Imaging of deep level domains in semi-insulating GaAs by voltage contrast

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Abstract
We have used the voltage contrast effect to image deep level domains in semi-insulating (SI) GaAs n-i-n resistor structures. Our samples consisted of SI, undoped, liquid encapsulated Czochralski material with alloyed AuGe/Ni contacts at spacings from 1.3 to 2.27 mm. By viewing the contact side of the samples with a scanning electron microscope while the devices were biased in the oscillation region, we observed domain formation and motion from cathode to anode in real time. Long range potentials in the GaAs were observed by viewing the polished back surface of the samples. That is, the domains which are launched from the front contacts were clearly evident in voltage contrast measurements on the back of the sample. Also, because of the nonuniform charging of the semiconductor surface by the electron beam, we observed interactions between the propagating domains and the cellular dislocation structure in the SI GaAs.