Continuum transitions and phonon coupling in single self-assembled Stranski-Krastanow quantum dots

Continuum transitions in the absorption spectra of self-assembled InGaAs quantum dots are demonstrated to have an intrinsic origin, and to arise from transitions between the wetting layer quantum well and quantum dot confined states, in agreement with recent theory predictions. The spectra are shown to fall into two distinct groups, below 50 meV corresponding to sharp line transitions expected in an ideal atom picture, and above 50 meV where coupling of discrete transitions to the continuum is demonstrated. Electric-field-controlled resonant coupling to LO phonons is also demonstrated.