  Experimental investigation of nuclear spin effects on the electron spin
polarization in singly negatively charged InP quantum dots is reported.
Pump-probe photoluminescence measurements of electron spin relaxation in the
microsecond timescale are used to estimate the time-period $T_{N}$ of the
Larmor precession of nuclear spins in the hyperfine field of electrons. We find
$T_{N}$ to be $\sim 1$ $\mu$s at $T \approx 5$ K, under the vanishing external
magnetic field. From the time-integrated measurements of electron spin
polarization as a function of a longitudinally applied magnetic field at $T
\approx 5$ K, we find that the Overhauser field appearing due to the dynamic
nuclear polarization increases linearly with the excitation power, though its
magnitude remains smaller than 10 mT up to the highest excitation power (50 mW)
used in these experiments. The effective magnetic field of the frozen
fluctuations of nuclear spins is found to be 15 mT, independent of the
excitation power.
