245 research outputs found
Progression of group-III sesquioxides: epitaxy, solubility and desorption
In recent years, ultra-wide bandgap semiconductors have increasingly moved into scientific
focus due to their outstanding material properties, making them promising candidates for future
applications within high-power electronics or solar-blind photo detectors. The
group-III-sesquioxides can appear in various polymorphs, which influences, for instance, the
energy of the optical bandgap. In gallium oxide, the optical bandgap ranges between 4.6 and
5.3 eV depending on the polymorph. For each polymorph it can be increased or decreased by
alloying with aluminum oxide (8.8 eV) or indium oxide (2.7–3.75 eV), respectively, enabling
bandgap engineering and thus leading to an extended application field. For this purpose, an
overview of miscibility limits, the variation of bandgap and lattice constants as a function of the
alloy composition are reviewed for the rhombohedral, monoclinic, orthorhombic and cubic
polymorph. Further, the effect of formation and desorption of volatile suboxides on growth rates
is described with respect to chemical trends of the discussed ternary materials
Electronic properties of E3 electron trap in n-type ZnO
International audienceDeep level transient spectroscopy measurements were per- formed on three non-intentionally doped n-type ZnO samples grown by different techniques in order to investigate the electronic properties of E3 electron trap. The ionization energy and the capture cross-section are found respectively at 0.275 eV from the conduction band and 2.3×10^−16 cm2 with no electric field dependence. This center is present irrespective of the synthesis method. In view of its physical properties and recent works published in the literature, its physical origin is discussed. Based mainly on its insensibility to the macroscopic electric field, the best candidates turn out to be dual defects with opposite charges on adjacent sites, like the dual vacancy VO -VZn
Wavelength-selective ultraviolet (Mg,Zn)O photodiodes: Tuning of parallel composition gradients with oxygen pressure
We report on ultraviolet photodiodes with integrated optical filter based on the wurtzite (Mg,Zn)O
thin films. Tuning of the bandgap of filter and active layers was realized by employing a
continuous composition spread approach relying on the ablation of a single segmented target in
pulsed-laser deposition. Filter and active layers of the device were deposited on opposite sides of a
sapphire substrate with nearly parallel compositional gradients. Ensure that for each sample position
the bandgap of the filter layer blocking the high energy radiation is higher than that of the
active layer. Different oxygen pressures during the two depositions runs. The absorption edge is
tuned over 360 meV and the spectral bandwidth of photodiodes is typically 100 meV and as low as
50 meV
Mechanical Stress Stability of Flexible Amorphous Zinc Tin Oxide Thin-Film Transistors
Due to their low-temperature processing capability and ionic bonding configuration,
amorphous oxide semiconductors (AOS) are well suited for applications within future
mechanically flexible electronics. Over the past couple of years, amorphous zinc tin oxide
(ZTO) has been proposed as indiumand gallium-free and thus more sustainable alternative
to the widely deployed indium gallium zinc oxide (IGZO). The present study specifically
focuses on the strain-dependence of elastic and electrical properties of amorphous zinc tin
oxide thin-films sputtered at room temperature. Corresponding MESFETs have been
compared regarding their operation stability under mechanical bending for radii ranging
from 5 to 2 mm. Force-spectroscopic measurements yield a plastic deformation of ZTO as
soon as the bending-induced strain exceeds 0.83%. However, the electrical properties of
ZTO determined by Hall effect measurements at room temperature are demonstrated to
be unaffected by residual compressive and tensile strain up to 1.24 %. Even for the
maximum investigated tensile strain of 1.26 %, the MESFETs exhibit a reasonably
consistent performance in terms of current on/off ratios between six and seven orders
of magnitude, a subthreshold swing around 350 mV/dec and a field-effect mobility as high
as 7.5 cm2V−1s−1. Upon gradually subjecting the transistors to higher tensile strain, the
channel conductivity steadily improves and consequently, the field-effect mobility
increases by nearly 80% while bending the devices around a radius of 2 mm. Further,
a reversible threshold voltage shift of about −150 mV with increasing strain is observable.
Overall, amorphous ZTO provides reasonably stable electrical properties and device
performance for bending-induced tensile strain up to at least 1.26% and thus
represent a promising material of choice considering novel bendable and transparent
electronics
Visible-blind and solar-blind ultraviolet photodiodes based on (InxGa1-x)2O3
UV and deep-UV selective photodiodes from visible-blind to solar-blind were realized based on a
Si-doped (InxGa1–x)2O3 thin film with a monotonic lateral variation of 0.0035<x<0.83. Such
layer was deposited by employing a continuous composition spread approach relying on the ablation
of a single segmented target in pulsed-laser deposition. The photo response signal is provided
from a metal-semiconductor-metal structure upon backside illumination. The absorption onset was
tuned from 4.83 to 3.22 eV for increasing x. Higher responsivities were observed for photodiodes
fabricated from indium-rich part of the sample, for which an internal gain mechanism could be
identified. VC 2016 AIP Publishing LLC
Nickel oxide-based heterostructures with large band offsets
We present research results on the electronic transport in heterostructures
based on p-type nickel oxide (NiO) with the n-type oxide semiconductors zinc
oxide (ZnO) and cadmium oxide (CdO). NiO is a desirable candidate for
application in (opto-)electronic devices. However, because of its small
electron affinity, heterojunctions with most n-type oxide semiconductors
exhibit conduction and valence band offsets at the heterointerface in excess of
1 eV. ZnO/NiO junctions exhibit a so called type-II band alignment, making
electron-hole recombination the only process by which a current can vertically
flow through the structure. These heterojunctions are nevertheless shown to be
of practical use in efficient optoelectronic devices, as exemplified here by
our UV-converting transparent solar cells. These devices, although exhibiting
high conversion efficiencies, suffer from two light-activated recombination
channels connected to the type-II interface, one of which we identify and
analyse in more detail here. Furthermore, CdO/NiO contacts were studied - a
heterostructure with even larger band offsets such that a type-III band
alignment is achieved. This situation theoretically enables the development of
a 2-dimensional electronic system consisting of topologically protected states.
We present experiments demonstrating that the CdO/NiO heterostructure indeed
hosts a conductive layer absent in both materials when studied separately
Highly rectifying p-ZnCo2O4/n-ZnO heterojunction diodes
We present oxide bipolar heterojunction diodes consisting of p-type ZnCo2O4 and n-type ZnO
fabricated by pulsed-laser deposition. Hole conduction of ZnCo2O4 (ZCO) was evaluated by Hall
and Seebeck effect as well as scanning capacitance spectroscopy. Both, ZCO/ZnO and ZnO/ZCO
type heterostructures, showed diode characteristics. For amorphous ZCO deposited at room
temperature on epitaxial ZnO/Al2O3 thin films, we achieved current rectification ratios up to
2x1010, ideality factors around 2, and long-term stability
Low frequency noise of ZnO based metal-semiconductor field-effect transistors
The low frequency noise of metal-semiconductor field-effect transistors (MESFETs) based on
ZnO:Mg thin films grown by pulsed laser deposition on a-plane sapphire was investigated. In order
to distinguish between noise generation in the bulk channel material, at the semiconductor surface,
and at the gate/channel interface, ohmic ZnO channels without gate were investigated in detail,
especially concerning the dependency of the noise on geometrical variations. The experiments
suggest that the dominating 1/f noise in the frequency range below 1 kHz is generated within the
bulk channel material, both for bare ZnO channels and MESFETs
Method of choice for fabrication of high-quality ZnO-based Schottky diodes
We present a comprehensive comparison of electrical properties of differently fabricated high
quality Schottky contacts on ZnO thin films grown by pulsed laser deposition. Thermally
evaporated Pd/ZnO Schottky contacts exhibit ideality factors as low as 1.06 due to their high
lateral homogeneity. The effective Richardson constant determined using these homogeneous
contacts is (7.7±4.8)A cm−2 K−2 close to the theoretical value of 32 A cm−2 K−2. However, their
rectification ratio is at most five orders of magnitude due to their comparably small barrier height
(≈0.7eV). The largest effective barrier height (1.11 eV) and rectification ratio(7×1010) was
obtained for reactively sputtered PdOx/ZnO Schottky contacts. Eclipse pulsed laser deposited
IrOx/ZnO Schottky contacts were found to combine very good lateral homogeneity (n≈1.1), with
a reasonably large barrier height (0.96 eV) and large rectification ratio (≈9 orders of magnitude).
Our results for differently fabricated Schottky contacts suggest that the barrier formation is highly
dependent on the presence of oxygen vacancies close to the interface and the different
compensation mechanisms involved
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