III–V Heterojunction Platform for Electrically Reconfigurable Dielectric Metasurfaces

• Published in: ACS photonics Vol. 6; no. 6; pp. 1345 - 1350
• Main Authors: Iyer, Prasad P, Pendharkar, Mihir, Palmstrøm, Chris J, Schuller, Jon A
• Format: Journal Article
• Language: English
• Published: American Chemical Society 19-06-2019
• Subjects: optical antennas; Mie resonators; phased array optics; metasurfaces; III−V devices
• ISSN: 2330-4022; 2330-4022
• DOI: 10.1021/acsphotonics.9b00178

Achieving an electrically tunable phased array optical antenna surface has been a principal challenge in the field of metasurfaces. In this Letter, we demonstrate a device platform for achieving reconfigurable control over the resonant wavelength of a subwavelength optical antenna through free-carrier injection. We engineer and grow, using molecular beam epitaxy, a heterostructure of In1–x Al x As/InAs/Al y Ga1–y Sb layers designed to achieve large amplitude and phase modulation of light by maximizing the refractive index change in regions of resonant field enhancement The p-i-n layers are grown on a heavily doped n-InAs layer which forms a reflecting substrate to confine the Mie resonances within the nanowires of the index tunable layers. We outline the fabrication process developed to form such tunable metasurface elements using a four-step projection lithography process and a self-aligned vertical dry etch. We experimentally demonstrate the operation of an electrically reconfigurable optical antenna element where the resonant wavelength blue shifts by 200 nm only during carrier-injection. We extrapolate the experimentally measured InAs refractive index shifts to show we can achieve a nearly π-phase shift in a metasurface array. This solid-state device platform enables us to contact each resonant element independently to form a truly reconfigurable Fourier optical element with the promise of arbitrary control of the electromagnetic wavefront at the subwavelength scale.