The investigators propose a definitive experiment to resolve the controversy regarding the origin of the "DX phenomenon" in n-type A1GaAs semiconductor. Resolution of this question is crucial to the future development of high performance III-V semiconductors. The two models for the DX center, leading to loss of low temperature conductivity, predict different local geometries for dopant atoms. We propose to use Mossbauer spectroscpopy to probe the local environment of donor tellurium atoms in A1GaAs semiconductors at 77K. The spectrum of undistorted substitutional donor sites will be distinguishable from spectra of sites that are asymmetrically distorted or are associated with vacancies or other defects. Consequently, a careful Mossbauer experiment should be sufficient to distinguish between the models for the DX center.
