A Germanium Thin-Film Platform for Ultrafast Terahertz Electronics

High frequency electronics operating in the hundreds of gigahertz and terahertz frequencies are expected to transform modern communications, quantum technology, and increase the operating speeds of modern semiconductor devices.Traditionally, on-chip sources for generating signals in the terahertz and sub-terahertz frequency range were dominated by III-V epitaxially grown semiconductors. As such, the availability of ``ultrafast'' semiconductor material was scarce, expensive and more importantly not compatible with standard Silicon-based CMOS manufacturing.Germanium has emerged as a promising candidate for high-frequency electronics and opto-electronics, however, in its pure crystalline form has a very slow frequency response due to its indirect bandgap. In this work we explore evaporated amorphous germanium and its potential as a high-frequency source.Our findings show that evaporated amorphous germanium, grown through standard physical evaporation, exhibits ultrafast carrier dynamics with sub-picosecond durations. We further demonstrate that it can be used as an on-chip source for picosecond-duration signal generation with frequency bandwidths up to 0.7 THz. The presented technique provides a versatile and inexpensive approach, widely available to all nanofabrication facilities, for creating on-chip, CMOS-compatible THz sources aimed at high-frequency electronic circuitry.