Cathodoluminescence (CL) spectroscopy is performed on conducting 1- and 2-dimensional gratings of metals, semimetals
and semi-conductors of varying periods from 0.5 to 20 microns for a range of grating amplitudes from 0.1 to 4.6
microns. The overall emission spectrum consists of a 400 nm wide band centered at ~600 nm which depends little on the
grating period, grating amplitude, material, e-beam energy, or temperature. CL intensity increases and the center
wavelength blue shifts with increasing excitation beam current. For the larger amplitude 1-dimensional gratings fringes
appear in the emission spectrum, which is due to interference between emission from grating bars and grooves. Surface
corrugation is necessary to the emission as none is observed from smooth surfaces. The same band appears weakly in CL
of a Cu sample with random ~1 micron surface roughness, but this emission is strongly reduced when the same sample is
highly polished. The CL signal appears even when the ~10 nm electron-beam is at least 2 mm away from the grating
edge, suggesting electron-beam induced currents are important to the emission, whose precise mechanism remains
unclear. Previously suggested mechanisms--electron collision with image charge, transition radiation, surface
contamination, and inverse photoemission effect--all fail to explain the observed spectrum and its lack of beam-energy
dependence.
Cathodo-luminescence spectroscopy is performed on silver and gold lamellar gratings of period 7.5 or 20
microns for a range of grating amplitudes from 0.1 to 4.6 microns. The overall emission spectrum consists of a 400 nm
wide band centered at ~600 nm which depends little on the grating amplitude, metal, or e-beam energy. For the larger
grating amplitudes the emission spectrum is periodically modulated as a function of wavelength. Both the strength of the
emission envelop and the depth and phase of the modulation depend on grating orientation with respect to the light
collection axis, the distance of the excitation spot from the grating, and the distance between the grating and the
collection optics. The modulation can be explained as interference of surface emission from grating bars and grooves.
The origin of the emission remains unclear, as mechanisms of electron collision with image charge, transition radiation,
surface contamination, and inverse photo-electron effect all fail to explain the observed spectrum. This work is relevant
to the interpretation of cathodoluminescence studies of surface plasmons on structured metals for nano-photonic
applications.
Electrical properties of n-ZnO/n-GaN isotype heterostructures prepared by rf-sputtering of ZnO films on GaN layers
which in turn grown by metal-organic vapour phase epitaxy are discussed. Current-voltage (I-V) characteristics of the n-
ZnO/n-GaN diodes exhibited highly rectifying characteristics with forward and reverse currents being ~1.43x10-2 A/cm2
and ~2.4x10-4 A/cm2, respectively, at ±5 V. From the Arrhenius plot built representing the temperature dependent
current-voltage characteristics (I-V-T) an activation energy 0.125 eV was derived for the reverse bias leakage current
path, and 0.62 eV for the band offset from forward bias measurements. From electron-beam induced current
measurements and depending on excitation conditions the minority carrier diffusion length in ZnO was estimated in the
range 0.125-0.175 &mgr;m. The temperature dependent EBIC measurements yielded an activation energy of 0.462 ± 0.073
V.
Effects of electron irradiation on GaN and AlxGa1-xN doped with acceptor-forming species (Mg, C, Fe, and Mn) were
studied by cathodoluminescence and electron beam induced current techniques. Low energy electron beam irradiation was shown to induce a systematic decay of the cathodoluminescence intensity, which is accompanied by increased electronic carrier diffusion length, indicating the increase of carrier lifetime. Temperature-dependent
cathodoluminescence measurements allowed to estimate the activation energy for irradiation-induced effects, which was found to be comparable to the ionization energy of the dominant acceptor species. These observations are consistent with trapping of non- equilibrium electrons on deep, non-ionized acceptor levels. In (Al) GaN:Mg and GaN:C electrons are trapped by the ground state of the neutral acceptor atom, while in TM-doped compounds, electron irradiation induced processes appear to involve a more energetically accessible excited states of the acceptors.
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