Schottky Characteristics Research Articles

Hole transport mechanism at high temperatures in p-GaN/AlGaN/GaN heterostructure

This Letter reports an investigation of hole transport in p-GaN/AlGaN/GaN heterostructures through experimental and theoretical analyses under varied conditions. Highly non-linear current–voltage (I–V) characteristics, obtained via the linear transmission line method measurements, are utilized for this study. At low bias voltage, the transport can be ascribed to the Schottky nature of the contact, while at high bias, the conduction is observed to be governed by space-charge limited current (SCLC). The Schottky characteristics (Schottky barrier height and non-ideality factor) and the SCLC exponent were analyzed for devices with varying contact spacings and at different high temperatures. The SCLC exponent, m, is in the range of 2≤m≤4 depending on the applied voltage range, revealing the existence of the trap states in the channel region. The findings of this work indicate that the charge injection, field-induced ionization, and trap states in the p-GaN channel are critical factors in the current transport of p-GaN/AlGaN/GaN heterostructure.

Comparative Analysis of Ni/Ag and Ni/Au Contacts on GaN/AlGaN/GaN Platform

Herein, the electrical characteristics and Schottky barrier of Ni/Au and Ni/Ag contacts on the GaN/AlGaN/GaN heterojunction are investigated. Both contacts on the p‐GaN contact layer (Mg: ≈3 × 1019 cm−3) exhibit weak Schottky characteristics. The nonlinear current–voltage (I–V) characteristics are observed, leading to variations in contact resistance (RC) and sheet resistance (Rsh) with changing bias voltage. The Ni/Ag contact achieves a lower Schottky barrier height calculated by using the I–V method. Furthermore, when employing a p++‐GaN layer (Mg: ≈1 × 1020 cm−3) as the contact layer, the Ni/Ag contact forms an Ohmic contact without Schottky characteristics, achieving a satisfactory RC of 30.31 Ω mm. This result demonstrates its viability as a competitive candidate for p‐channel field‐effect transistors’ fabrication.

A voltage-driven dual-mode MoSe2 photodetector with graphene as van der Waals contact

Two-dimensional (2D) molybdenum selenide (MoSe2) is promising for use in the development of photodetectors for the harvesting of light from the ultraviolet to the near-infrared band, while high responsivity and fast response speed are difficult to simultaneously realize. Herein, we present a dual-mode MoSe2 photodetector with asymmetric electrodes, in which graphene and Cr metal are utilized as ohmic and Schottky contacts, respectively. The photodiode possesses fabulous Schottky characteristics, with a rectification ratio of ∼250 and a low dark current of ∼40 pA at −1 V. Under forward bias voltage of 1 V, the photodetector works in photoconductive mode with a slow response speed (decay time: ∼5 min) but high responsivity (632 mA W−1). However, at reverse bias voltage, the photodetector acts as a photovoltaic-type device due to the Schottky barrier between Cr and MoSe2. Because of the reinforced built-in electric field, the photodetector driven at −5 V shows much faster response speeds (rise time: 1.96 ms; decay time: 755 µs). This study provides a deep understanding of asymmetric structure MoSe2 photodetectors operated in two modes, which promotes a forward step toward 2D material optoelectronics.

Analysis of lead free CsSnBr3 based perovskite solar cells utilizing numerical modeling

In this study, we propose several CsSnBr3-based PSC configurations using the Solar Cell Capacitance Simulator (SCAPS-1D), incorporating various efficient Electron transport layers (ETLs) such as TiO2, PCBM, WS2, SnO2, ZnO, IGZO, C60, and Hole transport layers (HTLs) like CBTS, CFTS, CuO, CuI, Spiro-OMeTAD, PEDOT:PSS, P3HT, CuSbS2, CuSCN, and Cu2O. Numerical simulation results reveal that the device structure ITO/WS2/CsSnBr3/Cu2O/Au exhibits outstanding power conversion efficiency (PCE), retaining the closest photovoltaic parameter values among 70 different configurations. In this configuration, WS2 served as the ETL, and Cu2O acted as the HTL. This device achieved an outstanding peak PCE of 20.02%. It also boasted a high open circuit voltage (Voc) of 1.23 V, a short circuit current density (Jsc) of 19.32 mA cm−2, and an impressive fill factor (FF) of 84.18%. In comparison, devices utilizing materials like TiO2, PCBM, SnO2, ZnO, IGZO, and C60 yielded PCE values of 19.72, 19.73, 19.72, 19.73, 19.72, and 15.60%, respectively. Furthermore, for the seven best-performing configurations, we investigated the effects of CsSnBr3 absorber thickness, absorber-acceptor doping density (NA), conduction band offset (CBO), ETL doping density (ND), Capacitance–Voltage (C-V), Mott–Schottky (M-S) characteristics, generation and recombination rates, series resistance (Rse), shunt resistance (Rsh), temperature, current–voltage characteristics (J-V), and quantum efficiency (QE) on performance metrics. Our findings indicate that all seven ETLs, when combined with Cu2O HTL, can serve as excellent materials for fabricating high-efficiency CsSnBr3-based PSCs with the ITO/ETL/CsSnBr3/Cu2O/Au structure. To validate our results, we compared the simulation outcomes obtained with SCAPS-1D for the best seven CsSnBr3-PSC configurations with previously published research works. This comprehensive simulation study opens a promising avenue for the cost-effective production of high-performance, lead-free CsSnBr3-based PSCs, contributing to a greener and pollution-free environment.

Reliable electrical performance of β-Ga2O3 Schottky barrier diode at cryogenic temperatures

Electrical and trap characteristics of a large-size (2 × 2 mm2) β-Ga2O3 Schottky barrier diode (SBD) from 50 to 350 K have been reported. The ideality factor (n) decreases from 1.34 to nearly unity as temperature rises from 50 to 350 K, demonstrating near-ideal Schottky characteristics. The leakage current at cryogenic temperature (100 K) was significantly suppressed, indicating excellent off-state blocking performance at low temperatures. The weak temperature dependence of the carrier concentration (NS) and Schottky barrier height (ΦB) infers stable electrical characteristics of the β-Ga2O3 SBD. The stressed current density-voltage (J-V) and on-the-fly measurements reveal reliable dynamic performance under harsh low temperature conditions. Via deep-level transient spectroscopy, an electron trap, which is related to the dynamic performance instability and Lorentzian hump in low frequency noise spectra, is revealed for a β-Ga2O3 epilayer. The study reveals enormous potential of the utilization of a large-size β-Ga2O3 SBD for extreme temperature environments.

Optimizing the Efficiency of Lead‐Free Cs2TiI6‐Based Double Halide Perovskite Solar Cells Using SCAPS‐1D

Conventional lead halides perovskites have attracted much attention to become a next‐generation solar technology. Besides their low cost and excellent efficiency, high toxic nature and device instability become the major issue to limit their wide applications. Ti‐based (Cs2TiI6) double halide perovskite solar cells (PSCs) have emerged as a potential candidate to become the best alternate. However, poor device efficiency is still a restriction. Therefore, proper optimization and deep device analysis are needed to explore the full potential of Cs2TiI6‐based PSCs. In the present research work, the open‐circuit voltage (Voc), current density (Jsc), fill factor (FF), and power conversion efficiency of Cs2TiI6‐based PSC are successfully optimized. The device optimization is performed using the different combinations of electron transport layers and hole transport layers along with absorber thickness, acceptor doping density, and interface defect density. The effect of Rseries and Rshunt is explored and identified the best device efficiency of 28.07% along with other photovoltaic (PV) parameters; Voc = 1.41 V, Jsc = 22.44 mA cm−2, and FF = 88.15%, respectively. The supportive analysis of C–V and Mott–Schottky characteristics helps to get deep insight into the device's performance. Furthermore, the resultant PV parameters are compared to the previous studies as well.

Electrical Characteristics of Thermally Stable Ag–Pd–Cu Alloy Schottky Contacts on n-Al0.6Ga0.4N

We report the fabrication of high-barrier-height and thermally reliable Schottky contacts to n-Al0.6Ga0.4N by using an Ag-Pd-Cu (APC) alloy. The Schottky barrier heights (SBHs) and ideality factors computed using the current-voltage (I–V) model ranged from 0.82 to 0.97 eV and from 3.15 to 3.44, respectively. The barrier inhomogeneity model and capacitance-voltage (C–V) method yielded higher SBHs (1.62–2.19 eV) than those obtained using the I–V model. The 300 °C-annealed APC sample exhibited more uniform electrical characteristics than the 500 °C-annealed Ni/Au Schottky samples (each with the best Schottky behavior). Furthermore, the scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) results indicated that the APC Schottky contacts were more thermally stable than the Ni/Au contacts. On the basis of the X-ray photoemission spectroscopy (XPS) results, the improved Schottky characteristics of the APC alloy contacts are described and discussed.

Study of Scandium Based Ohmic Contacts to AlGaN/GaN Heterostructures

Development of semiconductor devices based on AlGaN/GaN heterostructure requires study and improvement of ohmic contacts, whose necessary improvement lies in process of checking new metallic compositions and thermal formation process parameters. Usually, in metallic ohmic annealed contacts of AlGaN/GaN heterostructures, titanium is applied as the first layer, but scandium may be an alternative. It was proved to be useful to obtain both ohmic and Schottky characteristics, depending on annealing temperature of the contact. In the presented research, contacts including scandium (Sc/Al/Mo/Au) were fabricated, and, as reference sample, contacts with titanium including metallziation (Ti/Al/Mo/Au). Reference sample was annealed at 825°C, and forming temperatures for scandium contacts were 825°C, 625°C, and 425°C. All samples after thermal formation process were additionally thickened with Ru/Au bilayer. To quickly compare level of metals in metallization mixing during formation process and to check applicability of EDS (Energy-Dispersive X-ray Spectroscopy), the simulations of electrons trajectories and EDS point scans were performed.

Drain Side Area-Modulation Effect of Parasitic Schottky Diode on ESD Reliability for High Voltage P-Channel Lateral-Diffused MOSFETs

This letter focused on the additive effect of horizontal Schottky diodes on the drain side of a high-voltage p-channel laterally diffused metal–oxide–semiconductor (pLDMOS). These components were evaluated using transmission-line pulse and human body model (HBM) tests. When the parasitic Schottky area at the drain was smaller, the Schottky characteristics were less obvious; the device’s current mostly flowed through the heavily doped $\text{P}^{+}$ area, and the improvement in ${I}_{\text {t2}}$ was minor. When the parasitic Schottky area covered more than 60% of the drain side, the Schottky area accounted for the majority of current flow; therefore, the electrostatic discharge current could flow more evenly. These modified pLDMOSs can withstand higher voltages because of their parasitic Schottky diodes and higher impedance. In addition, their ${I}_{\text {t2}}$ values are superior to those of normal pLDMOSs. With the drain side of the pLDMOS completely covered by Schottky diodes, the device produced the highest ${I}_{\text {t2}}$ value of 1.659 A (130.4% higher than that of the reference sample), an HBM value of 5 kV (300% higher than the reference), and an improved holding voltage (4% greater than that of the reference).

Analysis of Floating Limiting Rings Termination Under Repetitive Avalanche Current Stress for 4H-SiC JBS Rectifiers

The reverse breakdown characteristics of 4H-SiC Junction Barrier Schottky (JBS) rectifiers adopting the different floating limiting rings (FLRs) termination structures are experimented and analyzed under the repetitive avalanche current stress. The experimental results indicate that the breakdown voltage (BV) shift of the device after the repetitive avalanche current stress is highly dependent on the FLRs design, which determines the distributions of the surface electric field and avalanche current at avalanche condition. It is proved that the uniform surface electric field distribution of the FLRs structure at avalanche condition is helpful for the device achieve to achieve better BV shift robustness on the repetitive avalanche current stress. Additionally, the FLRs structure, which has smaller S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and enough N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , can present both higher BV and excellent BV shift robustness on the repetitive avalanche current stress.

Effects of silicon surface defects on the graphene/silicon Schottky characteristics

Distinct characteristics and yet adverse in some cases have been widely reported in the graphene/silicon Schottky junction under DC biasing, for biological and chemical sensing, or as a photodetector. The explanations to these observations are often attributed to the nature of the graphene layer but are still far from satisfactorily for many cases. In this work, we conducted a detailed analysis on both the forward and reverse current-voltage characteristics under different temperatures and we proposed that the silicon surface defects, which had been well-known as Pb0 centers or ≡Si, should play an important role in the adverse characteristics observed in the Gr/Si junction. Compared with the metal/Si and oxide/Si interface, the graphene-isolated Pb0 centers at the Gr/Si interface are chemically inactive but are still electrically active and that modify the carrier transportation over the junction barrier. Without efficient chemical passivation, the graphene-covered Si surface should maintain the most native Si surface such that it preserves a much higher amount of Pb0 centers as compared with other Si junctions or interfaces. This should be the main origin for the reported adverse current-voltage characteristics.

Temperature dependent performance of ITO Schottky contacts on β-Ga2O3

Sputtered indium tin oxide (ITO) was used as a rectifying contact on lightly n-type (n ∼ 1016 cm−3) β-Ga2O3 and found to exhibit excellent Schottky characteristics up to 500 K, with no thermally driven degradation to this temperature. The barrier height extracted from current–voltage characteristics was 1.15 ± 0.04 eV at 300 K and 0.78 ± 0.03 eV at 500 K, with thermionic behavior of charge carriers over the image force lowered Schottky barriers dominating the carrier transport at low temperatures. The breakdown voltages were 246, 185, and 144 V at 300, 400 and 500 K, respectively. At 600 K, the diodes suffered irreversible thermal damage. The diode on/off ratio was &amp;gt;105 for reverse biases up to 100 V. At higher reverse voltage, the current shows an I ∝ Vn relationship with voltage, indicating a trap-assisted space-charge-limited conduction (SCLC) mechanism. We observed this SCLC relation when the reverse voltage was larger than 100 V for 300 and 400 K and at &amp;lt;100 V at 500 K. The ITO can also be used to make Ohmic contacts on heavily doped Ga2O3 suggesting the possibility of completely optically transparent power devices.

Diamond Schottky p-i-n diodes for high power RF receiver protectors

The electrical characteristics of diamond Schottky p-i-n diodes grown by plasma enhanced chemical vapor deposition have been measured from DC to 25 GHz and used to extract the small-signal parameters for a lumped-element compact model. The model accurately reproduces the forward and reverse bias DC characteristics, the capacitance-voltage behavior, as well as the insertion and reflection loss. The high thermal conductivity of diamond makes the diodes ideally suited for high power radar receiver protector applications. We demonstrate that under forward bias a single diode can provide 14 dB of input power attenuation. For self-biased limiter applications, a two-stage circuit with back-to-back diodes has been simulated using the diode model to show > 20 dB of attenuation at an input power of 50 dBm.

Differences in electrical responses and recovery of GaN p+n diodes on sapphire and freestanding GaN subjected to high dose 60Co gamma-ray irradiation

We investigate the effects of high-rate and high total doses of 60Co gamma rays on the current–voltage (IV) characteristics of GaN p+n diodes grown by metal-organic chemical vapor phase epitaxy on Ga-face (0001) sapphire and hydride vapor phase epitaxy freestanding GaN substrates. We show that diodes grown on sapphire undergo more permanent changes upon irradiation at doses up to 3900 kGy than those grown on freestanding GaN. By combining diode and circular transfer length method measurements, we show that the p-type contact interface and adjacent p++ Mg-doped layer are sensitive to irradiation. In initial experiments, diodes grown on sapphire exhibited p-type contacts with Schottky characteristics, while those on freestanding GaN were Ohmic. Serendipitously, we identified and subsequently irradiated a freestanding sample with a pre-irradiation spatial gradient of p-contact Schottky vs Ohmic behavior across the die. This sample allowed the root cause of induced change to be identified as differences in the p++ contacting layer. We show that the p-type contact's pre-irradiation Schottky behavior is predictive of diodes' IV characteristics changing significantly upon gamma-ray irradiation. Further, we observe that the IV curves of diodes on freestanding GaN recover fully over several weeks at room temperature to be indistinguishable from pre-irradiation. IV curves from diodes on sapphire do not fully recover; we thus hypothesize that interactions between radiation-induced point defects and threading dislocations affect the evolution of radiation damage.

Temperature dependence of barrier height inhomogeneity in β-Ga2O3 Schottky barrier diodes

From an analysis of Pd contact Schottky diodes fabricated on (100) β-Ga2O3 wafers, in combination with data extracted from published work, we show that the barrier height inhomogeneity commonly observed in β-Ga2O3 Schottky diodes has a strong correlation to the temperature. For doping of ∼5 × 1017 cm−3, the barrier height arising from an inhomogeneous contact continues to increase to a temperature of ∼440 K followed by a decrease upon a further increase in temperature, which is commonly attributed to the bandgap narrowing of the semiconductor referred to as the Varshni shift. At this regime, Schottky characteristics representing close to homogeneous behavior is obtained. Thus, a device under normal operating conditions in a system, which results in an elevated temperature, is expected to exhibit near-homogeneous electrical characteristics.

Mapping of photo-electrochemical etched Ni/GaN Schottky contacts using scanning internal photoemission microscopy—comparison between n- and p-type GaN samples

We present the experimental results on mapping characterization of the effects of photo-electrochemical (PEC) and inductive coupled plasma (ICP) etchings for both p-type and n-type GaN Schottky contacts by using scanning internal photoemission microscopy to clarify the current transport mechanism. The photoyield (Y) increased in the PEC etched regions by 4%–5% for the n-GaN, by 15% for the p-GaN samples. We proposed a model that the ICP etching induced donor-type damages in the vicinity of the GaN surfaces. In the ICP etched regions, Y increased by 10% for the n-GaN as well, but significantly decreased by 80% for the p-GaN samples. The PEC etching has less effect on the Schottky characteristics than the ICP etching, especially in the p-type sample.

Research on the Negative Resistance Characteristics of Silicon-based Trench MOS Barrier Schottky Diodes

The negative resistance characteristics of Trench MOS Barrier Schottky (TMBS) diodes were studied by simulation and theoretical calculation. A reasonable simulation model was established according to the experimental results of Schottky Barrier Diodes (SBD), which were utilized to simulate the TMBS diodes. A theoretical calculation model of TMBS diodes under forward bias was constructed based on existing SBD theoretical analysis to systematically understand the simulation results. Both simulation and theoretical calculation demonstrate that the negative resistance characteristics of TMBS diodes under forward bias are caused by the accumulation of minority carriers at the epitaxial region and the accumulation of majority carriers at the epitaxial region and oxide layer.

Surface roughness effect on the electrical characteristics of Pd/SiC nanocontacts

We report on the effect of the surface roughness of Pd nanostructures on the electrical characteristics (Schottky barrier height) of Pd nanostructures/SiC nano-contacts as probed by conductive atomic force microscopy.We produced Pd nanostructures on 6H-SiC surface by thermal-induced dewetting of a nanoscale-thick deposited Pd film. We changed the Pd nanostructures mean diameter <D> and mean surface roughness <σ> by controlling the annealing temperature. Scanning Electron Microscopy and Atomic Force Microscopy allowed us to quantify <D> and <σ> in various annealing conditions. In addition, current–voltage characteristics were acquired on single Pd nanostructure/SiC contacts by placing the tip of Conductive Atomic Force Microscopy on the Pd nanostructure. Typical rectifying Schottky characteristics were recorded from which the Schottky barrier heights ΦB were extracted. For ballistic Pd nanostructures (<D>≈25 nm), ΦB was found to increase by increasing the nanostructures surface roughness above a critical value. For non-ballistic Pd nanostructures (<D> in the range 150–200 nm), no effect of the surface roughness was observed on ΦB. Regarding the ballistic Pd/SiC contact, the observed phenomenon is ascribed to the conducting electrons surface scattering relaxation mechanism and the surface roughness scattering mean free path for electrons is evaluated in the range 1.5–3.5 nm.

Growth of Carbon Dot-Decorated ZnO Nanorods on a Graphite-Coated Paper Substrate to Fabricate a Flexible and Self-Powered Schottky Diode for UV Detection.

The fabrication of flexible as well as self-powered optoelectronic devices is a growing and challenging area of research. Some scientists have reported the fabrication of either flexible or self-powered photodetectors recently. However, most of the literature studies fail to report the fabrication of self-powered as well as flexible photodetectors. This study reports the fabrication of self-powered, carbon dot (CD)-enhanced, flexible ZnO/graphite heterojunction-based UV detector where cellulose paper has been used as the substrate. A detailed study on the crystallinity and the defects of the ZnO nanorods has been done with appropriate characterizations. The CD-enhanced ZnO/graphite heterojunction showed Schottky characteristics. The Schottky parameters such as the barrier height, ideality factor, and the series resistance have also been calculated using the Cheung-Cheung method. The observed values of barrier height, ideality factor, and the series resistance are 0.74 eV, 3.74, and 503 kΩ, respectively. The transient response at self-powered condition has been demonstrated. The response time and the recovery time at self-powered condition have also been calculated with the help of the transient response, and those values are ∼2 and ∼3.2 s, respectively. The responsivity and the specific detectivity of the fabricated UV detector have been calculated as 9.57 mA/W and 4.27×108 Jones, respectively, at 330 nm wavelength, which is quite comparable with literature-reported values, considering a self-powered photodetector.

Compact electrothermal model of laboratory made GaN Schottky diodes

PurposeThe purpose of this paper is to propose a simple electrothermal model of GaN Schottky diodes, and its usefulness for circuit-level electrothermal simulation of laboratory-made devices is proved.Design/methodology/approachThe compact electrothermal model of this device has the form of a subcircuit for simulation program with integrated circuit emphasis. This model takes into account influence of a change in ambient temperature in a wide range as well as influence of self-heating phenomena on dc characteristics of laboratory-made GaN Schottky diodes. The method of model parameters estimation is described.FindingsIt is shown that temperature influences fewer characteristics of GaN Schottky diodes than classical silicon diodes. The discussed model accurately describes properties of laboratory made GaN Schottky diodes. Additionally, the measured and computed characteristics of these diodes are shown and discussed.Research limitations/implicationsThe presented model together with the results of measurements and computations is dedicated only to laboratory-made GaN Schottky diodes.Originality/valueThe presented investigations show that characteristics of laboratory-made GaN Schottky diodes visibly change with temperature. These changes can be correctly estimated using the compact electrothermal model proposed in this paper. The correctness of this model is proved for four structures of such diodes characterised by different values of structure area and a different assembly process.