Visible light emission from silicon: a quantum effect in highly porous materials

Although crystalline silicon is not expected to emit light in the visible range, bright red emission has been reported for high-porosity porous silicon films. This discovery, which opens the door to silicon-based optoelectronics, has raised great interest in the scientific community. The authors present the state of art of the question after a year of investigations. After a short presentation of the main features of porous silicon, they describe the different characteristics of the photoluminescence phenomena in some detail. The evolution of the emission spectra with the properties of the material which can be varied by chemical or electrochemical methods is presented. Results confirm that quantum size effects within the crystalline material can be responsible for the light emission far above the band gap of silicon. The relatively high quantum efficiencies are discussed in terms of material properties (oxidation level, surface passivation) and of radiative and nonradiative recombination rates. It is shown that, at room temperature, the luminescence decay is dominated by nonradiative processes. Bright electroluminescence has also been evidenced during anodic oxidation of the material.<>