Researchers at the University of California, Davis (UC Davis), are at the forefront of a pioneering effort to amplify the light absorption capabilities of thin silicon films. This involves developing silicon-based photodetectors with finely structured surfaces at both micro and nano scales to efficiently trap light, achieving performance levels comparable to advanced semiconductors like gallium arsenide (GaAs) and other group III-V semiconductors.
Silicon has historically dominated the semiconductor arena. However, its weak light absorption in the near-infrared (NIR) spectrum, compared to counterparts like GaAs, has limited its application potential. GaAs and related alloys, though excelling in photonics, face compatibility challenges with conventional CMOS processes used in electronics manufacturing, leading to elevated production costs.
The breakthrough centers around strategically placed micro and nano holes in silicon, enabling incident light to bend by nearly 90° and travel laterally along the silicon plane. This innovative trapping mechanism significantly enhances light absorption in the NIR band.
The devised photodetectors feature a micrometer-thick cylindrical silicon (SI) slab atop an insulating substrate. Critically, the bulk silicon hosts periodic circular holes, acting as efficient photon-trapping sites. This unique structure redirects incident light, prompting lateral travel along the silicon plane. This lateral propagation increases the length of light travel, effectively slowing it down, and resulting in enhanced light-matter interaction and subsequent absorption improvement.
Additionally, the researchers conducted comprehensive optical simulations and theoretical analyses to comprehend the effects of these photon-trapping structures. Numerous experiments were carried out to compare photodetectors with and without these structures, affirming a substantial increase in absorption efficiency over a wide band in the NIR spectrum, consistently remaining above 68% and peaking impressively at 86%.
The observed absorption coefficient of the photon-trapping photodetector surpassed that of plain Si by several times and even exceeded that of GaAs in the NIR band. Remarkably, simulations involving 30- and 100-nm silicon thin films, compatible with CMOS electronics, demonstrated similarly enhanced performance, highlighting the flexibility of the proposed design.
The researchers envision that this study’s findings present a promising strategy to elevate the performance of silicon-based photodetectors for emerging photonics applications. Achieving high absorption, even in ultrathin silicon layers, is vital to maintaining low parasitic capacitance in high-speed systems. Moreover, this proposed approach aligns with modern CMOS manufacturing processes and holds the potential to revolutionize the integration of optoelectronics into conventional circuits. Ultimately, this innovation could pave the way for cost-effective ultrafast computer networks and significant advancements in imaging technology.
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Diagram illustrating the silicon MSM photodetector employing photon-trapping mechanisms. The cylindrical hole arrays designed for photon trapping enable lateral light propagation through the bending of incident light, significantly boosting photon absorption in silicon (Si).