  The photoelectric effect has a sister process relevant in optoelectronics
called internal photoemission. Here an electron is photoemitted from a metal
into a semiconductor. While the photoelectric effect takes place within less
than 100 attoseconds, the attosecond time scale has so far not been measured
for internal photoemission. Based on the new method CHArge transfer time
MEasurement via Laser pulse duration-dependent saturation fluEnce
determinatiON, CHAMELEON, we show that the atomically thin semi-metal graphene
coupled to bulk silicon carbide, forming a Schottky junction, allows charge
transfer times as fast as (300 $\pm$ 200) attoseconds. These results are
supported by a simple quantum mechanical model simulation. With the obtained
cut-off bandwidth of 3.3 PHz for the charge transfer rate, this
semimetal-semiconductor interface represents the first functional solid-state
interface offering the speed and design space required for future light-wave
signal processing.
