We have carried out van der Pauw resistivity and Hall effect measurements on a series of Molecular Beam Epitaxy InAs/GaAs superlattice samples containing InAs quantum dots. Three growth parameters were varied, the InAs coverage, the number of repetitions of the InAs/GaAs layers, and the GaAs spacer thickness. The results can be grouped in two sets, those samples presenting low and high resistivity. The group presenting low resistivity is composed by the samples with GaAs spacer of 30 monolayers (ML) and InAs coverage of 1.9 monolayers. The group presenting high resistivity is composed of samples with GaAs spacer of 40 ML. We claim that the high resistivity characteristic is due to the presence of deep level. Increasing the spacer from 30 to 40 ML decouples the InAs planes favouring the deep level formation.

In this work we present studies for the behavior of impurity breakdown of two GaAs samples grown by Molecular Beam Epitaxy at 200°C and 300°C. We vary the temperature and the illumination intensity. For the sample grown at 200°C, the transport mechanism after the breakdown is of the same type of the main free carriers at low electric fields. Below 100K, a clear dependence of the threshold electric field with temperature was observed. The sample grown at 300°C shows a breakdown due to an acceptor level at 41meV from the valence band. The threshold electric field increases with illumination due to the generation of free electrons by deep levels. A similar behavior was also observed for a Cr doped GaAs sample.

The adsorption and desorption of Te on GaAs (100) has been investigated using Soft X-ray Spectroscopy (SXS) and X-ray Photoelectron Spectroscopy (XPS). The SXS measurements have been done at the Brazilian synchrotron facility LNLS, and the XPS study was performed using laboratory sources. The samples were MBE GaAs (100) layers covered in-situ by Te from an effusion cell. Two families of samples were studied: samples analyzed in-situ, and samples that were exposed to air for at least one week. The desorption of Te of the non-oxidized samples indicates that traces of Te remains in the surfaces for temperatures as high as 680 °C. However, for the case of the oxidized samples, the Te film sublimates easily at around of 250 °C, leaving a clean GaAs surface. It seems that the oxidized Te film works as a suitable protection for epitaxial GaAs layers.