Abstract
Spontaneous and stimulated emission from a series of Al0.7Ga0.3As -Al0.49Ga0.51As-GaAs ultrathin single [1,2, and 3 monolayer (ML), 1 ML=2.83 Å] and multiple (2 ML) quantum well separate confinement heterostructures are demonstrated and compared to a control sample (0 ML). Spectra from sample to sample are very different and depend on the alignment of the n=1, Γ electron bound state in the quantum well with the Xminima (lowest band edge) in the indirect-gap (Al0.49Ga0.51As) confining layers. Some samples (3 ML single and 2 ML multiple quantum well) can support stimulated emission despite the fact that the quantum well is undoped, unstrained, and very thin (Lz ≪scattering path length) and that most of the wave function is in the indirect-gap confining layers. These experimental results can be explained using a simple model based on the spatial extent of the wave function (rather than the well width) under the special condition of band alignment between the Γ and X states.
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