Optical gain of the 1.54 μm emission in MBE-grown Si:Er nanolayers

We present investigations of the optical gain cross section of 1.54 μm Er-related emission at 4.2 K in Si/Si:Er molecular-beam-epitaxy-grown multinanolayers. This ultranarrow (full width at half maximum below 8 μeV) emission originating from the unique Er-related optical complex, Er-1 center, ensures the best condition to achieve stimulated emission. The experiments were carried out using a combination of the variable stripe length and shifting excitation spot techniques under pulsed and continuous-wave excitations. The comparison of results for both excitation regimes enables to estimate an optical gain within the strong optical losses due to the free carrier absorption. Based on these measurements, the upper limit of the optical gain cross section of 10⁻¹⁷cm² and the gain coefficient of 8.8 cm⁻¹ are deduced.