GeSn-Based Multiple-Quantum-Well Photodetectors for Mid-Infrared Sensing 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 Ge_1-xSn_x 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 Ge_0.87Sn_0.13/Ge_0.92Sn_0.08 quantum-wells with an additional Ge_0.91Sn_0.09 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 [Formula: see text] 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 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.