Space charge currents, domains and instabilities viewed with voltage contrast spectroscopy

Abstract

We have used the voltage contrast mode of a scanning electron microscope (SEM) to image deep level domains in semi-insulating (SI) GaAs n -i -n resistor structures. Our samples consisted of SI undoped, Cr doped and In alloyed liquid encapsulated Czochralski (LEC) material with alloyed AuGe/Ni contacts at spacings from 10 μm 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. We observe interactions between the propagating domains and the cellular dislocation structure in the SI GaAs. The spatial incoherence manifests itself as high frequency noise in the time series current waveform by producing an apparent higher dimensionality for the carriers. We also present the first time observation of chaotic behavior in an AlAs/GaAs superlattice structure.