Near-field photocurrent spectroscopy: A novel technique for studying defects and aging in high-power semiconductor lasers
We present the first comparative study of spatially resolved near-field photocurrent spectra for high power laser diode arrays with different wave guide characteristics before and after accelerated aging of the laser device. Sub-wavelength spatial resolution is demonstrated by using a near-field fiber probe as the excitation source. The potential of the technique for analyzing microscopic aging processes in optoelectronic devices is demonstrated. The experiments provide insight into mechanisms of defect formation within the p-i-n junction of InAlGaAs/GaAs laser diodes upon aging. The effect of the wave guide structure and of surface recombination processes on the near-field photocurrent images is discussed and analyzed in terms of a beam propagation model. The nondestructiveness makes this technique a particularly attractive method for in-situ analysis in high power laser diodes.