Temperature behavior of stimulated emission delays in GaAs diodes and a proposed trapping model

The delay time between the application of a current pulse and the onset of coherent stimulated emission has been investigated for several of our diffused GaAs junction lasers from 77°K to above room temperature. A "transition temperature" Ttwas found for most diodes above which the delays are long (of the order 10-7seconds) in contrast to the 1- or 2-ns delay found below Tt. Four delay properties, reported here for the first time, were found from investigating the regions near Tt. 1) The location of Ttdepends on the originaln-type substrate material, the specific diffusion conditions, and subsequent heat treatments. 2) Transition regions for various diodes occur in the entire range fromTₜ = 120 to above 300°K. 3) An anomolous increase in threshold occurs at Tt. 4) The width of the transition region becomes narrower as Ttis lowered. These experimental results led us to postulate a new trapping center. For temperaturesT < Tₜ, the trap is in its initial state Tr1(nonabsorbing). WhenT Tₜ, the trap can capture an electron to produce the Tr2state, which causes delays by introducing an optical absorption as proposed by Fenner. Using this model, qualitative explanations of the experimental data are given.