$7\mathrm{.}4$ The diffusion length $L_D$ or the average distance moved by charge carriers before recombination in the active region of an LED is given by:

$L_D=(D{)}^{\frac{1}{2}}$

This strategy is often referred to as intensity modulation$/$direct detection, or IM$/$DD$.$

Problems $437$

where $D$ is the diffusion coefficient and $$ is the total carrier recombination lifetime. Calculate the diffusion coefficient in gallium arsenide when the diffusion length is $21m$ and the radiative and nonradiative carrier recombination lifetimes are equal at $90$ ns $.$