Investigation of defect and electronic interactions associated with GaAs device processing

Research on new semi-insulating behaviour in 3-5 compounds completed the determination of electronic levels and related optical properties of substitutional titanium in bulk grown InP and GaAs. In the course of the corresponding crystal growth study we have also identified impurity gettering by transition elements. This gettering takes place due to melt (or solution), and it can be beneficial or detrimental for obtaining SI materials. An example of the beneficial role is provided by the interaction of vanadium with silicon, which reduces Si donor concentration in the grown crystal. An example of detrimental effect is provided by the interaction of titanium with carbon, which reduces the concentration of deep compensating Ti donors in epitaxial or melt grown crystals. Appropriate redesign of the epitaxial growth cell (eliminating all graphite elements in contact with the solution) is in progress. An investigation has been carried out on the extension of liquid phase electroepitaxy to the growth of bulk InGaAs crystals. We have successfully developed procedures for the electroepitaxial growth of InGaAs ingots 14 mm in diameter and up to 3 mm thick. To our knowledge, these are the first bulk InGaAs crystals to show excellent compositional uniformity (in accord with theoretical predictions for electroepitaxy).