Characterization of the Si:H network during transformation from amorphous to micro- and nanocrystalline structures

Abstract

Optical, structural, and electrical characterizations of the Si:H network have been performed during its changes occurred by the increasing H2 dilution to the SiH4 ensemble in hot-wire chemical vapor deposition (HWCVD). A rapid structural transformation from a mostly amorphous phase to comprehensive micro/nanocrystallinity was attained at a relatively low H2 dilution, even at a low substrate temperature, because of the associated abundance of atomic H in HWCVD. However, elevated H2 dilution induces enormous polyhydrogenation and formation of lesser dense network full of voids, mostly around the tiny micro/nanocrystallites. This highly defective grain boundary zone provides high density of electronic trapping centers and contributes significantly to the transport of carriers. The overall electrical transport in the amorphous-micro-nano-crystalline heterogeneous Si:H network has been accounted in the framework of a three-phase model comprised of amorphous and crystalline (micro- and nano-) components while the grain boundary being the third phase, separately contributing to a potential energy barrier in between. The three-phase model to the electrical phenomena of nanocrystalline structures convincingly explains the dual activation energies arising in the electrical conduction with distinguishably different temperature dependent behaviors from that occurs in the conventional amorphous matrix.