First-principles perspective on full-spectrum infrared photodetectors from doping an excitonic insulator

Innovations in imaging technology involve finding strategies and materials suitable for detection applications over the entire infrared range. Herein, we propose a new design concept based on the unique feature of an excitonic insulator, namely, negative exciton transition energy (${E}_t$). We demonstrate this concept using first-principles $GW$-Bethe-Salpeter equation calculations on one-dimensional organometallic wire ${(\mathrm{CrBz})}_{\ensuremath{\infty}}$. The pristine ${(\mathrm{CrBz})}_{\ensuremath{\infty}}$ exhibits an excitonic instability due to a negative ${E}_t$ for the lowest exciton. Substitutional doping can continuously tune the ${E}_t$ from $\ensuremath{\sim}\phantom{\rule{0.16em}{0ex}}0$ to $\ensuremath{\sim}\phantom{\rule{0.16em}{0ex}}0.6$ eV, which shows the ability of photon detection from terahertz to near infrared. This type of detector has advantages of outstanding wavelength selectivity, reduced thermal disturbance, and elevated working temperature. Our paper not only adds another member in the family of rare one-dimensional excitonic insulators, but also opens a new avenue for the development of high-performance infrared photodetectors in the future.