High-performance photodetector based on an interface engineering-assisted graphene/silicon Schottky junction

Abstract

Graphene/silicon Schottky junctions have been proven efficient for photodetection, but the existing high dark current seriously restricts applications such as weak signal detection. In this paper, a thin layer of gadolinium iron garnet (Gd₃Fe₅O₁₂, GdIG) film is introduced to engineer the interface of a graphene/silicon Schottky photodetector. The novel structure shows a significant decrease in dark current by 54 times at a -2 V bias. It also exhibits high performance in a self-powered mode in terms of an I_light/I_dark ratio up to 8.2 × 10⁶ and a specific detectivity of 1.35 × 10¹³ Jones at 633 nm, showing appealing potential for weak-light detection. Practical suitability characterizations reveal a broadband absorption covering ultraviolet to near-infrared light and a large linear response with a wide range of light intensities. The device holds an operation speed of 0.15 ms, a stable response for 500 continuous working cycles, and long-term environmental stability after several months. Theoretical analysis shows that the interlayer increases the barrier height and passivates the contact surface so that the dark current is suppressed. This work demonstrates the good capacity of GdIG thin films as interlayer materials and provides a new solution for high-performance photodetectors.

Keywords: Nanoscale devices; Optics and photonics.

Fig. 1. Device model and fabrication flow.

a 3D schematic view and b Cross-section of the proposed Gr/GdIG/Si photodetector. c Schematic illustration of the fabrication process of the Gr/GdIG/Si photodetector

Fig. 2. Characterization of the proposed Gr/GdIG/Si photodetector.

a Surface morphology and thickness (inset) of the as-prepared GdIG film. b XPS spectrum of the GdIG film. c Optical image of the graphene transferred on GdIG coated n-type silicon, forming a square photosensitive area. d Raman spectrum of the monolayer graphene

Fig. 3. Photoresponse mechanism analyses.

a Semi-log I-V curve (inset) and its linear fitting of Gr/Si Schottky junction to extract the parameters. b Semi-log I-V curve (inset) and its linear fitting of Gr/GdIG/Si Schottky junction. Energy band diagrams of c Gr/Si junction under dark condition, d Gr/GdIG/Si junction under dark condition, e Gr/GdIG/Si junction under illumination and f Gr/GdIG/Si junction under illumination with a reverse bias voltage. Here, Φ_B, V_bi, e, E_C, E_V, E_F(Gr), E_F(Si), and V_bias represent the Schottky barrier height, built-in electric field, electronic charge, conduction band edge, valence band edge, Fermi level of Gr, Fermi level of Si, and the reverse bias voltage, respectively. The arrows indicate the direction of movement

Fig. 4. Photoresponse, power-dependent, and spectrum-dependent characteristics of the Gr/GdIG/Si photodetector.

a Comparison of I-V curves between the photodetectors with and without GdIG interlayer. b Photocurrent versus time characteristics, showing the enhanced I_light/I_dark ratio. c Photoresponse at large-scale power density variation (down to nW/cm² level, demonstrating the weak-light detectability). The arrow indicates the direction of power increase. d Photoresponse with small steps of power variation at high intensities, indicating a near-linear behavior. e Multiband response at different incident wavelengths. f Specific detectivity and noise equivalent power from UV to NIR spectrum

Fig. 5. Response speed and stability characteristics of the Gr/GdIG/Si photodetector.

a Photocurrent under varying light frequencies. b Transient response and recovery time. c Stability and repeatability test during 500 continuous ON/OFF cycles with a period of 10 seconds. d Stability measurements when exposed to air after one month and two months

Fig. 6. Performance comparison between the proposed Gr/GdIG/Si photodetector with similar structures.

a specific detectivity and I_light/I_dark ratio. b sensitive spectrum