High-quality single-crystal silicon-germanium (SiGe) multi-quantum-well layers were epitaxially grown on silicon substrates by researchers at Bilkent University (Ankara, Turkey), the Massachusetts Institute of Technology (Cambridge, MA), Korea University (Seoul, South Korea), and the Masdar Institute of Science and Technology (Abu Dhabi, UAE). The layers were fashioned into mesa-structured p-i-n photodetectors functioning at telecommunications wavelengths with reverse leakage currents of about 10 mA/cm² and responsivities above 0.1 A/W in the 1300 to 1600 nm range. The spectral response of the photodetectors was voltage-tunable via altering the reverse bias, shifting the absorption edge by tens of nanometers.

The creation of GeSi devices on silicon is important for large-scale optical and optoelectronic circuits, as SiGe fabrication is compatible with complementary metal-oxide semiconductor (CMOS) technologies used to fabricate silicon computer chips. The ten quantum wells for the p-i-n detectors consisted of 10-nm-thick germanium wells and 20-nm-thick Si_0.1Ge_0.9 barriers, with the strained germanium lattice contributing to a high light absorption. Photodiodes were made with mesa diameters ranging between 20 and 120 μm; for devices with mesa areas less than 100 μm², the RC time constant was estimated to be below one picosecond. Contact Ali Okyay at aokyay@ee.bilkent.edu.tr.