Charge-carrier concentration and temperature in quantum wells of laser heterostructures under spontaneous-and stimulated-emission conditions

Abstract

The charge-carrier concentration and the temperature of hot electrons and holes in quantum-well laser nanostructures in the regimes of spontaneous and stimulated emission are determined as functions of the current density j, with InGaAs/GaAs structures as an example. Under spontaneous-emission conditions, the carrier concentration in the active region of a laser structure grows as the current increases, while carrier heating is insignificant. The spontaneous-emission spectra calculated taking into account forbidden optical transitions agree well with the experimental ones. Under stimulated-emission conditions, the behavior is quite different. When the pump current density is comparatively low (several times above the threshold), the concentration of injected charge carriers levels off and does not grow as the current increases, while the carrier temperature rises considerably. When the current density exceeds the threshold value by orders of magnitude, stabilization of the charge-carrier concentration does not take place; the carrier concentration exhibits a severalfold increase and the carrier temperature rises to about 450 K at j = 80 kA/cm2. The number of the charge carriers escaping from the quantum wells into the barriers, which determines the laser efficiency, also increases under these conditions because of the carrier heating. This undesirable effect can be weakened by increasing the depth of the quantum wells.