Diode Turn-on Voltage Research Articles

Ga+ Focused Ion Beam Damage in n-type Ga2O3 and Its Recovery after Annealing Treatment

In this study, the focused ion beam (FIB) Ga+ irradiation damage on β-Ga2O3 Schottky diode structure under different ion energies were tested, and the effective recovery of diode characteristics after rapid thermal annealing (RTA) post-annealing were also studied.β-Ga2O3 based Schottky diodes have attracted increasing attention because of the prospects for use in next-generation high-power electronics. Focused ion beam (FIB) machining is one of the newest processing techniques, which is mainly used in semiconductor and chip manufacture and transmission electron microscopy (TEM) sample preparation. During FIB sample preparation, the energetic Ga ions are incident onto the sample to induce physical sputtering of the material, which in turn, modifies its chemical composition, crystallinity and electrical properties. It has been found in many studies that 20-30 nm amorphous layer can form on silicon after irradiation with 30 keV Ga ions. From our previous study, the FIB ion beam induced damages could cause significant degradation on diode on-resistance and turn-on voltage. Milling at lower energy has been used to reduce the electrical damage. However low energy milling is more time consuming and less precise. Short-time, high-temperature post-annealing treatments, such as RTA has been proved could remove the crystal damage. Thus, there is a great need to determine the maximal ion beam energy and post-annealing temperature for FIB without degrading diode characteristics.In this work, energies ranging from 2 keV to 30 keV were employed to mill off a part of Ga2O3 epi-layer and Schottky diodes were fabricated on milled surface. Forward IV characteristic shows less degradations with lower ion beam energies. For the diodes exposed to 2, 5, and 10 keV Ga+ ion beams exhibited significant recovery of diode on resistance and turn-on voltage after 300°C RTA annealing. For the diodes exposed to 30 keV Ga+ ion beams recovered significantly after 400 °C annealing. In conclusion, decreasing the FIB energy shows effective alleviations on the FIB damage, and post annealing treatment effectively recovered the damage from Ga+ implantation.This is the first time the thermal annealing treatment was performed for Ga2O3 Schottky diode recovering from FIB cutting, it is an effective and simple way to mitigate the degradation, especially for higher ion beam energies. This work could broaden the FIB’s usability and release tremendous potential as a specimen preparation and imaging tool in materials science applications. Figure 1

Accurately Modeling Zero-Bias Diode-Based RF Power Harvesters With Wide Adaptability to Frequency and Power

This paper proposes an analytical method for effectively evaluating the performances of zero-bias diode-based RF power harvesters. The method allows the accurate calculation of both the diode power conversion efficiency (PCE) and matching efficiency, while showing the wide adaptability to frequency and input power. To calculate the diode PCE accurately, the junction voltage is built based on modeling the diode junction capacitance and turn-on voltage. Using the accurate diode PCE, the equivalent nonlinear resistance of the diode is calculated, and thus the diode impedance is obtained. This helps to design a matching network with required bandwidths and evaluate the corresponding matching efficiency. The total PCE of the RF power harvester is finally obtained by multiplying the diode PCE and matching efficiency. For verification, dual-band RF power harvesters based on diodes of SMS7630 and HSMS-2850 are developed to cover the two 5G frequency bands for three telecom operators in China (2.515-2.675, 3.4-3.5 & 3.5-3.6 GHz). They are designed to operate in the low power range of −25-−5 dBm for low power harvesting scenarios. Compared with the simulated results, the calculation discrepancy of less than 3.12% can be achieved in evaluating the total PCEs of the RF power harvesters. Prototypes of the designed RF power harvesters were fabricated and measured for validation. It shows that the proposed analytical method can provide design guidelines for developing a multi-band RF power harvester.

Ultraviolet light tunable single walled carbon nanotubes/n-Si junction diode

Semiconducting p-doped single walled carbon nanotubes (SWCNT) were deposited at the edge of a cleaved n-Si/SiO2 wafer. The p-n junction formed at the SWCNT/n-Si interface was tested in the presence of UV irradiation, and an immediate decrease was observed in the diode on-state current upon UV exposure. The diode ideality parameter and turn-on voltage however stayed relatively constant at 1.9 and 0.65 V respectively during the first ten minutes of UV exposure. With prolonged UV irradiation beyond 10 min these parameters increased, and the on-state current decreased by a factor of 400. We attribute this to a change in charge carriers from holes to electrons in the SWCNT’s due to UV induced photo-desorption of O2. Annealing in air at 70 °C resets the diode to its initial operating condition, thus the photo desorption process is reversible and the diode reusable. The diode was successfully tested as a signal rectifier, and its potential to sense UV radiation makes it multifunctional. It also provides a useful platform to study UV induced charge dynamics at the SWCNT/n-Si interface as carriers in the SWCNT’s switch from hole to electrons and vice versa.

Temperature-Dependent Electrical Characteristics of Ni/Au Vertical Schottky Barrier Diodes on β-Ga2O3 Epilayers

Temperature dependent current transport mechanism in Ni/β-Ga2O3 Schottky Barrier Diodes was studied using current-voltage (I-V) and capacitance-voltage (C-V) characterization techniques in the range of 78–350 K. Schottky barrier height ϕb0 and ideality factor ɳ from I-V characteristics were found to be 1.27 eV and 1.12, respectively, at room temperature. Plots of barrier height and ideality factor with inverse of temperature show strong temperature dependency and a deviation from barrier height obtained from C-V characteristics. The temperature dependence of barrier height and ideality factor assigned to barrier inhomogeneity at Ni/β-Ga2O3 interface, and modulated by the potential fluctuation model. Diode turn-on voltage and turn-on resistance at 300 K were found to be 1.08 eV and 7.80 mΩ-cm2, respectively. A large rectification ratio of the order of 1012 was obtained at room temperature and also the rectification ratio of the order of 109 was consistent over the whole temperature range (78–350 K).

Rectifying effect in a MoS2 monolayer crossed with an electro-spun PEDOT-PSS nano-ribbon

A chemical vapor-deposited monolayer MoS2 crystal was crossed with an electro-spun PEDOT-PSS nano-ribbon under ambient conditions. The current–voltage (I–V) curve measured across the hetero-junction was nonlinear and asymmetric, similar to a diode. Under thermal equilibrium, electrons flowed from the MoS2 conduction band into the PEDOT-PSS LUMO level. This occurred via band bending that established a constant Fermi level across the interface. Consequently, a potential barrier was formed that restricted the current. Under normal operation in air, the diode turn-on voltage was 0.1 V and the rectification ratio at ± 1 V was 20. The thermionic emission Schottky junction model was employed for data analysis. The ideality factor was 1.9, and height of the barrier was 0.18 eV. The easy fabrication, low turn-on voltage and high rectification ratio could make this diode useful in cheap, low-power-consumption signal rectifiers.

Low absorption loss p-AlGaN superlattice cladding layer for current-injection deep ultraviolet laser diodes

Current injection into AlGaN-based laser diode structures with high aluminum mole fractions for deep ultraviolet emission is investigated. The electrical characteristics of laser diode structures with different p-AlGaN short period superlattice (SPSL) cladding layers with various aluminum mole fractions are compared. The heterostructures contain all elements that are needed for a current-injection laser diode including cladding and waveguide layers as well as an AlGaN quantum well active region emitting near 270 nm. We found that with increasing aluminum content in the p-AlGaN cladding, the diode turn-on voltage increases, while the series resistance slightly decreases. By introducing an SPSL instead of bulk layers, the operating voltage is significantly reduced. A gain guided broad area laser diode structure with transparent p-Al0.70Ga0.30N waveguide layers and a transparent p-cladding with an average aluminum content of 81% was designed for strong confinement of the transverse optical mode and low optical losses. Using an optimized SPSL, this diode could sustain current densities of more than 4.5 kA/cm2.

Cryogenic Characterization of Commercial SiC Power MOSFETs

The cryogenic performance of two commercially available SiC power MOSFETs are presented in this work. The devices are characterised in static and dynamic tests at 10 K intervals from 20-320 K. Static current-voltage characterisation indicates that at low temperatures threshold voltage, turn-on voltage, on-state resistance, transconductance, and the body diode turn-on voltage all increase while saturation current decreases. Dynamic, 60 V, 3A switching tests within the cryogenic chamber are also reported and the trends of switching speed, losses, and total power losses, which rise at low temperature, are presented. Overall, both MOSFETs are fully operable down to 30 K with both positive and negative changes in behaviour.

Au-Cu2O core-shell nanowire photovoltaics

Semiconductor nanowires are among the most promising candidates for next generation photovoltaics. This is due to their outstanding optical and electrical properties which provide large optical cross sections while simultaneously decoupling the photon absorption and charge carrier extraction length scales. These effects relax the requirements for both the minority carrier diffusion length and the amount of semiconductor needed. Metal-semiconductor core-shell nanowires have previously been predicted to show even better optical absorption than solid semiconductor nanowires and offer the additional advantage of a local metal core contact. Here, we fabricate and analyze such a geometry using a single Au-Cu2O core-shell nanowire photovoltaic cell as a model system. Spatially resolved photocurrent maps reveal that although the minority carrier diffusion length in the Cu2O shell is less than 1 μm, the radial contact geometry with the incorporated metal electrode still allows for photogenerated carrier collection along an entire nanowire. Current-voltage measurements yield an open-circuit voltage of 600 mV under laser illumination and a dark diode turn-on voltage of 1 V. This study suggests the metal-semiconductor core-shell nanowire concept could be extended to low-cost, large-scale photovoltaic devices, utilizing for example, metal nanowire electrode grids coated with epitaxially grown semiconductor shells.

Schottky barrier diode embedded AlGaN/GaN switching transistor

We developed a Schottky barrier diode (SBD) embedded AlGaN/GaN switching transistor to allow negative current flow during off-state condition. An SBD was embedded in a recessed normally-off AlGaN/GaN-on-Si metal-oxide-semiconductor heterostructure field-effect transistor (MOSHFET). The fabricated device exhibited normally-off characteristics with a gate threshold voltage of 2.8 V, a diode turn-on voltage of 1.2 V, and a breakdown voltage of 849 V for the anode-to-drain distance of 8 µm. An on-resistance of 2.66 mΩcm2 was achieved at a gate voltage of 16 V in the forward transistor mode. Eliminating the need for an external diode, the SBD embedded switching transistor has advantages of significant reduction in parasitic inductance and chip area.

Au-Free AlGaN/GaN Power Diode on 8-in Si Substrate With Gated Edge Termination

High-performance AlGaN/GaN diodes are realized on 8-in Si wafers with Au-free CMOS-compatible technology. The diodes are cointegrated on the same substrate together with the AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors and with only one extra lithographic step. The diode anode and the transistor gate are processed together and the same metallization is used for both, avoiding extra metal deposition dedicated to the Schottky junction. A gated edge termination allows obtaining low reverse leakage current (within 1 μA/mm at -600 V), which is several orders of magnitude lower than the one of conventional Schottky diodes processed on the same wafer. Recess is implemented at the anode, resulting in low diode turn-on voltage values.

1,3,4-Oxadiazole Containing Silanes as Novel Hosts for Blue Phosphorescent Organic Light Emitting Diodes

Five rigid oxadiazole (OXD) containing silanes, denoted 1-5, have been developed with high morphological stability. Disruption of the π-aromatic conjugation by introduction of Si atoms leads to a large band gap and high triplet energy. Among the OXDs we studied, 2,5-bis(triphenylsilylphenyl)-1,3,4-oxadiazole 5 is the best host for FIrpic, with a phosphorescent organic light emitting diode (PHOLED) turn-on voltage of 6.9 V, maximum luminance of 5124 cd/m(2), current efficiency of 39.9 cd/A, and external quantum efficiency of 13.1%. Special molecular stacking in the single crystal of 5 was discussed.

A Fully Tunable Single-Walled Carbon Nanotube Diode

We demonstrate a fully tunable diode structure utilizing a fully suspended single-walled carbon nanotube. The diode's turn-on voltage under forward bias can be continuously tuned up to 4.3 V by controlling gate voltages, which is ∼6 times the nanotube band gap energy. Furthermore, the same device design can be configured into a backward diode by tuning the band-to-band tunneling current with gate voltages. A nanotube backward diode is demonstrated for the first time with nonlinearity exceeding the ideal diode. These results suggest that a tunable nanotube diode can be a unique building block for developing next generation programmable nanoelectronic logic and integrated circuits.

Effect of neutron irradiation on electrical and optical properties of InGaN/GaN light-emitting diodes

InGaN/GaN multiquantum well light-emitting diodes (LED) with emission wavelength of 450 nm were irradiated with average energy of 9.8 MeV and dose of 5.5×1011 cm−2 neutrons. Right after irradiation, the forward current of the irradiated LEDs was decreased as a result of the creation of deep levels by the neutron-induced lattice displacement. However, unstable lattice damages resulting from the collisions with the incoming neutrons were removed at room temperature 6 days after the irradiation. The diode turn-on voltage, ideality factor, and optical emission intensity were recovered to preirradiated state by self-annealing process at room temperature.

Room Temperature Annealing Effects on Leakage Current of Ion Implanted p<sup>+</sup>n 4H-SiC Diodes

The current-voltage characteristics of Al+ implanted 4H-SiC p+n junctions show an important reduction of leakage currents with diode aging at room temperature. The case of a family of diodes that immediately after manufacture had forward current density increasing from 10-9 to 10-6 A/cm2 when biased from 0 and 2 V, and had a reverse leakage current density of @ 5×10-7 A/cm2 when biased at 100 V, is here presented and discussed. During diode manufacturing a post implantation annealing at 1600 °C for 30 min was followed by a 1000 °C 1 min treatment for metal contacts alloying. After 700 days of storage at room temperature, the diode reverse current density reached an asymptotical value of @ 4×10-11 A/cm2 that is four order of magnitude lower than the initial one. A 430 °C annealing that was made after 366 days is responsible of a decrease of one of these four orders of magnitude, but it does not interrupt the decreasing trend versus increasing time. This same annealing has been effective also for minimizing forward current for bias < 2 V, and sticking the diode turn-on voltage on 1.4 V and the current trend on an ideality factor of 2. These results show that in Al+ implanted 4H-SiC p+n junction there are defects that have an annihilation dynamic at very low temperatures, i.e. room temperature and 430 °C.

High Optical Response in Forward Biased (In,Ga)N–GaN Multiquantum-Well Diodes Under Barrier Illumination

The authors report on the current-voltage (I-V) characteristic under forward biases obtained in low leakage, small size p-(In,Ga)N-GaN-n multiquantum well diodes. Under barrier illumination, the devices present a high optical response with capabilities to detect optical powers in the pW range without further amplification. This response is attributed to the screening of the internal electric fields. Recombination times of a few seconds are found to be associated to this mechanism. Moreover, a step-like feature is found in the I-V characteristic before the diode turn-on voltage. Our model proposes tunneling current through the multiquantum-well structure as responsible of this feature. Fast modulation of the tunneling effect under barrier illumination is used to evaluate the detection of low photon fluxes.

Forms and behaviour of vacuum emission electronic devices comprising diamond or other carbon cold cathode emitters

Nanocarbon-derived electron emission devices, specifically nanodiamond lateral field emission (FE) diodes and gated carbon nanotube (CNT) triodes, are new configurations for robust nanoelectronic devices. These novel micro/nanostructures provide an alternative and efficient means of accomplishing electronics that are impervious to temperature and radiation. For example, nitrogen-incorporated nanocrystalline diamond has been lithographically micropatterned to use the material as an electron field emitter. Arrays of laterally arranged 'finger-like' nanodiamond emitters constitute the cathode in a versatile diode configuration with a small interelectrode separation. A low diode turn-on voltage of 7V and a high emission current of 90 microA at an anode voltage of 70V (electric field of approx. 7V microm(-1)) are reported for the nanodiamond lateral device. Also, a FE triode amplifier based on aligned CNTs with a low turn-on voltage and a small gate leakage current has been developed.

Field emission devices for advanced electronics comprised of lateral nanodiamond or carbon nanotube emitters

Nanocarbon-derived electron emission devices, specifically, nanodiamond lateral field emission diodes and gated carbon nanotube triodes are new configurations for robust nanoelectronic devices. These novel micro/nanostructures provide an alternative and efficient means of accomplishing electronics that are impervious to temperature and radiation. Nitrogen-incorporated nanocrystalline diamond has been lithographically micropatterned to utilize the material as an electron field emitter. Arrays of laterally arranged “finger-like” nanodiamond emitters constitute the cathode in a versatile diode configuration with small interelectrode separation. Nanodiamond lateral tip conditioning techniques are employed to improve emission and the subsequent device performance discussed. A low diode turn-on voltage of 7 V and a high emission current of 90 μA at an anode voltage of 70 V (electric field of ∼ 7 V/μm) is reported for the nanodiamond lateral device. Also, the development of a field emission triode amplifier based on aligned carbon nanotubes (CNTs) with low turn-on voltage and small gate leakage current, utilizing a dual-mask microfabrication process is reported. The2 × 20 μm CNT triode array displays a gate turn-on voltage of ∼ 44 V, and low gate currents less than 3% of the anode currents. The low gate leakage currents observed confirmed the effectiveness of the convex-shaped gated CNT emitter in alleviating the cathode-gate leakage problem that compromises the operation of a field emission triode.

Interfaces between Metal and Arylamine Molecular Films As Probed with the Anode Interfacial Engineering Approach in Single-Layer Organic Diodes

The interfaces between metal and arylamine molecular films were studied by measurement of current-voltage characteristics in single-layer organic diodes with the aid of the anode interfacial engineering method. The diode turn-on voltage is shown to be very sensitive to the arylamine/metal interface and thus can serve as a means for characterizing such organic/metal interfaces. We show that the diode electrical performance depends on the arylamine substituent groups and chemical/electrical properties of the anode. The conduction mechanism of the diodes is shown to be injection limited, which can be well described with the Richardson-Schottky thermionic emission model. This work may provide some insight into the use of single-layer organic diodes and the interfacial engineering method to rapidly probe the organic/metal and even organic/organic interfaces.

Microwave Performance of ( Al0.3Ga0.7 ) 0.5In0.5P , In0.5Ga0.5P , Al0.28Ga0.72As Enhancement-Mode Pseudomorphic HEMT with Succinic Acid Gate Recess Process

, , compounds on GaAs substrates are important materials that are used as Schottky layers in microwave transistors. This study systematically explores the electrical characteristics of various enhancement-mode pseudomorphic high electron mobility transistors (E-mode pHEMTs) with , , Schottky layers. These E-mode pHEMTs were fabricated using a high-selectivity succinic acid solution for gate recess and buried-Pt gate technology. The E-mode pHEMT has a Schottky diode turn-on voltage of . The corresponding values for and E-mode pHEMTs are 0.72 and , respectively. Because a larger can be obtained at the interface, the E-mode pHEMT also more effectively confined carriers and yielded a higher sheet charge density than other Schottky materials. Based on these measured results, this E-mode pHEMT is more appropriate for microwave low-noise and high-power device applications.

Comparison of Quasi-/Pseudo-Floating Gate Techniques and Low-Voltage Applications

The quasi- or pseudo-floating gate (QFG) technique addresses a key issue with the floating-gate MOS transistor technique, by using ultra-high resistances to provide dc paths to otherwise floating nodes. Several ways have been suggested to implement the quasi-infinite resistors (QIRs). In this paper, basic QIR structures are analyzed and compared, and three sources of error, dc offset, signal distortion, and signal-dependent offset, are defined. Then, through simulations and experiments, the suitability of several QIR implementations for use in various applications is compared. A particular QIR implementation is found to minimize dc offset, but requires voltage swings to be limited to less than a diode turn-on voltage. Some application circuits using quasi-floating gate are presented, including a QFG translinear geometric-mean circuit and QFG low-voltage fully-differential amplifiers with QFG common-mode feedback using several QIR structures. Measurements on current-mode QFG circuits exhibit large offsets and very long turn-on transients, which could limit practical application of this technique.