Infrared photodetection in graphene-based heterostructures: bolometric and thermoelectric effects at the tunneling barrier

TL;DR

This study uncovers the microscopic mechanisms of photocurrent generation in graphene/hBN/graphene tunnel devices under mid-IR light, linking it to tunneling probability changes due to electron heating, and proposes their use for electronic temperature measurement.

Contribution

The paper develops a theoretical model explaining photocurrent origins in graphene tunnel devices and demonstrates their potential for precise electronic temperature sensing.

Findings

Photocurrent is proportional to the second derivative of tunnel current w.r.t. bias voltage.

Photocurrent peaks during tunneling through impurity levels in hBN.

Devices can measure electronic temperature accurately via photocurrent analysis.

Abstract

Graphene/hBN/graphene tunnel devices offer promise as sensitive mid-infrared photodetectors but the microscopic origin underlying the photoresponse in them remains elusive. In this work, we investigated the photocurrent generation in graphene/hBN/graphene tunnel structures with localized defect states under mid-IR illumination. We demonstrate that the photocurrent in these devices is proportional to the second derivative of the tunnel current with respect to the bias voltage, peaking during tunneling through the hBN impurity level. We revealed that the origin of the photocurrent generation lies in the change of the tunneling probability upon radiation-induced electron heating in graphene layers, in agreement with the theoretical model that we developed. Finally, we show that at a finite bias voltage, the photocurrent is proportional to the either of the graphene layers heating under the illumination, while at zero bias, it is proportional to the heating difference. Thus, the photocurrent in such devices can be used for accurate measurements of the electronic temperature providing a convenient alternative to Johnson noise thermometry.