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" T
t
was found for most diodes above which the delays are long (of the order 10
^-7
seconds) in contrast to the 1- or 2-ns delay found below T
t
. Four delay properties, reported here for the first time, were found from investigating the regions near T
t
. 1) The location of T
t
depends on the original
n
-type substrate material, the specific diffusion conditions, and subsequent heat treatments. 2) Transition regions for various diodes occur in the entire range from
T_{t} = 120\deg
K to above 300°K. 3) An anomolous increase in threshold occurs at T
t
. 4) The width of the transition region becomes narrower as T
t
is lowered. These experimental results led us to postulate a new trapping center. For temperatures
T < T_{t}
, the trap is in its initial state Tr
1
(nonabsorbing). When
T \simeq T_{t}
, the trap can capture an electron to produce the Tr
2
state, which causes delays by introducing an optical absorption as proposed by Fenner. Using this model, qualitative explanations of the experimental data are given.