This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Detecting short-wave infrared (SWIR) light, a region of the electromagnetic spectrum just beyond the light visible to the human eye, could be advantageous for many real-world applications. For instance, it could enable more advanced systems for capturing images at night, as well as sophisticated medical imaging, environmental monitoring and industrial inspection technologies.
Despite their potential, most SWIR detection devices developed so far are based on expensive semiconducting materials that are often difficult to integrate with existing electronic hardware. This is because silicon, the most widely used semiconductor in the electronics industry, cannot absorb SWIR photons due to its wide band gap. Researchers at Complutense University of Madrid have developed a silicon photodiode that can efficiently absorb SWIR light and is compatible with current electronics manufacturing processes.
The new device, introduced in a paper published in Physical Review Letters, is based on silicon doped with a high concentration of tellurium (Te) atoms. "Our primary objective with this research was to essentially 'democratize' SWIR technology," Eric García-Hemme, first author of the paper, told Phys.org. "Currently, SWIR detection relies on expensive materials like InGaAs, but by enabling silicon to see in this spectrum, we can drastically lower manufacturing costs and open the door to mass-market applications.
The scientific community working on hyperdoped silicon for photodetection had hit a performance ceiling. "When we analyzed the problem, we realized that while the material successfully detects SWIR light, the specific fabrication methods we use (which operate outside thermodynamic equilibrium) only allow us to create very thin active layers." When they reviewed earlier efforts aimed at creating SWIR detectors based on hyperdoped silicon, the researchers realized that previously produced materials were simply too thin to absorb much of the incoming light. To overcome this limitation, they tried to decouple a material's light absorption properties from its thickness.
"We implemented advanced light-trapping techniques, including micro-texturing the silicon surface with pyramids and adding a gold mirror," said García-Hemme. "This architecture forces the light to reflect back and forth inside the thin hyperdoped layer, significantly increasing its optical path and dramatically boosting the device's overall photoresponse." Typically, silicon is transparent to much of the SWIR spectrum, as photons in this range do not carry enough energy to push electrons across its relatively wide band gap. García-Hemme and his colleagues thus tried to create additional energy levels by implanting the silicon lattice with high concentrations of Te atoms via a process called hyperdoping.
"This introduces new intermediate energy levels inside the material," explained García-Hemme. "You can think of them as steppingstones that allow low-energy SWIR photons to excite electrons and generate an electrical signal. Combined with the micro-pyramids and a rear gold mirror, we physically trap the light inside the active layer (the hyperdoped layer) to ensure maximum absorption." The team's newly developed photodiode is compatible with standard complementary metal-oxide-semiconductor (CMOS) manufacturing methods.
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