We report on the demonstration of photodetectors based on large scale two-dimensional molybdenum disulfide (MoS2) transition metal dichalcogenides. Excellent film uniformity and precise control of the MoS2 thickness down to a monolayer (~0.75nm) were achieved by magnetron sputtering synthesis approach. In particular, the photodetectors integrated with five MoS2 monolayers exhibit a high photoresponsivity of 1.8 A/W, an external quantum efficiency exceeding 260%, and a photodetectivity of ~5 x 10(8) Jones for a wavelength of 850 nm, surpassing the performance of mechanically exfoliated based photodetectors.

We report the demonstration of a germanium-tin (GeSn) multiple-quantum-well p-i-n photodiode on silicon (Si) substrate for 2 μm-wavelength light detection. Characterization of the photodetector in both direct current (DC) and radio frequency (RF) regimes was performed. At the bias voltage of -1 V, a dark current density of 0.031 A/cm is realized at room-temperature, which is among the lowest reported values for GexSnx-on-Si p-i-n photodiodes. In addition, for the first time, a 3 dB bandwidth (f3dB) of around 1.2 GHz is achieved in GexSnx photodetectors operating at 2 μm. It is anticipated that further device optimization would extend the f3dB to above 10 GHz.

We demonstrate that a complementary metal-oxide-semiconductor (CMOS) compatible silicon (Si) surface passivation technique effectively suppress the dark current originating from the mesa sidewall of the Ge(0.95)Sn(0.05) on Si (Ge(0.95)Sn(0.05)/Si) p-i-n photodiode. Current-voltage (I-V) characteristics show that the sidewall surface passivation technique could reduce the surface leakage current density (Jsurf) of the photodiode by ~100 times. A low dark current density (Jdark) of 0.073 A/cm(2) at a bias voltage of -1 V is achieved, which is among the lowest reported values for Ge(1-x)Sn(x)/Si p-i-n photodiodes. Temperature-dependent I-V measurement is performed for the Si-passivated and non-passivated photodiodes, from which the activation energies of dark current are extracted to be 0.304 eV and 0.142 eV, respectively. In addition, the optical responsivity of the Ge(0.95)Sn(0.05)/Si p-i-n photodiodes to light signals with wavelengths ranging from 1510 nm to 1877 nm is reported.

GeSn-on-insulator (GeSnOI) on Silicon (Si) substrate was realized using direct wafer bonding technique. This process involves the growth of Ge 1-x Sn x layer on a first Si (001) substrate (donor wafer) followed by the deposition of SiO 2 on Ge 1-x Sn x , the bonding of the donor wafer to a second Si (001) substrate (handle wafer), and removal of the Si donor wafer. The GeSnOI material quality is investigated using high-resolution transmission electron microscopy, high-resolution X-ray diffraction (HRXRD), atomic-force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. The Ge 1-x Sn x layer on GeSnOI substrate has a surface roughness of 1.90 nm, which is higher than that of the original Ge 1-x Sn x epilayer before transfer (surface roughness is 0.528 nm). The compressive strain of the Ge 1-x Sn x film in the GeSnOI is as low as 0.10% as confirmed using HRXRD and Raman spectroscopy.

The effect of sulfur passivation of the surface of Ge 0.83 Sn 0.17 is investigated. X-ray photoelectron spectroscopy (XPS) was used to examine the interfacial property between HfO 2 and Ge 0.83 Sn 0.17 . Sulfur passivation is effective in reducing both the Ge oxides and Sn oxides formation and the Sn atoms segregation. In addition, sulfur passivation reduces the interface trap density D it at the HfO 2 /Ge 0.83 Sn 0.17 interface from the valence band edge to the midgap. After the implementation of sulfur passivation, Ge 0.83 Sn 0.17 p-MOSFETs show improved subthreshold swing S and effective hole mobility μ eff . 25% μ eff enhancement can be observed in Ge 0.83 Sn 0.17 p-MOSFETs with sulfur passivation at a high inversion carrier density N inv of 1 × 10 13 cm −2 .