the mobile charge carriers in the chalcogenide semiconductors.

literature

• Peter W. Heywang: Amoprphe and polycrystalline semiconductors . Springer, Berlin, Heidelberg, New York, Tokyo 1984, ISBN 3-540-12981-2 .
• Peter Y. Yu, Manuel Cardona: Fundamentals of Semiconductors . Physics and Materials Properties. Springer, Berlin, Heidelberg 1996, ISBN 3-540-61461-3 .

Individual evidence

1. ^ Peter Y. Yu, Manuel Cardona: Fundamentals of Semiconductors , Springer Verlag Berlin Heidelberg 1996, ISBN 3-540-61461-3 , pp. 550 ff.
2. ↑ W. Heywang: Amorphous and polycrystalline semiconductors . Springer publishing house. Berlin / Heidelberg / New York / Tokyo 1984, ISBN 3-540-12981-2 , p. 38 ff.