Diode detectors (DD) are widely used in electronic information and communication systems. In this paper the numerical modeling of the electrical potential distribution and current passing in the contacts of niobium nitride (NbN) with semiconductor alloy bismuth-antimony (Bi-Sb) was made. The optimization for high frequency signal was realised, when the signal frequency is more 10 GHz. There were analyzed possibilities to create the diode detectors based on these contacts and working at temperatures (T) of liquid helium 4.2 K and 1 K. The dependences of the current responsivity (CR), the voltage responsivity (VR) and the noise equivalent power (NEP) on the signal frequency (f) were analyzed. The obtained results were compared with literature data. Both DD working at temperature of liquid nitrogen (T = 77.4 K) and liquid helium were considered. The comparison with existent literature data shows the proposed DD can be 10100 times better. The physical reasons of these advantages were discussed. It is shown that unique properties of Bi-Sb alloys and especially of Bi0.88Sb0.12 alloy make these alloys to be the very perspective materials for cryoelectronics.