Photoluminescence and stimulated emission from monolayer-thick pseudomorphic InAs single-quantum-well heterostructures

Spontaneous- and stimulated-emission spectra from a series of ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As/GaAs/InAs separate-confinement strained single-quantum-well heterostructures are demonstrated for well widths as thin as 1 monolayer (3 Å). These undoped samples, grown by molecular-beam epitaxy, are the thinnest single quantum wells ever reported to support stimulated emission. Continuous-wave (cw) laser thresholds at 77 K are generally quite low (0.78 kW/${\mathrm{cm}}^2$) despite the fact that the single quantum wells are undoped and of dimensions (${\mathit{L}}_{\mathit{z}}$) which were previously thought to be too small to effectively collect excess carriers (${\mathit{L}}_{\mathit{z}}$≪scattering 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.