ACOUSTIC-EMISSION STUDY OF DEFECTS IN GALLIUM-PHOSPHIDE LIGHT-EMITTING DIODES

Acoustic emission was observed from GaP:N light emitting diodes during stress operation and correlated with the degradation of light output. Acoustic emission was found to be due to the generation of dislocations which were revealed by etch pits after degradation. Acoustic signals were detected with a PZT transducer directly placed under the diode chip. Two components of acoustic signals were recorded, i.e., sharp pulses and a CW component. The light output decreased in proportion to the logarithm of time for a certain period after which the light output degraded irregularly. In the logarithmic decay period no acoustic emission was observed and the etch pit density did not increase.- The irregular degradation was always accompanied by acoustic emission and the etch pit density increased remarkably. Luminescence spectra and effective carrier concentration profiles were also compared before and after degradation. It is shown that the acoustic emission monitoring provides a novel technique to reliability physics of compound semiconductors. © 1979 AIME.