2D-material heterojunctions for “post-Moorean-era” microelectronics.

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Figure 1. Scheme of a photodetector integrated into a waveguide with a van der Waals heterojunction. Credit: Light Publishing Center, Changchun Institute of Optics, Fine Mechanics and Physics, CAS

Photon integrated circuits (FIS) use photons as data carriers and are characterized by ultra-high transmission speeds, low latency and anti-electromagnetic crosses. It is expected that these benefits will solve the bottlenecks of microelectronic chips in terms of speed, power consumption and integration density. This is key to advancing breakthroughs in microelectronics, quantum information technology and micro-research technologies in the “post-Moore era”.

Nowadays, thanks to the application of information technology, photon integrated chips have made great progress. For example, silicon PIC is compatible with persistent CMOS technology for low-cost and large-scale production; PIC of silicon nitride can tolerate moderately high optical power and large manufacturing errors; and lithium niobate PIC can achieve perfect electro-optical modulation with low controlled voltage and high linearity.

However, one of the disadvantages of these PICs is the monolithic integration of waveguides and photodetectors with a single material. To maintain light transmission in waveguides, PIC materials cannot absorb the optical signal, making it impossible to implement an integrated photodetector from a single material. To solve this problem, heterointegrations of bulk absorption materials (e.g., Ge, III-V semiconductor compounds, etc.) on the PIC have been implemented. Although it still creates open problems such as high costs, complex manufacturing processes and interface problems with materials.

BP / MoTe2 PN heterojunction band alignment

Figure 2. Alignment of the BP / MoTe2 PN heterojunction band in the state of thermal equilibrium (left panel); Image of the manufactured device in an optical microscope (right panel). Credit: Light Publishing Center, Changchun Institute of Optics, Fine Mechanics and Physics, CAS

Recently, two-dimensional (2D) materials have become an attractive photon absorption material for photodetectors with a chip. 2D materials do not have surface dangling bonds, which eliminates lattice mismatch constraints to hetero-integrate them with the PIC. The 2D family of materials has a rich array of electronic and optical properties, including semi-metallic[{” attribute=””>graphene, insulating boron nitride, semiconducting transition metal dichalcogenides, and black phosphorus. As a consequence, chip-integrated photodetectors operating at various spectral ranges could be constructed by choosing appropriate 2D materials.

In a new paper published in the journal Light Science & Application on April 20, 2022, a research team, led by Professor Xuetao Gan from Key Laboratory of Light Field Manipulation and Information Acquisition, Ministry of Industry and Information Technology, and Shaanxi Key Laboratory of Optical Information Technology, School of Physical Science and Technology, Northwestern Polytechnical University, China have reported that integrating van der Waals PN heterojunctions of 2D materials on optical waveguides can provide a promising strategy to realize chip-integrated photodetectors with low dark current, high responsivity, and fast speed.

With the 2D layered structure and no dangling bonds, researchers can stack 2D materials with different properties in different orders by “stacking wood” to form van der Waals heterostructures with atomically flat interfaces. The “arbitrary combination” of van der Waals heterojunctions can not only give the advantages properties of a single material, but also generate novel properties, achieving a leap of 1+1>2, as shown in Figure 1.

In this research, the researchers made full use of natural p-doped BP and n-doped MoTe2 for hetero-stacking, and successfully fabricated an efficient van der Waals PN heterojunction.

Second, since there are no dangling bonds on the surface of 2D materials, compared with traditional semiconductors, 2D materials do not need to consider lattice mismatch when integrating with various photonic integration platforms.

Finally, the preparation of source-drain electrodes can also be integrated on the photonic platform through the “stacking wood” technology and placed on both sides of the material, without the cumbersome processes such as photolithography.

This also greatly simplifies the fabrication process of the device, avoiding the contamination of the device interface in processes such as photolithography, which greatly improves the performance of the device.

Reference: “Chip-integrated van der Waals PN heterojunction photodetector with low dark current and high responsivity” by Ruijuan Tian, Xuetao Gan, Chen Li, Xiaoqing Chen, Siqi Hu, Linpeng Gu, Dries Van Thourhout, Andres Castellanos-Gomez, Zhipei Sun and Jianlin Zhao, 20 April 2022, Light: Science & Applications.
DOI: 10.1038/s41377-022-00784-x

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