Highly sensitive hBN/graphene hot electron bolometers with a Johnson noise readout

Graphene has remarkable opto-electronic and thermo-electric properties that make it an exciting functional material for various photo-detection applications. In particular, owed to graphenes unique combination of an exceedingly low electronic heat capacity and a strongly suppressed electron-phonon thermal conductivity G$_{th}$, the electronic and phononic temperatures are highly decoupled allowing an operation principle as a hot electron bolometer (HEB). Here we demonstrate highly sensitive HEBs made of high quality hBN/graphene/hBN stacks and employ a direct electronic temperature read out scheme via Johnson noise thermometry (JNT). We perform combined pump-probe and JNT measurements to demonstrate strongly damped C$_{e}$ and G$_{th}$ in the ultra-low impurity $\sigma_{i}=$10$^{9}$ cm$^{-2}$ hBN/G/hBN stacks, which result in unprecedented photo-detection sensitivity and noise equivalent power for graphene HEBs.