Group-IV GeSn material systems have recently considered as a new material for sensitive photodetection in the short-wave infrared (SWIR) region. The introduction of Sn into Ge can effectively narrow the bandgap energies, thereby extending the absorption edges toward the longer wavelengths and enabling effective photodetection in SWIR region. Here we present an experimental and modeling study of GeSn/Ge quantum well (QW) photodetectors on silicon substrates for effective SRIW photodetection. Epitaxial growth of pseudomorphic GeSn/Ge QW structures was realized on Ge-buffered silicon substrates using low-temperature molecular beam epitaxy. Normal incident GeSn/Ge QW photodetectors were then fabricated and characterized. The optical responsivity experiments demonstrate that the photodetection cutoff wavelengths is extended to beyond 1800 nm, enabling effective photodetection in SWIR spectral region. We then develop theoretical models to calculate the composition-dependent strained electron band structures, oscillation strengths, and optical absorption spectra for the pseudomorphic GeSn/Ge QW structures. The results show that Ge<sub>1-x</sub>Sn<sub>x</sub> well sandwiched by Ge barriers can achieve a critical type-I alignment at Γ point to provide necessary quantum confinement of carriers. With an increase in the Sn content, the band offsets between the GeSn well and Ge barreirs increases, thus enhancing the oscillation strengths of direct interband transitions. In addition, despite stronger quantum confinement with increasing Sn content, the absorption edge can be effectively shifted to longer wavelengths due to the direct bandgap reduction caused by Sn-alloying. These results suggest that GeSn/Ge QW photodetectors are promising for low-cost, high-performance SWIR photodetection applications.
An efficient Si-based laser is one of the most important components for photonic integrated circuits to break the bottleneck of data transport over optical networks. The main challenge is to create gain media based on group-IV semiconductors. Here we present an investigation of using low-dimensional Ge<sub>1-xS</sub>n<sub>x</sub>/Ge quantum-well (QW) structures pseudomorphically grown on Ge-buffered Si substrates as optical gain media for efficient Si-based lasers. Epitaxial growth of Ge<sub>1-xS</sub>n<sub>x</sub>/Ge QW structures on Ge-buffer Si substrate was carried out using low-temperature molecular beam epitaxy techniques. The light emission properties of the grown Ge<sub>1-xS</sub>n<sub>x</sub>/Ge QW structure were studied using photoluminescence spectroscopy, and clear redshifts of emission peaks were observed. Theoretical analysis of band structures indicates that Ge<sub>1-xS</sub>n<sub>x</sub> well sandwiched by Ge barriers can form type-I alignment at Г point with a sufficient potential barrier height to confine carriers in the Ge<sub>1-xS</sub>n<sub>x</sub> well, thereby enhancing efficient electron-hole direct recombination. Our calculations also show that the energy difference between the lowest Г-conduction subband and L conduction subband can be reduced with increasing Sn content, thereby enabling optical gain. These results suggest that Ge<sub>1-xS</sub>n<sub>x</sub>/Ge QW structures are promising for optical gain media to develop efficient Si-based light emitters.
We report the fabrication and characterization of GeSn waveguide structures on Si substrates grown by molecular
beam epitaxy for efficient light-detection and emission. For photodetectors, GeSn waveguide structures exhibit a higher
optical response compared to a reference Ge device as revealed by the photocurrent experiments. For light-emission,
room-temperature photoluminescence experiments show a redshifted emission wavelength for the GeSn samples
compared to the Ge reference sample due to the Sn incorporation. Besides, we observe ripple characteristics in the
amplified spontaneous emission spectrum of the GeSn waveguide structure, which are attributed to the waveguide
modes. Those results suggest that GeSn waveguide structures are promising for high-performance Si-based lightdetectors
and emitters integrable with Si electronics.