Roadmap for gain-bandwidth-product enhanced photodetectors: opinion

Abstract

Photodetectors are key optoelectronic building blocks performing the essential optical-to-electrical signal conversion, and unlike solar cells, operate at a specific wavelength and at high signal or sensory speeds. Towards achieving high detector performance, device physics, however, places a fundamental limit of the achievable detector sensitivity, such as responsivity and gain, when simultaneously aimed to increasing the detector’s temporal response (speed) known as the gain-bandwidth product (GBP). While detector’s GBP has been increasing in recent years, the average GBP is still relatively modest (∼106-109 Hz-A/W). Here we discuss photoconductor-based detector performance limits and opportunities based on arguments from scaling length theory relating photocarrier channel length, mobility, electrical resistance with optical waveguide mode constrains. We show that short-channel detectors are synergistic with slot-waveguide approaches, and when combined, offer a high-degree of detector design synergy especially for the class of nanometer-thin materials. Indeed, we find that two-dimensional material-based detectors are neither limited by their low mobility nor by associated carrier velocity saturation limitations and can, in principle, allow for 100 GHz fast response rates, which is unlike traditional detector designs that are based on wide channel lengths. However, the contact resistance is still a challenge for such thin photo absorbing materials – a research topic that is still not addressed yet. An interim solution is to utilize heterojunction approaches for functionality separation. Nonetheless, atomistic and nanometer-thin materials used in such next-generation scaling length theory based detectors also demand high material quality and monolithic integration strategies into photonic circuits including foundry-near processes. As it stands, this letter aims to guide the community if achieving the next generation photodetectors aiming for a performance target of GBP ∼ 1012 Hz-A/W.