Structural, Optical and Thermo-physical Properties of Mesoporous Silicon Layers: Influence of Substrate Characteristics
Résumé
ABSTRACT: In this paper, the structural, optical and thermal properties of n-type (100),
p-type (100) and (111) mesoporous silicon (MePSi) are reported. The mesoporous silicon was
prepared by an electrochemical process from bulk silicon wafer. Depending on the etching
depth, analyses show that the porosity of p-type (111) increased by 32 to 40% compared to p
(100) which, in turn, increased by 22 to 48% compared to n-type (100). The structure
morphology and the abundance of Si-Ox and Si-Hy also depended heavily on the type and
crystal orientation of MePSi. The thermal properties of the MePSi layers such as thermal
conductivity (κ), volumetric heat capacity (ρCp) and thermal contact resistance (Rth) were
determined using the pulsed photothermal method. The thermal conductivity of bulk silicon
dropped sharply after etching, decreasing by more than twenty-fold in the case of n-type (100)
and by over forty-five fold for p-type (100) and (111). According to the percolation model
depending on both porosity and phonon confinement, the drop in thermal conductivity was
mainly due to the nanostructure formation after etching. Thermal investigations showed that
the volumetric heat capacity (ρCp) followed the barycentric model which depends mainly on
the porosity. The thermal contact resistances of MePSi layers were estimated to be in the
range of 1x10-8 to 1x10-7 K⋅m2⋅W-1.