Features of Photothermal Ionization in Photoconducting Spectra of Mid-Infrared Silicon Detectors Doped by Deep Selenium Double Donors

Diatomic centers of double donor doped silicon have lower chemical shifts as compared to the corresponding atomic impurity and by this essentially extend spectral sensitivity of silicon extrinsic infrared detectors towards longer wavelengths. Additional expansion of the detector spectral band, up to the effective-mass approximated theoretical value of about 2.7 THz, can be obtained by photothermal infrared absorption originated from intracenter transitions of a dopant. Due to large energy gaps between lowest excited states of double donors in silicon related photothermal transitions have not been considered yet as applicable for photoconductive light detection. We have investigated the operational conditions suitable for expanding the low temperature detection wavelength cut-off of selenium doped silicon infrared detectors towards 6.2 μm.