Visible emissions near 2.2 eV from InN films grown on Si (111) and sapphire (0001) substrates by electron cyclotron resonance plasma-assisted molecular-beam epitaxy

摘要

We have observed visible PL emissions at around 2.2 eV from limited areas with sizes of several tens μm distributed at densities of 2-3 mm~(-2) at 8.5-200 K in 400 nm-thick wurtzite-InN (α-InN) single crystalline films grown on Si (111) and sapphire (0001) substrates by electron cyclotron resonance-assisted molecular beam-epitaxy (ECR-MBE). The α-InN film grew on sapphire, exhibited very smooth surface morphology and took an ideal N-polarity surface as well as the case of α-GaN film grown by ECR-MBE. Moreover, it had an ideal six-fold symmetry α-InN crystal structure without rotation domains and with the sharp FWHM of 0.4° for the X-ray rocking curve of (0002)α-InN CuK_(α1) diffraction. From absorption spectros-copy, the fundamental bandgap energy of α-InN was estimated to be 1.5 eV at 6 K, which was larger than the bandgap energy of α-InN estimated by Wu et al. [Appl. Phys. Lett. 80, 3967 (2002)], but seemed to coincide well with those estimated from the visible PL emissions based on Burstein-Moss shift.