Photoluminescent porous silicon patterns of sub-micron dimension generated by metal-assisted electroless chemical etching

Soma Chattopadhyay, Paul W. Bohn

Department of Chemistry, Materials Research Laboratory, Beckman Institute for Advanced Science and Technology,

University of Illinois at Urbana-Champaign

Photoluminescent porous silicon (PSi) can be produced by metal-assisted wet i.e. non-electrochemical etching of Si (100) in a solution of methanol, HF and H₂O₂. A thin layer of Pt (d ~ 30 Å) is patterned onto Si prior to immersion in the etching solution. Unlike conventional fabrication methods, PSi formation takes place in a few seconds without use of electrical bias or illumination. Exciting the PSi thus produced with UV light causes photoluminescence and the emission wavelength can be tuned simply by varying the etch conditions. The Pt pattern deposited on Si prior to etching spatially directs the formation of PSi which in turn makes it possible to control the luminescence spatially. By patterning Pt onto Si with sub-micron resolution before subjecting it to the etching conditions, it is possible to produce photoluminescent pixels of sub-micron dimensions. In order to achieve sub-micron resolution of patterning, focused ion beam assisted deposition of Pt on Si has been employed. Characterization of the morphology and the optical characteristics of the sub-micron scale luminescent PSi is necessary to develop a better understanding of the process. Scanning electron microscopy and Atomic Force Microscopy have been employed for high resolution surface investigations. Moreover these techniques when coupled with photoluminescence spectroscopy and microscopy will help to correlate surface morphology of the etched structures with the optical properties of emission. Investigation of the optical characteristics of photoluminescent pixels of about 100 nm dimension is limited by the resolution achievable by conventional optical microscopes. To overcome this, Near-field Scanning Optical Microscopy will be used to obtain spatial information of the emission characteristics of the photoluminescent pixels.