ON THE SEMICONDUCTOR-LASER LOGARITHMIC GAIN CURRENT-DENSITY RELATION

The simplified relation, alpha = G0 ln (eta(i)J/J0), between material gain alpha and current density J is shown to be a very good shape approximation, for quantum wells and bulk materials, essentially independent of the type of recombination processes present. Simulations show that for a given material system, G0 decreases by only about 30% from pure electron-hole recombination dominated to pure Auger recombination dominated. A generic quantum-well situation is explored to reveal the density of states and recombination coefficient dependence of G0 and to formulate simple estimates for G0. The results were tested against published data for eight quantum-well diode lasers, five strained, in the GaAs-GaAs, InGaAs-GaAs, InGaAs-InP, InGaAsP-InP, and GaInAsSb-GaSb material systems. The predicted values of G0 were generally found to be in agreement with experiments only for the wider gap diodes. The discrepancies were attributed in part to carrier induced absorption and we show that the formalism can be modified in selected cases to incorporate this without changing the basic form of the gain. We also provide a new expression which relates the temperature dependence of the measured parameters to the characteristic temperature T0.