6.7 Stimulated Emission: Prospect
Although some encouraging results on enhanced PL from Si-based NCs or Er-doped systems have been obtained and also good EQE has been reported from LEDs, laser action from Si-based structures have not yet been observed. Some recent work reports appreciable values of optical gain by stimulated emission. It is expected that these findings will encourage researchers to design suitable structures for realizing laser action. Many workers believe that Si lasers will soon become a reality. It is to be noted that Si-based lasers based on stimulated Raman scattering were unveiled by Intel in 2004, the working principle of which will be described in Chapter 9. In this section, we report recent findings on positive gain coefficients in some of the structures discussed in this chapter.
6.7.1 Si Nanocrystals
Pavesi et al. 40 reported for the first time optical gain in Si-NCs. Since the first observation, a number of reports have been published by the group, and all the work has been summarized in Dal Negro et al. 41; see also Pavesi 42 and Fauchet 43. In this subsection, we shall essentially reproduce their findings.
Dal Negro et al. used Si-NC samples produced by high-temperature annealing of substoichiometric silicon oxide (SiOx) thin films grown by the PECVD process. The amplified spontaneous emission has been measured by a variable stripe length (VSL) geometry, and by using a pump–probe technique. In the VSL method, the length of the pumped region is varied ...