We have measured the electron-phonon energyrelaxation time, τ ep h , in superconducting boron-doped diamond films grown on silicon substrate by chemical vapor deposition. The observed electron-phonon cooling times vary from 160 ns at 2.70 K to 410 ns at 1.8 K following a T −2-dependence. The data are consistent with the values of τ ep h previously reported for singlecrystal boron-doped diamond films epitaxially grown on diamond substrate. Such a noticeable slow electron-phonon relaxation in boron-doped diamond, in combination with a high normal-state resistivity, confirms a potential of superconducting diamond for ultrasensitive superconducting bolometers. Index Terms-Superconducting boron-doped diamond, electron-phonon time, superconducting nanobolometers. I. INTRODUCTION A SUPERCONDUCTING film on a dielectric substrate is a key element of powerful and practically usable radiation detectors such as superconducting single-photon detectors (SSPDs) [1], microwave kinetic inductance detectors (MKIDs) [2] and hot electron bolometers (HEBs) [3]. Each type of detectors has become very prominent in the last decade. SSPDs are the fastest single-photon detectors for photon counting in optical and near infrared range, they are commercially available. MKID is promising detector technology due to the scalability and the simplicity of multiplexing a large number of pixels. HEB as a mixer is the most sensitive low noise devices Manuscript

Modern technologies of photonics, astrophysics, medicine and security systems have a demand for development of new types of sensitive detectors and/or optimization of existing ones. As an example, a strong demand exists for improvement of the characteristics of highly sensitive detectors based on superconducting materials. One way to optimize the performance of such detectors is to select a suitable superconducting material. This is due to the fact that the technical characteristics of devices are determined by relaxation mechanisms of nonequilibrium processes that occur in the material upon absorption of electromagnetic radiation. In this paper, we focused on the study of the relaxation of nonequilibrium processes in superconducting materials such as highly boron-doped polycrystalline diamond films, highly disordered titanium nitride (TiN) films and ultrathin amorphous tungsten silicide films (WSi). The experimental data allowed us to determine the temperature dependence of the inelastic relaxation time in the studied materials. These results can help us to evaluate the applicability of these materials for the different types of superconducting detectors.