Reid Juday

Effect of misfit dislocations on luminescence in m-plane InGaN quantum wells

A correlation has been established between the optical and structural properties of blue-light-emitting diode structures grown on free-standing m-plane GaN. A double-peak InGaN quantum well emission at room temperature has been observed with a strong inhomogeneous spatial distribution, which can be associated with the presence of dislocations originating at the InGaN layers. It is argued that the difference in peak energy positions is due to in-plane piezoelectric fields within the dislocated regions.

Strain-related optical properties of ZnO crystals due to nanoindentation on various surface orientations

Nanoindentations were performed on various crystallographic orientations of single crystal ZnO using a cono-spherical diamond tip with a radius of curvature of 260 nm. The crystal orientations were the (112¯0) a-plane, (101¯0) m-plane, and (0001) c-plane (Zn-face). The optical properties associated with nanoindentation have been investigated by cathodoluminescence. The load-displacement curves show that the c-plane is the most resistive to deformation, followed by the m-plane, and the a-plane. A large number of non-radiative defects are created directly below the indentation, regardless of the crystal orientation. Nanoindentation on the a- and m-plane crystals activates slip along the (0001) basal planes, creating a band of non-radiative defects as well as tensile strain along the basal planes. Compressive strain is observed perpendicularly to the basal planes due to an absence of easy-glide mechanisms in these directions. The nanoindentation on the c-plane crystal results in regions under tensile strain ...

Effect of Growth Temperature on the Electron-Blocking Performance of InAlN Layers in Green Emitting Diodes

InAlN layers grown lattice-matched to GaN have been used to optimize the internal quantum efficiency of InGaN quantum-well device structures emitting in the green region of the visible spectrum. The electron-blocking properties of InAlN layers significantly depend on their growth temperature. Devices with InAlN layers grown at 780 and 840 °C exhibit significant variations in the quantum well emission characteristics, with 780 °C producing the highest emission efficiency. Three- and two-dimensional growth modes are observed in the layers grown at low and high temperatures, respectively. The former should allow higher hole transport through the narrow regions of the blocking layer.

Hydrogen-related, deeply bound excitons in Mg-doped GaN films

Luminescence in the near band-edge spectral region of Mg-doped GaN films grown by metalorganic chemical vapor deposition has been studied at liquid-helium temperatures. Radiative transitions at 3.37 and 3.416 eV were observed to evolve in cathodoluminescence spectra during electron-beam irradiation at 5 kV. The intensity of the 3.37 eV peak correlates monotonically with the resistivity of the films. By annealing the films in N2 and N2/H2 atmospheres, the 3.37 and 3.416 eV transitions are shown to be related to hydrogen.

Plasticity and optical properties of GaN under highly localized nanoindentation stress fields

Nanoscale plasticity has been studied on (0001) GaN thin films, using tips with very small radius of curvature. Cross-section transmission electron microscopy images of the nanoindentations indicate that the primary slip systems are the pyramidal {11¯01}⟨112¯3⟩ and {112¯2}⟨112¯3⟩, followed by the basal {0002}⟨112¯0⟩. Incipient plasticity was observed to be initiated by metastable atomic-scale slip events that occur as the crystal conforms to the shape of the tip. Large volumetric material displacements along the {11¯01}⟨112¯3⟩ and {112¯2}⟨112¯3⟩ slip systems were observed at an average shear stress of 11 GPa. Hexagonal shaped nanoindentation impressions following the symmetry of GaN were observed, with material pile-up in the ⟨112¯0⟩ directions. Spatially resolved cathodoluminescence images were used to correlate the microstructure with the optical properties. A large number of non-radiative defects were observed directly below the indentation. Regions under tensile stress extending from the nanoindentati...

Improved Hole Transport by

Studied is the effect of indium (In) mole fraction in p-InxGa1-xN:Mg layers with 0 ≤ xIn ≤ 0.035 on hole injection and transport behaviors in InGaN/GaN multiple quantum wells (MQWs) using dual-wavelength and triple-wavelength active regions. Electro-optical characteristics of light-emitting diodes containing p-layers with different In content and with silicon doping in selected QW barriers (QWBs) are compared to evaluate hole transport in the active region. The results show that enhanced hole transport and corresponding more uniform distribution of holes across the MQW region are achieved by increasing xIn in the p-InxGa1-xN:Mg layer, possibly due to modification in energy of holes by a potential barrier between the p-InGaN and GaN QWB.