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Ferroelectricity in hafnium zirconium oxide (Hf1 − xZrxO2) and the factors that impact it have been a popular research topic since its discovery in 2011. Although the general trends are known, the interactions between fabrication parameters and their effect on the ferroelectricity of Hf1 − xZrxO2 require further investigation. In this paper, we present a statistical study and a model that relates Zr concentration (x), film thickness (tf), and annealing temperature (Ta) with the remanent polarization (Pr) in tungsten (W)-capped Hf1 − xZrxO2. This work involved the fabrication and characterization of 36 samples containing multiple sets of metal-ferroelectric-metal capacitors while varying x (0.26, 0.48, and 0.57), tf (10 and 19 nm), and Ta (300, 400, 500, and 600 ° C). In addition to the well-understood effects of x and Ta on the ferroelectricity of Hf1 − xZrxO2, the statistical analysis showed that thicker Hf1 − xZrxO2 films or films with higher x require lower Ta to crystallize and demonstrated that there is no statistical difference between samples annealed to 500 and 600 ° C, thus suggesting that most films fully crystallize with Ta ∼ 500 ° C for 60 s. Our model explains 95% of the variability in the Pr data for the films fabricated, presents the estimates of the phase composition of the film, and provides a starting point for selecting fabrication parameters when a specific Pr is desired. [ABSTRACT FROM AUTHOR]

Ir is a common impurity in the edge-defined film-fed growth method used to produce high-power Ga2O3 device structures and growth substrates; yet, the effects of this deep level defect on carrier transport and recombination, particularly at high device processing and operating temperatures and at metal interfaces, have yet to be explored. The optical and electronic nature of Ir in Ga2O3 and at Ir/ Ga2O3 interfaces change on a near-nanometer to micrometer scale after nitrogen rapid thermal annealing; the understanding and control of which could lower defect-assisted tunneling, improve diode rectification, and preserve critical electric field strength. Depth-resolved cathodoluminescence spectroscopy, interface electronic current, and capacitance–voltage measurements reveal how this dominant impurity in bulk, edge-fed crystal growth diffuses, evolves with temperature, and impacts defect formation and Schottky barrier formation. [ABSTRACT FROM AUTHOR]

Thin (40–150 nm), highly doped n+ (1019–1020 cm−3) Ga2O3 layers deposited using pulsed laser deposition (PLD) were incorporated into Ti/Au ohmic contacts on (001) and (010) β-Ga2O3 substrates with carrier concentrations between 2.5 and 5.1 × 1018 cm−3. Specific contact resistivity values were calculated for contact structures both without and with a PLD layer having different thicknesses up to 150 nm. With the exception of a 40 nm PLD layer on the (001) substrate, the specific contact resistivity values decreased with increasing PLD layer thickness: up to 8× on (001) Ga2O3 and up to 16× on (010) Ga2O3 compared with samples without a PLD layer. The lowest average specific contact resistivities were achieved with 150 nm PLD layers: 3.48 × 10−5 Ω cm2 on (001) Ga2O3 and 4.79 × 10−5 Ω cm2 on (010) Ga2O3. Cross-sectional transmission electron microscopy images revealed differences in the microstructure and morphology of the PLD layers on the different substrate orientations. This study describes a low-temperature process that could be used to reduce the contact resistance in Ga2O3 devices. [ABSTRACT FROM AUTHOR]

Thermally stimulated techniques—thermally stimulated current (TSC) spectroscopy and thermally stimulated depolarization current (TSDC) spectroscopy—were used to comparatively study the electrical properties and deep level defects in β-Ga2O3 pulsed laser deposited thin films and Czochralski-grown bulk crystals. It was found that the samples are highly resistive and each sample may have different dark current activation energy. Deep level defects revealed by the thermally stimulated techniques vary from sample to sample. In addition to the common traps E1 (∼0.56 eV), E2 (∼0.84 eV), and E3 (∼0.99 eV), reported in the literature and revealed by DLTS studies of Ga2O3 bulk crystals, that were also found in our samples by the thermally stimulated techniques, a trap at ∼110 meV and several other traps are revealed specifically by TSDC between 105 and 225 K. [ABSTRACT FROM AUTHOR]

We demonstrated 500 °C operation of field-effect transistors made using ultra-wide bandgap semiconductor β-Ga2O3. Metal–semiconductor field-effect transistors were fabricated using epitaxial conductive films grown on an insulating β-Ga2O3 substrate, TiW refractory metal gates, and Si-implanted source/drain contacts. Devices were characterized in DC mode at different temperatures up to 500 °C in vacuum. These variable-temperature measurements showed a reduction in gate modulation of the drain current due to an increase in gate leakage across the gate/semiconductor Schottky barrier. Devices exhibited a reduction in transconductance with increasing temperature; despite this, drain current increased with temperature due to a reduction in threshold voltage caused by the de-trapping of electrons from deep-level traps. Devices also showed negligible change in semiconductor epitaxy and source/drain contacts, hence demonstrated recovery to their room-temperature electrical properties after the devices were tested intermittently at different high temperatures in vacuum. The mechanism of gate leakage was also explored, which implicated the presence of different conduction mechanisms at different temperatures and gate electric fields. [ABSTRACT FROM AUTHOR]

A wafer-level thin-film encapsulation process has been demonstrated to package radio-frequency (RF) microelectromechanical systems (MEMS) switches in this paper. Individual shunt capacitive switches were packaged in a ~ 1 nL inorganic enclosure with process temperatures not exceeding 300 [degrees]C. A shell covering the switch consisted of 10 nm of sputtered alumina and 1.67 [micro]m of sputtered silicon nitride dielectric film. The switch and dielectric shell were simultaneously wet-released through access channels in the shell. Following release, access channels were sealed with 10 nm of sputtered alumina and 2-4 [micro]m of either plasma-enhanced chemical vapor deposited silicon dioxide or silicon nitride. Electromagnetic simulation and RF test results before and after sealing show minimal RF degradation of switch performance. Before sealing, the insertion loss and isolation at 10 GHz averaged 0.12 and 10.7 dB, respectively. After sealing, the same devices had an average insertion loss and isolation of 0.12 and 10.1 dB, respectively. Complete characterization of the package atmosphere was not completed due to challenges in assessing nanoliter-scale volumes. [1724] Index Terms--Dielectric films, encapsulation, microelectromechanical devices, switches.

There is limited work on understanding Schottky barrier (SB) field-effect transistor (FET) behavior, and subsequent evolution of sensitivity metrics under wet detection conditions for neurotransmitter sensing applications. In this work, we report low-power deep subthreshold (DST) characteristics of SB InGaZnO4 (IGZO) thin film transistors (TFTs) and implement this regime for sensitive and selective ex vivo detection of Dopamine against Adenosine Triphosphate (ATP). Device regeneration was performed under liquid solution environment over 34 days and sensor response was observed to drift less than two orders of magnitude. Nevertheless, the quantified trends due to buffer solution baseline versus target conjugation were virtually preserved across the TFTs. Widely improved detection metrics were extracted from the detection tests, namely the limit of detection (LoD) in the 100fM-100pM range, a binding affinity ($k_{D}$) between $2.03\times 10^{-11}$ - $3.02\times 10^{-9}\text{M}$ limits, and high sensitivity around 31-42mV/decade of target concentration. Although a steady drift with clear, repeatable differences between the device state at the start and end of the 34-day period were obtained, these devices were functional even after the regeneration test period. Such results can be used to estimate the regenerative lifetime of TFT biosensors under aptamer-immobilized solution environment detection conditions. [ABSTRACT FROM AUTHOR]

Gallium Oxide has undergone rapid technological maturation over the last decade, pushing it to the forefront of ultra-wide band gap semiconductor technologies. Maximizing the potential for a new semiconductor system requires a concerted effort by the community to address technical barriers which limit performance. Due to the favorable intrinsic material properties of gallium oxide, namely, critical field strength, widely tunable conductivity, mobility, and melt-based bulk growth, the major targeted application space is power electronics where high performance is expected at low cost. This Roadmap presents the current state-of-the-art and future challenges in 15 different topics identified by a large number of people active within the gallium oxide research community. Addressing these challenges will enhance the state-of-the-art device performance and allow us to design efficient, high-power, commercially scalable microelectronic systems using the newest semiconductor platform. [ABSTRACT FROM AUTHOR]

Conductive homoepitaxial Si-doped β-Ga2O3 films were fabricated by pulsed laser deposition with an as-deposited 2323 S cm−1 conductivity (resistivity = 4.3 × 10−4 Ω-cm, carrier concentration = 2.24 × 1020 cm−3, mobility = 64.5 cm2 V−1 s−1, and electrical activation efficiency = 77%). High quality homoepitaxial films deposited on commercial (010) Fe-compensated β-Ga2O substrates were determined by high-resolution transmission electron microscopy and x-ray diffraction. The β-Ga2O3 films have ∼70% transparency from 3.7 eV (335 nm) to 0.56 eV (2214 nm). The combination of high conductivity and transparency offers promise for numerous ultrawide bandgap electronics and optoelectronic applications. [ABSTRACT FROM AUTHOR]

The gallium vacancy is one of the dominant native point defects in β-Ga2O3, one that, together with its complexes, can have a major effect on free carrier densities and transport in this wide bandgap semiconductor. We used a combination of depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to identify the optical and energy-level properties of these defects as well as how their defect densities and spatial distributions vary with neutron irradiation and temperature-dependent-forming gas anneals. These studies reveal optical signatures that align closely with theoretical energy-level predictions. Likewise, our optical techniques reveal variations in these defect densities that are consistent with hydrogen passivation of gallium vacancies as a function of temperature and depth from the free Ga2O3 surface. These techniques can help guide the understanding and control of dominant native point defects in Ga2O3. [ABSTRACT FROM AUTHOR]

Experimental results pertaining to plasmon resonance tunneling through a highly conductive zinc oxide (ZnO) layer with subwavelength hole-arrays is investigated in the mid-infrared regime. Gallium-doped ZnO layers are pulsed-laser deposited on a silicon wafer. The ZnO has metallic optical properties with a bulk plasma frequency of 214 THz, which is equivalent to a free space wavelength of 1.4 μm. Hole arrays with different periods and hole shapes are fabricated via a standard photolithography process. Resonant mode tunneling characteristics are experimentally studied for different incident angles and compared with surface plasmon theoretical calculations and finite-difference time-domain simulations. Transmission peaks, higher than the baseline predicted by diffraction theory, are observed in each of the samples at wavelengths that correspond to the excitation of surface plasmon modes. [ABSTRACT FROM AUTHOR]

The path to achieving integrated RF and power conversion circuitry using the β-Ga2O3 material system is described with regard to the materials high Johnson's RF figure of merit. Recent results, including large signal data at VD = 50 V, are provided, showing progress in achieving high-voltage RF operation. Additionally, progress in achieving high-gain devices through gate length scaling is also benchmarked by a record RF power device with a gate length of 0.5 μm achieving a 2.1 GHz μm f T − L G product. These results are compared with state-of-the-art RF devices, and the expectations for β-Ga2O3 at this point in its maturity throughout this Letter with future milestones laid out to measure progress. The conclusion includes near- and long-term projections for β-Ga2O3 devices for RF based on the results and projected milestones presented. [ABSTRACT FROM AUTHOR]

InGaZnO (IGZO) is an excellent semiconductor material for thin-film transistors (TFTs) used in direct-current and radio-frequency (RF) switching applications, especially since it can be grown at low temperatures on a wide variety of substrates. IGZO thin films with a composition of InGaZnO4 have been deposited and used as channel layers in TFTs for many applications to date; however, IGZO compositions can also be easily changed to vary their properties. These different compositions of IGZO may have different defect properties. In this study, we report the growth of IGZO with composition of In2O3:Ga2O3:5ZnO (In2Ga2Zn5O11) by pulsed laser deposition (PLD) and its electronic defects studied by thermally stimulated current (TSC) spectroscopy. It was found that the as-grown sample has a DC activation energy of 0.62 eV, and four major traps with activation energies between ∼0.16–0.50 eV and one at ∼0.90 eV. Electrical properties and the deep traps of PLD-grown IGZO thin film were found to be varied by post-processing conditions such as thermal history and measurement conditions such as the bias and light exposure applied to the samples. The instabilities induced by these conditions can be explained by structural and stoichiometric features—the ZnO4 tetrahedra and GaO6 octahedra in the structure may become distorted, caused by oxidation or reduction, so that the different defect states could be changed and/or lattice energy variations from the distortion can be observed. This work demonstrates that current-based trap emission, such as that associated with TSC, can effectively reveal electronic defects in highly-resistive semiconductor materials, especially those that are not amenable to capacitance-based techniques, such as deep-level transient spectroscopy, and provide an effective manner to study the trap instabilities in IGZO. [ABSTRACT FROM AUTHOR]

We used depth-resolved cathodoluminescence spectroscopy (DRCLS), absorption spectroscopy, and temperature-dependent Hall effect (TDH) measurements to study the effects of fluence dependent neutron irradiations on deep level defects and the associated changes of electrical properties of β-Ga2O3 grown by low pressure chemical vapor deposition and pulsed laser deposition. DRCLS enabled us to monitor systematic increases of three deep level defects after neutron irradiation which correlated with TDH measurements of significant free carrier removal and mobility decrease. The correlations between defect profiles and electrical property changes vs. irradiation dose link these dominant electrically active native point defects in Ga2O3 with their contributions to free carrier mobility, carrier density, and donor/acceptor depth profiles, further revealing their donor/acceptor electrical behavior and physical nature, consistent with the formation of compensating defects. After irradiation, temperature-dependent forming gas (FG) anneals were performed to reverse the radiation-induced damage and carrier removal. The evolution of defect concentrations with increasing neutron dose and their depth-resolved distributions with FG anneal temperature reveal an interplay between specific defects to control electronic properties. [ABSTRACT FROM AUTHOR]

DC, small, and large signal results are shown under continuous wave and pulsed conditions for a $\beta $ -Ga2O3 metal-oxide-semiconductor field-effect transistor operating at 1 and 2 GHz. The device has a maximum transducer gain, maximum output power, and peak power added efficiency of 13 dB (15 dB), 715 mW/mm (487 mW/mm), and 23.4% (21.2%), respectively at 1 GHz (2 GHz). We observe the continuous wave output power is limited to 213 mW/mm by drain dispersion likely from surface or interface traps in the gate-drain region as indicated by pulsed IV measurements. High parasitic resistances, as indicated by high knee voltages, also limit the power performance under continuous and pulsed large signal conditions. [ABSTRACT FROM AUTHOR]

We study the electrical and optical properties of degenerate ZnGa2O4 films grown by metalorganic chemical vapor deposition (MOCVD) on sapphire and semi-insulating films grown by pulsed laser deposition (PLD) on fused silica. After a forming-gas anneal at 700 °C, the MOCVD film is highly conducting, with a room-temperature carrier concentration of 2 × 1020 cm−3, a mobility of 20 cm2/V s, and direct bandgap absorptions at 3.65 eV and 4.60 eV. Under the same annealing conditions, the PLD film is semi-insulating, with a direct bandgap absorption at 5.25 eV. The phonon structure, important for electrical and thermal conduction as well as superconductivity and other quantum phenomena, is very complicated due to the large number of atoms (and, thus, phonon branches) in the unit cell. However, we show that the phonon contributions to electron mobility (μph) can be directly measured by quantum-based magnetoconductivity over the temperature span T = 10–200 K. From an approximate analytical formula, μph = function (Tph, T), we calculate an effective phonon energy kTph(T) that takes account of all phonon contributions at temperature T. For T = 10–200 K, the value of kTph ranges from about 10 to 90 meV, consistent with the energy range of the ZnGa2O4 phonon density of states (at 0 K) calculated by density functional theory. The total measured mobility can then be modeled by μtot−1 = μii−1 + μph−1, where μii is the mobility due to ionized-impurity scattering. With a high bandgap, controllable conductivity, high breakdown voltage, and bulk-growth capability, ZnGa2O4 offers opportunities for high-power electronics and UV detectors. [ABSTRACT FROM AUTHOR]

β-Ga2O3 thin-channel MOSFETs were evaluated using both dc and pulsed I – V measurements. The reported pulsed I – V technique was used to study self-heating effects in the MOSFET channel. The device was analyzed over a large temperature range of 23 °C–200 °C. A relationship between dissipated power and channel temperature was established, and it was found that the MOSFET channel was heating up to 208 °C when dissipating 2.5 W/mm of power. The thermal resistance of the channel was found to be 73 °C-mm/W. The results are supported with the experimental Raman nanothermography and thermal simulations and are in reasonable agreement with pulsed I – V findings. The high thermal resistance underpins the importance of optimizing thermal management in future Ga2O3 devices. [ABSTRACT FROM AUTHOR]

A ZnO thin film transistor (TFT), with barium strontium titanate (BST) as a gate oxide, has been fabricated and characterized. The ZnO and the BST layers were deposited using pulsed laser deposition. The I-V characteristics were measured, and an upward shift in the drain current was observed when the voltage sweeping was repeated. The reasons for this shift were investigated and it was found that the shift could be attributed to the combination effect of the reduction in the built-in potential of the grain boundaries, the population and depopulation of trap centers in the channel, and the existence of mobile charges in the gate oxide layer. [ABSTRACT FROM AUTHOR]

Carrier concentration control by impurity dopants in epitaxial Ga2O3 thin films is progressing to deliver high mobility films for device structures. Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on (010) β-Ga2O3 substrates from Ga2O3 targets with 0.01–1 wt. % SiO2 yielding films with an electron mobility range consistent with other vapor growth techniques. Single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction was observed, with a high Si dopant level causing film tensile strain as indicated by both techniques. The influence of oxygen on conductivity using different O2 pressures during deposition and O2/Ar mixtures with a fixed working pressure of 1.33 Pa was determined. With this optimized deposition pressure and atmosphere condition, a carrier concentration and mobility range of 3.25 × 1019 cm−3–1.75 × 1020 cm−3 and 20 cm2/V s–27 cm2/V s was achieved in films from Ga2O3-0.025 wt. % SiO2 and Ga2O3-1 wt. % SiO2 targets, respectively. A highest conductivity of 798 S cm−1 was achieved in films deposited at 550 °C–590 °C with targets of 0.05–1 wt. % SiO2. The electrically active and chemical Si content in films deposited at 550 °C was found to exceed the expected Si ablation target composition in all cases except the highest 1 wt. % SiO2 target attributed to imprecise target manufacturer compositional control at low SiO2 doping levels. Diminished electrical and structural quality films resulted from all targets at a 450 °C deposition temperature. [ABSTRACT FROM AUTHOR]

We report enhancement-mode \beta -Ga2O3 (BGO) MOSFETs on a Si-doped homoepitaxial channel grown by molecular beam epitaxy. A gate recess process is used to partially remove the epitaxial channel under the 1- \mu \text{m} gated region to fully deplete at {V}_{\textsf {GS}}= 0 V. BGO MOSFETs achieve drain current density near 40 mA/mm and I \mathrm{\scriptscriptstyle ON}/I \mathrm{\scriptscriptstyle OFF} ratio ~109 which is the highest reported for homoepitaxial normally-off BGO transistors. At {V}\textsf {GS}= \textsf {0} V, a breakdown voltage of 198 and 505 V is achieved with the source–drain spacing of 3 and 8~\mu \textm , respectively. The power switching figure of merits for dc conduction and dynamic switch losses meet or exceed the theoretical silicon limit and previously reported depletion-mode BGO transistors. [ABSTRACT FROM AUTHOR]

Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) β-Ga2O2 and (0001) Al2O3 substrates. Films deposited onβ-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystallineβ-Ga2O3 with a preferred (201) orientation. An average conductivity of 732 S cm-1 with a mobility of 26.5 cm2 V-1 s-1 and a carrier concentration of 1.74×1020 cm-3 was achieved for films deposited at 550°C on β-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in β-Ga2O3 devices. [ABSTRACT FROM AUTHOR]

We report on MOSFETs fabricated on Ge-doped \beta -Ga2O3 homoepitaxial material grown by molecular beam epitaxy on (010) Fe-doped semi-insulating substrates. The Ge-doped channel devices performed similar to previously reported devices with Sn- and Si-doped channels with the drain current ON/OFF ratios of > 10^{8} and the saturated drain current of >75 mA/mm at V_{G}=0 V. Hall effect measurements showed a high carrier mobility of 111 cm2/( \textV\cdot \texts ) with 4\times 10^17 cm ^-3 active carriers. A MOSFET with a gate-drain spacing of 5.5~\mu \textm had a three-terminal breakdown voltage of 479 V. [ABSTRACT FROM PUBLISHER]

We demonstrate a \beta -Ga2O3 MOSFET with record-high transconductance ( {g}_{m} ) of 21 mS/mm and extrinsic cutoff frequency ( {f}_{T} ) and maximum oscillating frequency ( f\max ) of 3.3 and 12.9 GHz, respectively, enabled by implementing a new highly doped ohmic cap layer with a sub-micron gate recess process. RF performance was further verified by CW Class-A power measurements with passive source and load tuning at 800 MHz, resulting in {P}{OUT} , power gain, and power-added efficiency of 0.23 W/mm, 5.1 dB, and 6.3%, respectively. These preliminary results indicate potential for monolithic or heterogeneous integration of power switch and RF devices using $\beta $ -Ga2O3. [ABSTRACT FROM PUBLISHER]

The plasmonic resonance wavelength λres in ZnO doped with 3 wt.% Ga2O3 can be controlled over the range 1 to 4  μm by simple furnace annealing in flowing Ar. For each annealing temperature TA, the reflectance Rm and transmittance Tm are measured over a wavelength range, λ=185 to 3200 nm, (energy range, E=6.7 to 0.387 eV), and the reflectance coefficient R is calculated from Rm and Tm. The value of λres is then determined from a Drude-theory analysis of R versus E that yields fitting parameters nopt (optical carrier concentration), μopt (optical mobility), high-frequency dielectric constant ϵ∞, and thickness d at each annealing temperature TA. The validity of this process is confirmed by comparison of ϵ∞ with literature values and comparison of nopt and μopt with analogous quantities n and μH measured by the Hall effect. [ABSTRACT FROM AUTHOR]

For single slabs of uniform material, such as bulk semiconductors, we derive closed-form expressions for absorption and reflection coefficients, α and R, respectively, in terms of measured reflectance and transmittance, Rm and Tm. The formula for α can replace the several commonly used approximations for α as a function of Tm and in particular does not require αd ≫ 1, where d is the thickness. Thus, it can be applied to weak impurity absorptions, such as Fe absorption in Fe-doped GaN. Finally, the real (η) and imaginary (κ) parts of the index of refraction (n = η + iκ) can be obtained from α and R and agree well with η and κ results obtained from other experiments. For multilayer structures, “effective” values of α, R, η, and κ are obtained, but they can often be assigned to a particular layer. This technique has been successfully applied to many bulk and layered structures. [ABSTRACT FROM AUTHOR]

Sn-doped gallium oxide (Ga2O3) wrap-gate fin-array field-effect transistors (finFETs) were formed by top-down BCl3 plasma etching on a native semi-insulating Mg-doped (100) β-Ga2O3 substrate. The fin channels have a triangular cross-section and are approximately 300 nm wide and 200 nm tall. FinFETs, with 20 nm Al2O3 gate dielectric and ~2 µm wrap-gate, demonstrate normally-off operation with a threshold voltage between 0 and +1 V during high-voltage operation. The ION IOFF ratio is greater than 105 and is mainly limited by high on-resistance that can be significantly improved. At VG = 0, a finFET with 21 lm gate-drain spacing achieved a three-terminal breakdown voltage exceeding 600V without a field-plate. [ABSTRACT FROM AUTHOR]

A Sn-doped (100) \beta -Ga2O3 epitaxial layer was grown via metal–organic vapor phase epitaxy onto a single-crystal, Mg-doped semi-insulating (100) \beta -Ga2O3 substrate. Ga2O3-based metal–oxide–semiconductor field-effect transistors with a 2- \mu \textm gate length ( LG) , 3.4- \mu \textm source–drain spacing ( L\textrm {SD}) , and 0.6- \mu \textm gate–drain spacing ( L\textrm {GD}) were fabricated and characterized. Devices were observed to hold a gate-to-drain voltage of 230 V in the OFF-state. The gate-to-drain electric field corresponds to 3.8 MV/cm, which is the highest reported for any transistor and surpassing bulk GaN and SiC theoretical limits. Further performance projections are made based on layout, process, and material optimizations to be considered in future iterations. [ABSTRACT FROM PUBLISHER]

Disordered ionic-bonded transition metal oxide thin-film transistors (TFTs) show promise for a variety of dc and RF switching applications, especially those that can leverage their low-temperature, substrate-agnostic process integration potential. In this paper, enhancement-mode zinc-oxide TFTs were fabricated and their switching performance evaluated. These TFTs exhibit the drain-current density of 0.6 A/mm and minimal frequency dispersion, as evidenced by dynamic current–voltage tests. A high-frequency power switch figure of merit $R_{{\mathrm{\scriptscriptstyle ON}}}Q_{G} of 359 \textm\Omega \,\cdot \, nC was experimentally determined for 0.75- \mu \textm long-channel devices, and through scaling 45.9 \textm\Omega \,\cdot \, nC is achievable for 11 V-rated devices (where R\mathrm{\scriptscriptstyle ON} is ON-state drain–source resistance, and QG is gate charge). An RF switch cutoff frequency fc of 25 GHz was measured for the same 0.75- \mu \textm TFT, whereas fc exceeding 500 GHz and power handling in the tens of watts are projected with optimization. [ABSTRACT FROM AUTHOR]

We report effects for up to 100 Mrad (SiO_2) gamma-ray exposure on polycrystalline ZnO thin film transistors (TFTs) deposited by two different techniques. The radiation related TFT changes, either with or without electrical bias during irradiation, are primarily a negative VON shift and a smaller VT shift (\Delta VON\sim - 2.5~\V and \Delta VT\sim - 1.5~\V for 100 Mrad (SiO_2) exposure). Field-effect mobility remains nearly unchanged. Both, VON and VT shifts are nearly completely removed by annealing at 200^\circ C for 1 minute and some recovery is seen even at room temperature. We find that our ZnO TFTs are insensitive to electrical bias during irradiation; that is, unbiased measurements are useful worst case test results. To the best of our knowledge, these are the most radiation-hard thin film transistors reported to date. [ABSTRACT FROM PUBLISHER]

ZnO nanocrystals grown at relatively low temperatures using various vacuum deposition techniques can yield semiconducting thin films of self-assembled nanocolumns 20-50 nm in diameter. Such films are suitable for the fabrication of high speed and transparent thin film transistors (TFTs). Unlike amorphous TFTs, the performance of ZnO transistors depends both on the crystal quality of nanocrystals and the electrical properties of boundary layers between them. We investigated the use of radio frequency sputtering, atomic layer deposition, and pulsed laser deposition techniques to fabricate self-assembled nanocrystalline thin films and determined the influence of deposition conditions on the performance of transistors. Device design and fabrication parameters were also optimized to demonstrate TFTs with high current density and high speed performance comparable to single crystalline-based transistors. [ABSTRACT FROM AUTHOR]

Ga-doped ZnO (GZO) films grown by pulsed-laser deposition on quartz and other lattice-mismatched substrates can routinely attain resistivities of 2×10-4 ·cm and thus compete with Sn-doped In2O3 (ITO) in large-area transparent-electrode applications. Nondestructive, high-resolution (1-mm) maps of thickness d, concentration n, and mobility µ on such films can be obtained automatically from commercial spectroscopic ellipsometers. From n and µ, degenerate-electron scattering theory yields donor ND and acceptor NA concentrations at each point. Finally, ND and NA can be identified as [Ga] and [VZn], respectively, demonstrating high-density mapping of impurities and point defects in a semiconductor thin film. [ABSTRACT FROM AUTHOR]