The symmetry and thermal activation energy of the EL2 defect center in gallium arsenide
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The symmetry and thermal activation energy of a dominant defect center in n-type liquid encapsulated Czochralski grown gallium arsenide (GaAs) crystal, called EL2, is investigated experimentally by the deep level transient spectroscopy (DLTS) and uniaxial stress techniques. A brief presentation of what has been done and known about this defect center is given first. A numerical fitting method improved upon the standard DLTS analysis is then presented. This method deals with a situation where the standard rate window DLTS is no longer sufficient, and gives an EL2 thermal activation energy of 0.76 ± 0.001 eV, different from the 0.82 ± 0.006 eV obtained by the standard DLTS. The symmetry of the EL2 center is then investigated through a more sophisticated data analysis method. From the experimental capacitance transients data measured under uniaxial stress, which superficially appears compatible with Tj symmetry, we extract reproducible defect energy level splittings under uniaxial stress and conclude that EL2 has Csv symmetry, supporting the proposed EL2 structure as the arsenic antisite and arsenic interstitial pair, Asca — Asi, with Asi weakly bound to Asca.