Graphene-Silicon Device for Visible and Infrared Photodetection

Abstract

The fabrication of a graphene-silicon (Gr-Si) junction involves the formation of a parallel metal-insulator-semiconductor (MIS) structure, which is often disregarded but plays an important role in the optoelectronic properties of the device. In this work, the transfer of graphene onto a patterned n-type Si substrate, covered by Si₃N₄, produces a Gr-Si device, in which the parallel MIS consists of a Gr-Si₃N₄-Si structure surrounding the Gr-Si junction. The Gr-Si device exhibits rectifying behavior with a rectification ratio up to 10⁴. The investigation of its temperature behavior is necessary to accurately estimate the Schottky barrier height (SBH) at zero bias, φ_b0 = 0.24 eV, the effective Richardson's constant, A* = 7 × 10^-10 AK^-2 cm^-2, and the diode ideality factor n = 2.66 of the Gr-Si junction. The device is operated as a photodetector in both photocurrent and photovoltage mode in the visible and infrared (IR) spectral regions. A responsivity of up to 350 mA/W and an external quantum efficiency (EQE) of up to 75% are achieved in the 500-1200 nm wavelength range. Decreases in responsivity to 0.4 mA/W and EQE to 0.03% are observed above 1200 nm, which is in the IR region beyond the silicon optical band gap, in which photoexcitation is driven by graphene. Finally, a model based on two parallel and opposite diodes, one for the Gr-Si junction and the other for the Gr-Si₃N₄-Si MIS structure, is proposed to explain the electrical behavior of the Gr-Si device.

Keywords: Gr-Si junction; Schottky diode; graphene; heterojunction; infrared; noise equivalent power; photodetector; quantum efficiency; responsivity; visible.

Figure 1

(a) Schematic of the device showing a Gr-Si junction modeled by a diode in parallel with a MIS structure, here represented as a capacitor. (b) Raman spectrum confirming high-quality monolayer graphene. The inset shows an optical top image of the device, displaying the graphene flake and the window etched through the Si₃N₄ layer corresponding to the Gr-Si junction.

Figure 2

(a) Measured IV characteristic of the device in the dark (black line). The green and magenta lines represent the fit using, respectively, eqs 1 and 3. Red and orange lines represent the fit using eq 6 with Cheung and Richardson’s parameters, respectively. The inset represents the diode model with a series and a parallel resistance corresponding to eq 6. (b) Cheung’s method plots for the evaluation of Schottky barrier height, ideality factor, and series resistance.

Figure 3

IV characteristics versus temperature ranging from 400 to 220 K (a) in the dark and (b) under light (3 mm diameter spot, incident power 1 mW/cm², wavelength λ = 500 nm). (c) Rectification ratio at V = ±2.5 V, (d) ideality factor, (e) series resistance, and (f) Schottky barrier height versus temperature, estimated using Cheung’s method.

Figure 4

Linear fits used to extract I₀ at V = 0 V (a) in the dark and (b) under illumination light (3 mm diameter spot, incident power 1 mW/cm², wavelength λ = 500 nm). Richardson’s plots obtained from IV measurements (c) in the dark and (d) under illumination.

Figure 5

(a) IV characteristics in the dark and with incident white laser. (b) Photoresponse as a function of the laser emitted power and the laser integral intensity incident on the device (in mW/cm²). (c) Photocurrent when the photodetector is operated in the photocurrent mode at V = −2.5 V and (d) photovoltage mode at I = 0 A under a laser beam with 1000 nm wavelength and 950 μW/cm² light intensity on the device.

Figure 6

(a) Responsivity and EQE of the device in the visible and IR spectral regions. (b) NEP and (c) IV characteristics in the dark and under light at different wavelengths in the (c) visible and (d) near-spectral IR regions. The insets in (c) and (d) show the Fowler–Nordheim plots of the reverse IV characteristic at 550 and 850 nm, respectively.

Figure 7

Schematic model of the Gr-Si device and charge carrier transport in reverse bias for (a) −1.2 V < V < 0 V and (b) V < −1.2 V.