Abstract
AbstractThe donor and exciton states in ultra high-quality heteroepitaxial GaN grown by hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD) on sapphire substrates are investigated using low temperature photoluminescence (PL), reflectance, magnetospectroscopy in fields up to 12 T, and resonant electronic Raman scattering (RERS). The A free exciton is confirmed to have a binding energy of about 26.4 meV, independent of strain in the material. Bound n=2 exciton peaks are distinguished in the PL spectrum by their thermalization and sample dependence. The Si donor is shown to have a binding energy of about 21 meV using Si-doped HVPE samples grown at Epitronics. Up to five additional residual donor species are observed when comparing various HVPE and MOCVD samples. Pronounced temperaturedependence of the two-electron satellites is observed, suggesting the existence of unresolved excited rotator states of the neutral donor-bound exciton. Highly resolved magnetic splitting patterns are observed in the two-electron satellites. A nonperturbative theory of these donor splittings is developed, including anisotropy. Resonant electronic Raman scattering from residual donors is reported, and yields improved linewidths compared to PL.
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