Spikes in the light output of room temperature GaAs junction lasers

Observations of the light intensity of pulsed, GaAs injection lasers at room temperature have revealed a regular, damped spiking behavior. The lasers were made by diffusing Zn into an
n
-type substrate. A stripe contact permits the excitation of only a very narrow region of the junction. The spiking was most clearly observed with a rectangular current pulse of 50 ns in width and a 0.5-ns risetime. Because of the long delays inherent in these diodes, the laser light appears at the very end of the current pulse, as the threshold value of the current is crossed. With increased pumping, the emission starts at earlier times and extends to the end of the current pulse. Only three or four spikes can be seen clearly because of the fast damping. The decay time is of the order of 2 ns and the interval between the spikes is about 1 to 1.4 ns. The spiking theory advanced by Statz and Tang to explain the time behavior of ruby has been applied to GaAs lasers. The rate equations in this formulation are derived under the assumption that the standing-wave nature of the field in the cavity creates a spatially inhomogeneous inversion along the resonator. Numerical solutions to these equations have been obtained for the cases of one and three longitudinal modes. The approximations used are first, that the pump power is kept near threshold, second, that there is no diffusions of carriers, third, that the gain curve is Lorentzian in shape, and last, that the modes are located symmetrically with respect to the line center. The two parameters that are needed to solve the equations are the cavity
Q
and the spontaneous recombination lifetime. Using the values available in the literature, good agreement has been found between theory and experiment.