Violation of Local Electroneutrality in the Quantum Well of a Semiconductor Laser with Asymmetric Barrier Layers

Resumo

A self-consistent model for calculating the threshold and high-power characteristics of semiconductor quantum well lasers with asymmetric barrier layers is developed. The model, which is based on a system of rate equations, uses the universal condition of global charge neutrality in the laser structure. The electron and hole concentrations in the waveguide region and in the quantum well (QW) and the concentration of photons of stimulated emission are calculated. The local neutrality in the QW is shown to be strongly violated, especially at high injection currents. The violation of neutrality in a QW makes the electron and hole concentrations there dependent on the injection current under lasing conditions: in the structures under consideration, the electron concentration in the QW decreases while the hole concentration increases with increasing injection current. In the case of the ideal functioning of asymmetric barrier layers, when electron–hole recombination in the waveguide region is completely suppressed, the violation of neutrality in the QW has almost no effect on the dependence of the output optical power on the injection current: the quantum efficiency is close to unity and the light–current characteristic is linear. Nevertheless, the violation of neutrality in the QW causes weakening of the temperature dependence of the threshold current and, hence, an increase in the characteristic temperature T₀ of the laser.