Porous Si patterning


Porous Si is of interest because of its photoluminescence (PL) and electroluminescence properties. A potentially important application is the production of combined optical/electronic devices incorporating patterned porous material directly onto a Si substrate with high spatial resolution. At CIBA we have undertaken a comprehensive study of the effects of ion irradiation on a wide range of different resistivity p-type Si wafers, and recorded the resultant PL intensity and wavelength. There are two resistivity regimes of p-type Si where PL is affected in different ways by ion irradiation: for low resistivity (~0.01 Ω.cm) wafers irradiation primarily results in a large PL increase, whereas for moderate resistivity (0.1-10 Ω.cm) wafers irradiation primarily results in a large PL wavelength red shift. A demonstration of this different behavior is shown in Figs. 1a,b. In low resistivity p-type Si, the irradiated dragon produces bright, red PL compared with the faint unirradiated background. In moderate resistivity Si, bright orange/red PL is produced from the dragon, whereas the background produces green PL of a similar intensity. In Fig. 1c, a range of fluences have been irradiated in a continuous distribution in moderate resistivity Si, producing a gradual change in PL emission wavelength. Fig. 1d shows a PL image of the painting The Ancient of Days by William Blake, reproduced in porous Si. The fluence of each region was adjusted so that the PL color emission from the porous Si resembles the original as closely as possible.

Fig. 1. PL images of dragons formed by irradiating a p-type Si (a) 0.02 Ω.cm wafer and (b) 3 Ω.cm wafer. (c) Concentric ring patterns formed by linearly increasing the fluence from the outer edge to the center. (d) The Ancient of Days by William Blake, fabricated in a 500 × 500 μm2 area using helium ion irradiation. The picture was irradiated with a helium fluence of 5×1013/cm2 for black, 1×1013/cm2 for red, 5 × 1012/cm2 for orange and 1 × 1012/cm2 for yellow-green.