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We study the effect of temperature and doping in Si-based GeSn heterojunction phototransistors (HPTs) for low-power-consuming, low-cost, and high-speed mid-infrared (MIR) applications. The incorporation of ${\rm{G}}{{\rm{e}}_{1 - x}}{\rm{S}}{{\rm{n}}_x}$ alloy in the base of our HPTs significantly shortens the emitter-to-collector transit time, leading to high cut-off frequency ( ${f_T}$ ) due to an increase in mobility. Furthermore, the ${\rm{G}}{{\rm{e}}_{1 - x}}{\rm{S}}{{\rm{n}}_x}$ base extends the optical detection over a wide range (up to 2500 nm) due to the shrinkage of the bandgap energy caused by alloying with Sn. Additionally, spectral responsivity increases with Sn alloying due to the increased absorption coefficient. Our results show that ${f_T}$ and responsivity are strongly dependent not only on doping but also on temperature. The impact of temperature on the noise behavior of phototransistors was also analyzed for frequencies up to 100 GHz. As the temperature increased, the signal-to-noise ratio (SNR) decreased; however, spectral responsivity significantly improved. The high SNR, responsivity, and ${f_T}$ values of the GeSn HPT make it a potential candidate for future Si-based uncooled high-speed MIR photodetection.

We present a comprehensive analysis of practical p-n-p Ge/Ge1-xSnx/Ge heterojunction phototransistors (HPTs) for design optimization for efficient infrared detection. Our design includes a Ge1-xSnx narrow-bandgap semiconductor as the active layer in the base layer, enabling extension of the photodetection range from near-infrared to mid-infrared to perform wide-range infrared detection. We calculate the current gain, signal-to-noise ratio (SNR), and optical responsivity and investigate their dependences on the structural parameters to optimize the proposed Ge1-xSnx p-n-p HPTs. The results show that the SNR is strongly dependent on the operation frequency and that the introduction of Sn into the base layer can improve the SNR in the high-frequency region. In addition, the current gain strongly depends on the Sn content in the Ge1-xSnx base layer, and a Sn content of 6%-9% maximizes the optical responsivity achievable in the infrared range. These results provide useful guidelines for designing and optimizing practical p-n-p Ge1-xSnx HPTs for high-performance infrared photodetection.

We present an investigation of the use of a low refractive index buffer layer to improve the sensitivity of grating coupler biosensor for different-sized bio-molecular. Our experimental results show that the bulk and surface sensitivities can be improved by optimizing the matching conditions.

We present a study of Franz-Keldysh effect in GeSn alloys for mid-infrared photonic applications. The electric-field-dependent absorption coefficient of GeSn alloys with different Sn compositions are calculated and discussed.

We present a design of Ge 1−x Sn x waveguide electroabsorption modulators on silicon and analyze the Franz-Keldysh modulation properties. The introduction of Sn into Ge allows for considerably narrowing the direct bandgap energy, thereby extended the absorption edge toward mid-infrared region to achieve mid-infrared optical modulation. We calculate the change in absorption coefficient of Ge 1−x Sn x induced by the Franz-Keldysh effects. The results show that significant absorption coefficient variation associated with the Franz-Keldysh effect can be achieved for optical modulation in the mid-infrared region.

A n-p-n heterojunction phototransitor with Ge 1-x Sn x base is presented. The work is focussed on effect of Sn concentration on the gain performance of the device based on optimised base and collector doping.

We report mid-infrared optical modulation in GeSn photodiodes on silicon. The incorporation of Sn into Ge shrinks the direct bandgap energy, redshifting the absorption edge to longer wavelengths and enabling electro-absorption optical modulation based on Franz-Keldysh effect in the mid-infrared range.

We report cavity-enhanced direct band electroluminescence from GeSn p-i-n diodes on silicon-on-insulator substrates. A Fabry-Perot cavity was created between the buried oxide layer and the deposited oxide layer to enhance electroluminescence from the GeSn active layer.

We present a variational study of direct transitions in GeSn/Ge quantum well system for photonic applications. The exciton radiuses, binding energies, and oscillator strengths are calculated for various Sn contents are calculated and discussed.

We present a theoretical analysis of strain effect on optical gain in biaxially-stressed Ge 1−x Sn x alloys. The electronic band structure for biaxially-stressed Ge 1−x Sn x alloys is calculated using deformation potential theory and k·p method. For unstrained Ge 1−x Sn x alloys, a Sn content of 6.7% is required to achieve a direct bandgap for providing optical gain. The introduction of tensile strain can further soften the requirements for indirect-to-direct bandgap transition, thereby enhancing optical gain. On the other hand, compressive strain significantly increases the energy difference between the Γ- and L-valley conduction band edges, and hence quenching optical gain in Ge 1−x Sn x alloys.

We propose and analyze a strain-free GeSn/SiGeSn quantum-well structure for elec-troabsorption modulators based on the quantum-confined Stark effect at 1550 nm wavelength.

The aim of this paper is to analyze a single-crystal micro-ring gyroscope. It is found that Si(111) ring is in-plane isotropic but out-of-plane anisotropic, while Si(100) ring is fully anisotropic. Hamiltonian's principle is used to derive the equations of vibration, which is a set of partial differential equations with variable coefficients. The exact solutions for frequencies and mode shapes are found. It is also found that the degeneracy of frequencies for isotropic ring splits for anisotropic ring Then structure design and dynamic analysis of silicon resonant micro-ring gyroscope are presented. The perturbation method of multiple scales is used to find the explicit expression for the relationship between input (angular velocity) and output (nodal displacement of the ring). The effectiveness of phase-locking for enhancing the output signal is proved and quantitatively analyzed.