Charge transfer in few-layer InSe/gas Interface*

Few-layer InSe shows a strong potential for gas sensing applications primarily due to high sensitivity of electron lone pairs on Se to external gas molecules. Based on the results from first principles Density Functional Theory calculations, we carefully analyzed electronic band structures of few-layer InSe/Gas configurations. Our calculations show that charge transfer across few-layer InSe/gas system depends on the orientation and the type of the gas molecules. Therefore, it was seen that for certain gas molecules such as ethanol, the InSe layers are p-doped, while for other molecules such as methanol the InSe layers are n-doped. These results were verified through gas sensing experiments using few layer InSe FET devices. Further we show, while majority charge transfer happens through InSe/Gas interface, the polarity of external molecule can tune interlayer spacing through an induced dipole moment between the layers. The change in interlayer spacing is not monotonic, which results in pinning of impurity band with respect to valence band maximum. Fundamental understanding of charge transfer in few-layer InSe/gas interfaces at the atomic level is expected to pave the path for designing gas sensing devices based on few-layer InSe