Electroluminescence from silicon pn diodes

The indirect band gap of silicon makes this material an inherently bad light emitter. However, since silicon is the key material of electronics, there is a tremendous effort for realizing silicon based light emitters in order to take full advantage of silicon process technology. The different routes pursued so far include porous silicon, 2 dimensional silicon nanostructures, silicon nanocrystals in a SiO2 matrix [1], Er3+ doped silicon, and silicon-germanium quantum cascade lasers.
Recently, the light emission from bulk silicon received considerable interest [2,3]. We pursue a similar route for preparing silicon pn-diodes via high-dose boron implantation. Under forward bias these diodes emit electroluminescence close beneath the silicon bandgap. The origin of the electroluminescence is based on high local boron concentration, which leads to the localization of holes at doping spikes similar as observed in delta doped layers produced by MBE. The relevance of excitons bound at the B doping spikes on the electrical [4] and optical properties will be discussed with respect to the prospects of obtaining efficient room temperature light emitters.

[1] L. Pavesi, et al., Optical gain in silicon nanocrystals, Nature 408, 440 (2000).
[2] W.L. Ng et al., An efficient room temperature silicon based light emitting diode, Nature
410, 192 (2001).
[3] M.A. Green et al., Efficient silicon light-emitting diodes, Nature 412, 805 (2001).
[4] J. Sun et al, Bound-exciton-induced current bistability in a silicon light-emitting diode, Appl. Phys. Lett. 82, 2823 (2003).