Tensile-Strained Mid-Infrared GeSn Detectors Wrapped in Si 3N 4 Liner Stressor: Theoretical Investigation of Impact of Device Architectures

In this paper, we comparatively studied the energy band diagram and the cutoff wavelength characteristics of germanium-tin (GeSn) fin and pillar array detectors wrapped in a Si₃N₄ liner stressor to unveil the impacts of tensile strain and device architecture in the absorption spectra of the devices. A large tensile strain is introduced into GeSn devices by the expansion of the Si₃N₄ liner stressor. Compared to the fin detector, a larger tensile volume strain is demonstrated in the GeSn pillar architecture. With the tensile strain induced by the Si₃N₄ liner stressor, the direct bandgap E_G,Γ of GeSn is obviously shrinked by lowering the energy of the Γ conduction band valley, which results in a significant extension of absorption edge in the GeSn detectors. As the Si₃N₄ liner stressor releases internal stress and expands, the absorption edge of the tensile-strained Ge_0.90Sn_0.10 pillar array detector with the length of side of pillar L_pillar of 100 nm is extended to 4.35 μm. With further improvement, the tensile-strained GeSn pillar architecture with the Si₃N₄ liner stressor will be competitive for the application in 2-5-μm mid-infrared spectra.