Indian Team Makes Photodetector From 2D Graphitic Carbon Nitride On Si


Binary switching device could have applications from optical interconnects to solar cells, say researchers

Researchers at the CSIR-National Physical Laboratory in New Delhi, India have demonstrated a highly sensitive, ultrabroadband photodetector made of 2D graphitic carbon nitride (g-C3N4) on silicon.

The device demonstrates binary photoswitching over wavelengths from 250 to 1350 nm, which suggests it could be used in optical interconnects and weak signal detection. An overlayer of g-C3N4 could also enhance the performance of silicon solar cells, according to the team.

The image above shows a simplified schematic of the hybrid photodetector. The device consists of ultrathin g-C3N4/Si heterojunction with top and bottom silver contacts. The idea is to create a light induced transition that switches the output of the photodetector between logic1 and logic0 for an ultrabroadband wavelength range.

New breed of semiconductor

g-C3N4 is one of a new breed of 2D semiconductors with potential applications in energy harvesting, storage and photo-catalysts, in addition to optoelectronics.

C3N4‘s chemical inertness and tunable bandgap points to a promising future, however understanding of the material and its integration with silicon is in its infancy. Poor efficacy for photodetection, for example, has impeded its potential use in optoelectronic applications, say Prabir Pal and Suraj P Khanna who jointly led the research team.

They have overcome this bottleneck by ultra-thinning g-C3N4 using a versatile and low-cost technique of ultrasonic exfoliation. The ultrathin g-C3N4 was then integrated with surface modified silicon substrate via a two stage etching process.

“The prolonged sonication results in critical structural rearrangement with a high degree of exfoliation in g-C3N4 nanosheets which in-turn significantly affects the optoelectronic properties with enhanced light absorption capabilities," says Surinder P Singh part of the interdisciplinary team.

“Because of the reduced dimensionality and large specific area of g-C3N4 there is a significant enhancement of light absorption, in the entire ultrabroadband spectral range," says Pal.

The result is a high-performance detector with a dramatic enhancement in photosensitivity as compared to the available commercial photodetectors, according to the team. In-addition the device displays a novel binary photoswitching (change in current from positive to negative) in response to OFF/ON light illumination at small forward bias (≤0.1 V) covering.

At zero bias, the device displays an extremely high ON/OFF ratio of ≈1.2 × 105 under 680 nm (49 μW cm−2) illumination with a dark current of 23 pA. The device also shows highly sensitive behaviour over the entire operating range at low light illuminations, with highest responsivity (1.2 A W−1), detectivity (2.8 × 1014 Jones), and external quantum efficiency (213 percent) at 680 nm. The response and recovery speeds are typically 0.23 and 0.60 ms, respectively, under 288 Hz light switching frequency.

The research was undertaken with support from Council of Scientific & Industrial Research- National Physical Laboratory, University Grants Commission and Department of Science and Technology, India.

'Binary Multifunctional Ultrabroadband Self-Powered g-C3N4/Si Heterojunction High-Performance Photodetector', by Prakash et al; Advanced Optical Materials, 18 May 2018

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