Infrared study of Large scale h-BN film and Graphene/h-BN heterostructure

TL;DR

This study uses infrared spectroscopy to compare high-temperature and low-temperature grown h-BN films and their effects on graphene's electronic properties, revealing that high-temperature h-BN improves graphene quality by reducing impurities.

Contribution

It demonstrates that high-temperature CVD h-BN films effectively decouple graphene from substrate impurities, enhancing its electronic quality compared to low-temperature films.

Findings

High-temperature h-BN shows a single E1u phonon mode, indicating aligned 2D planes.

Graphene on high-temperature h-BN has lower residual carrier density.

Interband transition width in graphene is reduced on high-temperature h-BN.

Abstract

We synthesize a series of CVD h-BN films and perform critical infrared spectroscopic characterization. For high-temperature (HT, Temp = 1400 degrees) grown h-BN thin film only E1u-mode infrared phonon is activated demonstrating highly aligned 2D h-BN planes over large area, whereas low-temperature (LT, Temp = 1000 degrees) grown film shows two phonon peaks, E1u and A2u, due to stacking of h-BN plane at tilted angle. For CVD graphene transferred on HT h-BN/SiO2/Si substrate, interband transition spectrum s1 shifts strongly to lower energy compared with that on LT h-BN/SiO2/Si and on bare SiO2/Si substrate, revealing that residual carrier density n in graphene is suppressed by use of HT h-BN layer. Also the interband transition width of s1 defined by effective temperature is reduced from 400 K for G/SiO2/Si to 300 K for HT h-BN/SiO2/Si. The behaviors of n and effective temperature show that HT h-BN film can decouple CVD graphene from the impurity and defect of SiO2 leading to large scale free-standing like graphene.