Silicon photonic circuits do an exceptional job at routing light via waveguides and passive devices, do a good job of detecting the (usually) near-IR light used in them, and, because silicon is not an intrinsic light emitter, have a terrible time at producing the very light they need to produce a signal. There have been numerous workarounds, the main one being the hybrid addition of II-V semiconductor-based light sources to photonic circuits; this is an expensive and complicated, although workable, approach. A different way is to alter silicon somehow to make it, however inefficiently, emit light; these workarounds include creating avalanche LEDs in silicon, silver-coated silicon nanowires, using nanocrystalline silicon, and coating silicon with films of other light-emitting materials.
An effective way to solve this is to introduce dislocations in silicon. Researchers have come to the conclusion that a high concentration of dislocations can be achieved in the silicon surface layer by irradiating it with silicon ions with energy on the order of a hundred kiloelectronvolts and then annealing it at high temperatures. In this case, silicon emits light at exactly the right wavelength—close to 1.5 µm. One way to achieve dislocation-related photoluminescence in silicon samples is to implant silicon ions into silicon with subsequent annealing. Scientists at Lobachevsky University and their colleagues from the RAS Institute of Solid State Physics and the Alekseev State Technical University (both in Russia) discovered that additional boron ion doping can enhance the luminescence; however, the phenomenon of enhanced luminescence properties alone does not solve the main problem. Moreover, it remained unclear how boron-ion doping affects the luminescence thermal stability, and under what conditions such an effect would be most pronounced.
In a new study, the scientists have confirmed experimentally the increase in thermal stability of silicon doped with boron ions. “It is important to note that the ‘beneficial’ effect of boron is unique in the sense that the replacement of boron ions by another acceptor impurity does not lead to the effect described above,” says professor David Tetelbaum, one of the researchers. “After refining the modes of boron-ion doping and heat treatment of silicon samples where centers of dislocation-related luminescence were formed by irradiation with silicon ions, we have found that with the highest previously used dose of boron ions and an additional heat treatment at 830°C, it is possible to achieve a measurable level of luminescence at room temperature.” The results obtained during further optimization of the implantation and heat treatment conditions brighten the prospects for silicon-based light sources in optoelectronics. Reference: Al Nikolskaya et al., Phys. Res. B: Beam Interact. Mater. Atoms (2020); https://doi.org/10.1016/j.nimb.2020.03.032.
