Deep level spectroscopy in high-power laser diode arrays

High-power laser diode arrays (LDA) are of utmost importance for a number of applications such as for pumping solid state lasers, laser frequency conversion, material processing and printing. For these applications device operation conditions include heavy thermal load, resulting in aging processes which limit lifetime and reliability. In order to overcome these limits microscopic insight into the aging processes is needed. Device aging is well-known to be accompanied by deep level creation, however, the mechanism trough in which specific deep levels are associated with a failure event must be separately proved for each device design. Thus analytical work and the development of new analytical techniques are required. Here we introduce Fourier-transform photo-current (FTPC) spectroscopy as a new method for the spectroscopy of deep levels in devices, e.g. for monitoring changes in the deep level concentration within the optically active layer. The basic idea of this technique is to measure the spectral sensitivity of the LDA for front facet illumination by the light coming from a FT spectrometer. The electrical signal generated within the LDA is taken from the power supply contacts of the device and is fed into the signal input port of the spectrometer. We find that the spectra obtained in this way are extremely sensitive to the aging processes and in particular to the increase of deep level contributions