3 research outputs found
Carrier Transport at Metal/Amorphous Hafnium–Indium–Zinc Oxide Interfaces
In
this paper, the carrier transport mechanism at the metal/amorphous
hafnium–indium–zinc oxide (a-HIZO) interface was investigated.
The contact properties were found to be predominantly affected by
the degree of interfacial reaction between the metals and a-HIZO;
that is, a higher tendency to form metal oxide phases leads to excellent
Ohmic contact via tunneling, which is associated with the generated
donor-like oxygen vacancies. In this case, the Schottky–Mott
theory is not applicable. Meanwhile, metals that do not form interfacial
metal oxide, such as Pd, follow the Schottky–Mott theory, which
results in rectifying Schottky behavior. The Schottky characteristics
of the Pd contact to a-HIZO can be explained in terms of the barrier
inhomogeneity model, which yields a mean barrier height of 1.40 eV
and a standard deviation of 0.14 eV. The work function of a-HIZO could
therefore be estimated as 3.7 eV, which is in good agreement with
the ultraviolet photoelectron spectroscopy (3.68 eV). Our findings
will be useful for establishing a strategy to form Ohmic or Schottky
contacts to a-HIZO films, which will be essential for fabricating
reliable high-performance electronic devices
Fabrication and Characteristics of GaN-Based Light-Emitting Diodes with a Reduced Graphene Oxide Current-Spreading Layer
A reduced graphene oxide (GO) layer
was produced on undoped and n-type GaN, and its effect on the current-
and heat-spreading properties of GaN-based light-emitting diodes (LEDs)
was studied. The reduced GO inserted between metal electrode and GaN
semiconductor acted as a conducting layer and enhanced lateral current
flow in the device. Especially, introduction of the reduced GO layer
on the n-type GaN improved the electrical performance of the device,
relative to that of conventional LEDs, due to a decrease in the series
resistance of the device. The enhanced current-spreading was further
of benefit, giving the device a higher light output power and a lower
junction temperature at high injection currents. These results therefore
indicate that reduced GO can be a suitable current and heat-spreading
layer for GaN-based LEDs
Recrystallization of Highly-Mismatched Be<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>O Alloys: Formation of a Degenerate Interface
We investigate the effect of thermally
induced phase transformations on a metastable oxide alloy film, a
multiphase Be<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>O (BZO), grown on Al<sub>2</sub>O<sub>3</sub>(0001)
substrate for annealing temperatures in the range of 600–950
°C. A pronounced structural transition is shown together with
strain relaxation and atomic redistribution in the annealed films.
Increasing annealing temperature initiates out-diffusion and segregation
of Be and subsequent nucleation of nanoparticles at the surface, corresponding
to a monotonic decrease in the lattice phonon energies and band gap
energy of the films. Infrared reflectance simulations identify a highly
conductive ZnO interface layer (thicknesses in the range of ≈10–29
nm for annealing temperatures ≥800 °C). The highly degenerate
interface layers with temperature-independent carrier concentration
and mobility significantly influence the electronic and optical properties
of the BZO films. A parallel conduction model is employed to determine
the carrier concentration and conductivity of the bulk and interface
regions. The density-of-states-averaged effective mass of the conduction
electrons for the interfaces is calculated to be in the range of 0.31<i>m</i><sub>0</sub> and 0.67<i>m</i><sub>0</sub>. A
conductivity as high as 1.4 × 10<sup>3</sup> S·cm<sup>–1</sup> is attained, corresponding to the carrier concentration <i>n</i><sub>Int</sub> = 2.16 × 10<sup>20</sup> cm<sup>–3</sup> at the interface layers, and comparable to the highest conductivities
achieved in highly doped ZnO. The origin of such a nanoscale degenerate
interface layer is attributed to the counter-diffusion of Be and Zn,
rendering a high accumulation of Zn interstitials and a giant reduction
of charge-compensating defects. These observations provide a broad
understanding of the thermodynamics and phase transformations in Be<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>O
alloys for the application of highly conductive and transparent oxide-based
devices and fabrication of their alloy nanostructures