Identification of residual donors in high-purity epitaxial GaAs with the use of magneto-optical spectroscopy

We report the first identification of residual donors in high-purity, vapor-phase epitaxial GaAs using the photoluminescence technique in the presence of applied magnetic fields. Identifications were made from complexes of the neutral-donor-bound-exciton type in which the transitions occurred between excited initial and final states of the complex. The same residual donors were identified from ionized-donor-bound-exciton complexes in the same crystal. These measurements were also made in applied magnetic fields. The magnetic field compresses the wave function which sharpens the optical transitions. It also separates the different donors when viewed from neutral-donor-bound-exciton transitions. The magnetic field separation of different donors, when viewed from the ionized-donor-bound-exciton transitions, was not significant in fields up to 40 kG. An exchange energy of ∼30 μV was measured from the magnetic field splitting of the ionized-donor-bound-exciton $\pi$ lines.