  We present experiments to systematically study the time constants of
spin-dependent recombination processes in semiconductors using pulsed
electrically detected magnetic resonance (EDMR). The combination of
time-programmed optical excitation and pulsed spin manipulation allows us to
directly measure the recombination time constants of electrons via localized
spin pairs and the time constant of spin pair formation as a function of the
optical excitation intensity. Using electron nuclear double resonance, we show
that the time constant of spin pair formation is determined by an electron
capture process. Based on these time constants we devise a set of rate
equations to calculate the current transient after a resonant microwave pulse
and compare the results with experimental data. Finally, we critically discuss
the effects of different boxcar integration time intervals typically used to
analyze pulsed EDMR experiments on the determination of the time constants. The
experiments are performed on phosphorus-doped silicon, where EDMR via spin
pairs formed by phosphorus donors and Si/SiO2 interface dangling bond defects
is detected.
