Ultrafast relaxation of hot phonons in Graphene-hBN Heterostructures

TL;DR

This study demonstrates that graphene-hBN heterostructures enable ultrafast hot phonon relaxation, significantly improving carrier cooling rates compared to traditional substrates, which is crucial for high-performance graphene devices.

Contribution

The paper reveals that hBN substrates facilitate four times faster hot phonon relaxation in graphene, overcoming the hot phonon bottleneck and enhancing carrier cooling.

Findings

Carriers cool four times faster on hBN than on SiO2.

hBN substrate overcomes hot phonon bottleneck in graphene.

Ultrafast pump-probe spectroscopy used to track cooling dynamics.

Abstract

Fast carrier cooling is important for high power graphene based devices. Strongly Coupled Optical Phonons (SCOPs) play a major role in the relaxation of photoexcited carriers in graphene. Heterostructures of graphene and hexagonal boron nitride (hBN) have shown exceptional mobility and high saturation current, which makes them ideal for applications, but the effect of the hBN substrate on carrier cooling mechanisms is not understood. We track the cooling of hot photo-excited carriers in graphene-hBN heterostructures using ultrafast pump-probe spectroscopy. We find that the carriers cool down four times faster in the case of graphene on hBN than on a silicon oxide substrate thus overcoming the hot phonon (HP) bottleneck that plagues cooling in graphene devices.