  Nonlinear interactions between ultrashort optical waveforms and solids can be
used to induce and steer electric current on a femtosecond (fs) timescale,
holding promise for electronic signal processing at PHz frequencies [Nature
493, 70 (2013)]. So far, this approach has been limited to insulators,
requiring extremely strong peak electric fields and intensities. Here, we show
all-optical generation and control of directly measurable electric current in a
semiconductor relevant for high-speed and high-power (opto)electronics, gallium
nitride (GaN), within an optical cycle and on a timescale shorter than 2 fs, at
intensities at least an order of magnitude lower than those required for
dielectrics. Our approach opens the door to PHz electronics and metrology,
applicable to low-power (non-amplified) laser pulses, and may lead to future
applications in semiconductor and photonic integrated circuit technologies.
