Limiting performance of graphene bilayer sub-terahertz detectors at large induced band gap

TL;DR

This study investigates the limits of graphene bilayer detectors at cryogenic temperatures for sub-terahertz radiation, showing that responsivity and NEP improve with larger induced band gaps up to near 90 meV, revealing plasmonic effects.

Contribution

It provides the first detailed analysis of detector performance at large induced band gaps close to 90 meV, highlighting the non-saturation of responsivity and NEP improvements.

Findings

NEP drops from ~450 to ~30 fW/Hz^{1/2} with increasing band gap.

Responsivity does not saturate up to the maximum induced gap.

Plasmonic oscillations become significant at large band gaps.

Abstract

Electrically induced $p-n$ junctions in graphene bilayer (GBL) have shown superior performance for detection of sub-THz radiation at cryogenic temperatures, especially upon electrical induction of the band gap $E_g$. Still, the upper limits of responsivity and noise equivalent power (NEP) at very large $E_g$ remained unknown. Here, we study the cryogenic performance of GBL detectors at $f=0.13$ THz by inducing gaps up to $E_g \approx 90$ meV, a value close to the limits observed in recent transport experiments. High value of the gap is achieved by using high-$\kappa$ bottom hafnium dioxide gate dielectric. The voltage responsivity, current responsivity and NEP optimized with respect to doping do not demonstrate saturation with gap induction up to its maximum values. The NEP demonstrates an order-of-magnitude drop from $\sim450$ fW/Hz$^{1/2}$ in the gapless state to $\sim30$ fW/Hz$^{1/2}$ at the largest gap. At largest induced band gaps, plasmonic oscillations of responsivity become visible and important for optimization of sub-THz response.