Influence of hydrogen on optical properties of a-Si : H

Abstract

We report on the optical properties of a-Si : H prepared by cathodic sputtering of a Si target in an 80% argon/20% hydrogen reactive gas at ∼9×10−3 Torr. The deposition rate φ (by means of the rf voltage) and the substrate temperature were varied. The total hydrogen content [H] and the concentration of hydrogen involved in SiH bonds [H1] or in SiH2 bonds [H2] were measured. We find [H]≳[H1]+[H2], two times higher in some preparation ranges (ν?15 Å/min or ν=100 Å/min), which implies the occurrence of hydrogen atoms H′ not bonded in the usual SiH or SiH2 forms. The optical absorption coefficient, the optical energy gap E0, and the refractive index ns were measured. E0 decreases as v increases, is independent of Ts for φ≳30 Å/min, and decreases as Ts increases for v≳30 Å/min. ns increases toward the crystalline value as φ increases and Ts decreases. The similarity of the properties of the layers obtained by sputtering and glow discharge is emphasized. We suggest equilibrium between hydrogen bonds as SiH and SiH2 and the other form(s) and that the optical gap is controlled by the deformation of the silicon matrix by the various hydrogen species.

Real-time spectroscopic ellipsometry studies of the growth of amorphous and epitaxial silicon for photovoltaic applications

“…15 Films grown at higher temperatures will have greater short-range order, producing higher carrier lifetimes, which are important in collecting carriers photoexcited in the a-Si:H emitter. Films deposited at lower temperatures tend to have a higher concentration of hydrogen, producing a wider band gap.…”

Preferential Attachment of H in Amorphous Hydrogenated Binary Semiconductors and Consequent Inferior Reduction of Pseudogap State Density

“…These results are of significant importance since they represent an unambiguous determination of the range of energy migration in this class of stoichiometric materials used as "minilasers" for low-threshold, high-gain applications. 5 ' 6 The mechanism causing concentration quenching of the fluorescence in these materials is not understood but it is known to have quite different properties from other neodymium laser materials. 5 This is not only an interesting fundamental physics question, but it is also important in material development for laser applications.…”

Real-time spectroscopic ellipsometry as an in-situ probe of the growth dynamics of amorphous and epitaxial crystal silicon for photovoltaic applications

“…Films deposited at lower temperatures tend to have a higher concentration of hydrogen, producing a wider band gap [15]. Films deposited at lower temperatures tend to have a higher concentration of hydrogen, producing a wider band gap [15].…”