Cathodoluminescence imaging and spectroscopy study of he thermal quenching of luminescence in AlN/Si

Full Text:Spatially and spectrally resolved cathodoluminescence (CL) measurements were performed for high-quality thin AlN films grown on Si(111). CL spectra for a sample temperature of 49 K exhibited a sharp peak at 5.960 eV, corresponding to the near-band-edge excitonic emission of AIN. Additional broader peaks related to deep-level oxygen impurities were seen at 3.040 eV and 3.430 eV. Excitation-dependent measurements were performed by varying the electron beam current from 30 pA to 10 nA revealing that the impurity-related emissions saturate at low-beam currents, while the near band-edge emission increases nearly linearly with beam current. Monochromatic CL imaging of the near-band edge emission exhibited a spotty emission pattern where defect-induced nonradiative recombination results in large spatial variations in the luminescence efficiency. Scanning electron microscopy revealed the presence of hexagonal-shaped V-defects on the surface. Cross-sectional transmission electron microscopy revealed the single crystal nature of the AIN film with threading dislocations propagating from the Si substrate interface to the AIN surface. Local CL spectroscopy was performed to assess temperature-dependent variations in the luminescence efficiency for regions of high- and low-defect densities. Temperature-dependent CL further revealed spatial variations in the activation energy, Ea, for the thermal quenching of the near-band edge luminescence. For regions of high- and low-luminescence efficiencies (i.e., bright and dark spots in the CL images), thermal activation energies of 29meV and 19meV, respectively, were measured. We propose a model that attempts to explain the local reduction in Ea with a corresponding local increase in the defect/dislocation density