Damage Due to Nitrogen Molecular Ions of GaN Heteroepitaxial Layers Grown on Si(001) Substrates by Molecular Beam Epitaxy Assisted by Electron Cyclotron Resonance

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We have observed that the intensity of plasma emission at 391 nm from nitrogen molecular ions in nitrogen plasma is closely related to the crystalline quality and the surface morphology of GaN heteroepitaxial layers grown on Si(001). When plasma emission intensity is increased, the surface morphology is degraded, the photoluminescence (PL) intensities of two donor bound exciton (D 0 X) emissions from mixed crystal grains of wurtzite -GaN (α-GaN) and zincblende -GaN (β-GaN) and of yellow emissions are abruptly decreased, and the full-width at half maximum of the D 0 X is broadened. These reflect the influences of damage due to nitrogen molecular ions. The damage generates nonradiative centers. A small number of (001)- and (111)-oriented β-GaN crystal grains exist in the layers, together with a large number of (0001)-oriented GaN. PL efficiency from β-GaN is markedly higher than that from α-GaN, probably because the majority of the carriers accumulate in the β-GaN side at the interface between α- and β-GaN. The broad PL emissions at 3.10 and 3.29 eV with weak intensities are not changed by the damage. The peak energy position of the 3.29 eV emission almost coincides with that of D 0 X(β-GaN). The damage is not easily eliminated even by high-temperature growth at 900°C.