L. Koker et Kw. Kolasinski, Observation and application of optical interference and diffraction effects in reflection from photochemically fabricated Gaussian interfaces, J APPL PHYS, 86(4), 1999, pp. 1800-1807
A HeNe laser has been used to fabricate photochemically a photoluminescent
porous Si thin film on top of crystalline Si. The porous Si film has Gaussi
an shaped upper and lower interfaces. When the reflection of a laser beam f
rom this film during, or after, the photochemical process is observed, two
distinct, concentric circular interference patterns are observed. A pattern
of thick rings is superimposed upon a pattern of fine rings. The reflected
beam is far more divergent than the incident beam. The formation of the ou
ter rings is a coherent phenomenon. Analysis of the patterns indicates that
reflection from the upper interface is not involved in the ring formation
process but that optical interference and Fresnel diffraction of the light
reflected from the bottom interface cause the pattern formation. It is show
n that the radius of the pattern is linearly proportional to the optical pa
th length through the film. Therefore, measurements of pattern sizes yield
information about the depth and index of refraction of the porous Si film.
This observation provides us with a novel, in situ technique for measuring
the kinetics of formation of the photoluminescent silicon thin films and mi
ght be exploited for applications in chemical sensing. (C) 1999 American In
stitute of Physics. [S0021-8979(99)05316-5].