PHOTOACOUSTICS, NEW METHODS TO STUDY OPTICAL PROPERTIES OF DISLOCATIONS ?

The principles of the so-called photoacoustic methods are briefly described and the three main types of experimental approaches are reviewed : microphone and closed cell ; piezoelectric transducer and open cell ; mirage effect detection of photothermal deflection. Such methods being sensitive to non-radiative transitions are complementary to photoluminescence. The main advantage of photoacoustics over regular absorption is a good sensitivity due to detection over a "black background" just as in photoluminescence excitation. For instance, absorbance values as small as 10-6cm-1 have been detected for non-radiative centers. Besides spectroscopy, photoacoustic methods can also be used for topography with depth profiling capabilities. Though the applications of these methods to optical properties of dislocations is still in its enfancy, the first few promizing results in the literature shall be reviewed.