Wafer-level 2D MoTe2 enables highly sensitive wide-band integrated infrared light detectors

Wide-band detection covering shortwave, medium-wave, to long-wave infrared plays an important role in many fields, including scientific research and a wide range of industrial technology applications, including target recognition, imaging, remote monitoring, and gas sensing. At present, mature commercial infrared photodetectors are mainly based on traditional narrow bandgap semiconductors such as In1-xGaxAs, InSb and Hg1-xCdxTe, which work in the shortwave infrared (SWIR, 1-3 μm), mid-wave infrared (MWIR, 3-6 μm) and long-wave infrared (LWIR, 6-15 μm) bands, respectively. These photodetectors not only rely on expensive and time-consuming material growth processes and complex processing procedures, but are also constrained by low-temperature cooling conditions with high power consumption. In addition, some technical challenges, such as poor compatibility of complementary metal-oxide semiconductors (CMOS) and large module size and low efficiency, seriously hinder the improvement of infrared detection performance and the expansion of application fields. Therefore, the researchers looked for new infrared absorbing materials with good optoelectronic properties, low cost, and easy integration and preparation. Due to its gapless electronic structure and linear energy dispersion relationship, two-dimensional topological semimetals are ideal candidates for wide-band infrared detection. However, limited by the preparation process, the current preparation of two-dimensional semimetals has low yield, micron-level sample size, low charge separation efficiency, high noise level and difficult integration, which greatly limits its application in the field of infrared detection.

Recently, Professor Wu Zhai and Professor Li Xinjian of Zhengzhou University, Longhui Zeng of the University of California, San Diego and Professor Jiansheng Jie of Soochow University demonstrated a van der Waals growth process for simple in-situ metal conversion, which successfully realized the controllable preparation of 2-inch two-dimensional MoTe2. At the same time, the type II Weyl semimetal 1T’-MoTe2 was synthesized on Si by this growth process, so as to realize the in-situ construction of 1T’-MoTe2/Si vertical Schottky junction. The high-quality Schottky junction interface, vertical device structure, and top graphene electrode ensure efficient carrier transport and reduced carrier recombination, enabling the detector to achieve an ultra-wide detection range of up to 10.6 μm and a room temperature ratio detection rate of more than 108 Jones in the mid-infrared region. In addition, thanks to the wafer-level large-area two-dimensional MoTe2, integrated array devices were successfully constructed to achieve high-resolution uncooled mid-infrared imaging.

Figure 1 Schematic diagram of two-dimensional MoTe2 synthesis and 2-inch sample photo

In this study, pre-deposited Mo films were converted to two-dimensional MoTe2 by in situ metal transformation van der Waals growth method. By controlling the growth time, 2-inch two-dimensional 1T?(semimetallic) and 2H (semiconductor) phase MoTe2 samples can be obtained, respectively, with good large-area homogeneity and high crystallization quality. Thanks to the simple growth strategy, the thickness of two-dimensional MoTe2 can be precisely controlled by the thickness of the initial Mo film, and continuous regulation from few layers to thick film can be realized.

Figure 2 Schematic diagram of a Graphene/1T?-MoTe2/Si Schottky junction device. The response of the b device to optical signals of different wavelengths at zero bias. c Comparison of device specific detection rate with other devices at room temperature

Wafer-level 2D MoTe2 provides greater flexibility in the fabrication of highly sensitive optoelectronic devices. High-quality 1T?-MoTe2/Si vertical Schottky junction devices were prepared by growing 1T?-MoTe2 in situ on Si substrates. To ensure efficient carrier collection, a single layer of graphene was chosen as the top transparent electrode. The device exhibits highly sensitive, self-actuated, ultra-wide band detection performance with detection wavelengths ranging from deep UV 265 nm to long wave infrared 10.6 μm. At the same time, the detector also demonstrated a room temperature ratio detection rate of more than 108 Jones in the mid-infrared band, which is better than most two-dimensional infrared detectors and some conventional infrared detectors.

Figure 3 Single-pixel and 8×8 integrated array devices with room temperature medium and long wave infrared imaging

Based on the excellent room temperature infrared detection ability of the photodetector, the researchers further demonstrated the room temperature infrared imaging ability of Gr/1T?-MoTe2/Si Schottky junction device. Firstly, a single-pixel scanning photocurrent imaging system obtains a photocurrent mapping image of the detector’s “LWIR” pattern under infrared illumination at room temperature of 10.6 μm, which has large current contrast and clear edges. In addition, the researchers further developed the 1T?-MoTe2/Si Schottky junction 8 × 8 integrated array device and applied it to infrared imaging applications, and obtained high-resolution imaging results of heart-shaped patterns under infrared light irradiation at room temperature of 3.0 μm, 4.6 μm, and 10.6 μm. Excellent room-temperature imaging capabilities and good uniformity of array device performance confirm its great promise in room-temperature mid-infrared imaging applications.

The in-situ metal conversion van der Waals growth method demonstrated in this work can be extended to transition metal sulphides, selenides and tellurides, as well as other two-dimensional material systems. This wafer-level 2D material fabrication process compatible with silicon processes shows great potential in next-generation low-power and low-cost silicon CMOS systems, which will greatly promote the application of 2D materials in optoelectronic devices and integrated systems.

The research was published in Light: Science & Applications under the title “Phase-Controlled van der Waals Growth of Wafer-Scale 2D MoTe2 Layers for Integrated High-Sensitivity Broadband Infrared Photodetection”. (Source: LightScience Applications WeChat public account)

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