We report a room temperature study of the direct band gap photoluminescence of tensile-strained Ge/Si0.13Ge0.87 multiple quantum wells grown on Si-based germanium virtual substrates by ultrahigh vacuum chemical vapor deposition. Blueshifts of the luminescence peak energy from the Ge quantum wells in comparison with the Ge virtual substrate are in good agreement with the theoretical prediction when we attribute the luminescence from the quantum well to the cΓ1-HH1 direct band transition. The reduction in direct band gap in the tensile strained Ge epilayer and the quantum confinement effect in the Ge/Si0.13Ge0.87 quantum wells are directly demonstrated by room temperature photoluminescence.

This work designed an ITO/Ag/n-Si Schottky photodetector with broad wavelength detection and low dark current. The introduction of Ag interfacial layer and post rapid thermal annealing dramatically increase the barrier height of ITO/n-Si Schottky diode by 0.32 eV, leading to the 2300 × reduction of dark current. A well-behaved ITO/Ag (8 nm)/n-Si Schottky diode with a high rectification ratio ( ± 1 V) of 4 × 10⁵ and low dark current (−1 V) of 9.2 nA was achieved. Such low dark current device spontaneously provides high sensitivity for visible/near infrared wavelength detection, in which substantial responsivity for wavelengths from 360 to 1650 nm was realized through both inter-band and internal photoemission. The design here provides an encouraging strategy for monolithically integrated pure Si photodetectors operating at long wavelength up to 1650 nm.

Mixed-dimensional van der Waals (vdW) heterostructures based on two-dimensional transition metal dichalcogenides and three-dimensional semiconductors have led to a new era in next-generation optoelectronics due to the high-quality interfaces and energy band complementation, especially in broadband photodetectors which can be used for all-weather navigation, object identification, etc. However, the reported photodetectors conventionally operated in photodiode mode with low responsivity and a narrow response spectrum. In this study, we report a p-WSe₂/n-Ge vdW heterojunction phototransistor with a Schottky barrier collector on n-Ge for broadband photodetection. Large hole/electron injection ratio from p-WSe₂/n-Ge heterojunction under forward bias due to their large bandgap offset renders the high photocurrent gain, while the Ge Schottky barrier limits the dark current. The responsivities of the phototransistor at 1.0 V emitter-collector bias are 55, 95, and 120 A·W⁻¹ at 405, 1,310, and 1,550 nm, respectively, which is superior to that of the corresponding p-WSe₂/n-Ge photodiodes. The phototransistor shows a high photocurrent gain of 80, a specific detectivity of 10¹¹ Jones, as well as a fast response time of 290 µs at 1,550 nm. The results suggest that the novel phototransistor being implemented with complementary metal-oxide-semiconductor processing is an ideal strategy for high-performance broadband photodetection.