Improvement of nonlinearity and extension of wavelength region using tandem (PV+PC) type HgCdTe detector (dual-MCT) in FTIR spectrometer

Journal of Electronic Materials, Jun 1999 by Abe, O, Kawasaki, K, Wakaki, M

A single beam spectrum of the wide band type Dual-MCT is shown in Fig. 7. The linearity is almost the same as a middle band type, because the upper limit of linearity is limited by the PV type. But it is a feature of a wide band Dual-MCT that S/N in the 10 Fm region is higher than a wide band PC-type.

CONCLUSIONS

The improvement of linearity of a MCT detector used for FTIR spectrometer was obtained by the improvement of the detector itself. A good result was obtained by fabricating a composite type device with a separated function instead of a single function device. The composite structure was obtained by the integration of a PV type with a PC type giving a tandem structure. In the improved detector which we named "Dual-MCT," the enhancement of linearity by a factor of about 30 for the incident light intensity was realized compared with a conventional PC type for versatile FTIR spectrometer application. The enhancement of the absorbance by a factor of 100 was also obtained in the wavelength region around 10 (mu)m. The linear range of the intensity is a part of the whole variable light flux of the instrument remaining the room of more improvement. The idea to use 2D arrays of a PV type MCT is discussed for the problem.

As for an application of this device to a microscopic attachment of the FTIR spectrometer, it is considered that the problem of linearity is completely solved from the observation of the spectra. It is possible to make a wide band PV type MCT by using high technology, which extends high linearity to a longer wavelength region. But such a detector claims high cost and is insufficient for mass production. We covered this by using a conventional versatile PC type MCT.

Generally speaking, it is quite depressing to obtain an almighty performance by using a single element. In a present time, it is often seen to expect excessively the sophisticated computer signal processing. In this research, the excellent performance of the detector was realized by separating the function using a rather simple idea.

ACKNOWLEDGMENT

We thank the members of Spectroscopic Products Division of JASCO Corporation for helping us to evaluate the Dual-MCT.

(Received October 20, 1998; accepted December 15,1998)

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O. ABE,1 K. KAWASAKI,1 and M. WAKAKI2

1.-JASCO Corporation, 2967-5 Ishikawa-cho, Hachioji-shi, Tokyo 192-8537 Japan. 2.-Department of Electro-Photo-Optics Engineering, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292 Japan