Simultaneous control of spectral and directional emissivity with gradient epsilon-near-zero InAs photonic structures

Controlling both the spectral bandwidth and directional range of emitted thermal radiation is a fundamental challenge in modern photonics and materials research. Recent work has shown that materials with a spatial gradient in their epsilon near zero response can support broad spectrum directionality in their emissivity, enabling high radiance to specific angles of incidence. However, this capability has been limited spectrally and directionally by the availability of materials supporting phonon-polariton resonances over long-wave infrared wavelengths. Here, we design and experimentally demonstrate an approach using doped III-V semiconductors that can simultaneously tailor spectral peak, bandwidth and directionality of infrared emissivity. We epitaxially grow and characterize InAs-based gradient ENZ photonic structures that exhibit broadband directional emission with varying spectral bandwidths and peak directions as a function of their doping concentration profile and thickness. Due to its easy-to-fabricate geometry we believe this approach provides a versatile photonic platform to dynamically control broadband spectral and directional emissivity for a range of emerging applications.