Far infrared and Terahertz thermal detectors for radiometry using a carbon nanotube array
John H. Lehman, Erich N. Grossman
We present a description of a 1.5 mm long, vertically aligned carbon nanotube array (VANTA) on a thermopile, and separately on a pyroelectric detector. Three VANTA samples, having average lengths of 40 µm, 150 µm and 1.5 mm were evaluated with respect to reflectance at a laser wavelength of 394 υm (760 GHz) and we found that the reflectance decreases substantially with increasing tube length; ranging from 0.38, 0.23 and 0.01 respectively. After transferring the 1.5 mm long VANTA sample to the active area of each detector, we evaluated the absolute responsivity of the thermopile and the frequency response of the pyroelectric detector. The responsivity of the thermopile by electrical heating (98.4 mA/W) was equal to that by optical heating (98.0 mA/W) within the uncertainty of the measurement. We analyzed the temporal response and found a thermal decay time of 500 msec, which is consistent with the specific heat of comparable VANTAs in the literature. The extremely low (0.01) reflectance of the 1.5 mm VANTAs and the fact that the array is readily transferable to the detectors surface is unprecedented.
carbon nanotube, far infrared, pyroelectric detector, terahertz, thermopile