We describe the use of magnetospectroscopy of donor-bound excitons in the low-temperature (1.7 K) photoluminescence spectrum of GaAs for the identification of shallow donor species in low-doped epitaxial GaAs. Magnetic fields up to 12 T are employed. In particular, we discuss the selective excitation of individual donor species in excited final-state (2p-, 2p0) transitions (“two-electron” replicas) by tuning a dye laser into resonance with a corresponding component of the principal neutral donor-bound exciton lines. Under these resonant conditions, the sensitivity to low-level contaminants is considerably improved. In addition, a better than 2× reduction in linewidth can be obtained, using a suitably narrowed laser line. Detection of specific circular polarizations is used to simplify the spectra. Individual components of the principal neutral donor-bound exciton peaks corresponding to different donor species are directly resolved in luminescence for the first time. The separation between these components, which has generally been neglected in past studies, is shown to account for the differences in the (1s - 2p-) excitation energies observed in comparison to far-infrared measurements. Individual donors are also resolved in the ionized donor-bound exciton peaks, and Haynes’ rule relationships are determined for both neutral and ionized donor-bound excitons. Shallow acceptors are identified in high fields from the principal neutral acceptor-bound exciton peaks; the central-cell corrections to the exciton localization energies are found to be increased by the field. The capabilities and limitations of the magnetospectroscopy technique are compared and contrasted with those of far-infrared photothermal ionization spectroscopy, and magnetospectroscopy is shown to have a number of important advantages.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics
- Electrical and Electronic Engineering