Absorbing one-dimensional planar photonic crystal for amorphous silicon solar cell.

We report on the absorption of a 100nm thick hydrogenated amorphous silicon layer patterned as a planar photonic crystal (PPC), using laser holography and reactive ion etching. Compared to an unpatterned layer, electromagnetic simulation and optical measurements both show a 50% increase of the absorption over the 0.38-0.75micron spectral range, in the case of a one-dimensional PPC. Such absorbing photonic crystals, combined with transparent and conductive layers, may be at the basis of new photovoltaic solar cells.

Laterally graded porous silicon optical filter fabricated by diffusion-limited etch process.

We report a method of producing a lateral gradient in the optical properties of anodically etched porous silicon layers. Lateral gradation details of the porous silicon layer are governed by the etch mask pattern involved. Unlike other methods that rely on uneven hole current distribution, we believe that in our method the diffusion of reactive ions in the etchant plays a key role. As an implementation of the proposed method, we demonstrate a linearly graded optical bandpass filter operating at the lambda=1550 nm range by employing a tapered etch window opening. The resultant optical filter exhibited a approximate 60 nm tuning range with a sharp transmission bandwidth of approximately 3 nm. Computer simulations indicate that an uneven hole current distribution cannot be the reason for the observed gradient along the taper axis, supporting the view that the diffusion-limited etch process plays the key role.