The crossover between the electron-phonon relaxation and the diffusion
transport of hot electrons in an NbC microbolometer has been studied.
At least an 80 ps relaxation time can be achieved in 0.2 mu m long br
idges of the material with a diffusivity of 8 cm(2)/s. The high diffus
ivity is accompanied by a large sheet resistance (approximate to 10 Om
ega) that simplifies the match of the mixer device made of NbC to plan
ar antenna at terahertz frequencies. The intrinsic noise mechanisms im
ply a very low mixer noise temperature of the order of a few tens of K
elvin, independent on the radiation frequency. (C) 1996 American Insti
tute of Physics.