Approaches for Silicon Based Light Emitters

The realization of an efficient Si based light emitter or even a laser would be a breakthrough for micro- and optoelectronics, since it would allow for full integration of optical functionality on a chip. Being an indirect semiconductor, Si is an inherently bad light emitter, yet recently some remarkable progress has occurred. Light emitting devices based on Si pn junctions, Si MOS structures doped with rare earth elements, or containing Si nanoclusters have been demonstrated. I will present our work in some of these areas.

We have fabricated Si light emitting pn diodes (LED) by high-dose boron implantation into n-type Si. The free-exciton electroluminescence (EL) increases with temperature, reaching wall-plug efficiencies of more than 0.1% at room temperature. A model which is based on excitons localized near nanoscale boron doping spikes can explain the EL dependence on current and temperature as well as an electrical bistability occurring at low temperature. We have integrated such structures into a microcavity with a buried metallic CoSi2 bottom mirror and a Si/SiO2 Bragg mirror on top, representing the first electrically driven resonant-cavity LED based on silicon. This resonant-cavity LED exhibits significant spectral narrowing, consistent with the quality of the cavity.

A second class of devices are metal-oxide-semiconductor (MOS) structures, which are implanted with various rare-earth elements. Here the emission results from 4f intrashell transitions, impact excited by hot electrons in the oxide. The most widely studied example is the Er3+ ion emitting at the telecom wavelength of 1.54 microns. We have also fabricated a Gd doped MOS structure, which emits in the deep UV at 316 nm. This is, to our knowledge, the first Si based UV light emitter, with many potential applications in areas such as bio-sensing. Finally we demonstrate a bright-green MOS light emitter based on Tb ions implanted into the oxide, which could find applications in low-cost micro-displays.