Abstract
Thermal behavior of arsenic precipitates in undoped semi-insulating GaAs crystals has been investigated. Crystals heat-treated at a temperature between 500 and 1150°C were observed by infrared light scattering tomography, which is powerful technique capable of detecting the arsenic precipitates. The arsenic particles on the dislocations became large increased in scattering intensity with temperatures from 800 to 1000°C. A dramatic change occurred above 1100°C: the images disappeared over the whole area. This disappearance means that the arsenic precipitates dissolves into the GaAs crystal. Using the samples in which the excess arsenic was solid-soluted, the same experiments were repeated. At 800–1000°C, the scattering images of the dislocations again appeared. Below 600°C, new images, consisting of misty zones of scattering, were observed in the dislocation-free areas. This suggests that the excess arsenic condenses like mist over the limit of saturation solubility.
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