Optical Multilayers

Our work on porous silicon initially concentrated on the intrinsic luminescence from porous silicon (pSi) and optimising its properties. Modelling of pSi microcavities, showing how emission from each layer must be considered, demonstrated that modes of a Bragg mirror could compete with microcavity modes in luminescence efficiency.

SEM image of microcavity produced in the group for erbium doping (described below).

The model of multilayer mirrors that we developed was then used to examine the behaviour of mirrors in other circumstances. An analysis of vapour sensing by measuring changes in reflectivity of Bragg mirrors strongly contributed to the expanding field of optical sensors in porous silicon (66 citations by Feb 2006) and the dissolution of derivatised mesoporous mirrors in simulated human blood plasma was also modelled.

Reflectivity changes in Bragg mirrors were also time-resolved to explore the concentration gradient in the mirror layers as organic vapours condensed in the pore structure.

Reflectivity of thermally processed erbium-doped microcavity showing narrowing of erbium emission into cavity mode.

In the 1.5µm region, optical absorption in pSi is negligible and erbium ions can be electrochemically implanted in very high quality mirrors. Investigations of erbium-doped microcavities examined the effects of thermal processing (needed to activate the erbium) on the multilayer mirrors and led to the first observation of strong modification of the erbium photoluminescence in a pSi microcavity.