R. Butte et al., Structural, optical and electronic properties of hydrogenated polymorphoussilicon films deposited at 150 degrees C, J NON-CRYST, 266, 2000, pp. 263-268
When silicon thin films are deposited by plasma enhanced chemical vapor dep
osition in a plasma regime close to the formation of powder, a new type of
material, called hydrogenated polymorphous silicon (pm-Si:H) is obtained. T
his material has increased transport properties with respect to device-grad
e hydrogenated amorphous silicon (a-Si:H). To understand the origin of such
improved transport properties, we made electrical measurements from which
we deduced that the density of states at the Fermi level N(E-F) and the car
rier capture cross-section, sigma(c), in pm-Si:H films are at least 10 time
s lower and 5 times lower, respectively, than in a-Si:H films. The crystall
ite sizes deduced from Raman spectra confirm high-resolution transmission e
lectron microscopy measurements. The infrared stretching modes of pm-Si:H f
ilms have a band at similar to 2035 cm(-1) which is attributed to hydrogen
platelets. The smaller density of states at the Fermi level N(E-F) is expla
ined in terms of improved amorphous matrix as confirmed by optical measurem
ents. We suggest that the low capture cross-section, sigma(c), observed in
these films results from a preferential carrier recombination path at grain
boundary dangling bonds as predicted by theoretical calculations. (C) 2000
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