Quantum cascade (QC) lasers achieve population inversion by selecting quantum wells (QW) thicknesses so that the inherent scattering mechanisms ensure a higher population of electrons in the upper laser state compared to the lower laser state. Previously, longitudinal optical (LO) phonons have been considered the fastest, most significant scattering process in QC lasers. Recently, it has been shown that interface roughness (IFR) can have substantial effects in determining the effective lifetimes within QW systems . Simulations have shown that IFR scattering lifetimes can be the dominant scattering process for selected QW configurations .
Here we have designed and fabricated three QC structures, which differ in the positioning of a strategically placed monolayer barrier to selectively affect the IFR scattering lifetimes of the energy levels in the QC structures. Initial current-voltage characteristics suggest a shorter carrier transit time through the QC structure due to increased interface roughness interactions. We also observed an expected narrowing of the EL spectra based on these same interactions. Using these results, we have also designed a QC laser using IFR scattering as the determining process for maintaining population inversion. By using IFR scattering, we were able to design an energy separation between the lower laser level and subsequent injector levels much greater than the LO phonon energy without compromising fast carrier depopulation from the lower laser level. This in effect opens doors for completely new intersubband design techniques. This work is supported in part by MIRTHE (NSF-ERC).
Akil Word-Daniels, Pierre M. Bouzi, Deborah Sivco, and Claire F. Gmachl, "The effects of interface roughness on quantum cascade lasers (Conference Presentation)," Proc. SPIE 10123, Novel In-Plane Semiconductor Lasers XVI, 101231K (Presented at SPIE OPTO: February 02, 2017; Published: 20 April 2017); https://doi.org/10.1117/12.2252547.5398643869001.
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