Progress toward nanoscale silicon light emitters

Impressive advances have been made over the last few years in teaching silicon how to emit light. Recently, light-emitting devices (LEDs) made of porous silicon and other forms of nanoscale silicon have been demonstrated with specifications that start to make them attractive for commercial applications. This paper reviews the state-of-the-art in the materials science and device properties of nanoscale silicon-based LED's, including their integration with microelectronic circuits. Porous silicon and other forms of nanoscale silicon contain crystallites smaller than 10 nm. Their intrinsic optical properties are dominated by quantum confinement, which produces an opening of the bandgap and an increase of the luminescence energy with decreasing nanocrystal sizes. The mechanical, thermal, and electrical properties of porous silicon are strongly degraded compared to those of bulk crystalline silicon. In addition, special techniques should be used to maintain a good passivation of the internal surface and the mechanical integrity of porous silicon. As a result, the design and optimization of LEDs made of nanoscale silicon is difficult. The stability, efficiency, response time, and spectral characteristics of porous silicon LEDs are discussed. The progress toward the integration of porous silicon LEDs with microelectronic circuits is reviewed and a simple alphanumeric display is shown.