Surface-normal illuminated pseudo-planar Ge-on-Si avalanche photodiodes with high gain and low noise.

Germanium-on-Silicon (Ge-on-Si) avalanche photodiodes (APDs) are of considerable interest as low intensity light detectors for emerging applications. The Ge absorption layer detects light at wavelengths up to ≈ 1600 nm with the Si acting as an avalanche medium, providing high gain with low excess avalanche noise. Such APDs are typically used in waveguide configurations as growing a sufficiently thick Ge absorbing layer is challenging. Here, we report on a new vertically illuminated pseudo-planar Ge-on-Si APD design utilizing a 2 µm thick Ge absorber and a 1.4 µm thick Si multiplication region. At a wavelength of 1550 nm, 50 µm diameter devices show a responsivity of 0.41 A/W at unity gain, a maximum avalanche gain of 101 and an excess noise factor of 3.1 at a gain of 20. This excess noise factor represents a record low noise for all configurations of Ge-on-Si APDs. These APDs can be inexpensively manufactured and have potential integration in silicon photonic platforms allowing use in a variety of applications requiring high-sensitivity detectors at wavelengths around 1550 nm.

Recent advances in the synthesis of trifluoromethyl-containing heterocyclic compounds via trifluoromethyl building blocks.

Trifluoromethylated heterocyclic compounds have played an increasingly significant role in pharmaceuticals, agrochemicals, and materials. This is because the introduction of trifluoromethyl could enhance the lipophilicity, metabolic stability, and pharmacokinetic properties of heterocyclic drug molecules. Therefore, the synthesis of trifluoromethylated heterocyclics has become a major subject of research. The construction of trifluoromethylated heterocyclics via the annulation of trifluoromethyl building blocks with suitable partners has been proved to be a powerful strategy. In this review, we systematically summarize and discuss recent advances in the preparation of trifluoromethyl-containing heterocyclics via trifluoromethyl building block strategies over the period from 2019 to the present.

Solvent-Controlled Enantiodivergent Construction of P(V)-Stereogenic Molecules via Palladium-Catalyzed Annulation of Prochiral N-Aryl Phosphonamides with Aromatic Iodides.

In this work, we describe an efficient and modular method for enantiodivergent accessing P(V)-stereogenic molecules by utilizing the catalytic atroposelective Catellani-type C-H arylation/desymmetric intramolecular N-arylation cascade reaction. The enantioselectivity of this protocol was proved to be tuned by the polarity of the solvent, thus providing a wide range of both chiral P(V)-stereogenic enantiomers in moderate to good yields with good to excellent enantiomeric excesses. Noteworthy is that the strategy developed herein represents an unprecedented example of solvent-dictated inversion of the enantioselectivity of P(V)-stereogenic compounds.