The Graphene Structure's Effects on the Current-Voltage and Photovoltaic Characteristics of Directly Synthesized Graphene/n-Si(100) Diodes

Abstract

Graphene was synthesized directly on Si(100) substrates by microwave plasma-enhanced chemical vapor deposition (MW-PECVD). The effects of the graphene structure on the electrical and photovoltaic properties of graphene/n-Si(100) were studied. The samples were investigated using Raman spectroscopy, atomic force microscopy, and by measuring current-voltage (I-V) graphs. The temperature of the hydrogen plasma annealing prior to graphene synthesis was an essential parameter regarding the graphene/Si contact I-V characteristics and photovoltaic parameters. Graphene n-type self-doping was found to occur due to the native SiO₂ interlayer at the graphene/Si junction. It was the prevalent cause of the significant decrease in the reverse current and short-circuit current. No photovoltaic effect dependence on the graphene roughness and work function could be observed.

Keywords: MW-PECVD; graphene; photovoltaics.

Figure 1

Schematic diagram of the graphene/n-Si(100) fabricated diodes.

Figure 2

Typical Raman scattering spectra (a) and typical I−V characteristics (b) of directly synthesized graphene/Si(100) devices. The I−V characteristics of the device produced from the C2 sample exhibited diode behavior (red), ohmic contact was seen for the device produced from a sample B3 (green), and the A1 sample had diode-like I-V features (blue).

Figure 3

Relation between different Raman scattering spectra parameters: (a) I_2D/I_G vs. I_D/I_G; (b) FWHM_2D vs. I_2D/I_G; (c) Pos_2D vs. I_2D/I_G; (d) Pos_2D vs. Pos_G; (e) FWHM_2D vs. Pos_2D; (f) FWHM_2D vs. FWHM_G. Samples were grouped according to the temperature of Si(100) substrate hydrogen plasma annealing before graphene growth: 700 °C (red), 800 °C (green), 900 °C (blue).

Figure 4

I−V characteristic parameters (I_R(0.3 V), I_R(0.1 V)/I_F(0.1 V), I_R(0.3 V)/I_F(0.3 V)) in relation with: (a–c) FWHM_G; (d–f) Pos_2D; and (g–i) FWHM_2D. Samples were grouped according to the temperature of Si(100) substrate hydrogen plasma annealing before graphene growth: 700 °C (red), 800 °C (green), 900 °C (blue).

Figure 5

Typical I−V characteristics of directly synthesized graphene/Si heterojunctions measured under the illumination by 800 nm wavelength (solid) and 406 nm wavelength (dashed) LEDs.

Figure 6

Structural effects on graphene/Si(100) diode’s photovoltaic parameters at 800 nm illumination: (a) I_SC vs. I_2D/I_G plot; (b) U_OC and I_2D/I_G relation; (c) I_SC relation with FWHM_2D; (d) U_OC vs. FWHM_2D plot; (e) I_SC with respect to Raman 2D peak position; and (f) I_SC and Pos_G correlation. Samples were grouped according to the temperature of Si(100) substrate hydrogen plasma annealing before graphene growth: 700 °C (red), 800 °C (green), 900 °C (blue).

Figure 7

Diode I−V and photovoltaic parameter (at 800 nm illumination) relation: (a) I_SC vs. I_R(0.3 V) plot; I_SC correlation with diode’s I-V curve shape estimated using reverse and forward current ratio measured at 0.1 V (b) and 0.3 V (c); U_OC vs. I_SC/I_R(0.3 V) plot (d) (solid and hollow markers indicate device illumination at 800 and 406 nm, respectively).