Planar m-plane GaN was grown on
(11¯00) m-plane 6H-SiC substrates using high-temperature AlN nucleation layers by
metalorganic chemical vapor deposition. Scanning electron microscopy (SEM) and atomic force microscopy (AFM)
images showed striated features on the sample surface aligned along the GaN
[11¯20] direction, which are perpendicular
to those associated with a-plane
(11¯20) GaN. The epitaxial relationship between the m-GaN and 6H-SiC was analyzed
using high-resolution x-ray diffraction (XRD). In order to reduce the defect density, epitaxial lateral overgrowth (ELO)
was carried out on an m-GaN template with mask stripes along the GaN
[11¯20] direction, which makes the lateral
growth fronts advance along the GaN c-axis. On-axis XRD rocking curves show that the full width at half maximum
(FWHM) values for the ELO samples were reduced by nearly half when compared to those of the m-plane template
without ELO. Clear atomic steps were observed in the wing regions by AFM. The absence of the striated features that
are associated with the template could be indicative of the reduction of basal stacking faults in the ELO wings. Lowtemperature
photoluminescence (PL) spectra showed an excitonic emission at 3.47eV, a basal stacking fault (BSF)-
related emission at 3.41 eV, and other defect-related emissions at 3.29 eV and 3.34 eV.
For exact notation please see manuscript
The effect of plasma-induced ion damage on the optical properties of ZnO films grown by plasma-assisted molecular
beam epitaxy on a-sapphire substrates and GaN(0001)/c-sapphire templates prepared has been studied using steady-state
and time-resolved photoluminescence. We observed that the deflecting the ions produced by the RF oxygen plasma
away from substrate results in improved excitonic emission and modification of the defect-related PL spectrum. The
intensity of the near-band-edge lines in the photoluminescence spectra from the layers grown with the ion deflection was
found to increase by factors 7 to 20 for the layers grown on GaN(0001)/c-sapphire at a plasma power of 350 W and by 3
to 4 times for ZnO grown on a-sapphire substrates at a plasma power of 265 W as compared to the controls grown
without the ion deflection. The yellow-green spectral range was dominated by different defect bands in the films grown
with and without ion deflection. The effect of RF power on peak positions of the defect band was studied for the films
grown without ion deflection. For the ZnO films grown on a-plane sapphire substrates, time-resolved photoluminescence
showed a significant increase in luminescence decay times both at RT and 89 K. However, for ZnO on GaN(0001)/csapphire
substrates, virtually no improvement in decay time was found at 89 K with only a moderate increase in decay
constant at room temperature.
Deep levels in thin GaN epilayers grown by metal-organic chemical vapor deposition on different
templates were studied by photocapacitance spectroscopy and deep-level transient spectroscopy
(DLTS) using Schottky barrier diodes. We observed the reduction of electrically and optically active
traps in GaN grown with in situ SiNx nanonetwork and SiO2 striped mask or conventional epitaxial
lateral overgrowth technique (ELO) as compared to a typical control layer on a sapphire substrate.
All samples measured by DLTS in the temperature range from 80 K to 400 K exhibited traps with
activation energies 0.55-0.58 eV and 0.21-0.28 eV. The lowest concentration of both traps was
achieved for the sample with 6 min deposition of SiNx nanonetwork, which was lower than that for
the sample prepared by conventional ELO, and much lower than that in the control. The steady-state
photocapacitance spectra of all samples taken at 80 K over the spectral range 0.75-3.50 eV
demonstrated a similar trend for all the layers. The photocapacitance spectra exhibited defect levels
with optical threshold energies of 1.2-1.3, 1.6, 2.2 and 3.1 eV. The determined concentrations of
traps were compared and the results were consistent with DLTS measurements. The layer with SiNx
nanonetwork has the lowest concentrations of optically active traps with the standard GaN control
layer being the worst in terms of trap concentrations. The consistent trend among the
photocapacitance spectroscopy and DLTS results suggests that SiNx network can effectively reduce
deep levels in GaN, which otherwise can deteriorate both optical and electrical performance of GaN-based
devices.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.