Phase Transition and Conductivity Modification of Porous Silicon via CO2 Laser Processing

Abstract

This study explores how CO₂ laser irradiation modifies the optical, structural, and electrical properties of porous silicon (PS). PS layers were fabricated by electrochemical etching of p-type silicon wafers, followed by irradiation with a 10.6 μm continuous-wave CO₂ laser at powers of 5–40 W. Characterisation techniques including SEM, AFM, XRD, XPS, SIMS, KPFM, Raman spectroscopy, and I–V measurements reveal two stages of modification. In the pre-melting stage, localised heating consolidates pore walls, reduces porosity, smooths the surface, and thins the PS layer. At higher intensities, full melting collapses pores and recrystallises the silicon, restoring crystallinity but introducing stress and oxidation. Electrical measurements show metallic-like conduction in laser-modified regions, linked to boron redistribution and high carrier density. These tunable structural and electronic changes demonstrate the potential of controlled laser processing for engineering PS for advanced photonic, electronic, and energy devices.