Study of nanocrystalline silicon films synthesized Below 100 degrees C by catalytic chemical vapor deposition.

Nanocrystalline silicon (nc-Si) films were synthesized by catalytic chemical vapor deposition at a low substrate temperature (100 degrees C) for use as an active layer in bottom-gate thin-film transistors. The hydrogen-dilution technique was employed to increase the crystalline volume fraction of the synthesized films. The incubation layer thickness was estimated to be 5.1 nm for a hydrogen-dilution ratio, R(H) (= [H2]/[SiH4]), of 54. When R(H) was increased from 64 to 74, the deposition rate decreased from 20 to 0.5 nm/min. In order to achieve a high deposition rate and high crystallinity near the interface region, we modulated R(H) through the film thickness. We also fabricated metal-insulator-semiconductor-insulator-semiconductor diodes from multilayer structures consisting of an nc-Si layer sandwiched between two silicon nitride layers. By analyzing the capacitance-voltage characteristics of these diodes, we found that the hysteresis and rectifying behavior of these diodes were affected by the the nc-Si layer thickness.

Optical and structural properties of nanocrystalline silicon potential well structure fabricated by cat-chemical vapor deposition at 200 degrees C.

We attempted to fabricate multi-layer, thin film structures by catalytic chemical vapor deposition (Cat-CVD) at a low temperature (200 degrees C). A 5-10-nm-thick nanocrystalline silicon (nc-Si) layer was positioned asymmetrically between two silicon nitride (SINx) layers. The compositions of the SiNx layers were varied between silicon-rich and nitrogen-rich. Each layer was deposited continuously in the Cat-CVD chamber without post-annealing. High-resolution transmission electron microscopy (HRTEM) revealed that the nc-Si layer grew in columns on the surface of the bottom SiNx layer, and the columnar structure extended up to a few nanometers of the top SiNx layer. In photoluminescence (PL) spectra, the overall intensity increased with the thickness of the nc-Si layer, but the primary peak position changed more sensitively relative to the composition of the SiNx layers. Capacitance-voltage (C-V) hysteresis was observed only when 10-nm-thick nc-Si layers were inserted between the nitrogen-rich silicon nitride (NRSN) layers. Under a bias voltage of 5 V, the current in the sample with a 10-nm-thick nc-Si layer was higher by at least two orders of magnitude than that in the sample with a 5-nm-thick nc-Si layer. The I-V curve was fitted well using both the Fowler-Nordheim and the Poole-Frenkel models for electric fields of magnitudes greater than 1.1 MV/cm, thereby implying that both mechanisms contribute to the increase in the leakage current.