except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone.

We have performed photoluminescence studies on porous, p-type as well as n-type silicon wafers which have been prepared in air or in a dry nitrogen atmosphere, utilizing a spark-erosion technique. This sample preparation, which does not involve aqueous solutions or fluorine contaminants, yields similar photoluminescence spectra as those obtained by anodic etching in HF or unbiased etching in various HF-containing reagents. The wavelength of the photoluminescence peaks are somewhat shifted into the blue region compared to porous silicon obtained by anodic etching. We have also taken photoluminescence spectra on amorphous silicon, SiO2, and oxidized, annealed porous silicon. Our results are interpreted in the light of the presently suggested theories.

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except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone.

Microstructure and origin of the orange photoluminescence (PL) band of visible luminescing spark-processed germanium (sp-Ge) has been studied using simultaneous micro-Raman and -PL spectroscopy and scanning electron microscope. Instability of the sp-Ge film to energetic electron beams (⩾5 keV) during SEM measurements suggested that sp-Ge is not composed exclusively of purely Ge–Ge bonded material (elemental Ge) but also of other form(s) of material(s) of different chemistry. Indeed, micro-Raman spectra of the films showed that sp-Ge is composed of mainly substoichiometric germanium oxides (GeOxs) and elemental Ge (in the form of nano- or micro-crystals). Further, it is proposed that the Ge particles were embedded in thick GeOx (0<x<2) layers. Sizes of the Ge nanocrystals were estimated using a phonon confinement model and it was found that the spark processing method can generate Ge crystals with sizes as small as 6–8 nm. However, the micro-PL of sp-Ge indicated unambiguously that the orange PL band (near 1.9 eV) does not originate from or involve these Ge nanocrystals but the Ge–O bonded material, i.e., GeOxs.