In this paper the effect of junction capacitance

spontaneous recombination

DC-bias and injected pulse current on time delay’ of turn-on of injection lasers modulated by pulse currents is analysed comprehensively. Kinetic equations considering those factors are developed. A variety of possible cases for are discussed

and results for some typical parameters are given. The calculated results are found to coincide with the measured values. When the junction capacitance is not very small （>20 pF）

it is an important factor for the time delay just like spontaneous recombination. The reduction of the time delay by DC bias is not linear

becoming small gradually from zero-bias to DC-bias at threshold. Thus we can obtain the best modulation by DC-bias below threshold.