1.3 Micron Photodetectors Enabled by the SPARK Effect

Abstract

In this work, we present a graphene-based photodetector operating at a wavelength of 1310 nm. The device leverages the SPARK effect, which has previously been investigated only at 1550 nm. It features a hybrid waveguide structure comprising hydrogenated amorphous silicon, graphene, and crystalline silicon. Upon optical illumination, defect states release charge carriers into the graphene layer, modulating the thermionic current across the graphene/crystalline silicon Schottky junction. The photodetector demonstrates a peak responsivity of 0.3 A/W at 1310 nm, corresponding to a noise-equivalent power of 0.4 pW/Hz^1/2. The experimental results provide deeper insights into the SPARK effect by enabling the determination of the efficiency × lifetime product of carriers at 1310 nm and its comparison with values previously reported at 1550 nm. The wavelength dependence of this product is analyzed and discussed. Additionally, the response times of the device are measured and evaluated. The silicon-based fabrication approach employed is versatile and does not rely on sub-micron lithography techniques. Notably, reducing the incident optical power enhances the responsivity, making this photodetector highly suitable for power monitoring applications in integrated photonic circuits.

Keywords: graphene; near-infrared; photodetectors; silicon; waveguide.

Figure 1

Band diagram of the Gr/c-Si/Al metal semiconductor metal junction in flat-band conditions [35]. The Gr is capped with the a-Si:H. Under NIR light irradiating the trap states at the a-Si:H/Gr interface, electrons are released in the Gr increasing the Fermi level from $E_F^D$ (Fermi level in dark) to $E_F^L$ (Fermi level upon illumination). Consequently, a higher thermionic current $I_{N,light}^{Gr}$ flows in the device because of the smaller Gr/c-Si Schottky barrier ${\varphi }_B^{Gr}$ [15,32]. ${\Delta \varphi }_B$ represents the Fermi level shift upon NIR illumination while $I_P^{Al}$ the hole current flowing through the Al/c-Si Schottky junction ${\varphi }_B^{Al}$.

Figure 2

(a) Sketch of the Gr-based PD integrated into the hybrid c-Si/a-Si:H WG. (b) SEM image of the fabricated device illustrating the measurements of the incident optical power on the Gr Layer $P_{inc}$. At the top of the image, there is the c-Si/a-Si:H waveguide used for the measurements of the incident optical power $P_{out1}$. The other waveguide includes the SLG layer located between c-Si and a-Si:H, highlighted within the black dashed line.

Figure 3

(a) Photo of the device during electro-optical measurements, showing two probes biasing the PD on the right and the optical fiber aligned with the PD waveguide on the left. (b) IV characteristics of the Gr/c-Si/Al MSM junction in dark conditions. The inset provides a more detailed view over a wider range, focusing on the region where c-Si is grounded and Gr is subjected to a negative bias, representing the typical operating conditions of our photodetector.

Figure 4

(a) Schematic of the experimental setup for measuring incident optical power. (b) Incident optical power values on the Gr layer embedded between a-Si:H and c-Si, measured at varying peak voltages (V_max) of the electrical square wave, ranging from 1.5 V to 5 V.

Figure 5

(a) Schematic of the experimental setup for measuring photogenerated current. (b) Measured photogenerated current values on the Gr layer embedded between a-Si:H and c-Si, measured at different peak voltages (V_max) of the electrical square wave in a range from 1.5 V to 5 V.

Figure 6

(a) Responsivity of the SPARK effect-based PD at 1310 nm as a function of incident optical power, with the corresponding curve fit (red) based on Equation (6). (b) Dependence of the efficiency-lifetime carrier product on incident optical power at 1310 nm (red curve) and 1550 nm (blue curve).

Figure 7

(a) Real-time voltage generation of the photodiode (PD) under 1310 nm-light exposure. (b) Rising part of the real-time photocurrent response, showing a rise time of 22 μs.