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Differential Photoacoustic Analysis of Semiconductors

IP.com Disclosure Number: IPCOM000051450D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Coufal, H: AUTHOR [+2]

Abstract

Photoacoustics proved to be, in addition to a spectroscopic method, a very powerful technique for the non-destructive analysis of materials. Depth profiles of samples can be taken or microscopic inhomogeneities on the surface or very close to the surface of the sample can be analyzed. Recently, the time domain of photoacoustic signals was analyzed. Combining all of the above gives rise to differential photoacoustic probing. This is very useful in the analysis of semiconductors because both the optical and thermal properties of the materials may be investigated.

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Differential Photoacoustic Analysis of Semiconductors

Photoacoustics proved to be, in addition to a spectroscopic method, a very powerful technique for the non-destructive analysis of materials. Depth profiles of samples can be taken or microscopic inhomogeneities on the surface or very close to the surface of the sample can be analyzed. Recently, the time domain of photoacoustic signals was analyzed. Combining all of the above gives rise to differential photoacoustic probing. This is very useful in the analysis of semiconductors because both the optical and thermal properties of the materials may be investigated.

In this method, a sample is irradiated with chopped light at two or more (n) locations in such a way that the light beams at those locations are m x 360 over n, m=1 . . . n for the n/th/ location out of phase. The different light beams can be of different wavelength. The method will be discussed for n=2 with reference to Fig. 1.

The photoacoustic signal is detected with conventional techniques, i.e., with a piezoelectric pick-up directly coupled to the under side of the sample, or a microphone coupled via a gas- or liquid-filled volume to the front side of the sample contains information for both locations 1 and 2. The difference in the signal amplitude can be conveniently detected by a lock-in amplifier locked to the chopping frequency. This signal can be used to characterize differences between two or more locations at the sample. A Laplace transformation may be used to...