Broadband THz radiation emission from photoexcited GaSb1-xBix (0 < x < 1.65%) was investigated. We observed an enhancement in the THz emission with Bi incorporation in GaSb. GaSb1-xBix alloy with showed an emission amplitude comparable to that from LT-GaAs, which is over an order of magnitude higher compared to GaSb. Transient photocurrents due to p-type surface band bending was found to be the dominant emission mechanism in these alloys. Strengthening of the surface field due to Bi induced p-doping is responsible for the observed enhancement. The NIR pump incident angle and THz detection angle study suggests that the photocarrier momentum is preferentially aligned along the refracted excitation beam direction inside the semiconductor alloy. GaSb1-xBix emitter showed better spectral performance compared to a commercially available photoconductive antenna in a THz time domain spectroscopy system. This demonstrates the application potential of this material in THz spectroscopy. © 2018 IOP Publishing Ltd.