Vertical Schottky Barrier Research Articles

Vertical GaN-on-GaN Schottky Barrier Diodes With Multi-Floating Metal Rings

Vertical GaN Schottky barrier diodes (SBDs) with floating metal rings (FMRs) as edge termination structures have been fabricated on bulk GaN substrates. Devices with different FMR geometries were investigated including various numbers of rings and various spacings between rings. These devices have a low Ron of 1.16~1.59 mΩ·cm 2 , a turn-on voltage of 0.96~ 0.94 V, a high on-off ratio of 10 9 , a nearly ideal ideality factor of 1.03~1.09, and a Schottky barrier height of 1.11~1.18 eV at room temperature. These devices have similar forward electrical characteristics, indicating that FMRs don't degrade the device rectifying performance. The ideality factor decreased and the Schottky barrier height increased with increasing temperature from 300 K to 420 K, where the temperature dependencies of the two parameters indicate the inhomogeneity of the metal/semiconductor Schottky interface. In addition, FMRs can improve device breakdown voltages. As the number of FMRs increased from 0 to 20, the reverse breakdown voltage increased from 223 to 289 V. As the spacing between the FMRs increased from 1.5 to 3 μm, the reverse breakdown voltage increased from 233 to 290 V, respectively. These results indicate multiple FMRs with proper spacings can effectively improve breakdown performance without degrading the device forward characteristics. This work represents a useful reference for the FMR termination design for GaN power devices.

High-Voltage ($\overline{\text{2}}01$ ) $\beta$ -Ga2O3 Vertical Schottky Barrier Diode With Thermally-Oxidized Termination

In this letter, a high-performance ( $\overline {{2}} 01$ ) $\beta $ -Ga2O3 vertical Schottky Barrier Diode (SBD) with a thermally oxidized termination is reported. A novel edge termination at the Schottky contact edge is formed by using thermal oxidation treatment, which reduces the electron concentration and effectively suppresses the peak electric field. By using a thermal oxidation termination, the breakdown voltage ( ${V}_{\text {br}}$ ) of $\beta $ -Ga2O3 SBD increases from 380 V to 940 V, and the specific on-resistance ( ${R}_{\text {on,sp}}$ ) just increases from 2.9 $\text{m}\Omega \cdot $ cm2 to 3.0 $\text{m}\Omega \cdot $ cm2. Our device demonstrates a power figure of merit ( ${V}_{\text {br}}^{{2}}/{R}_{\text {on,sp}})$ as high as 295 MW/cm2. These results indicate that the thermally oxidized termination shows a new way to improve the breakdown characteristics of $\beta $ -Ga2O3 SBD.

Field-Plated Ga2O3 Trench Schottky Barrier Diodes With a BV2/$R_{\text{on,sp}}$ of up to 0.95 GW/cm2

We report the realization of field-plated vertical Ga2O3 trench Schottky barrier diodes (SBDs). The trench SBDs show significantly lower leakage current than regular SBDs. With employment of field plate, a breakdown voltage (BV) of 2.89 kV is achieved, which is ~ 500 V higher than those without field plate. Trench sidewall depletion is observed, and the average depletion width is extracted using an analytical model. The trench SBDs have a differential specific on-resistance ( $\text {R}_{\text {on,sp}}$ ) of 10.5 (8.8) $\text{m}\Omega ~\cdot {\mathrm {cm}}^{\text {2}}$ from DC (pulsed) measurements, which leads to a Baliga’s figure-of-merit ( ${\mathrm {BV}}^{{2}}/\text {R}_{\text {on,sp}}$ ) of 0.80 (0.95) GW/cm2— the highest among Ga2O3 power devices to date.

Dry and wet etching for β-Ga2O3 Schottky barrier diodes with mesa termination

We investigated dry and wet etchings of β-Ga2O3 and fabricated vertical Schottky barrier diodes (SBDs) with mesa termination using the optimal etching condition. Using an inductively-coupled plasma reactive-ion etching with a nickel-hard mask, a β-Ga2O3 (010) mesa structure with a smooth sidewall is obtained at an etching rate of 77 nm min−1 in BCl3/Cl2 mixture gas. By immersing β-Ga2O3 (001) vertical SBDs with mesa termination in hot phosphoric-acid solution, the specific on resistance and ideality factor of the SBDs are reduced to 0.91 mΩcm2 and 1.03, respectively. Current density at reverse bias is in good agreement with thermionic field emission model.

Vertical β‐Ga2O3 Schottky Barrier Diodes with Enhanced Breakdown Voltage and High Switching Performance

Herein, vertical Schottky barrier diodes (SBDs) based on a bulk β‐Ga2O3 substrate are developed. The devices feature an ion‐implanted planar edge termination (ET) structure, which can effectively smoothen the electric field peak and reduce the electric field crowding at the Schottky junction edge. Greatly enhanced reverse blocking characteristics including ≈103× lower reverse leakage current and 1.5× higher breakdown voltage (VB) are achieved, whereas good forward conduction such as a reasonably high on‐state current density and near‐unity ideality factor is maintained. In addition, the switching performance of the fabricated vertical β‐Ga2O3 SBDs is investigated using a double‐pulse test circuit. When switching from an on‐state current of 350 mA to a reverse‐blocking voltage of −100 V, the vertical β‐Ga2O3 SBDs exhibit fast reverse recovery with a reverse recovery time (trr) of ≈14.1 ns and reverse recovery charge (Qrr) of ≈0.34 nC, outperforming the Si fast recovery diode (FRD) of similar ratings. The results indicate a great promise of vertical β‐Ga2O3 SBDs for high‐voltage fast switching applications.

Vertical Ga2O3 Schottky Barrier Diodes With Guard Ring Formed by Nitrogen-Ion Implantation

A guard ring (GR) was employed to improve the breakdown voltage ( ${V}_{\text {br}}$ ) of vertical Ga2O3 Schottky barrier diodes (SBDs) with or without a field-plate (FP) by eliminating electric field concentration at the edges of anode and FP electrodes. The GR structure was formed by nitrogen (N)-ion implantation. Four types of vertical SBD structures with: 1) neither a GR nor a FP; 2) a GR; 3) a FP; and 4) both a GR and a FP were fabricated on the same substrate. The SBDs with a GR [structures 2) and 4)] showed larger ${V}_{\text {br}}$ values than their GR-free counterparts [structures 1) and 3)]. Considering the trade-off relationship between ${V}_{\text {br}}$ and specific on-resistance ( ${R}_{\text {on}}$ ), a ${V}_{\text {br}}/{R}_{\text {on}}$ combination of 1.43 kV/ $4.7~\text {m}\Omega \cdot \text {cm}^{2}$ for the GR/FP-SBD corresponds to one of the best balanced data for Ga2O3 SBDs.

Vertical Ga2O3Schottky Barrier Diodes With Small-Angle Beveled Field Plates: A Baliga’s Figure-of-Merit of 0.6 GW/cm2

This letter demonstrates vertical Ga2O3 Schottky barrier diodes (SBDs) with a novel edge termination, the small-angle beveled field plate (SABFP), fabricated on thinned $\text{G}_{{2}}\text{O}_{{3}}$ substrates. Non-punch-though design is used for the drift region with a donor concentration of ${3}\sim {3.5} \times {10} ^{{16}}$ cm−3, rendering a device differential ON-resistance of $\sim 2~\text{m}\Omega ~\cdot $ cm2. A new wet-etch technique is developed by using a bi-layer mask, which consists of spin-on-glass (SOG) and plasma-enhanced chemical vapor deposited (PECVD) SiO2, to fabricate a very small bevel angle (∼ 1°) in the mesa and field plates. This SABFP structure facilitates the electric field spreading at device edges, rendering a breakdown voltage of 1100 V, a peak electric field of 3.5 MV/cm in Ga2O3 at the Schottky contact edge, and an averaged electric field over 3.4 MV/cm underneath the contact. Our device demonstrates a Baliga’s figure of merit of 0.6 GW/cm2, which is among the highest in all reported Ga2O3 power devices and comparable to the state-of-the-art GaN SBDs. These results show the great potential of Ga2O3 SBDs for future power applications.

Performance Improved Vertical Diamond Schottky Barrier Diode With Fluorination-Termination Structure

We have demonstrated performance improved vertical diamond Schottky barrier diodes (SBDs) with fluorination-terminated (FT) structure. A turn-on voltage of 1.6 V, an on-resistance of 50.2 $\text{m}\Omega \cdot $ cm2, a breakdown voltage of 117 V, and a breakdown field of 3.3 MV/cm are achieved for the SBD with an FT length of $20~\mu \text{m}$ . We verified that the SBD with FT structure could obtain lower turn-on voltage and larger breakdown field compared to that of the SBD without FT structure. The results show that the SBDs with FT structure have significant potential for future high-performance power electronics application.

Detection of Defects in Diamond by Etch‐Pit Formation

Correlation between the reverse current densityJRof diamond vertical Schottky barrier diodes (SBD) and the shape of the etch pits is investigated. Etch pits form throughout the whole epitaxial layer area with a density of 6.8 × 104–3.0 × 105 cm−2. Most etch pits are isolated‐type, with flat‐bottom or point‐bottom shape. A typical pit size is 3–5 μm in width and 1–3 μm in depth. Some etch pits aggregate linearly with a size of >10 μm. The SBDs show largeJRwhen these etch pit clusters appear. The etch pit cluster density is <103 cm−2.

All-Inkjet-Printed Vertical Heterostructure for Wafer-Scale Electronics.

In this study, we fabricated an array of all-inkjet-printed vertical Schottky barrier (SB) transistors and various logic gates on a large-area substrate. All of the electronic components, including the indium-gallium-zinc-oxide (IGZO) semiconductor, reduced graphene oxide (rGO), and indium-tin-oxide (ITO) electrodes, and the ion-gel gate dielectric, were directly and uniformly printed onto a 4 in. wafer. The vertical SB transistors had a vertically stacked structure, with the inkjet-printed IGZO semiconductor layer placed between the rGO source electrode and the ITO drain electrode. The ion-gel gate dielectric was also inkjet-printed in a coplanar gate geometry. The channel current was controlled by adjusting the SB height at the rGO/IGZO heterojunction under application of an external gate voltage. The high intrinsic capacitance of the ion-gel gate dielectric facilitated modulation of the SB height at the source/channel heterojunction to around 0.5 eV at a gate voltage lower than 2 V. The resulting vertical SB transistors exhibited a high current density of 2.0 A·cm-2, a high on-off current ratio of 106, and excellent operational and environmental stabilities. The simple device structure of the vertical SB transistors was beneficial for the fabrication of all-inkjet-printed low-power logic circuits such as the NOT, NAND, and NOR gates on a large-area substrate.

Remote Gating of Schottky Barrier for Transistors and Their Vertical Integration.

This paper introduces a strategy to modulate a Schottky barrier formed at a graphene-semiconductor heterojunction. The modulation is performed by controlling the work function of graphene from a gate that is placed laterally away from the graphene-semiconductor junction, which we refer to as the remote gating of a Schottky barrier. The remote gating relies on the sensitive work function of graphene, whose local variation induced by locally applied field effect affects the change in the work function of the entire material. Using Kelvin probe force microscopy analysis, we directly visualize how this local variation in the work function propagates through graphene. These properties of graphene are exploited to assemble remote-gated vertical Schottky barrier transistors (v-SBTs) in an unconventional device architecture. Furthermore, a vertical complementary circuit is fabricated by simply stacking two remote-gated v-SBTs (pentacene layer as the p-channel and indium gallium zinc oxide layer as the n-channel) vertically. We consider that the remote gating of graphene and the associated device architecture presented herein facilitate the extendibility of graphene-based v-SBTs in the vertical assembly of logic circuits.

Electronic devices fabricated on mist-CVD-grown oxide semiconductors and their applications

This review summarizes progress in the fabrication of Schottky diodes (SDs), metal–semiconductor and metal–oxide–semiconductor FETs on mist-chemical vapor deposition-(CVD)-grown oxide semiconductor thin films for optical displays, high power devices, and gas sensing applications. These devices generally showed high on-currents, high rectification and on–off ratios. Mist-CVD-grown IGZO and ZTO MESFETs displayed an extreme stability against numerous standard stress conditions. Negative bias temperature stress produced a significant and permanent improvement in the performance of amorphous oxide SDs and MESFETs. Sub-kV breakdown voltage and low specific on-resistance of 0.4 mΩ cm2 were realized in vertical Sn-doped α-Ga2O3 Schottky barrier diodes by Oda et al. [Appl. Phys. Express 9, 021101 (2016)] but severe current collapse was observed in planar Sn-doped α-Ga2O3 MESFETs. Mist CVD has demonstrated its capacity for not only atomic layer-by-layer control but also the growth of active layers in high-performance electronic devices, even though it is a solution-processed atmospheric pressure technique.

Review of the Recent Progress on GaN-Based Vertical Power Schottky Barrier Diodes (SBDs)

Gallium nitride (GaN)-based vertical power Schottky barrier diode (SBD) has demonstrated outstanding features in high-frequency and high-power applications. This paper reviews recent progress on GaN-based vertical power SBDs, including the following sections. First, the benchmark for GaN vertical SBDs with different substrates (Si, sapphire, and GaN) are presented. Then, the latest progress in the edge terminal techniques are discussed. Finally, a typical fabrication flow of vertical GaN SBDs is also illustrated briefly.

Fin-channel orientation dependence of forward conduction in kV-class Ga2O3 trench Schottky barrier diodes

Ga2O3 vertical trench Schottky barrier diodes with four different fin-channel orientations are realized on (001) substrates and compared. Fin-channels along the [010] direction with (100)-like sidewalls result in the highest forward current, while other channel orientations all lead to a shallow turn-on behavior and much lower forward current, indicative of severe sidewall depletion attributed to negative interface charges. The comparison indicates that the interface charge density is the smallest on the (100)-like surfaces. The breakdown voltage of the diodes with 1-μm fin width is around 2.4 kV, with no apparent dependence on the channel orientation.

High-voltage vertical GaN-on-GaN Schottky barrier diode using fluorine ion implantation treatment

This paper reports on a high-voltage vertical GaN Schottky barrier diode (SBD) using fluorine (F) ion implantation treatment. Compared with the GaN SBD without F implantation, this SBD effectively enhanced the breakdown voltage from 155V to 775V and significantly reduced the reverse leakage current by 105 times. These results indicate that the F-implanted SBD showed improved reverse capability. In addition, a high Ion/Ioff ratio of 108 and high Schottky barrier height of 0.92 eV were also achieved for this diode with F implantation. The influence of F ion implantation in this SBD was also discussed in detail. It was found that F ion implantation to GaN could not only create a high-resistant region as effective edge termination but be employed for adjusting the carrier density of the surface of GaN, which were both helpful to achieve high breakdown voltage and suppress reverse leakage current. This work shows the potential for fabricating high-voltage and low-leakage SBDs using F ion implantation treatment.

GaN drift-layer thickness effects in vertical Schottky barrier diodes on free-standing HVPE GaN substrates

Vertical Schottky barrier diodes (SBD) with different drift-layer thicknesses (DLT) of GaN up to 30 μm grown by metalorganic chemical vapour deposition (MOCVD) were fabricated on free-standing GaN grown by hydride vapour phase epitaxy (HVPE). At room temperature, SBD’s exhibited average barrier heights (ΦB) in the range of 0.73 eV to 0.81 eV. The effective barrier heights (ΦBeff) of SBDs with different DLT also exhibited a similar range of ΦB measured at room temperature. The measured reverse breakdown voltages (VBD) of SBDs increased from 562 V to 2400 V with an increase in DLT. The observation of high VBD of SBDs could be due to the lower effective donor concentration (7.6×1014 /cm3), which was measured from SIMS analysis. The measured VBD of 2400 V is the highest value ever reported for a 30 μm DLT vertical GaN SBD without additional edge termination or field plate (FP).

Reduction in reverse leakage current of diamond vertical Schottky barrier diode using SiNX field plate structure

Abstract Diamond vertical Schottky barrier diodes (SBDs) with SiNX field-plate (FP) structure has been investigated. Ti/Au and Zr/Ni/Au metal stacks are used as ohmic and Schottky metal, respectively. The forward current density of SBDs with and without FP are 1600 and 3300 A/cm2 at −10 V, respectively. The depletion layer’s thickness and net doping concentration are 380 nm and 1.4 × 1016 cm−3, respectively, as extracted from the capacitance-voltage measurement. The reverse leakage current of SBDs with and without FP are 1.8 × 10−6 and 6.3 A/cm2 at 100 V, respectively, indicating that the FP technique can significantly suppress reverse leakage current at the Schottky junction edge.

Effect of temperature on photoresponse properties of solar-blind Schottky barrier diode photodetector based on single crystal Ga2O3**Project supported by National Key Research and Development Plan of China (Grant Nos. 2016YFB0400600 and 2016YFB0400601), the National Natural Science Foundation of China (Grant Nos. 61574026, 11675198, 61774072, and 11405017), the Natural Science Foundation of Liaoning Province, China (Grant Nos. 201602453 and 201602176), China

A solar-blind photodetector is fabricated on single crystal Ga2O3 based on vertical structure Schottky barrier diode. A Cu Schottky contact electrode is prepared in a honeycomb porous structure to increase the ultraviolet (UV) transmittance. The quantum efficiency is about 400% at 42 V. The Ga2O3 photodetector shows a sharp cutoff wavelength at 259 nm with high solar-blind/visible (=3213) and solar-blind/UV (=834) rejection ratio. Time-resolved photoresponse of the photodetector is investigated at 253-nm illumination from room temperature (RT) to 85.8 °C. The photodetector maintains a high reversibility and response speed, even at high temperatures.

Vertical GaN Schottky barrier diodes on Ge-doped free-standing GaN substrates

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on Ge-doped free-standing GaN substrates grown by hydride vapor phase epitaxy. Detailed material characterization was performed, and the results indicate the superiority of Ge doping in the GaN, which contributed to the SBDs with lower stress, fewer defects and higher quality. Based on the capacitance-voltage and current–voltage measurements performed, SBDs achieved together with a low turn-on voltage Von (0.71–0.74 V), high current Ion/Ioff ratio (3.9 × 107–2.9 × 108), high Schottky barrier height (0.96–0.99 eV), and high breakdown voltage Vb (802 V for a 100 μm diameter). This shows that vertical GaN SBDs on the Ge-doped substrates are promising candidates for high power applications.

1230 V β-Ga2O3 trench Schottky barrier diodes with an ultra-low leakage current of <1 μA/cm2

β-Ga2O3 vertical trench Schottky barrier diodes (SBDs) are realized, demonstrating superior reverse blocking characteristics than the co-fabricated regular SBDs. Taking advantage of the reduced surface field effect offered by the trench metal-insulator-semiconductor structure, the reverse leakage current in the trench SBDs is significantly suppressed. The devices have a higher breakdown voltage of 1232 V without optimized field management techniques, while having a specific on-resistance (Ron,sp) of 15 mΩ cm2. An ultra-low leakage current density of <1 μA/cm2 is achieved before breakdown, the lowest among all reported Ga2O3 Schottky barrier diodes. Fast electron trapping and slow de-trapping near the Al2O3/Ga2O3 interface are observed by repeated C-V measurements, which show an interface state ledge and positive shifts of flat-band voltages with increasing voltage stress. By comparison between pulsed and DC measurements, the device self-heating effect and the trapping effect are uncoupled. It is found that the trapping effect at the trench sidewall affects the on-resistance of the trench SBDs, even under pulsed conditions. With reduced trapping effect and better field management technique, the trench SBDs could further harvest the promising material properties of β-Ga2O3.