Blocked impurity band （BIB） detectors are the state-of-the-art choice for far infrared astronomical observation. Ge：B BIB far infrared detector has been successfully developed using near-surface processing techniques. The spectral response covers a wide range from 50 cm^-1 to 400 cm^-1. At a temperature of 3.5 K and a working voltage of 30 mV， the detector exhibits a highly competitive responsivity of 21.46 A?W^-1 and a highly competitive detectivity of 4.34×10¹⁴ cm?Hz^1/2?W^-1 at the peak response of 84.9 cm^-1. The influence of the interfacial barriers on the spectral response is investigated. A new excitation model that the carriers in the contact regions can be excited over the interfacial barriers is proposed. Moreover， a new method to enhance the relative response intensity of BIB detectors in the low wavenumber region is found.