Room-temperature photoluminescence (PL) from Si chemically etched (CE) in HF-HNO3-based solution has been observed. Scanning electron microscopy reveals that the etched Si has a surface morphology similar to that of luminescent porous Si fabricated by conventional anodization. PL spectra show an order of magnitude smaller luminescent intensity and a shorter wavelength intensity peak for CE Si. A CE Si thickness limitation was observed. The formation of CE Si can be readily explained by a local anodization model.

Thermal annealing studies of the photoluminescence (PL) intensity and Fourier-transform infrared spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures ≳300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. A brief etch in HF can restore the luminescence of the samples annealed below 400 °C. We conclude that SiH2 is essential to the visible luminescence in porous Si.

The recent observation of room temperature photoluminescence (PL) from porous Si layers (PSLs) has received considerable attention. Bulk crystalline Si does not luminesce efficiently at room temperature due to the indirect nature of the energy bandgap minimum. The PL from PSLs has been attributed to quantum confinement effects in nanometer‐sized crystalline features found in PSLs, typically of high porosity. In this paper, we review some of the major results and discuss the controversies of subsequent research. The basic methods of fabricating luminescent PSLs are described, including conventional anodic etching and chemical etching. The latter technique requires no applied bias, but is modeled as an electrochemical process. Other processing issues are also addressed, particularly with respect to postanodization control of the PL spectrum. Microscopic and spectroscopic studies of the material and optical characteristics of PSLs fabricated by the various techniques are presented and discussed. The basic models for the luminescence mechanism are described, including quantum‐sized crystalline Si, surface passivation, normalSi‐Hx , alloys, and molecular electronics. These models are discussed in terms of the supporting and contradicting evidence. Electroluminescence (EL) studies are discussed, including EL from anodic oxidation of PSLs as well as from light‐emitting diodes. The results are promising for optoelectronic applications. However, fundamental questions about the underlying chemistry, physics, and microstructure remain unanswered. More research will be required before any definitive statements can be conclusively made regarding the luminescence mechanism.

The formation of photoluminescent porous Si in an &chant solution made from the HF-HNOs-CH,COOH system is reported. The porous Si is characterized on the basis of its photoluminescence (PL) spectra and the degradation of the PL during exposure to laser irradiation. The surface topography as characterized by atomic force microscopy (AFM) reveals features on the order of 400-600 A. The effect of annealing the porous Si in vacuum on the PL intensity is described and correlated to the breakdown of Si-H bonds on the porous Si surface.

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