High-performance normal-incidence p-i-n Ge photodetectors for 1550 and 1310 nm were grown by selective epitaxial growth on SOI substrate with in situ thermal annealing and surface Si passivation. Bulk leakage current density and surface leakage density as low as 3.4 mA/cm$^2$ and 0.4 μA/cm are achieved under -1 V, respectively. Resonance optical responsivity at 1550 and 1310 nm are 0.27 and 0.59 A/W under zero-bias, respectively. A 3-dB bandwidth as high as 48 GHz is obtained at -3 V. Clear open eye diagrams at 40 Gbps are demonstrated under zero-bias at 1550 nm.

The Sn composition graded GeSn layer with Sn content increased from 11% to 14.3% was grown on a Si substrate by molecular beam epitaxy. The structural properties of the GeSn layer are investigated, and the film is gradually relaxed along the thickness, reaching approximately 71.6%. The GeSn p–i–n detectors were fabricated by using a complementary metal oxide semiconductor compatible process. The GeSn detectors demonstrated a cutoff wavelength of approximately 3.3 μm at room temperature with a dark current of 0.3 A/cm² @ -1 V. At a wavelength of 2000 nm, the GeSn detectors had a responsivity of 110 mA/W and -3 dB bandwidth (f_3 dB) about 3 GHz. These results suggest that high Sn content relax GeSn can be grown by MBE and paves the way toward the feasibility of mid-infrared GeSn photonics.

We report the design and fabrication of a high-speed GeSn normal-incidence p-i-n photodetector. To realize high-speed detection in all telecommunication bands, we optimize the Sn content in the absorption layer, the absorption-layer thickness, and the device size. The responsivity of the 18-m-diameter device at 1550 nm reaches 0.32 A/W with an extended cutoff wavelength of 1700 nm and a 3-dB bandwidth as high as 28 GHz under 3 V bias, clear open eye diagrams are also obtained under zero bias at 1630 nm. All the results indicate that the device has a significant potential for applications in Si-based optical telecommunication in all telecommunication bands.

The enhanced room-temperature photoluminescence of porous Si nanowire arrays and its mechanism are investigated. Over 4 orders of magnitude enhancement of light intensity is observed by tuning their nanostructures and surface modification. It is concluded that the localized states related to Si-O bonds and self-trapped excitations in the nanoporous structures are attributed to the strong light emission.

A compact high-power germanium photodetector (Ge PD) is experimentally demonstrated by re-engineering light distribution in the absorber. Compared with a conventional Ge PD, the proposed structure shows a DC saturation photocurrent improved by 28.9% and 3 dB bandwidth as high as 49.5 GHz at 0.1 mA. Under the same photocurrent of 10.5 mA, the proposed Ge PD shows a 3 dB bandwidth of 11.1 GHz, which is almost double the conventional Ge PD (5.6 GHz). The 25 Gb/s eye-diagram measurement verifies the improved power handling capability. The compact size and manufacturing simplicity of this structure will enable new applications for integrated silicon photonics.

We propose a thin-film Ge-on-Si-on-insulator (Ge-on-SOI) photodetector with enhanced performance by exploiting induced guided mode resonance (GMR) employing Ge/SiO₂ grating on Si-on-insulator (SOI). Numerically calculated results and theoretical analysis demonstrate that normal-incidence light can be coupled to the GMR and partly be converted into the spatial resonance mode which propagates along the whole properly designed grating structure. A notable absorption efficiency of higher than 70% is obtained in the photodetector with only 280 nm-thick Ge/SiO₂ grating, which is about 35 times larger than that of the counterpart without the designed grating structure. Remarkable enhanced light absorption can be achieved in the device with very few grating periods, which significantly promotes a theoretical 3-dB bandwidth-efficiency product of ∼66 GHz. The result is promising for a compact Ge-on-Si photodetector design with low dark current, high-bandwidth, and high-responsivity.