Mid-Infrared Photodetectors Based on Lattice Matched SiGeSn/GeSn Heterojunction Bipolar Transistor With an i-GeSn Absorber Layer

This work proposes a high-performance lattice-matched SiGeSn/GeSn/SiGeSn heterojunction bipolar phototransistors (HPTs) and p-i-n photodiodes grown on strain-free SiGeSn virtual substrate (VS) capable of working in mid-wave infrared (MWIR) bands. To obtain a strain-free structure, the lattice matching requirement at the SiGeSn/GeSn/SiGeSn heterointerfaces is considered to significantly minimize the interface and defect states in the proposed device. In order to have the same lattice constant, appropriate Si and Sn alloying can be used to grow lattice-matched SiGeSn/GeSn/SiGeSn heterostructures. Using the finite element method (FEM), device structures considering the material’s experimental data are simulated and also compared against theoretical data. Additionally, at
$\lambda = {2000}$
nm, the effect of theoretical and experimental values of the absorption coefficient on the responsivity is also demonstrated at room temperature. The result reveals that the experimental absorption coefficient has a significant impact and greatly lowers the devices’ responsivity. A strain-free HPT (p-i-n PD) structure(s) allows for attaining a responsivity and bandwidth of 28.5 (0.97) A/W and 29.5 (91.22) GHz, respectively, at
$\lambda = {2000}$
nm. Moreover, the proposed HPT (p-i-n PD) exhibits a high signal-to-noise ratio (SNR) of 68.4 (31.8) dB up to 10 GHz operating frequency. These values are higher than previously reported results, showing the potential of the proposed lattice-matched detectors for MWIR applications.