Camphor-Based CVD Bilayer Graphene/Si Heterostructures for Self-Powered and Broadband Photodetection

Abstract

This work demonstrates a self-powered and broadband photodetector using a heterojunction formed by camphor-based chemical vaper deposition (CVD) bilayer graphene on p-Si substrates. Here, graphene/p-Si heterostructures and graphene layers serve as ultra-shallow junctions for UV absorption and zero bandgap junction materials (<Si bandgap (1.1 eV)) for long-wave near-infrared (LWNIR) absorption, respectively. According to the Raman spectra and large-area (16 × 16 μm²) Raman mapping, a low-defect, >95% coverage bilayer and high-uniformity graphene were successfully obtained by camphor-based CVD processes. Furthermore, the carrier mobility of the camphor-based CVD bilayer graphene at room temperature is 1.8 × 10³ cm²/V·s. Due to the incorporation of camphor-based CVD graphene, the graphene/p-Si Schottky junctions show a good rectification property (rectification ratio of ~110 at ± 2 V) and good performance as a self-powered (under zero bias) photodetector from UV to LWNIR. The photocurrent to dark current ratio (PDCR) value is up to 230 at 0 V under white light illumination, and the detectivity (D*) is 8 × 10¹² cmHz^1/2/W at 560 nm. Furthermore, the photodetector (PD) response/decay time (i.e., rise/fall time) is ~118/120 μs. These results support the camphor-based CVD bilayer graphene/Si Schottky PDs for use in self-powered and ultra-broadband light detection in the future.

Keywords: camphor-based CVD; graphene; graphene/Si PDs; self-power photodetector.

Figure 1

Schematic diagram of our atmospheric pressure chemical vapor deposition (APCVD) setup.

Figure 2

Process flow diagram of the camphor-based chemical vaper deposition (CVD) bilayer graphene/p-Si photodetector (PD) that was fabricated.

Figure 3

(a) Field emission scanning electron microscope (FESEM) image and (b) Raman spectra and (c) I_2D/I_G Raman mapping of the bilayer graphene on a p-Si substrate (excitation laser:532 nm).

Figure 4

(a) Schematic of the camphor-based CVD bilayer graphene/p-Si Schottky PD; (b) I-V and fitting curves of the camphor-based CVD bilayer graphene/p-Si Schottky PDs in the dark; (c) I-V curves of the camphor-based CVD bilayer graphene/p-Si Schottky PDs in the dark and under white light illumination with 6.25 and 112 mW/cm⁻², respectively. (d) Spectral responsivity of the camphor-based CVD bilayer graphene/p-Si Schottky PDs under zero bias.

Figure 5

Schematic cross-section of the camphor-based CVD bilayer graphene/p-Si Schottky PD structure.

Figure 6

Band diagram of the camphor-based CVD bilayer graphene/p-Si PDs, where E_Fg, E_FSi, qΦ_B (~0.81 eV), and qΦ_bi (~0.62 eV) are the Fermi energy of graphene, the Fermi energy of Si, the Schottky barrier height (SBH), and the hole barrier height, respectively. (a) Under zero bias, (b) under reverse bias, and (c) under forward bias. Charge carriers (holes) are shown as open circles.

Figure 7

(a) The photocurrent and dark current as a function of time of the prepared bilayer graphene/p-Si Schottky PD under a 3 V bias. (b) High-resolution time response of the prepared bilayer graphene/p-Si Schottky PD.