Measurement of photocurrents using the variable frequency chopped light technique shows that the reported photocurrents are due to photogeneration of carriers rather than a bolometric effect. The carrier lifetime, which is 10 to 40 ms at room temperature is independent of wavelength, but dependent on temperature according to the equation t = to eElkT with E = 0.255 eV.La mesure de photocourrants, utilisant la technique du lumiere coupke avec une frkquence variable, se demontre que les photocourrants rapport& sout due i la photogeneration des carrikres plus qu'a l'effet bolometrique. Le temps de vie du carriiires, qui est entre 10 40 ms & la tempkrature ambiante, est independent de la longeur de I'onde, mais dependent A la temperature, selou: z = z , eEIBT, E = 0,255 eV.