  Modulation of donor electron wavefunction via electric fields is vital to
quantum computing architectures based on donor spins in silicon. For practical
and scalable applications, the donor-based qubits must retain sufficiently long
coherence times in any realistic experimental conditions. Here, we present
pulsed electron spin resonance studies on the longitudinal $(T_1)$ and
transverse $(T_2)$ relaxation times of phosphorus donors in bulk silicon with
various electric field strengths up to near avalanche breakdown in high
magnetic fields of about 1.2 T and low temperatures of about 8 K. We find that
the $T_1$ relaxation time is significantly reduced under large electric fields
due to electric current, and $T_2$ is affected as the $T_1$ process can
dominate decoherence. Furthermore, we show that the magnetoresistance effect in
silicon can be exploited as a means to combat the reduction in the coherence
times. While qubit coherence times must be much longer than quantum gate times,
electrically accelerated $T_1$ can be found useful when qubit state
initialization relies on thermal equilibration.
