REVEALING PROCESS-INDUCED STRAIN FIELDS IN GAAS/ALGAAS LASERS VIA ELECTRON-IRRADIATION IN A SCANNING ELECTRON-MICROSCOPE

An electron beam induced current study has been performed on single quantum well graded index separate confinement heterostructure GaAs/AlGaAs ridge geometry lasers. It has been shown that electron irradiation in the KeV range combined with the electron beam induced current technique can be used to reveal process-induced strain fields and to study strain-related degradation phenomena in these devices on a microscopic scale. This technique has revealed a strain field below the ridge and below an opening in the metal layer. Enhanced susceptibility to degradation processes has been detected close to the lower corners of the ridge. It is shown that a correct interpretation of electron beam induced current images requires, including as contrast mechanism, local fluctuations in the distribution of the electric potential in the device and capture properties of quantum wells; (in the past, electron beam induced current images of degraded lasers were interpreted under the assumption that the contrast reflects the distribution of defects which act as recombination centers). A possible role of process-induced strain fields in the formation of fluctuations in the material's built-in electric potential distribution within the active part of the laser during degradation is discussed.