Electron beam charging thermography of mirrors of semiconductor laser diodes

Abstract

Charging insulating films in a scanning electron microscope is shown to be a potentially useful thermographic technique which makes it possible to reveal hot regions in microelectronic devices, with a spatial resolution in the submicrometer range. This technique entails depositing an insulating film on the device to serve as thermographic medium. A focused, low-energy electron beam charges the insulator during the scanning process. Hot regions modify the local charge, which in turn modifies the secondary electron signal and thus generates a thermal contrast. This technique has been applied to investigate mirrors of GaAs/AlGaAs graded index separate confinement single quantum well laser diodes. Thermographic images of these mirrors have been obtained with a spatial resolution of 0.25 μm. Since the thermal images can be observed using the scanning electron microscope's TV mode, the course of fast thermal phenomena at laser mirrors can be imaged. As an example, the thermal drift prior to the thermal runaway at laser mirrors has been investigated.