An engineered barrier Mid-IR nBn photodetector based on III-Antimonide semiconductor alloys and its applications to use as a high-photoresponsivity optical device in multiple gas detection

In the present study, we focus on designing an III-Sb-based back-illuminated nBn photodetector with a 50% cutoff wavelength greater than 5µm for multiple gas detection applications in the mid-wavelength infrared (MWIR) range. For the first time, in the proposed nBn photodetector, the barrier layer is designed based on core/crown hetero-structure, which includes the AlAsSb (x_As = 0.03) ternary semiconductor as the core region and the InAlAsSb (x_Al = 0.99, y_As = 0.08) quaternary semiconductor as the crown region, and is compared with the InAlAsSb (x_Al = 0.99, y_As = 0.08) bulk barrier layer. The results show that the band structure engineering performed using the AlAsSb/InAlAsSb core/crown barrier layer reduces the valence band offset at the absorber/barrier interface and brings a hole barrier to near zero at unbiased conditions. Therefore, the main components of dark current, especially the Shockley–Read–Hall (SRH) recombination process, are suppressed. So that the designed device shows limited diffusion behavior in the range of 140–300 K. Under -0.5 V bias voltage, the dark current density at 150 K and 200 K reaches 1.058 × 10^–8 A/cm² and 6.667 × 10^–7 A/cm², respectively. In addition, we present the device's capability to detect direct greenhouse gases such as methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) and indirect greenhouse gas such as carbon monoxide (CO) by evaluating the merit criteria such as current responsivity (R_λ), specific detectivity (D^*), noise equivalent power (NEP), noise equivalent irradiance (NEI), linear optical dynamic range (LODR) and current sensitivity (S_cur). Considering the absorption wavelength of the CH₄, CO₂, N₂O and CO gases, the R_λ is calculated 1.10 A/W, 1.66 A/W, 1.89 A/W, and 1.60 A/W respectively, the D^* is estimated ~ 1.54 × 10¹² cmHz^1/2/W, ~ 2.32 × 10¹² cmHz^1/2/W, ~ 2.65 × 10¹² cmHz^1/2/W, and ~ 2.25 × 10¹² cmHz^1/2/W, respectively and the NEP is earned ~ 1.94 × 10^–15 WHz^1/2, ~ 1.32 × 10^–15 WHz^1/2, ~ 1.31 × 10^–15 WHz^1/2 and ~ 1.33 × 10^–15 WHz^1/2, respectively at—0.5 V. Also, the S_cur of the designed device for CH₄, CO₂, N₂O, and CO gases is obtained as ~ 217.95, ~ 331.96, ~ 332.60, and ~ 317.74, respectively. Analysis of the simulation results proves that the proposed III-Sb-based nBn photodetector can be a promising candidate for a multiple gas detector device.