  Miniaturized photodetectors are becoming increasingly sought-after components
for a range of next generation technologies, such as autonomous vehicles,
integrated wearable devices, or gadgets embedded in the Internet of Things. A
major challenge, however, lies in shrinking the device footprint, while
maintaining high efficiency. This conundrum can be solved by realizing
non-trivial relation between the energy and momentum of photons, such as
dispersion-free angle-independent devices, known as flat bands. Here, we
leverage flat band meta-optics to simultaneously achieve critical absorption
over a wide range of incidence angles. For a monolithic silicon meta-optical
photodiode, we achieved ~10-fold enhancement in the photon-to-electron
conversion efficiency. Such enhancement over a large angular range of ~36
degrees allows incoming light to be collected via a large aperture lens and
focused on a compact photodiode, potentially enabling high-speed and low-light
operation. Our research unveils new possibilities for creating compact and
efficient optoelectronic devices with far-reaching impact on various
applications, including augmented reality and light detection and ranging.
