Spectroscopic investigation of light-emitting porous silicon photoetched in aqueous HF∕I2 solution

Abstract

The optical properties of porous silicon ͑PSi͒ photoetched in aqueous HF/ I 2 solution are investigated using spectroellipsomety ͑SE͒, electroreflectance ͑ER͒, photovoltage ͑PV͒, photoconductivity ͑PC͒, photoluminescence ͑PL͒, and Fourier transform infrared ͑FTIR͒ spectroscopy. The PSi layers were formed in a HF/ I 2 solution on n-Si substrates under Xe lamp illumination. The SE ͑E͒ and related data show an interference oscillation in the region below E ϳ 3 eV, where the PSi material is nearly transparent. The PV and PC spectra reveal three individual peaks A, B, and C at ϳ1.2, ϳ1.7, and ϳ2.5 eV, respectively, arising from the PSi layer itself. Peak C is also observed in the ER spectrum, together with a broadened E 1 peak at ϳ3.4 eV. Change in the fundamental-absorption-edge nature ͑E g X ͒ from the indirect gap in crystalline silicon to the quasidirect gap in PSi is found in the PV and PC spectra. The PL spectrum shows a broad peak at ϳ2.0 eV͑B͒. Peaks A, B, and C observed in the PSi layer may originate from the nondirect optical transitions at and above the lowest absorption edges E g X ͑A and B͒ and E g L ͑C͒. The quantum-mechanical size effect, i.e., a relaxation of the momentum conservation, makes possible the nondirect or quasidirect transitions at and above E g X and E g L in porous materials. The FTIR data support that the PL emission is due to the surface-sensitive quantum confinement effect.

Review—Photoluminescence Spectroscopy of Mn2+-Activated Phosphors: Part I. Fundamentals

“…Note that the weakened ε 2 (E) nature in the PSi sample is due to density deficits, i.e., a lot of voids present in its sample. 106,107 Figure 38b shows the phonon dispersion curves along the principal symmetry directions of c-Si and its phonon-DOS curve on the left-hand side. Note that the phonon-DOS curve can be theoretically obtained in the same way as for the electron-DOS in Fig.…”

“…38a. 106,107 The Raman scattering spectra for both the c-Si and PSi samples are also shown on the right-hand side of Fig. 38b.…”

Dense SixGe1–x (0 < x < 1) Materials Landscape Using Extreme Conditions and Precession Electron Diffraction

“…There is a strong drive, however, to extend the functionality of (Si, Ge)-based technology from microelectronics into optoelectronics. This has led to the investigation of a number of avenues, all based on processing of cubic diamond-structured Si or Ge, to address this constraint. , These avenues include doping Si with erbium (Er) to serve as a lasing center, etching Si with hydrogen fluoride to create pores resulting in luminescence due to quantum confinement effects, inducing tensile strain coupled with n-type doping in Ge to access direct-gap emission in the indirect-gap material, and hybrid approaches interfacing Si with other light-emitting chemical compounds.…”