The photoluminescence properties of porous layers prepared by anodization of p/p+ silicon epitaxial wafers are presented. The shift of the photoluminescence spectrum towards shorter wavelength due to the porosity increase and the experimental dependence of the photoluminescence maximum position on HF concentration during anodization are shown. Degradation of the photoluminescence intensity dependence on the storage time is described. PACS numbers: 78.55.Ηx, 81.60.-j The observation made by

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... m [1] of photoluminescence phenomena in porous silicon has led to new studies of this material as it may have promising applications in Si-based optoelectronic integrated circuits and displays. The luminescence is often interpreted as resulting from the quantum confinement in small size crystallites of porous Si [1-4]. The quantum size effect leads to an increase in the band gap of the crystallites compared to the bulk Si, which could explain the light emission in the visible range. Other models based on the luminescence properties of polysilanes [5] and siloxene [6] have been also proposed. Porous Si layers are produced by the anodic dissolution of single-crystalline Si wafers in hydrofluoric acid (HF) solution. In our experiments we have used the 3 inches epitaxial wafers consisting of boron doped substrate with the resistivity of 0.01-0.02 Ω cm and 15 μm thick boron doped epitaxial layer with the resistivity of 10 Ω cm, deposited in the standard chemical vapour deposition (CVD) process. As the substrate was of low resistivity, no additional procedure such as an ion implantation or a metal deposition on the back side of the wafer was needed. The current density was kept 10 mA/cm2 . To obtain the layers of different porosity the etching processes were performed in the HF-isopropyl alcohol solutions with the HF concentration ranging from 40 wt% to 10 wt%. The decrease in the HF concentration caused an increase in the layer porosity. The porosity was estimated by the standard gravimetric method. For the photoluminescence measurements a conventional setup was used including the SPM-2 monochromator and the Si cathode photomultiplier in conjunction with lock-in technique. (713)