GeSn-Based Multiple-Quantum-Well Photodetectors for Mid-Infrared Sensing Applications
Harshvardhan Kumar, Ankit Kumar Pandey
Abstract
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\rm Ge}_{\rm 1-x}{\rm Sn}_{\rm x}$ </tex-math></inline-formula> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</i> MIR photodetectors (PDs) with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\rm Ge}_{0.87}{\rm Sn}_{0.13}/{\rm Ge}_{0.92}{\rm Sn}_{0.08}$ </tex-math></inline-formula> quantum-wells with an additional Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.91</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.09</sub> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> and 3dB bandwidth were also studied using a small-signal equivalent circuit model. The proposed device exhibited the extended photodetection wavelength at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\sim }3370\,{\mathrm {nm}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\rm ph} \mathord {\left /\right. } I_{\rm dark}$ </tex-math></inline-formula> up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\sim }7.3\times {10}^{3}$ </tex-math></inline-formula> with a dark current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\sim }56.3\,{\mathrm {nA}}$ </tex-math></inline-formula> for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {N}}=8$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5\times 10^{9}$ </tex-math></inline-formula> Jones and a NEP less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.1\times 10^{-13}\,{\mathrm {W}}{\rm Hz}^{-0.5}$ </tex-math></inline-formula> for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {N}}=8$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {N}}=8$ </tex-math></inline-formula> . Thus, these results indicate that the proposed GeSn-based QW <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</i> PDs pave the pathway towards the realization of new and high-performance detectors for sensing in the MIR regime.