Novel Technique of Texturing Germanium for Anti-reflection in the Infrared Range


Electronics - Semiconductors


Anisotropic wet etching used to form inverted pyramid structures has been widely used in the complementary metal oxide semiconductor (CMOS) process of the silicon (Si) industry for the application of micro-electromechanical systems (MEMS) and optoelectronics. However, such CMOS-compatible anisotropic wet etching technique is still scarce for the germanium (Ge) industry. This technology offer is a technique to enable the formation of microscale Ge inverted pyramid and v-groove structures by wet etching, catalysed by CMOS-compatible metals. The technique has been proven feasible and the long-term durability in the etchant has also been verified. The dimensions of the Ge structures were totally determined by the patterned catalyst, which makes it easy for tuning desired sizes of Ge inverted structures. The Ge microscale textures show outstanding anti-reflective performance in the infrared (IR) range.

The targeted users of this technique are Ge-based MEMS and optoelectronic device manufactures which requires CMOS-compatible fabrication flow to produce microscale structures with antireflective performance, but on Ge substrate. The technology owner is interested to out-license this process, or do research collaborations with foundries handling CMOS and photonics related processes.


This technique provides a CMOS-compatible etching approach to fabricate inverted pyramid and v-groove arrays of Ge structures by novel metal-assisted chemical etching, which cannot be realized by either dry etching, i.e., reactive-ion etching (RIE), and traditional wet etching. Conventional metal-assisted chemical etching approach employs a noble metal catalyst (e.g., gold) and highly toxic hydrogen fluoride, which is not CMOS-compatible and not easy to manipulate. This technology offer provides users with a CMOS-compatible approach for Ge micro- and nano-structures, leading to potential application in Ge MEMS and optoelectronic devices.


This technology offer provides users with an CMOS-compatible approach for fabricating Ge micro- and nano-structures, leading to primary potential application in Ge MEMS and optoelectronic devices (e.g., photodetectors). The Ge microstructures exhibit outstanding antireflection properties, with reflectance as low as 5% in IR range of 2-5 µm, which makes it possible to function as an IR absorber.

Unique Value Proposition

  • This technique offers facile fabrication of Ge inverted pyramidal and v-groove structures by noble metal-free and acid-free anisotropic wet etching technique.
  • Dimensions of the fabricated structures can be precisely tuned solely by the patterned metals, making the technique versatile for different dimensions of the Ge structures desired.
  • This technique avoids using expensive noble metals such as silver and gold, as well as the extremely toxic hydrogen flouride, making it economically and environmentally friendly.
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