Sensitive Characterization of the Graphene Transferred onto Varied Si Wafer Surfaces via Terahertz Emission Spectroscopy and Microscopy (TES/LTEM)

Abstract

Graphene shows great potential in developing the next generation of electronic devices. However, the real implementation of graphene-based electronic devices needs to be compatible with existing silicon-based nanofabrication processes. Characterizing the properties of the graphene/silicon interface rapidly and non-invasively is crucial for this endeavor. In this study, we employ terahertz emission spectroscopy and microscopy (TES/LTEM) to evaluate large-scale chemical vapor deposition (CVD) monolayer graphene transferred onto silicon wafers, aiming to assess the dynamic electronic properties of graphene and perform large-scale graphene mapping. By comparing THz emission properties from monolayer graphene on different types of silicon substrates, including those treated with buffered oxide etches, we discern the influence of native oxide layers and surface dipoles on graphene. Finally, the mechanism of THz emission from the graphene/silicon heterojunction is discussed, and the large-scale mapping of monolayer graphene on silicon is achieved successfully. These results demonstrate the efficacy of TES/LTEM for graphene characterization in the modern graphene-based semiconductor industry.

Keywords: BHF etching; graphene; silicon; terahertz emission spectroscopy (TES).

Figure 1

Illustration of THz emission mechanism from semiconductor surface with laser excitation. The THz emission is generated from the ultrafast photoelectrons transport within the band bending (shown as the black THz arrays) and the THz radiation from the laser-illuminated area is shown as the green cone and detected by the THz antenna.

Figure 2

The procedure of graphene transferring onto the Si substrates.

Figure 3

Diagram of the TES/LTEM system.

Figure 4

(a) THz emission from graphene/n-Si with or without BHF treatment and the comparison with bare n-Si with or without BHF treatment. (b) THz emission from graphene/p-Si with or without BHF treatment and the comparison with bare p-Si with or without BHF treatment.

Figure 5

The comparison of the THz emission waveform from different samples (a) n-Si vs. Gr/n-Si (b) BHF n-Si vs. Gr/BHF n-Si (c) Gr/n-Si vs. Gr/BHF n-Si (d) p-Si vs. Gr/p-Si (e) BHF/p-Si vs. Gr/BHF p-Si (f) Gr/p-Si vs. Gr/BHF p-Si.

Figure 6

A band diagram of the graphene/Si heterojunction in different situations. (a) graphene/native oxide/n-Si, (b) graphene/BHF n-Si, (c) graphene/native oxide/p-Si, (d) graphene/BHF p-Si. The $\Delta E$ is equal to the interface potential ($V_{bi}$), where $V_{bi}={\varphi }_{Si}-{\varphi }_{Gr}$.

Figure 7

A comparison between the calculated interface-band bending and the THz emission intensity.

Figure 8

The LTEM images of graphene on the Si substrates compared with optical images. Optical images: (a) graphene/n-Si, (c) graphene/BHF n-Si, (e) graphene/p-Si, (g) graphene/BHF p-Si; and the LTEM images: (b) graphene/n-Si, (d) graphene/BHF n-Si, (f) graphene/p-Si, (h) graphene/BHF p-Si. The shapes of graphene are shown with the black line in both LTEM images and optical images.