Comparative Raman analysis of porous silicon DBRs before and after lift-off under visible and near-infrared laser excitation

Abstract

Porous silicon (PSi) distributed Bragg reflectors (DBRs) were fabricated via electrochemical etching of arsenic-doped n-type Si (100) wafers, followed by lift-off to produce free-standing films (LO-DBR). The structural and vibrational properties of both DBR and LO-DBR were investigated using Raman spectroscopy under visible (532 nm) and near-infrared (785 nm) laser excitation. Under visible excitation, the DBR exhibited primary peak broadening and downshifting from 520 cm⁻¹ to 502 cm⁻¹ due to laser-induced thermal effects, accompanied by an oxide-related secondary peak shifting from 496 cm⁻¹ to 462 cm⁻¹. The LO-DBR showed enhanced thermal sensitivity with stabilization into amorphous Si-O phases. Near-infrared excitation revealed superior thermal stability for DBR/Si with primary peak position at 518 cm⁻¹ while LO-DBR exhibited progressive downshifting from 516 cm⁻¹ to 512 cm⁻¹, and broadening due to reduced heat dissipation. These results demonstrate how both substrate-supported DBR and free-standing LO-DBRs enable distinct approaches for thermally tunable photonic applications.