Swift heavy ion irradiation reduces porous silicon thermal conductivity

• Published in: Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Vol. 341; pp. 27 - 31
• Main Authors: Massoud, M., Canut, B., Newby, P., Frechette, L., Chapuis, P.O., Bluet, J.M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.12.2014; Elsevier
• Subjects: Amorphisation; Electronics; Engineering Sciences; High energy; Ion irradiation; Irradiation; Mechanics; Microelectromechanical systems; Nanostructure; Porous silicon; Reduction; Semiconductors; Silicon; Thermal conductivity; Thermics; Irradiation; Thermal conductivity; High energy; Porous silicon; Amorphisation
• ISSN: 0168-583X; 1872-9584; 1872-9584; 0168-583X
• DOI: 10.1016/j.nimb.2014.06.032

While the electrical conductivity of semiconductors can be easily changed over order of magnitudes (8 in silicon) by playing on the doping, the thermal conductivity (TC) control is a challenging issue. Nevertheless, numerous applications require TC control in Si down to 1Wm−1K−1. Among them, there are thermal insulation requirements in MEMS, thermal management issues in 3D packaging or TC reduction for thermoelectric applications. Towards this end, the formation of nanoporous Si by electrochemical anodisation is efficient. Nevertheless, in this case the material is too fragile for MEMS application or even to withstand CMOS technological processes. In this work, we show that ion irradiation in the electronic regime is efficient for reducing TC in meso-porous Si (PSi), which is more mechanically robust than the nanoporous PSi. We have studied three different mass to energy ratios (238U at 110MeV and 130Xe at 91MeV and 29MeV) with fluences ranging from 1012cm−2 to 7×1013cm−2. The sample properties, after irradiation, have been measured by infrared spectroscopy, Raman spectroscopy and scanning electron microscopy. The TC has been measured using scanning thermal microscopy. Although, bulk Si is insensitive to ion interaction in the electronic regime, we have observed the amorphisation of the PSi resulting in a TC reduction even for the low dose and energy. For the highest irradiation dose a very important reduction factor of four was obtained.