A INTRODUCTION

Visible photoluminescence (PL) from porous Si was first reported some 13 years ago [1]. The work aroused only minor attention since (a) measurements were restricted to cryogenic temperatures (4.2 K), (b) it was not realised that the radiative processes could occur efficiently at room temperature and (c) it was attributed to amorphous phases in the material - a well-known phenomenon that had not led to the realisation of practical light-emitting devices. That situation changed dramatically in 1990 when efficient tunable room temperature output was demonstrated, and attributed to quantum size effects in crystalline silicon [2]. In the last seven years considerable world-wide interest has resulted in more than 1500 papers that refer to some aspect of the visible PL properties of porous silicon. Given such an enormous body of data, a short Datareview such as this can only be highly selective. We focus here on the spectral properties of the two main PL bands for which quantitative data exists, and also the large number of models proposed to account for such visible photoluminescence. In this manner, a relatively recent review [3] along similar lines is expanded and updated. A comprehensive review of the correlation between porous Si structure and its wavelength-tunable 'S-band' emission has recently appeared [4]. The interested reader should consult that review for a broader and more in-depth description of the so-called 'S-band' properties and a critical appraisal of the luminescence mechanisms proposed for that PL...