Transition dipole moment of InAs/InGaAs quantum dots from experiments on ultralow-threshold laser diodes

Semiconductor ultralow-threshold InAs quantum-dot lasers are investigated o perating at 1230-1250 nm at room temperature (laser threshold range is of 1 6-83 A/cm(2) for ground-state emission). The dependence of gain on current is derived from measurements of the threshold current as a function of the cavity length. The ground-state gain appears at very low current: the inver sion threshold of similar to 13 A/cm(2) is a record low value. Analysis of these data for diodes of different molecular beam epitaxial-grown wafers le ads to a squared dipole moment of the transition of similar to 9.2 x 10(-57 ) C-2 m(2) that corresponds to the length of elementary dipole of similar t o 0.6 nm. (C) 2000 American Institute of Physics. [S0003-6951(00)03228-9].