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.

Short wave infrared (SWIR) imaging has been used in various applications such as electronic board inspection, surveillance and gas detection. Unlike the conventional compound semiconductor focal plane array (FPA), in this work group IV back-illuminated imaging array with 320 $\times256$ pixels was demonstrated. For reference device with a diameter of 30 $\mu \text{m}$ , the dark current was 9.7 nA at 0 V. At 1550 nm, a responsivity of 0.61 A/W was obtained at −1 V using a Ge photodetector with a diameter of 75 $\mu \text{m}$ . The image of a halogen lamp was successfully captured at room temperature with a pixel operating bias of 0 V. Showing great compatibility with the existing CMOS technology, group IV imaging array becomes one of the promising candidates to be applied in SWIR imaging area.

Waveguide-integrated Ge/Si heterostructure avalanche photodetectors (APDs) were designed and fabricated using a CMOS-compatible process on 8-inch SOI substrate. The structure of the APD was designed as separate-absorption-charge-multiplication (SACM) using germanium and silicon as absorption region and multiplication region, respectively. The breakdown voltage (V _b) of such a device is 19 V at reverse bias and dark current appears to be 0.71 μA at 90% of the V _b. The device with a 10-μm length and 7-μm width of Ge layer shows a maximum 3-dB bandwidth of 17.8 GHz at the wavelength of 1550 nm. For the device with a 30-μm-length Ge region, gain-bandwidth product achieves 325 GHz.

On-chip integrated photonics with operating wavelength at short-wave infrared region is becoming popular for its potential advantages in extending the telecommunication bandwidth and the application in gas sensing. As an important component of integrated optoelectronic chips, high-performance waveguides have attracted widespread attention. In this work, high-performance Ge waveguides were designed and fabricated on the Ge-on-Si platform, in which germanium films were epitaxially grown by the chemical vapor deposition process. The propagation loss for the waveguide was measured to be 2.34 dB/cm at the wavelength of 2 μm through the cut-back method. The quantitative relationship between the waveguide propagation loss and sidewall roughness as well as material defect density was established by introducing an empirical coefficient m. The m value was calculated to be 3.8 × 10−4 dB for the waveguide with a fixed Ge thickness of 1.5 μm by fitting the experimental propagation loss data at an operating wavelength of 2 μm. This formula provides a significant reference for future design of waveguide dimension structures, where defect induced absorption loss is non-negligible.

GeSn materials with Sn contents ranging between 0% and 11% have been successfully grown by using Ge2H6 and SnCl4 in a hot-wall UHV-CVD system at low reaction pressures of 0.2–0.4 Torr. Both fully strained and partially relaxed materials have been produced. It was found that the materials were of high crystallinity as evidenced by few threading dislocations from cross-sectional TEM. Photoluminescence studies have shown that the PL spectra shift to longer wavelengths, and the PL intensity increases exponentially as the Sn contents increase. The photoemission cutoff for a 9.5% Sn sample is beyond 2600 nm, and low temperature PL measurements have confirmed that this sample is already in the direct gap material regime. Prototype photoconductor devices were fabricated with a partially strained 5% Sn sample, showing much smaller dark currents and similar spectral coverage as compared to a fully strained 7.8% Sn device reported in the literature. The reported technical route has provided a new path toward high quality, low cost GeSn epitaxy, and will contribute to the development of group IV optoelectronics.