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Spontaneous- and stimulated-emission spectra from a series of Al₀. ₃Ga₀. ₇As/GaAs/InAs separate-confinement strained single-quantum-well heterostructures are demonstrated for well widths as thin as 1 monolayer (3). These undoped samples, grown by molecular-beam epitaxy, are the thinnest single quantum wells ever reported to support stimulated emission. Continuous-wave (cw) laser thresholds at 77 K are generally quite low (0. 78 kW/cm^2) despite the fact that the single quantum wells are undoped and of dimensions (Lₙ) which were previously thought to be too small to effectively collect excess carriers (Lₙ path length). A simple model based on the spatial extent of the wave function, rather than the well width, is proposed to explain the experimental results. Also a simple modified square-well model with strain-induced band-gap correction is found to predict the experimentally measured energy levels of ultrathin quantum wells.
Lee et al. (Sun,) studied this question.