We observed strong band edge luminescence at 8.5–200 K from 200–880 nm thick InN films grown on 10 nm thick InN buffer layers on Si(001) and Si(111) substrates by electron cyclotron resonance-assisted molecular beam epitaxy. The InN film on the Si(001) substrate exhibited strong band edge photoluminescence (PL) emission at 1.814 eV at 8.5 K, tentatively assigned as donor to acceptor pair [DAP (α-InN)] emission from wurtzite-InN (α-InN) crystal grains, while those on Si(111) showed other stronger band edge PL emissions at 1.880, 2.081 and 2.156 eV, tentatively assigned as donor bound exciton [D0X(α-InN)] from α-InN grains, DAP (β-InN) and D0X (β-InN) emissions from zinc blende-InN (β-InN) grains, respectively.

For the first time, we observed strong band-edge photoluminescence at 1.814 eV, and two stronger emissions at 1.880 and 2.081 eV at 8.5 K from the respective 880 nm thick InN heteroepitaxial layers (heteroepilayers) with 10 nm thick InN buffer layers grown on Si(001) and Si(111) substrates by electron cyclotron resonance-assisted molecular beam epitaxy. The former was probably assigned as donor-to-acceptor pair (DAP(a-InN)) emission from wurtzite-InN (a-InN) crystal grains, the latter were assigned as donor bound exciton (D 0 X(a-InN)) emission, and D 0 X(b-InN) or DAP(b-InN) emission from zincblende-InN (b-InN) crystal grains, respectively. Substrate annealing before growth and the introduction of a buffer layer had strong influences on the crystal structure and crystalline quality of the initial InN heteroepilayers.

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 αand 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.

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