Threshold current of extremely narrow semiconductor quantum-well lasers

The threshold current of extremely narrow semiconductor quantum-well lasers is calculated, accounting for the reduced lateral optical filling factor and the gain saturation in the quantum well. It is shown that the reduced optical filling factor leads to a minimum in the threshold current at an optimum value of the quantum-well width. Analytic approximations of the optimal width and length of the laser cavity are derived. In addition, it is shown that two-dimensional separate-confinement quantum-well heterostructures can reduce the threshold current, particularly in the case of quantum-wire lasers.