Metal-semiconductor-metal photodetectors (MSM PDs) are effective for monolithic integration with other optical components of the photonic circuits because of the planar fabrication technique. In this article, we present the design, growth, and characterization of GeSn MSM PDs that are suitable for photonic integrated circuits. The introduction of 4% Sn in the GeSn active region also reduces the direct bandgap and shows a redshift in the optical responsivity spectra, which can extend up to 1800 nm wavelength, which means it can cover the entire telecommunication bands. The spectral responsivity increases with an increase in bias voltage caused by the high electric field, which enhances the carrier generation rate and the carrier collection efficiency. Therefore, the GeSn MSM PDs can be a suitable device for a wide range of short-wave infrared (SWIR) applications.

Silicon (Si)-based mid-infrared (MIR) photonics has promising potential for realizing next-generation ultra-compact spectroscopic systems for various applications such as label-free and damage-free gas sensing, medical diagnosis, and defense. The epitaxial growth of Ge1-xSnx alloy on Si substrate provides the promising technique to extend the cut-off wavelength of Si photonics to MIR range by Sn alloying. Here, we present the theory and simulation of heterojunction p-i-n MIR photodetectors (PDs) with Ge0.87Sn0.13/Ge0.92Sn0.08 quantum-wells with an additional Ge0.91Sn0.09 layer to elongate the photoabsorption path in the MIR spectrum. The incorporation of QW pairs (N) enables the light-matter interaction due to the carrier and optical confinement in the active region. As a result, the spectral response of the device is enhanced in the MIR range. Devices with varying N were compared in terms of various figure-of merits including dark-current, a photocurrent-to-dark current ratio, detectivity, spectral responsivity, and noise equivalent power (NEP). Additionally, parasitic capacitance-dependent RC and 3dB bandwidth were also studied using a small-signal equivalent circuit model. The proposed device exhibited the extended photodetection wavelength at ~3370 nm and Iph/Idark up to ~7.3 × 103 with a dark current of ~56.3 nA for N = 8 at 300 K. At a bias of -3V, the proposed device achieved the spectral responsivity of 0.86 A/W at 2870 nm and 0.55 A/W at 3300 nm, detectivity more than 2.5 × 109 Jones and a NEP less than 2.1 × 10-13 WHz-0.5 for N = 8 at 3250 3250 nm The calculated 3dB bandwidth of 47.8 GHz, the signal-to-noise ratio (SNR), and linear dynamic range (LDR) of 93 dB and 74 dB were achieved at 3300 nm for N = 8. Thus, these results indicate that the proposed GeSn-based QW p-i-n PDs pave the pathway towards the realization of new and high-performance detectors for sensing in the MIR regime.

This work reports an optimal design and modeling of a high-performance normal-incidence GeSn homojunction p-i-n PDs on p-doped silicon (Si) substrate via Intrinsic-Si buffer. Specifically, we optimize the Sn concentration and the absorption layer thickness to simultaneously achieve high-speed, responsivity, detectivity, and low-noise in the mid-infrared (MIR) spectral range (2-5 μm). We also show that a reduced defect density due to the homojunction GeSn layer can lead to a suppressed dark current. The photoresponse of the designed device was studied for the range between 1500-3000 nm, and the calculated responsivity is 3.26 A/W and 1.27 A/W at 2000 nm and 2500 nm, respectively for Sn = 9%. A specific detectivity, linear dynamic range (LDR), noise-equivalent power (NEP), and the signal-to-noise ratio (SNR) of 2.5 × 1010 Jones, 105.5 dB, 40.9 × 10-15 WHz-05, and 100.9 dB, respectively, were achieved at 2500 nm for Sn = 9%. Furthermore, the impact of intrinsic layer thickness and incident optical power was also studied in detail. The calculated results show that larger absorption layer thickness enhances the photocurrent, detectivity, LDR and SNR, however, the speed of the device degrades significantly. The increased incident optical power results in an increase in SNR and LDR of the device due to an increased photocurrent. The 3dB bandwidth was also calculated for varying Sn concentration and intrinsic layer thickness. The calculated result shows a 3dB bandwidth of > 26.2 GHz at -3V. All the calculated results show that the proposed device has significant potential applications in the MIR range.

This work presents the high-performance Si/SiO ₂ distributed Bragg reflector (DBR)-integrated lateral germanium (Ge) p-i-n photodetectors (PDs) for atmospheric gas sensing and fiber-optic telecommunication networks in the short-wave infrared (SWIR) regime. In addition, this study also proposes an optoelectronic compact small-signal noise equivalent circuit model (SSNECM) of the designed device to compute the noise performance at the detectors’ output. Various figure-of merits including current under dark and illumination, responsivity, detectivity, bandwidth, and the noise of the proposed device are estimated at the room temperature (RT) for an incident optical power of ${0}.{5} {\mu }{W}$ . Furthermore, the impact of width and height scaling on dark current, responsivity, and bandwidth are investigated to optimize the proposed device. The validation of the proposed model is done by comparing various parameters including dark current, responsivity, and detectivity of the designed device with other Ge PDs. The estimated results show the reduced trade-off between responsivity and bandwidth of the designed device. At ${\lambda }=1550 nm$ , the proposed device achieves a high detectivity and SNR of $>2\times {10}^{11}$ Jones and 120 dB (at 3 THz), respectively, with the bias voltage of −2V. These encouraging results pave the path for the future development of low-noise and high-speed detectors.

In this paper, we discuss the impact of interfaces and defects on the frequency performance of Si-based GeSn heterojunction phototransistors (HPTs) at room temperature. Furthermore, the effect of base-emitter (B-E) voltage on the spectral responsivity (SR) and detectivity (D*) has also been studied. The presented device consists of Ge1-xSnx alloy in the active layer to enhance the photodetection range. However, increasing Sn content in Ge1-xSnx causes a lattice mismatch between Ge1-xSnx and Ge virtual substrate (VS), which may increase defect density at the heterointerfaces. As a result, the diffusion length (Lp) and minority carrier lifetime (τp) may decrease, thereby, degrading the performance of the device. Three major noise components such as shot noise current components at the base-emitter (B-E) and base-collector (B-C) junctions and Johnson noise have been considered for the first time to calculate the detectivity and noise-equivalent-power (NEP) of the presented device. The calculated results show that the decrease in diffusion length does not cause a significant impact on the SR, D* and internal quantum efficiency (IQE), however, it significantly degraded the cut-off frequency (fT), maximum frequency (fmax), and sensitivity (S) of the GeSn HPT at 300 K.