Sub-cycle optical control of current in a semiconductor: From the multiphoton to the tunneling regime

Nonlinear interactions between ultrashort optical waveforms and solids can be used to induce and steer electric currents on femtosecond (fs) timescales, holding promise for electronic signal processing at PHz (10¹⁵ Hz) frequencies [Nature 493, 70 (2013)]. So far, this approach has been limited to insulators, requiring extreme peak electric fields (>1 V/Å) and intensities (>10¹³ W/cm²). Here, we show all-optical generation and control of electric currents 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 lowpower (non-amplified) laser pulses, and may lead to future applications in semiconductor and (photonic) integrated circuit technologies.