Search

To explore the potential of semi-insulating (SI) SiC substrate for radiation detector applications, p-i-n diodes with thick depletion layers are fabricated by using a dual-face ion implantation technique on SI 4H-SiC substrate. The Poole-Frenkel (P-F) emission is found responsible for the reverse leakage current transport of the p-i-n diode at elevated temperatures. The derived emission barrier height is likely induced by the residual boron-related shallow-level states, which are located ∼ 0.3 eV above the top of the valence band. Detection tests of α-particles are performed on each side of the p-i-n detector to determine the location of the depleted region, which reveals weak p-type conduction of the SI 4H-SiC substrate after high temperature post-implantation annealing. The energy resolution of the detector operating in photovoltaic mode is ∼ 4.3%, which would degrade at higher biases. The saturated charge collection efficiency (CCE) of ∼ 99% for detection of 5.48 MeV α-particles is obtained as reverse bias exceeds 80 V.

The recovery of high reverse gate leakage current in AlGaN/GaN HEMTs has been analyzed in this study. To demonstrate the recovery after a thermal stress for large time periods (8–12 h), two mechanisms: phonon assisted tunnelling (PAT) and trap assisted tunnelling (TAT) have been utilized. Charge-based analytical models from literature have been used to match experimental leakage currents in reverse bias conditions. The degradation in the devices has been activated through thermal stress and the effect of high electric field induced inverse piezo electric effect has been eliminated. PAT component shows dominance in higher temperature regime (T > 500 K) and the slow recovery at 300 K with characteristic τ values around 5–13 h has been attributed to the TAT component through a deep trap level within the AlGaN barrier.

A 700-V normally-off p-GaN gate HEMT featuring area-efficient distributed built-in Schottky barrier diode (SBD) is demonstrated with low-loss reverse conduction capability. The reverse conduction voltage of the device V RC is - {2.1 V (@ I_D = -20 mA/mm). As the reverse conduction is through the built-in SBD, the low V RC of the proposed transistor is independent of the HEMT's V TH and turn-off gate bias V GS . On the contrary, the V RC of a conventional p-GaN gate power transistor is not only much higher but also strongly dependent on the V TH and OFFstate V GS . The built-in SBD elements are embedded into the HEMT's source side in a distributed fashion along the width of the device, so that the SBD and HEMT share a common access region in forward and reverse conduction, leading to reduced ON-resistance (R ON ) compared to the scheme with side-by-side transistor/SBD pair. The anode of built-in Schottky contact is embedded at the source side and is shielded from the high electric field by the gate field plate. Thus, the reverse leakage current of Schottky contact is well-suppressed.

Electric field crowding at the Schottky edge and Schottky barrier lowering induced leakage current are two major problems that limit the performance of GaN-on-GaN vertical SBD. In this paper, we try to solve these issues. On one hand, a planar edge termination method based on high-energy fluorine ion implantation is explored for high voltage vertical GaN SBD. The space charge induced field modulation effect (SCIFM) is discovered in the ion implanted region. The electrons injected in the implanted region could effectively reduce the surface electric field, alleviating the field crowding at the metal edge. The SBD terminated with high-energy fluorine implanted region presents a breakdown voltage of 1300 V. Utilizing the depletion effect of space charges, the leaky path through the implanted region is partially blocked by the high-energy fluorine ion implanted guard rings. The reverse leakage current of SBD with guard rings is reduced by nearly 3 orders at the reverse bias of 300 V without the deterioration of forward characteristics. On the other hand, the fluorine ion implantation based quasi-JBS structure is investigated to shield the electric field seen by the Schottky contact and reduce the Schottky barrier lowering induced leakage current. The turn-on voltage modulation effect and improved breakdown voltage are observed in the fabricated quasi-JBS diodes, confirming the validity of the SCIFM mechanism in the ion implanted region.

The reverse leakage current through a Schottky barrier transitions from a thermionic-emission dominated regime to a barrier-tunneling dominated regime as the surface electric field increases. In this study, we evaluate such transition electric field ($E_{\rm T}$) in $\beta$-Ga$_{2}$O$_{3}$ using a numerical reverse leakage model. $E_{\rm T}$ is found to have very weak dependence on the doping concentration and barrier height, thus a near-universal temperature dependence suffices and is given by a simple empirical expression in Ga$_{2}$O$_{3}$. With the help of a field-plate design, we observed experimentally in Ga$_{2}$O$_{3}$ Schottky barrier diodes a near-ideal bulk reverse leakage characteristics, which matches well with our numerical model and confirms the presence of the transition region. Near the transition electric field, both thermionic emission and barrier tunneling should be considered. The study provides important guidance toward accurate design and modeling of ideal reverse leakage characteristics in $\beta$-Ga$_{2}$O$_{3}$ Schottky barrier diodes., Comment: 5 pages, 7 figures

The reverse leakage current in the rectifier is a key challenge in the design of RF energy harvesting (RF-EH) systems, especially in harvesting modulated RF signals from WLAN band. In this paper, we propose a dual-band energy harvesting system operating at GSM-900 (900 MHz) and WLAN (2.4 GHz) bands. To harvest the RF energy from the WLAN band more efficiently, an event-triggered 1:2 parallel-series switched-capacitor (SC) converter is proposed to reduce the reverse leakage current. Meanwhile, this SC converter can provide an output voltage bootstrapping function while maintaining an ultra-low-power consumption down to 28 nW by asynchronous control. The power management unit (PMU) with the rectifier is fully integrated in a CMOS 130-nm process. Measurement results have shown the PMU can boost up the output voltage by 1.73× with an input voltage as low as 0.2 V. When harvesting the modulated waveform, the RF-EH system output ripple is decreased by 6×, and reverse leakage current reduction is over 2500 × compared to the direct connection condition.

This letter reports the influence of material quality and device processing on the performance of AlGaN-based Schottky barrier deep ultraviolet photodetectors grown on Si substrates. The thermal annealing can significantly improve Schottky barrier height and wet chemical etching can effectively remove etching damage. Meanwhile, the decrease of threading dislocation density and the pit size, especially the later, can substantially suppress reverse leakage. As a result, the reverse leakage current density of the as-fabricated deep UV photodetector was reduced down to 3×10−8 A/cm2. Furthermore, the responsivity of the deep UV photodetectors was greatly improved by reducing the point defect concentration.

In this work, SiC Schottky diodes specifically developed for the BepiColombo space mission are studied by Lock-in Infrared Thermography (LIT) to analyse local defects observed in their top metallization and passivation layers appeared after thermal vacuum tests. Such defects might potentially be the root cause of the increase in reverse leakage current measured after such accelerated tests.

High reverse leakage current was observed on polysilicon diode with distinct failure signature at wafer edge. Investigation points to a measurement step that induced the damage at wafer bevel which resulted in the out-diffusion of dopants from highly doped substrate to the un-doped polysilicon. Experiments were been performed successfully to simulate and provoke the failure. Detail investigations with Cross Sectional Electron Microscopy (XSEM), electrical verification and simulation of out-diffusion profile were extracted, and the failure mechanism and result are discussed in this paper.

Simulation models for I-V characteristics of PV modules under mismatch conditions often assume ideal bypass diode and ignore the reverse leakage current of cells. In this paper, we present a SPICE based model in which customized reverse leakage current and real I-V characteristics of bypass diodes can be specified. This model is used to gain insight into root causes of some of the unusual I-V characteristics seen in field deployed modules. Different mismatch scenarios for a PV module were simulated for both the modules made up of leaky and non-leaky cells, and the resultant I-V curves were compared. The effect of Potential Induced Degradation (PID) on the I-V curves of PV modules was also simulated under the presence of mismatch. Using this model, we accurately reproduced the I-V characteristics of fielded modules degraded due to PID, and Bypass Diode failure in the short circuit condition.

The electrical and interfacial characteristics of AlN/GaN and AlGaN/GaN heterostructures prepared by thermal atomic layer deposition (ALD) were investigated in this work. According to the parallel conductance method, the AlGaN/GaN sample showed two border traps with energies of ~ 0.38 and ~ 0.46 eV, which were not observed for the AlN/GaN sample. The AlN/GaN sample also showed a lower interface trap density and a lower reverse leakage current. X-ray photoelectron spectroscopy analysis indicated that during the initial ALD deposition process, most of the Al and N atoms tended to combine with oxygen atoms as opposed to Ga atoms. As a result, AlGaN layer formation was delayed, resulting in the creation of a defective interfacial layer at the AlGaN/GaN interface. Thus, our results indicate that the initial ALD process should focus on removing the defective interfacial layer during AlGaN deposition for device optimization.

Low leakage current Schottky barrier diodes (SBDs) were fabricated on $\mathbf{30}\ \mu\mathbf{m}$ thick Mg-compensated GaN drift layer (DL) grown on a free-standing GaN substrate and tested up to 5.48 MeV $\alpha$ -particle energy. The Mg-compensated $\mathbf{30}\ \mu\mathbf{m}$ thick n--GaN DL was grown by MOCVD with low charge carrier density (CCD) of $\mathbf{4.1}\times \mathbf{10}^{\mathbf{15}}/\mathbf{cm}^{\mathbf{3}}$ . The observation of low CCD in the GaN DL by Mg-compensation helps to reduce the reverse leakage current (I R ) of SBDs to 2 pA and in the formation of $\mathbf{30}\mu\mathbf{m}$ depletion width (DW) even at 0 V. The fabricated GaN SBDs detected $\alpha$ -particle up to energy of 5.48 MeV with high charge collection efficiencies (CCE) of 100% emitted from 241 Am source.

The talk will describe the defect-to-device performance correlations for optoelectronic and power devices on hetero-epitaxially grown III-nitride epi-layers on silicon and sapphire. While UV detectors and power electronic devices might seem far apart, we see similarities between the defect origins of dark current in the former and leakage currents in the latter. Both have their origins in crystal growth. The first part of the work focuses on the correlation between performance parameters of vertical deep-ultraviolet photodetectors on c-plane sapphire and the density of extended defects vis-a-vis screw and edge dislocations. Through a careful optimization of nucleation density on the growth surface, state-of-the-art crystalline quality AlN epi-layers were grown. This led to the realization of record performance 289 nm p-i-n photodiodes with zero-bias quantum efficiency of 92 %, leakage current below 1 nA at 100 V and breakdown field in excess of 6 MV/cm. Performance of III-nitride power devices on silicon, on the other hand, was found to be more sensitive to structural defects such as surface pits as compared to dislocations. By utilizing a two-temperature growth technique which involved an AlN layer grown at high temperatures, a significant reduction in the pit density could be achieved. This resulted in three-orders of magnitude reduction in lateral as well as vertical leakage in AlGaN/GaN high electron mobility transistors (HEMTs) on silicon. To achieve a further reduction in the reverse leakage current and an enhancement in the device breakdown voltage, point defect control also becomes important. Carbon doping to reduce the background n-carrier concentration in the GaN epilayers is discussed as one of the possible approaches. Reduction of pit density and C-incorporation cumulatively led to the realization of 2 MV/cm vertical breakdown field in AlGaN/GaN HEMTs on silicon.

This paper reports on the modulation of Schottky barrier heights (SBH) on three different orientations of $\beta$-Ga$_2$O$_3$ by insertion of an ultra-thin SiO$_2$ dielectric interlayer at the metal-semiconductor junction, which can potentially lower the Fermi-level pinning (FLP) effect due to metal-induced gap states (MIGS). Pt and Ni metal-semiconductor (MS) and metal-interlayer-semiconductor (MIS) Schottky barrier diodes were fabricated on bulk n-type doped $\beta$-Ga$_2$O$_3$ single crystal substrates along the (010), (-201) and (100) orientations and were characterized by room temperature current-voltage (I-V) and capacitance-voltage (C-V) measurements. Pt MIS diodes exhibited 0.53 eV and 0.37 eV increment in SBH along the (010) and (-201) orientations respectively as compared to their respective MS counterparts. The highest SBH of 1.81 eV was achieved on the (010)-oriented MIS SBD using Pt metal. The MIS SBDs on (100)-oriented substrates exhibited a dramatic increment ($>$1.5$\times$) in SBH as well as reduction in reverse leakage current. The use of thin dielectric interlayers can be an efficient experimental method to modulate SBH of metal/Ga$_2$O$_3$ junctions., Comment: 8 pages, 10 figures, 2 tables

In this paper, the effects of applied voltage, temperature and structural parameters of MPS diodes on the reverse leakage current of these diodes are studied. A new analytical model for merged PiN Schottky (MPS) diodes is also developed to analyze and predict the reverse characteristics of these diodes. The model of the surface electric field is approximately solved by using the 2D Poisson equation. The reverse leakage current model of MPS diodes is analyzed and solved from the four parts of the thermionic emission, namely the leakage, tunneling, depletion and diffusion currents, based on the surface electric field model. The validated model and experimental results show good agreement.

Schottky diodes were formed by oxidizing Ru thin films deposited on n-type GaN at 400, 500, and 600 degrees C in normal laboratory air, and their electrical behavior was compared to that of a Ru/n-GaN reference device. The GaN epitaxial layers were grown via metalorganic chemical vapor deposition. The ruthenium films were deposited by electron beam evaporation. The Schottky barriers were characterized via current vs voltage (IV) and deep-level transient spectroscopy (DLTS) measurements between 70 and 400 K. The temperature dependent forward bias IV characteristics were fit, and the extracted temperature dependence of the effective barrier height for each device was shown to be caused by inhomogeneity at the metal/semiconductor interface. It was found that barrier inhomogeneity could be well described by a modified log-normal distribution. In reverse bias, it was shown that the low-energy tail of the barrier distribution is an important factor in determining leakage current. Favorable results occur for diodes oxidized at 400 and 500 degrees C, but raising the oxidation temperature to 600 degrees C results in a drastic increase in leakage current. DLTS measurements reveal one electron trap at E-C - 0.57 eV in each of the samples. It was found that the concentration of this 0.57 eV trap increases substantially at 600 degrees C and that trap-assisted tunneling likely contributes an additional pathway for reverse leakage current. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Bradley Graduate Fellowship by The Bradley Department of Electrical and Computer Engineering at Virginia Tech; ARPA-E SWITCHES program [DE-AR0000446] L.J.G. would like to acknowledge The Bradley Department of Electrical and Computer Engineering at Virginia Tech for operating and maintaining the Micron Technology Semiconductor Processing Lab. L.J.G. would also like to thank the MSE Department at Virginia Tech for its continuous support. N.P.A. is grateful for funding support from the Bradley Graduate Fellowship provided by The Bradley Department of Electrical and Computer Engineering at Virginia Tech. This research was funded by the ARPA-E SWITCHES program under Grant No. DE-AR0000446, monitored by program managers Dr. T. Heidel and Dr. I. Kizilyalli.

Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of GaN as an α-particle detector. Work in developing GaN-based radiation sensors are still evolving and GaN sensors have successfully detected α-particles, neutrons, ultraviolet rays, x-rays, electrons and γ-rays. This review elaborates on the design of a good radiation detector along with the state-of-the-art α-particle detectors using GaN. Successful improvement in the growth of GaN drift layers (DL) with 2 order of magnitude lower in charge carrier density (CCD) (7.6 × 1014/cm3) on low threading dislocation density (3.1 × 106/cm2) hydride vapor phase epitaxy (HVPE) grown free-standing GaN substrate, which helped ~3 orders of magnitude lower reverse leakage current (IR) with 3-times increase of reverse breakdown voltages. The highest reverse breakdown voltage of −2400 V was also realized from Schottky barrier diodes (SBDs) on a free-standing GaN substrate with 30 μm DL. The formation of thick depletion width (DW) with low CCD resulted in improving high-energy (5.48 MeV) α-particle detection with the charge collection efficiency (CCE) of 62% even at lower bias voltages (−20 V). The detectors also detected 5.48 MeV α-particle with CCE of 100% from SBDs with 30-μm DL at −750 V.

We for the first time demonstrate the heterogeneous integration of 2-inch β-Ga 2 O 3 thin films onto the 4H-SiC and Si (001) substrates by ion-cutting process, as well as the fabrication of high-performance β-Ga 2 O 3 MOSFETs on the heterogeneous wafers. 2-inch single-crystalline β-Ga 2 O 3 thin film with a wafer-level thickness non-uniformity below ±1.8% is transferred onto Si and SiC substrates. Three high-quality heterogeneous wafers, the Ga 2 O 3 -on-SiC (GaOSiC), Ga 2 O 3 -Al 2 O 3 -SiC (GaOISiC), and Ga 2 O 3 -Al 2 O 3 -Si (GaOISi) are fabricated, which have surface RMS roughness below 0.5 nm and the FWHM of XRD rocking curve of 130 arcsec. By varying the channel thickness, both enhancement- and depletion-mode MOSFETs are realized on GaOSiC wafer. As the ambient temperature increases from 300 K to 500 K, little degradation is observed in the on-resistance, forward saturation current, reverse leakage current and breakdown voltage (V br ) of the fabricated Ga 2 O 3 MOSFETs. A device V br above 600 V is achieved at 500 K with a weak dependence on temperature. These results show a significantly improved device thermal stability compared to the reported Ga 2 O 3 -on-Ga 2 O 3 devices. The technology demonstrated in this work is promising to overcome the fundamental thermal limitation of Ga 2 O 3 electronics for high-power applications.

In this paper, the dynamic range of the conventional differential drive rectifier is enhanced based on leakage current reduction technique, to solve the narrow dynamic range problem of the input power and improve the output rectifier performance. The proposed design uses auxiliary transistors to control the conductivity of the rectifying PMOS devices dynamically to reduce the reverse leakage current. Post layout simulations have been performed using 0.18 μm CMOS technology at 402 MHz with 10kΩ load resistor. The proposed rectifier increases the range of the RF input power about ten times compared to a conventional rectifier's dynamic range and reduces the reverse leakage current from ‒98 μA to ‒22 μA. It also boosts the output average voltage at high input power. In addition, the developed rectifier exhibits good performance over wide band of input frequencies up to 2.4 GHz. The proposed rectifier has a small area of about 0.19 mm2.

Atomic layer deposited AlN films on n-InP were electrically characterized. Compared to the sample without AlN, the interface state density obtained from the capacitance–voltage (C–V) measurements was found to decrease with a 7.4 nm thick AlN. According to X-ray photoelectron spectroscopy (XPS) measurements, the sample with a 0.7 nm thick AlN showed dominant peaks related with oxygen bonds (Al–O and In–O). For the sample with a 7.4 nm thick AlN, the dominant peak near the AlN/InP interface was associated with Al–O and N–In bonds whereas it was associated with Al–N bonds near the AlN surface. In addition, the strong emission peaks associated with Al–O bonds were observed across the AlN layer, which indicates that some part of AlN layer is composed of Al–O bonds (like Al2O3). The reverse leakage current for the sample with a 7.4 nm thick AlN at high electric field was explained by Poole–Frenkel (PF) emission, connected with nitrogen vacancy (VN) and oxygen substituting for nitrogen (ON) in the AlN layer.

This paper reports a comprehensive study on the anisotropic electrical properties of vertical ( $\overline {\textsf {2}}01$ ) and (010) $\beta $ -Ga2O3 Schottky barrier diodes (SBDs). The devices were fabricated on single-crystal substrates grown by an edge-defined film-fed growth method. The temperature-dependent current–voltage (I–V) and capacitance–voltage (C–V) characteristics were systematically measured, analyzed, and compared. The ( $\overline {\textsf {2}}01$ ) and (010) SBDs exhibited on-resistances ( ${R}_{{ \mathrm{\scriptscriptstyle ON}}}$ ) of 0.56 and $0.77~\textsf {m}\Omega \cdot \textsf {cm}^{{\textsf {2}}}$ , turn- ON voltages ( ${V}_{{ \mathrm{\scriptscriptstyle ON}}}$ ) of 1.0 and 1.3 V, Schottky barrier heights (SBHs) of 1.05 and 1.20 eV, electron mobilities of 125 and 65 cm2/( $\textsf {V}\cdot ~\textsf {s}$ ), respectively, with an on-current of ~1.3 kA/cm2 and on/off ratio of ~109. The (010) SBD had a larger ${V}_{{ \mathrm{\scriptscriptstyle ON}}}$ and SBH due to anisotropic surface properties (i.e., surface Fermi level pinning and band bending), as supported by X-ray photoelectron spectroscopy measurements. Temperature-dependent I–V also revealed the inhomogeneous nature of the SBH in both devices, where the ( $\overline {\textsf {2}}01$ ) SBD showed a more uniform SBH distribution. The homogeneous SBH was also extracted: 1.33 eV for the ( $\overline {\textsf {2}}01$ ) SBD and 1.53 eV for the (010) SBD. The reverse leakage current of the devices was well described by the two-step trap-assisted tunnelingmodel and the 1-D variable range hopping conduction model. The ( $\overline {\textsf {2}}01$ ) SBD showed a larger leakage current due to its lower SBH and/or smaller activation energy, and thus a smaller breakdown voltage. These results indicate that the crystalline anisotropy of $\beta $ -Ga2O3 can affect the electrical properties of vertical SBDs and should be taken into consideration when designing $\beta $ -Ga2O3 electronics.

Thin AlN layer was deposited on n-type 4H-SiC using atomic layer deposition and the electrical properties of Pt/SiC Schottky diodes with and without AlN layer were comparatively investigated. Based on the capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics, the interface state density decreased but the oxide trap density increased with an AlN layer. The border traps present near the AlN/SiC interface might produce such difference. Compared to the sample without AlN, both the barrier height and the ideality factor increased with an AlN. Analyses on the reverse leakage current density for Pt/AlN/SiC junction showed that the dominant transport mechanisms are ohmic conduction, trap assisted tunneling (TAT) and Fowler–Nordheim emissions at low, intermediate, and high electric field regions, respectively. Both the nitrogen vacancies and dangling bonds in Al in AlN layer were suggested to contribute to the TAT conduction.

An MOS field plate-protected Schottky-drain (gated Schottky-drain) is successfully integrated on a double-channel AlGaN/GaN MOS-HEMT to provide reverse blocking capability. The leakage suppression MOS field plate is deployed on the etched upper GaN channel layer after a barrier fully recess process, leading to a low reverse OFF-state leakage current of −20 nA/mm (at −100 V). The drain metal is deployed adjacent to the MOS field plate, contacting the upper MOS-channel and lower heterojunction channel from the sidewall. A metal-2DEG Schottky contact with a low turn-ON voltage of 0.5 V is achieved. Since the lower channel (below the MOS field plate) is separated from the etched surface of upper GaN channel layer, a high-conductivity MOS-gated channel with a sheet resistance of 806 $\Omega$ /Square is obtained. The device exhibits a threshold voltage of +0.6 V (at $10~\mu \text{A}$ /mm and +1.9 V from linear extrapolation) and an ON-resistance of ~18 $\Omega {\cdot} \text {mm}$ . Besides, a high forward (and reverse) breakdown voltage of 790 V (and −656 V, all at $10~\mu \text{A}$ /mm) is achieved.

The reverse-bias current-voltage characteristics of commercial 1200 V 4H-silicon-carbide junction barrier Schottky (SiC-JBS) rectifiers are studied both experimentally and through numerical simulation. The reverse leakage current measured from physical devices is observed to display both a strong temperature and field dependence. A model is presented to explain the observed behavior based on a combination of trap-assisted tunneling and a thermionic-emission mechanism through a potential barrier located at the metal-SiC interface. The study shows that a two-level trapping model can be necessary to properly explain the measured data. Excellent agreement between the models and the measurements is obtained over a wide range of bias and temperature.

The electrical characteristics of a V/p-GaN Schottky junction have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) characteristics under the assumption of the thermionic emission (TE) theory in the temperature range of 120–280 K with steps of 40 K. The zero-bias barrier height (ΦB0), ideality factor (n), flat-band barrier height (ΦBF) and series resistance (RS) values were evaluated and were found to be strongly temperature dependent. The results revealed that the ΦB0 values increase, whereas n, ΦFB and RS values decrease, with increasing temperature. Using the conventional Richardson plot, the mean barrier height (0.39 eV) and Richardson constant (8.10 × 10−10 Acm−2 K−2) were attained. The barrier height inhomogeneities were demonstrated by assuming a Gaussian distribution function. The interface state density (NSS) values were found to decrease with increasing temperature. The reverse leakage current mechanism of the V/p-GaN Schottky junction was found to be governed by Poole–Frenkel emission at all temperatures.

High-k zirconium oxide (ZrO2) thin insulating layer is deposited on n-type GaN and explored its chemical properties by XPS technique. XPS core level spectra confirms that the formation of ZrO2 thin film on the n-GaN substrate. Later, the Au/ZrO2/n-GaN MIS junction is constructed with a ZrO2 as insulating layer and correlated its electrical properties with the Au/n-GaN MS junction. Results present that a high barrier height (0.94 eV) is obtained for the MIS junction compared with the MS junction (0.73 eV), suggesting the barrier height is altered by the ZrO2 insulating layer. The estimated interface state density (NSS) of the MIS junction is lower compared with the MS junction, revealing that the high-k ZrO2 thin insulating layer decreased NSS. Results confirmed that the reverse leakage current mechanism is governed by a Poole-Frenkel emission in both MS and MIS junctions.

This paper presents the design of a triple-mode wireless power-receiving unit (TWPRU) for battery charger with high efficiency. The TWPRU is proposed based on Alliance for Wireless Power (A4WP), Wireless Power Consortium (WPC), and Power Matters Alliance (PMA) standards. An adaptive alignment gate controller technique is proposed in the triple-mode active rectifier to block the reverse leakage current and improve the power conversion efficiency (PCE). This technique can compensate for the delays in the gate control signals of the main switching mosfet s at different operating frequencies for A4WP, WPC, and PMA. The dead time of a dc–dc converter is optimally determined depending on the voltage and the temperature variations by phase calibration circuit. This chip with an active area of 5.0 mm × 3.5 mm is implemented in 0.18- μ m BCD technology. The maximum PCEs of the triple-mode active rectifier are 91.7% in the A4WP mode and 92.7% in the WPC/PMA mode, respectively. The maximum PCE of the dc–dc converter is 92.3% at a load current of 500 mA, while the system efficiencies of TWPRU at A4WP and WPC/PMA modes are about 84.5% and 85.5%, respectively.

This study discloses the diode’s influences on the piezoelectric energy harvesting performance. The piezoelectric-based energy harvesting system plays an important role in scavenging environment vibration energy into electrical energy, which can be utilized by low-power electronic devices. With respect to the interface circuit, a full-wave bridge circuit is usually needed to rectify the alternating current (AC) signal into a direct current (DC) signal. The full-wave bridge is composed of four diodes, whose characteristics may influence the harvested power significantly. Therefore, in this paper, the diodes’ properties and influences on the energy harvesting performance are analyzed and presented via simulation and experimental studies. It is found the harvested energy has close relationship with the diode characteristics. For the high source impedance case, diode with low reverse leakage current is favorable. For the low source impedance case, diode with low forward voltage drop is favorable. The corresponding experimental study is carried out via a piezoelectric beam, which shows that the measured harvested power differences can almost be up to 800% for the same test structure.

n-Type nanocrystalline FeSi2/p-type Si heterojunctions were formed by using facing-target direct- current sputtering at room temperature. The J-V characteristic results revealed that the reverse leakage current is large and the response under illumination of near-infrared light is very weak. The capacitance-voltage-frequency (C-V-f) and conductance-voltage-frequency (G-V-f) measurements were carried out at room temperature in order to estimate the series resistance (Rs) by using the Nicollian-Brews method and the density of interface state (Nss) by using the Hill-Coleman method. By estimation according to the Nicollian-Brews method, the Rs value increases with decreasing f value. The Rs values at zero bias voltage were 2.07 Ω at 60 kHz and 1.54 Ω at 2 MHz, which are consistent with those calculated by using the Cheung's and Norde's methods. The obtained Rs should be attributable to the Rs existing in the ohmic contact and neutral regions, which is the current-limiting factor for junctions. The nss values calculated by using the Hill-Coleman method were 2.70 × 1014 eV-1cm-2 at 60 kHz and 1.43 × 1013 eV-1cm-2 at 2 MHz. This result revealed the presence of interface states at the hetero-interface behaving as a leakage current center and a trap center of the photo-generated carrier, which degraded the junction properties at room temperature.

A novel Schottky contact super barrier rectifier (SSBR) with a top N-enhancement layer and a P-injector (P-TNEL-SSBR) is proposed and investigated by simulation. In addition to the concept of SSBR we presented recently, the proposed P-TNEL-SSBR has an extra P-injector structure and a top NEL design (TNEL, a modified structure of the N-enhancement layer we proposed earlier). The P-injector structure makes this new rectifier have the conductivity modulation effect by hole injection at large forward current densities which will be helpful for surge current capability. The TNEL decreases the barrier capacitance during the reverse recovery state and weakens the JFET effect further in the forward conducting state. Simulation results show that, with almost the same reverse leakage current density and breakdown voltage of approximately 57 V, P-TNEL-SSBR increases the figure of merit (FOM, equates to $${V}_{\mathrm{B}}^{2}/{R}_{\mathrm{on,sp}})$$ by 11.1% at the forward current density of 200 $$\hbox {A/cm}^{2}$$ and decreases the reverse recovery time by 13.3% at the reverse voltage of 12 V compared to those of NEL-SSBR we reported earlier.

In this work, the effects of oxygen plasma treatment by inductive coupled plasma on current transport of AlInN/GaN Schottky diodes were investigated. The current-voltage (I-V) results show that oxygen plasma treatment can significantly suppress reverse leakage current of the Schottky diodes by over three orders of magnitude, and meanwhile can enhance remarkably the effective barrier height and improve the ideality factor of the Schottky contact by forming a thin oxidation layer at the AlInN surface. However, I-V curve occurs a transient and recoverable reduction in current response at low forward bias. The further analysis indicates that donor-like traps related to nitrogen vacancies or their complexes induced by oxygen plasma treatment are responsible for this transient current reduction.

The effect of Co-60 Gamma irradiation on electrical characteristics of CdTe/CdS solar cell has been analyzed using in-situ current-voltage characterization (I-V) in dark condition. The irradiation was done over a wide range of doses from 1kGy to 100 kGy. Electrical parameters such as ideality factor (n), series resistance (RS) and reverse bias leakage current (IR) for each dose have been calculated from the I-V characteristics. The ideality factor of the pristine solar cell is found to be 1.80 and it gradually increased up to 3.38 for the dose of 10 kGy, then it is around 3.38-3.61 for higher doses up to 100 kGy. The I-V characteristics showed significant increase in forward bias and drastic increase in reverse leakage current. The value of IR is 16.8 µA for pristine solar cell and it increases to 1.46 mA for 10 kGy. Further there is four times observable change in the value of IR. However the value of Rs is 0.80 ohm for pristine and continuously decreases to 0.34 ohm for 50 kGy dose. Further there is slight increase in the series resistance to 0.38 ohm for 100 kGy dose.

The chemical, structural and electrical characteristics of a fabricated Au/Gd2O3/n-GaN heterostructure with gadolinium oxide (Gd2O3) as an insulating layer are explored by XPS, XRD and I–V techniques at room temperature and 400 °C annealing. XPS and XRD results reveal that the Gd2O3 films are formed at the interface. The electrical results of heterostructure are correlated with the conventional Au/n-GaN Schottky structure results. The as-deposited and 400 °C annealed heterostructures exhibited excellent rectifying behavior and very low reverse leakage current compared to the Schottky structure. Higher barrier height (BH) and on/off ratio are achieved for the heterostructure compared to the Schottky structure, which has led the barrier height modified by Gd2O3 insulating layer. Also, the results indicate that the BH slightly increases for the 400 °C annealed heterostructures. Further, the BH, ideality factor and series resistance are evaluated by Cheung’s, Norde functions and ΨS-V plot and the values are found to be similar with one another that indicates their consistency and validity. In addition, the mechanism of the BH modulation could be explained by feasible energy level band diagrams. These findings indicate that the Gd2O3 films could be a favored dielectric material for the development of metal/insulating/semiconductor devices.

The leakage current transport mechanism under reverse bias of Au/Ni/GaN Schottky diode is studied using temperature dependent current-voltage (I-V-T) and capacitance-voltage (C-V) characteristics. I-V measurement in this study is in the range of 140 K–420 K in steps of 10 K. A reduction in voltage dependent barrier height and a strong internal electric field in depletion region under reverse bias suggested electric field enhanced thermionic emission in carrier transport via defect states in Au/Ni/GaN SBD. A detailed analysis of reverse leakage current revealed two different predominant transport mechanisms namely variable-range hopping (VRH) and Poole-Frenkel (PF) emission conduction at low ( 260 K) temperatures respectively. The estimated thermal activation energies (0.20–0.39 eV) from Arrhenius plot indicates a trap assisted tunneling of thermally activated electrons from a deep trap state into a continuum of states associated with each conductive threading dislocation.

In this paper, a trench Schottky contact super barrier rectifier (SSBR) with a p-injector (P-T-SSBR) is proposed and investigated by simulation. In addition to the concept of SSBR, the proposed P-T-SSBR also includes a trench gate design and a p-injector plug. The trench gate design eliminating the junction-type field-effect transistor effect of planar gate structure enables the new rectifier to have ultralow forward voltages and a good tradeoff between the forward voltages and reverse leakage currents. The p-injector plug combined with the trenched SSBR cells equips this new rectifier with the merged p-i-n/Schottky operating mechanism resulting in bipolar conducting mode at large forward current densities (larger than 1500 A/cm2) which will be helpful for surge current capability. Compared to the modified SSBR with an ${N}$ -enhancement layer, we presented earlier, simulation results show that, with almost the same breakdown voltage of 57 V, the new rectifier increases the figure of merit (equates to ${V}_{B}^{{\,{2}}}/{R}_{\textsf {on,sp}}$ ) by 35.1% at the forward current density of 200 A/cm2, decreases the reverse leakage current by 34.9%, and decreases the reverse recovery time by 25.4% at the reverse voltage of 12 V.

A CMOS cross-coupled RF rectifier that improves power conversion efficiency (PCE) with low reverse leakage current for energy harvesting wireless sensors is proposed. In this Letter, the authors propose a CMOS cross-coupled differential RF rectifier that uses a thick-oxide MOSFET as a rectifying device to improve PCE by reducing reverse leakage current. The proposed rectifier is designed for UHF band application using 0.18 µm CMOS technology. Proposed rectifier achieves a peak PCE of 75.2% and sensitivity of − 17 dBm for 1 V output voltage. Peak PCE is improved by 8.8% compared to the conventional rectifier.

In this paper, lateral AlGaN/GaN Schottky barrier diodes are investigated in terms of anode construction and diode structure. An original GaN Schottky diode manufacturing-process flow was developed. A set of experiments was carried out to verify dependences between electrical parameters of the diode, such as reverse and forward currents, ON-state voltage, forward voltage and capacitance, anode-to-cathode distance, length of field plate, anode length, Schottky contact material, subanode recess depth, and epitaxial structure type. It was found that diodes of SiN/Al0.23Ga0.77N/GaN epi structure with Ni-based anodes demonstrated two orders of magnitude lower reverse currents than diodes with GaN/Al0.25Ga0.75N/GaN epitaxial structure. Diodes with Ni-based anodes demonstrated lower VON and higher IF compared with diodes with Pt-based anodes. As a result of these investigations, an optimal set of parameters was selected, providing the following electrical characteristics: VON = 0.6 (at IF = 1 mA/mm), forward voltage of the diode VF = 1.6 V (at IF = 100 mA/mm), maximum reverse voltage VR = 300 V, reverse leakage current IR = 0.04 μA/mm (at VR = −200 V), and total capacitance C = 3.6 pF/mm (at f = 1 MHz and 0 V DC bias). Obtained electrical characteristics of the lateral Schottky barrier diode demonstrate great potential for use in energy-efficient power applications, such as 5G multiband and multistandard wireless base stations.

The effect of KrF excimer laser irradiation on the optical and electrical properties of epitaxial wafers with a p-GaN surface were investigated at different laser energy densities and pulse numbers. The laser-irradiated samples were annealed in oxygen. The laser irradiation-induced changes in optical and electrical properties of GaN epitaxial wafers were examined using PL, I–V, XPS, SIMS, and Hall effect measurements. Experimental results show that under an appropriate laser-irradiated condition, optical and electrical properties of the samples were improved to different degrees. The samples which were annealed after laser irradiation have better electrical properties such as the hole concentration and sheet resistance than those without annealing. We hypothesize that the pulsed KrF excimer laser irradiation dissociates the Mg–H complexes and annealing treatment allows the hydrogen to diffuse out more completely under the oxygen atmosphere at a proper temperature, by which the crystalline symmetry of GaN is improved. Under appropriate laser conditions and O2-activated annealing, the light output of the laser-irradiated GaN-based LED sample is about 1.44 times that of a conventional LED at 20 mA. It is found that the wall-plug efficiency is 10% higher at 20 mA and the reverse leakage current is 80% lower at 5 V.

This work examined reverse leakage currents in GaN p-n junctions nearly free of dislocations. Diodes with shallow bevel mesas and breakdown voltages (BVs) in the range of 130–1000 V exhibited avalanche breakdown at the designed voltages. Significant leakage currents were observed in response to reverse bias values far below the BVs and a weak effect of temperature was also evident. The data were explained based on direct band-to-band tunneling (BTBT). The BTBT current was dominant in those devices having BVs of several hundred volts but was far below the detection limit in the case of a 1000 V-class diode.

The present study reports the fabrication and characterization of organic–inorganic hetero-junctions based on π-conjugated polymers on n-GaN and Al0.24Ga0.76N/GaN epi-structures. The polymer contact properties were investigated with n-GaN and AlGaN/GaN epi-structures. The PNA/n-GaN and PNA/AlGaN/GaN samples exhibited better diode characteristics with low ideality factor values of 3.15 and 2.79, respectively in comparison to PANI based n-GaN and AlGaN/GaN diodes. Also a reasonably good Schottky barrier height was achieved with PNA polymer for n-GaN (0.52 eV) and AlGaN/GaN (0.70 eV) samples. Low reverse leakage current ~10−12 A and 10−9 A at a reverse bias voltage of −10 V was observed for PNA/n-GaN and PNA/AlGaN/GaN samples, respectively. PNA is a promising candidate in comparison to PANI for π-conjugated polymer contact on n-GaN and AlGaN/GaN epitaxial hetero-structure. The studies also confirmed that the performance of the diode could be improved by using AlGaN/GaN inorganic structure than GaN.

The influence of constant current stress on the conduction mechanism of reverse leakage current in ultraviolet (UV) light emitting diodes (LEDs) in the UV-A spectral range has been investigated for the first time using temperature-dependent current-voltage measurement from 370 K to 55 K. Below 220 K, variable range hopping mechanism dominates in UV-A LEDs. While, above 220 K, the leakage current is attributed to Poole-Frenkel emission mechanism within the bias range of −3 ∼ −6 V. With the increasing of the reverse bias, the conduction mechanism transforms from Poole-Frenkel emission to space-charge-limited conduction mechanism. In particular, applying electrical stress yields an alteration of the transition voltage from −7.5 V to −6.5 V. We propose that stress could lead to a reduction of the thermal activation energy, and therefore alters the transition voltage.

In this paper, a high performance enhancement-mode (E-mode) Al2O3/GaN hybrid MOS-HFET and a novel AlGaN/GaN lateral diode are experimentally demonstrated. Based on the proposed approach to engineer the dielectric/GaN positive interface fixed charges ( Q it+) by postdielectric annealing, the E-mode metal–oxide–semiconductor heterojunction field-effect transistor (MOS-HFET) obtains a better tradeoff between the threshold voltage ( V TH) control and drain current drive capability due to the significant suppression of Q it+ and the associated remote scattering effect. Owing to the uniquely high V TH and gate swing, the E-mode MOS-HFET exhibits respectable higher faulty turn on immunity that is prone to improve the reliability of the device in power switching applications and simplify the gate driver design. On the other hand, by featuring a new turn-on mechanism of MIS-gate-controlled 2-D electron gas (2DEG) channel, the diode exhibits ultralow turn-on voltage and reverse leakage current, which are beneficial to lowering the conduction loss and off-state power consumption of GaN-on-Si power diodes. Moreover, the diode is compatible with E-mode hybrid MOS-HFET, which is promising for realizing full-GaN single-chip power ICs.

In this paper, a novel high-K/low-K compound passivation AlGaN/GaN Schottky Barrier Diode (CPG-SBD) is proposed to improve the off-state characteristics of AlGaN/GaN schottky barrier diode with gated edge termination (GET-SBD) by adding low-K blocks in to the high-K passivation layer. The reverse leakage current of CPG-SBD can be reduced to 1.6 nA/mm by reducing the thickness of high-K dielectric under GET region to 5 nm, while the forward voltage and on-state resistance keep 1 V and 3.8 Ω mm, respectively. Breakdown voltage of CPG-SBDs can be improved by inducing discontinuity of the electric field at the high-K/low-K interface. The breakdown voltage of the optimized CPG-SBD with 4 blocks of low-K can reach 1084 V with anode to cathode distance of 5 μm yielding a high FOM of 5.9 GW/cm 2 . From the C-V simulation results, CPG-SBDs induce no parasitic capacitance by comparison of the GET-SBDs.

This letter reports on a novel enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) that combines nanowire channel and fluorine plasma treatment using inductively coupled plasma (ICP). Compared with the conventional HEMTs, the threshold voltage of E-mode HEMT shifts from −2.8 to +0.7 V, and the Schottky reverse leakage current is reduced by one order of magnitude. The device exhibits a superior performance with a drain current of 460 mA/mm at ${V} _{{{\text {GS}}}}$ - ${V} _{{{\text {TH}}}} = 2$ V. High $\text{I}_{{ \mathrm{\scriptscriptstyle ON}}}/\text{I}_{{ \mathrm{OFF}}}$ ratio of approximately $10^{{\mathbf {9}}}$ and high breakdown voltage of 138 V with $\text{L}_{{{\text {DS}}}}=4~\mu \text{m}$ are obtained, i.e., the breakdown voltage of E-mode HEMT is improved by 25% than that in conventional HEMTs. The drain induced barrier lowering (DIBL) is as low as 4 mV/V, and the subthreshold swing (SS) of 70 mV/decade is achieved. The device exhibits an intrinsic current gain cutoff frequency $f_{{\text T}}$ of 22 GHz and a maximum oscillation frequency ${f} _{{\text {max}}}$ of 60 GHz.

The performance of gallium nitride (GaN) p-i-n diodes were investigated for use as a betavoltaic device. Dark IV measurements showed a turn on-voltage of approximately 3.2 V, specific-on-resistance of 15.1 mΩ cm 2 and a reverse leakage current of −0.14 mA/cm 2 at −10 V. A clear photo-response was observed when IV curves were measured under a light source at a wavelength of 310 nm (4.0 eV). In addition, GaN p-i-n diodes were tested under an electron-beam in order to simulate common beta radiation sources ranging from that of 3 H (5.6 keV average) to 63 Ni (17 keV average). From this data, we estimated output powers of 53 nW and 750 nW with overall efficiencies of 0.96% and 4.4% for our device at incident electron energies of 5.6 keV and 17 keV corresponding to 3 H and 63 Ni beta sources respectively.

In this paper, we investigated the effect of post-gate annealing (PGA) on reverse gate leakage and the reverse bias reliability of Al0.23Ga0.77N/GaN high electron mobility transistors (HEMTs). We found that the Poole–Frenkel (PF) emission is dominant in the reverse gate leakage current at the low reverse bias region (V th < V G < 0 V) for the unannealed and annealed HEMTs. The emission barrier height of HEMT is increased from 0.139 to 0.256 eV after the PGA process, which results in a reduction of the reverse leakage current by more than one order. Besides, the reverse step stress was conducted to study the gate reliability of both HEMTs. After the stress, the unannealed HEMT shows a higher reverse leakage current due to the permanent damage of the Schottky gate. In contrast, the annealed HEMT shows a little change in reverse leakage current. This indicates that the PGA can reduce the reverse gate leakage and improve the gate reliability.

A normally-off reverse blocking high electron mobility transistor (HEMT) with p-GaN gate and hybrid p-GaN ohmic drain (p-GaN RB-HEMT) has been fabricated and investigated to achieve reverse blocking capability. Compared with conventional p-GaN gate HEMT with ohmic drain (p-GaN HEMT), the proposed device features that a p-GaN layer is embedded into the ohmic drain. This could realize not only the reverse blocking capability, but also the effective suppression of reverse leakage current based on the formed pn junction drain, and an ultralow reverse leakage current of

In this Letter, the p-GaN high electron mobility transistor (HEMT) with hybrid drain of recessed Schottky (RS) and p-GaN isolation blocks' drain (HSP drain) is proposed and fabricated for good reverse blocking capability. The related operation mechanism has been investigated and revealed. The proposed device features a drain terminal consisting of the array-distributed recessed Schottky and p-GaN isolation blocks. Based on the features, the reverse leakage current (5 × 10−9 A/mm at VDS = −100 V) is obviously reduced by two orders of magnitude compared with that (5 × 10−7 A/mm) of p-GaN HEMTs only with recessed Schottky (RS) drain, which is the lowest leakage current among the reported GaN-on-Si reverse blocking transistors. The introduction of these p-GaN isolation blocks has a negligible impact on Von (Von = 0.63 V). Therefore, a good improvement in the trade-off between the reverse leakage current and Von could be achieved because of the significant reduction in the reverse leakage current without sacrificing Von. In addition, the reverse breakdown voltage of −800 V at 1 μA/mm with a substrate grounded in the proposed device is evidently improved compared with the counterpart (−680 V), which is attributed to effective alleviation of the high electric field near the HSP drain. These results demonstrate the significance and potential of p-GaN HEMTs with HSP drain in reverse blocking applications.