Investigation of Graphene Single Layer on P-Type and N-Type Silicon Heterojunction Photodetectors

Abstract

Photodetectors are of great interest in several technological applications thanks to their capability to convert an optical signal into an electrical one through light-matter interactions. In particular, broadband photodetectors based on graphene/silicon heterojunctions could be useful in multiple applications due to their compelling performances. Here, we present a 2D photodiode heterojunction based on a graphene single layer deposited on p-type and n-type Silicon substrates. We report on the electro-optical properties of the device that have been measured in dark and light conditions in a spectral range from 400 nm to 800 nm. The comparison of the device's performance in terms of responsivity and rectification ratio is presented. Raman spectroscopy provides information on the graphene single layer's quality and oxidation. The results showcase the importance of the doping of the silicon substrate to realize an efficient heterojunction that improves the photoresponse, reducing the dark current.

Keywords: graphene; heterojunction; photodetectors.

Figure 1

(a) Image of the SLGr present on the top surface of the devices (red lines report the width and length of the SLGr transferred on the substrate); (b,c) illustration of the devices’ structures (SLGr/p-Si heterostructure and SLGr/n-Si heterostructure, respectively). On the back side of the structure, both the devices have thin layers of Si p+ and Si n+ to guarantee ohmic contact between the silicon wafer and the Pt/Ti electrodes.

Figure 2

I-V curve of SLGr-based devices in dark conditions in the voltage range between −5 V and 5 V.

Figure 3

Energy band diagrams of the graphene/ Si₃N₄/Si heterojunctions in forward and reverse bias configuration.

Figure 4

I-V characteristic of (a) SLGr/p-type and (b) SLGr/n-type devices under illumination from 400 nm to 800 nm with a power of 0.5 mW.

Figure 5

(a) Raman image related to the D-band peak at 1345 cm⁻¹ collected on an area of 200 × 200 µm²; (b) the Raman spectra collected at points A and B; (c) Raman image related to the D-band peak at 2684 cm⁻¹ collected in an area of 200 × 200 µm².

Figure 6

(a) Current response of the SLGr/n-Si device to the periodic chopping of light source: 500 nm and 650 nm with a power of 0.5 mW, biasing the devices at 15 V. (b) Current as a function of power for the two devices at wavelength of 650 nm in the ranges from 0.1 mW to 1 mW and from 1 μW to 20 μW in the inset.

Figure 7

Comparison of the responsivity versus wavelength for both devices.