Carrier saturation in multiple quantum well metallo-dielectric semiconductor nanolaser: Is bulk material a better choice for gain media?

Although multi quantum well (MQW) structure is frequently suggested as the appropriate medium for providing optical gain in nanolasers with low threshold current, we demonstrate that in general bulk gain medium can be a better choice. We show that the high threshold gain required for nanolasers demands high threshold carrier concentrations and therefore a highly degenerate condition in which the barriers between the quantum wells are heavily pumped. As a result, there occurs spontaneous emission from the barrier in very dissipative low Q modes or undesired confined higher Q modes with resonance wavelengths close to the barrier bandgap. This results in a competition between wells and barriers that suppresses lasing. A complete model involving the optical properties of the resonant cavity combined with the carrier injection in the multilayer structure is presented to support our argument. With this theoretical model we show that while lasing is achieved in the nanolaser with bulk gain media, the nanolaser with MQW gain structure exhibits well emission saturation due to the onset of barrier emission.