A novel germanium （Ge）-based blocked-impurity-band （BIB） infrared detector with a planar PIN structure was developed， using a near-surface processing technique to fabricate the target and electrode contact regions. The detector demonstrates significant rectifying characteristics， exhibiting extremely low dark current under reverse bias， and its working temperature is extended to 15 K. At this temperature， the detector maintains a stable detectivity of 6 × 1012 cm·Hz^1/?·W?1 within the reverse bias voltage range of 0 V to -5 V. Through the band structure analysis， the dark current mechanism and the impact of temperature variation on optical response were discussed in detail， and the working principle based on the low-temperature weak ionization region was proposed. Additionally， tests of the detector’s blackbody response current and detectivity were systematically measured， and the mechanism of maintaining high performance at elevated working temperatures was clarified. The result provides innovative insights for enhancing the temperature performance of Ge-based BIB detectors and offers the theoretical and experimental support for the design and application of future infrared detectors.