Gallium oxide pn diodes; growing 2D layers; mini spectrometer.
Researchers at Nagoya University fabricated functional gallium oxide pn diodes that can carry twice as much electrical current as previous gallium oxide diodes and waste less energy than silicon-based diodes.
The key challenge in making the pn diode was creating a stable p-type gallium oxide layer. While gallium oxide’s crystal structure easily accepts the atoms needed to create n-type layers, it rejects the atoms required for p-type layers.
To create a stable p-type layer, nickel atoms were injected into the gallium oxide layer at high speed. The material was then heated twice, first at 300°C with activated oxygen radicals and then at 950°C in oxygen gas, which converted the embedded nickel into nickel oxide and integrated it with the gallium oxide crystal structure.
“Since this method uses standard industrial equipment and processes, it can be scaled up for mass production,” said Masaru Hori, a professor at the Center for Low-Temperature Plasma Sciences at Nagoya University, in a statement. “The implications for future energy efficiency and costs are substantial, particularly for electric vehicle and renewable energy industries.” [1]
Researchers from Rice University, Indian Institute of Technology, and Southern Illinois University used chemical vapor deposition (CVD) to grow 2D tungsten diselenide directly onto patterned gold electrodes, eliminating the need for a transfer process that can degrade the transferred material’s performance.
“We received a sample from a collaborator that had gold markers patterned on it,” said Lucas Sassi, a Rice doctoral alumnus, in a press release. “During CVD growth, the 2D material unexpectedly formed predominantly on the gold surface. This surprising result sparked the idea that by deliberately patterning metal contacts, we might be able to guide the growth of 2D semiconductors directly across them.”
The team optimized the precursor materials to lower the synthesis temperature of the 2D semiconductor and showed that it grows in a controlled, directional manner. Using advanced imaging and chemical analysis tools, the team confirmed the method preserves the integrity of the metal contacts, which are vulnerable to damage at high temperatures.
“The absence of reliable, transfer-free methods for growing 2D semiconductors has been a major barrier to their integration into practical electronics,” Sassi added. “This work could unlock new opportunities for using atomically thin materials in next-generation transistors, solar cells and other electronic technologies.” [2]
Researchers from North Carolina State University demonstrated a miniaturized spectrometer that can accurately measure wavelengths of light from ultraviolet to the near-infrared.
“We’ve created a spectrometer that operates quickly, at low voltage, and that is sensitive to a wide spectrum of light. Our demonstration prototype is only a few square millimeters in size – it could fit on your phone. You could make it as small as a pixel, if you wanted to,” said Brendan O’Connor, professor of mechanical and aerospace engineering at North Carolina State University, in a press release. “If you rapidly apply a range of voltages to the photodetector, and measure all of the wavelengths of light being captured at each voltage, you have enough data that a simple computational program can recreate an accurate signature of the light that is passing through or reflecting off of the target material. The range of voltages is less than one volt, and the entire process can take place in less than a millisecond.”
In proof-of-concept testing, the pixel-sized spectrometer was as accurate as a conventional spectrometer and had sensitivity comparable to commercial photodetection devices.
“In the long term, our goal is to bring spectrometers to the consumer market,” added O’Connor. “The size and energy demand of the technology make it feasible to incorporate into a smartphone, and we think this makes some exciting applications possible. From a research standpoint, this also paves the way for improved access to imaging spectroscopy, microscopic spectroscopy, and other applications that would be useful in the lab.” [3]
[1] N. Shimizu, A. K. Dhasiyan, O. Oda, et al. p-type layer formation study for Ga2O3 by employing Ni ion implantation with two-step oxygen plasma and thermal annealing. J. Appl. Phys. 14 August 2025; 138 (6): 065701. https://doi.org/10.1063/5.0282789
[2] L. M. Sassi, S. A. Iyengar, A. B. Puthirath, et al. Mechanistic Understanding and Demonstration of Direct Chemical Vapor Deposition of Transition Metal Dichalcogenides Across Metal Contacts. ACS Applied Electronic Materials 2025 7 (14), 6499-6510 https://doi.org/10.1021/acsaelm.5c00828
[3] H. M. Schrickx, A. Al Shafe, C. Moore, et al. Single pixel spectrometer based on a bias-tunable tandem organic photodetector. Device, 2025; 100866. http://dx.doi.org/10.1016/j.device.2025.100866
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