An InGaAsSb p-B-n structure has been designed and characterised for zero bias low power detection applications. Devices were grown by molecular beam epitaxy and fabricated into quasi-planar photodiodes with a 2.25 μm cut-off wavelength. Maximum responsivity was measured to be 1.05 A/W at 2.0 μm, achieved at zero bias. D* of 9.4×10¹⁰ Jones was determined from room temperature spectra of noise power measurements with calculated D* remaining >1×10¹⁰ Jones up to 380 K. With a view to simple miniaturised detection and measurement of low concentration biomarkers, optical powers down to 40 pW were detected, without temperature stabilisation or phase-sensitive detection, indicating the photodiode’s potential.