Stability of polydihydrosilane liquid films on solid substrates

The quality of polydihydrosilane liquid films is a key factor in the fabrication of solution-processed silicon films. This study investigates the stability of polydihydrosilane liquid films with a thickness L of ~ 40 nm on solid substrates by a comparison between the observed optical microscope images and the values of the Hamaker constant A_ALS for the air/liquid (polydihydrosilane)/solid substrate systems. A_ALS values for a series of SiO₂-based substrates were determined by adopting a simple spectrum method. We found that the micrographs of the polydihydrosilane films provide direct evidence of stability in accordance with the sign of A_ALS; a stable liquid film with A_ALS > 0 showed a continuous figure, while an unstable film with A_ALS < 0 exhibited an array of dots caused by the rupture of the film. The array of dots in the unstable liquid films has a slight orderly distribution with a period λ that is in accord with the characteristic wavelength of the undulation related to the spinodal-like decomposition in van der Waals unstable liquid.     

Pyrolytic transformation from polydihydrosilane to hydrogenated amorphous silicon film

The fabrication of thin film silicon devices based on solution processes rather than on conventional vacuum processes is of substantial interest since cost reductions may result. Using a solution process, we coated substrates with polydihydrosilane solution and studied the pyrolytic transformation of the material into hydrogenated amorphous silicon (a-Si:H). From thermal gravimetry and differential thermal analysis data a significant reduction in weight of the material and a construction of SiSi bonds are concluded for the pyrolysis temperature T_p = 270 to 360 °C. The appearance of amorphous silicon phonon bands in Raman spectra for films prepared at T_p ≥ 330 °C suggests the construction of a three-dimensional amorphous silicon network. Films prepared at T_p ≥ 360 °C exhibit a hydrogen content near 10 at.% and an optical gap near 1.6 eV similar to device-grade vacuum processed a-Si:H. However, the infrared microstructure factor, the spin density, and the photosensitivity require significant improvements.