Attosecond tuning of coherent electron dynamics in doped semiconductors

The intentional inclusion of impurities in semiconductors, or doping, enabled the establishment of modern electronics. However, the stagnation in performance caused by the approaching ultimate limits in the miniaturization of transistors calls for a disruptive change. Ultrafast laser pulses offer a promising route to overcome this limitation by shaping the electro-optical properties of solids at unprecedented speed. Yet, the coherent interaction between intense light transients and doped semiconductors has remained unexplored, leaving unanswered fundamental questions about the feasibility of ultrafast light control. Here we show how doping affects the field-driven attosecond electron dynamics in monocrystalline germanium. By measuring the absolute delay between the transient optical features and the driving field, we first identify the origin of the sub-femtosecond response in intrinsic germanium. A systematic comparison with doped samples reveals two distinct regimes. At moderate doping levels, photoinjection dominates the dynamics. For high doping concentrations (~1020 cm−3), we unveil a striking field-driven response governed by the coherent quantum interplay between majority carriers and light-induced charges, never observed in metals with similar equilibrium conductivity. These findings establish doping as a powerful lever to engineer the petahertz optical response of semiconductors, enabling sub-femtosecond light control in conductive materials, a key prerequisite for future electro-optical technologies.