Electronic and structural properties of doped amorphous and nanocrystalline silicon deposited at low substrate temperatures by radio-frequency plasma-enhanced chemical vapor deposition

The gas phase doping of hydrogenated amorphous silicon and hydrogenated nanocrystalline silicon thin films deposited on glass and on plastic (polyethylene terephthalate) substrates is reported. Two substrate temperatures were used during deposition: $25 °C$ and $100 °C.$ Films were deposited by radio-frequency plasma-enhanced chemical vapor deposition using phosphine or diborane for $n$- or $p$-type doping, respectively. Similar electronic and structural properties are obtained for the doped films deposited on either substrate. Hydrogen dilution of silane is used to improve the electronic and structural properties of the amorphous films and to obtain nanocrystalline films. The most conductive amorphous films have $n$-type dark conductivity at room temperature $∼10−3 Ω−1 cm−1$ and $∼10−5 Ω−1 cm−1$ when deposited at $100 °C$ and $25 °C,$ respectively, or $p$-type room-temperature dark conductivity $∼10−7 Ω−1 cm−1$ at both substrate temperatures. The most conductive nanocrystalline films deposited at $100 °C$ have $n$- and $p$-type dark conductivity at room temperature above $10−2 Ω−1 cm−1$ while nanocrystalline films deposited at $25 °C$ only have $p$-type conductivity higher than $10−2 Ω−1 cm−1$ at room temperature. Isochronal annealing at temperatures up to $300 °C$ showed that the dopants are fully activated at the deposition temperature in doped nanocrystalline samples and that they are only partially activated in amorphous films deposited at low substrate temperatures.