Photodetectors are core components of optoelectronic systems, widely used in communications, imaging, and other fields. Among them, silicon-based detectors have long dominated due to their mature technology and high cost-effectiveness. However, the inherent bandgap of silicon materials limits their spectral response range, making it difficult to meet the demand for broadband detection in modern emerging technologies. In recent years, two-dimensional materials with excellent optoelectronic properties have stood out, and their van der Waals layered structure enables seamless integration with silicon, forming hybrid-dimensional heterojunctions without lattice mismatch limitations. Among them, molybdenum ditelluride (MoTe₂), with its rich phase transition characteristics and tunable electronic properties, has become an ideal material for constructing high-performance heterojunction detectors of this type.

Although molybdenum ditelluride/silicon heterojunctions show promising detection prospects, further performance improvement at this stage still faces severe challenges. Traditional planar surface devices produce significant optical losses in practical applications, and high surface reflectivity severely restricts the responsivity and practical value of the devices. To solve this bottleneck, researchers are committed to introducing surface engineering strategies such as pyramidal textured silicon substrates. Enhancing light absorption by reducing reflectivity through the light-trapping effect of microstructures has become a key research direction for overcoming optical losses and constructing high-performance van der Waals heterojunction detectors.

In response to the above issues, a team composed of University of Electronic Science and Technology of China and others conducted systematic research using ZEPTOOLS' DMD maskless lithography system, successfully in-situ constructing a high-performance 1T'-molybdenum ditelluride/pyramidal silicon hybrid van der Waals heterojunction photodetector by introducing the light-trapping effect of surface micro-nano pyramidal structures to significantly reduce optical reflection loss.

Title:In-situ preparation of 1T'-MoTe2/pyramidal-Si mixed van der Waals heterojunction toward high performance photodetection
Journal:Applied Materials Today
Website:https://doi.org/10.1016/j.apmt.2026.103287

The research team first focused on how to solve the core issues of high-quality two-dimensional material preparation and reducing optical reflection loss on the device surface. They deposited a thin film on a silicon dioxide/silicon substrate using magnetron sputtering technology, followed by precise tellurization in a tube furnace, successfully preparing high-quality 1T'-molybdenum ditelluride thin films through an in-situ thermal conversion method. Subsequent morphological and structural characterization showed that the film thickness increased significantly by 3.1 times after the reaction, and the clear characteristic peaks in the Raman spectrum fully confirmed its complete transformation to the 1T'-molybdenum ditelluride phase. Meanwhile, the team successfully constructed micro-scale pyramidal structures with an average base size of 2 micrometers on the silicon surface using an anisotropic wet etching process. Reflection spectrum tests and finite-difference time-domain simulation data jointly confirmed that this pyramidal structure exhibits a strong light-trapping effect in the wide band from 400 to 1600 nanometers, successfully reducing the reflectivity at 820 nanometers from 35% for the planar surface to about 15%, achieving a 31% enhancement in light absorption rate, providing an ideal physical structure foundation for the construction of high-performance optoelectronic heterojunctions.

After clarifying the preparation process of high-performance materials and structures, how to achieve the complete construction of high-quality heterojunction devices through precision micro-nano processing became the next core issue. The research team designed and executed a precision device processing workflow based on silicon dioxide/silicon substrates, where the definition of the core heterojunction region strictly relied on high-precision patterning technology.The team used the DMD maskless lithography system developed by ZEPTOOLS for digital lithography process, precisely defining the specific reaction region of the target heterojunction on the substrate. After pattern definition, reactive ion etching technology was used to remove the silicon dioxide layer in this region to expose the silicon substrate. For pyramidal heterojunction devices, after wet etching to generate pyramidal microstructures, the team again used reactive ion etching to remove the edge silicon dioxide bridges, a key step that ensured the continuity of the thin film in subsequent processes. Finally, combined with lithography and thermal evaporation technology, chromium/gold top electrodes were successfully deposited in the periphery of the junction region, completing the complete construction of the high-performance photodetector device.

After completing device construction, the physical quality of the contact interface and the intrinsic electrical rectification mechanism became the core scientific issues that the researchers focused on. The research team systematically evaluated the current-voltage characteristics of planar surface heterojunction devices and pyramidal surface heterojunction devices under dark conditions. Experimental data showed that both types of devices exhibited extremely excellent unidirectional conductivity and rectification behavior, with rectification ratios as high as 4.3×10⁴ and 4.5×10⁴ at positive and negative 5 volts, respectively. This high rectification ratio is at the leading level among peers, strongly confirming the extremely high construction quality of the device interface. After specialized testing for contact characteristics, data confirmed that this rectification effect originates entirely from the heterojunction interface formed by molybdenum ditelluride and silicon, not from electrode contact. Analysis of extracted interface physical parameters showed that the Schottky barrier heights of planar and pyramidal devices were 0.616 electron volts and 0.612 electron volts, respectively, and the ideal factors were 3.6 and 2.9, respectively. This highly similar and excellent electrical barrier characteristic further indicates that pyramidal surface engineering significantly enhanced light absorption without damaging the excellent interface quality of the heterojunction.

The final focus of the research content is to comprehensively evaluate various key optoelectronic detection indicators of the device in practical applications and its array imaging capability. Under 850 nanometer wavelength incident light illumination,得益于微纳陷光结构带来的吸收增益，the pyramidal device achieved a responsivity as high as 451 milliamperes per watt at 820 nanometers, representing a 31% significant improvement compared to planar surface devices. Moreover, the device also demonstrated extremely high detection sensitivity, with a specific detectivity reaching 7.80×10¹¹ Jones in self-driven operation mode at zero bias, and possessed an ultra-large linear dynamic range of 162 decibels and an ultra-fast response speed of 4 microseconds. The spectral response characteristics of the device successfully covered a wide band from 400 to 1550 nanometers, and no obvious performance degradation was observed after storage in air for two months, demonstrating excellent long-term stability. To push the research toward practical applications, the team further constructed an 8x8 detector array, where each pixel unit showed extremely high current uniformity under dark and illuminated conditions, and successfully and clearly reconstructed the current distribution image of the target letter through a specific hollow mask, strongly demonstrating its application potential in next-generation high-performance broadband imaging systems.

ZEPTOOLS ZML series are DMD-based maskless lithography systems that use DMD to replace traditional masks, enabling rapid and flexible design of lithography patterns, supporting two-dimensional and 8-bit grayscale lithography, and meeting any micrometer-level lithography requirements, widely used in MEMS, microfluidics, and other fields.