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.
Photocurrents in single crystals and compressed discs of methyltriphenylphosphonium (TCNQ)z can be observed at low temperatures where the dark current is greatly reduced, or by the use of a chopped light source and a narrow band amplifier or oscilloscope display. By chopping a t appropriate frequencies the true photocurrent can be observed and bolometric effects eliminated. The true photocurrent, which is ohmic and linear with light intensity, shows a threshold a t (2.7 f-0.1) pm. The carrier lifetime is 140 ms above and below the phase change a t 310 K, but a t the phase change more than one lifetime is observed due to trapping.Fotostrome in Einkristallen und komprimierten Scheiben von Methyl-Triphenyl-Phosphonium (TCNQ)z werden bei niedrigen Temperaturen beobachtet, wo der Dunkelstrom stark reduziert ist, oder mit Hilfe zerhackten Lichts und eines Schmalbandverstarkers oder Oszillografen. Mit entsprechenden Zerhackerfrequenzen wird der wahre Fotostrom beobachtet, und bolometrische Effekte werden eliminiert. Der wahre Fotostrom, der ohmsch und linear zur Lichtstirke ist, zeigt eine Schwelle bei (2,7 f 0,l) pm. Die Ladungstriigerlebensdauer ist 140 ms oberund unterhalb der PhasenLnderung bei 310 K, aber am Phasengang wird auf Grund von Anhaftprozessen mehr als eine Lebensdauer beobachtet.
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