Formation, Phonon Structure, Transport and Thermoelectric Properties of Multilayer Heterostructures Si/NC β-FeSi₂/Si/ NC β-FeSi₂/…/Si(111) and Si/NC α-FeSi₂/Si/ NC α-FeSi₂/…/Si(111)

Multilayer (4 and 8 layers) samples with embedded β-FeSi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and α-FeSi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nanocrystals (NCs) on silicon-on-insulator (SOI) substrates with (100) orientation and p-type conductivity have been grown. It has been established from Raman data that β-FeSi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> NCs are formed with small portions of iron (0.5 nm) deposited at room temperature and annealed at T = 630°C with subsequent overgrowing with silicon, and α-FeSi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> NCs are formed after short-term annealing at T = 1000°C and overgrowing with silicon. The effect of doping of intermediate silicon layers on the conductivity and Seebeck coefficient in multilayers (4 and 8) in the temperature range of 80–450 K was studied. It was shown that with maximum doping of intermediate layers (1019 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>) with the number of layers equal to 8, the maximum Seebeck coefficient 600 μV/K and the maximum power factor 2.5 mW/(m×K2) were observed at T= 450 K, which is due to the contribution of injected holes from β-FeSi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nanocrystals.