High voltage 4H-SiC Schottky barrier diodes

Characteristics of 4H-SiC Schottky barrier diodes with breakdown voltages up to 1000 V are reported for the first time. The diodes showed excellent forward I-V characteristics, with a forward voltage drop of 1.06 V at an on-state current density of 100 A/cm². The specific on-resistance for these diodes was found to be low (2×10 ^-3 Ω-cm² at room temperature) and showed a T ^1.6 variation with temperature. Titanium Schottky barrier height was determined to be 0.99 eV independent of the temperature. The breakdown voltage of the diodes was found to decrease with temperature     

High performance of high-voltage 4H-SiC Schottky barrier diodes

High performance of high-voltage rectifiers could be realized utilizing 4H-SiC Schottky barrier diodes. A typical specific on-resistance (R_on) of these devices was 1.4×10³ Ω cm³ at 24°C (room temperature) with breakdown voltages as high as 800 V. These devices based on 4H-SiC had R _on's lower than 6H-SiC based high-power rectifiers with the same breakdown voltage. As for Schottky contact metals, Au, Ni, and Ti were employed in this study. The barrier heights of these metals for 4H-SiC were determined by the analysis of current-voltage characteristics, and the reduction of power loss could be achieved by controlling the barrier heights     

P-type 4H and 6H-SiC high-voltage Schottky barrier diodes

High-voltage Schottky barrier diodes have been successfully fabricated for the first time on p-type 4H- and 6H-SiC using Ti as the barrier metal. Good rectification was confirmed at temperatures as high as 250°C. The barrier heights were estimated to be 1.8-2.0 eV for 6H-SiC and 1.1-1.5 eV for 4H-SiC at room temperature using both I-V and C-V measurements. The specific on resistance (R_on,sp) for 4H- and 6H-SiC were found to be 25 mΩ cm^-2 and 70 mΩ cm^-2 at room temperature. A monotonic decrease in resistance occurs with increasing temperature for both polytypes due to increased ionization of dopants. An analytical model is presented to explain the decrease of R_on,sp with temperature for both 4H and 6H-SiC which fits the experimental data. Critical electric field strength for breakdown was extracted for the first time in both p-type 4H and 6H-SiC using the breakdown voltage and was found to be 2.9×10⁶ V/cm and 3.3×10⁶ V/cm, respectively. The breakdown voltage remained fairly constant with temperature for 4H-SiC while it was found to decrease with temperature for 6H-SiC     

High-barrier Schottky diodes on p-type silicon due to dry-etching damage

It is known that the barrier height of Schottky diodes made to dry-etched silicon surfaces deviate from the barrier height values obtained for diodes fabricated on wet chemically etched or cleaved silicon. This effect, in cases where neither a substantial residue layer nor a surface film is formed, can be exploited to yield diodes on p-type Si that display barrier enhancement together with excellent diode ideality factors. It is shown that the barrier heights produced on p-type Si, by exploiting this effect of dry etching, can achieve a value of ∼0.75 eV which is ∼0.15 eV better than the best value reported for wet chemically etched or cleaved p-Si. When this barrier height value is attained, it is found to be independent of metallization. The same barrier height is achieved by two very different dry etching techniques: Ar⁺ion-beam etching (IBE) and CCl4reactive ion etching (RIE).     

Device processing and characterisation of high temperature silicon carbide Schottky diodes

High temperature silicon carbide diodes with nickel silicide Schottky contacts were fabricated by deposition of titanium-nickel metal film on 4H-SiC epitaxial wafer followed by annealing at 550 °C in vacuum. Room temperature boron implantation have been used to form single zone junction termination extension. 4H-SiC epitaxial structures designed to have theoretical parallel-plain breakdown voltages of 1900 and 3600 V have been used for this research. The diodes revealed soft recoverable avalanche breakdown at voltages of 1450 and 3400 V, respectively, which are about 80% and 95% of theoretical values. I-V characteristics of fabricated 4H-SiC Schottky diodes have been measured at temperatures from room temperature up to 400 °C. The diodes revealed unchangeable barrier heights and ideality factors as well as positive coefficients of breakdown voltage.     

Nearly ideal enhanced barrier height Schottky contacts to n-InP for MESFET applications

The author reports the substantial enhancement of the Schottky barrier height of n-InP, using a new surface passivation process. Au contacts on the passivated surface resulted in nearly ideal Schottky diodes with barrier heights as large as 0.83 eV, ideality factors between 1.02 and 1.17 and high breakdown voltages. The passivation is found to promote the formation of a phosphorus oxide at the interface, which is believed to be responsible for the enhancement of the barrier height. The high quality of the contacts makes them ideal for InP MESFET gate electrodes.<>     

High-voltage (>1 kV) SiC Schottky barrier diodes with lowon-resistances

Au/6H-SiC Schottky barrier diodes with high blocking voltages were fabricated using layers grown by step-controlled epitaxy. A breakdown voltage of over 1100 V was achieved for silicon carbide (SIC) Schottky barrier diodes. These high-voltage SIC rectifiers had specific on-resistances lower than the theoretical limits of Si rectifiers by more than one order of magnitude. The specific on-resistance increased with temperature according to a T^2.0 dependence. The diodes showed good characteristics at temperatures as high as 400°C     

Effect of chemisorbed oxygen on the Au, Cu-CdS barrier height

The measured barrier heights of different Au-CdS and Cu-CdS contacts ranged from 0·77 to 0·91 eV and from 0·52 to 0·63 eV, respectively. These devices were fabricated by vacuum deposition of metal (Au, Cu) onto etched CdS surfaces which were exposed to air. A simple model which takes into account chemisorbed oxygen and an interfacial layer is presented to explain the variation in Schottky barrier heights observed in this study. A density of approximately 3 × 10¹¹ cm⁻² oxygen states on the CdS surface is calculated from the simple model. This density agrees well with the values reported in the literature. The presence of absorbed oxygen and an interfacial layer on etched CdS surfaces was confirmed by auger spectroscopy measurements.     

Schottky-barrier diodes of MBE-deposited antimony on n and p gallium arsenide

Sb---GaAs Schottky barrier diodes on n and p clean substrates have been prepared by in-situ metal deposition in a molecular beam epitaxy (MBE) system. The barrier heights for n and p specimens prepared on Ga-rich surfaces sum to the bandgap of the GaAs. Barriers prepared on As-rich surfaces are slightly lower and seem to sum to about 0.1 eV less than the bandgap. Reduction of the effective barrier heights on substrates with higher doping concentrations are in agreement with the theoretical predictions of Padovani and Stratton. Thermal annealings up to 250°C show changes in barrier heights that depend on whether the original surface was As- or Ga-rich.     

Schottky barrier heights of n-type and p-type Al0.48In0.52As

The authors report electrical measurements on four different metal contacts which formed Schottky barriers to lightly doped complementary n- and p-type Al_0.48In_0.52As epitaxial material grown by molecular beam epitaxy on semi-insulating InP substrates. The Schottky contact metals studied were Au, Al, Pt, and tri-layer Ti/Pt/Au. The Schottky barrier heights varied from 0.560 eV for Al on n-type AlInAs to 0.905 eV for Al on p-type AlInAs, with intermediate values for the other metals studied. The sum of n- and p-type Schottky barrier heights for each metal contact ranged from 1.440 to 1.465 eV, in good agreement with the accepted Al_0.48In_0.52As bandgap value of 1.45 eV     

High-voltage Ni- and Pt-SiC Schottky diodes utilizing metal fieldplate termination

We have fabricated 1 kV 4H and 6H SiC Schottky diodes utilizing a metal-oxide overlap structure for electric field termination. This simple structure when used with a high barrier height metal such as Ni has consistently given us good yield of Schottky diodes with breakdown voltages in excess of 60% of the theoretically calculated value. This paper presents the design considerations, the fabrication procedure, and characterization results for these 1 kV Ni-SiC Schottky diodes. Comparison to similarly fabricated Pt-SiC Schottky diodes is reported. The Ni-SiC ohmic contact formation has been studied using Auger electron spectroscopy and X-ray diffraction. The characterization study includes measurements of current-voltage (I-V) temperature and capacitance-voltage (C-V) temperature characteristics. The high-temperature performance of these diodes has also been investigated. The diodes show good rectifying behavior with ON/OFF current ratios, ranging from 10⁶ to 10 at 27°C and in excess of 10⁶ up to 300°C     

Enhancement of effective barrier height in Ti-silicon Schottky diode using low-energy ion implantation

Increasing the effective barrier height in a Ti-p-type silicon Schottky diode has been achieved by means of low-energy ion implantation to introduce a thin inversion layer on silicon substrate. It is shown theoretically that effective barrier height equal to the energy bandgap can be obtained in such structure if the thickness and dopant density of the implanted layer are properly chosen. Experimental results for several titanium (Ti) on phosphorus implanted p-type silicon Schottky diodes show that effective barrier heights were increased from 0.6 eV for the Ti-p Si Schottky diode to 0.96 eV for a Ti-n-p-Si Schottky diode with a phosphorus-implanted layer thickness of 400 Å and dose of 1.26 × 10¹²cm^-2. Good agreement is obtained between the calculated and the measured barrier height for several Ti-n-p silicon Schottky diodes.     

Schottky rectifiers on silicon using high barriers

Schottky diodes are presently used for power rectification because of their low forward voltage drop. However, they have only been fabricated on relatively low resistivity and thin semiconductor layers. Hence the reverse breakdown voltages are low. To make diodes that stand higher reverse voltages, low doped material of sufficient thickness is necessary. Ordinary Schottky barriers do not inject minority carriers and the resistive voltage drop at high forward currents will be large, However, for high Schottky barriers ～ 0.9eV, minority carriers are injected and the series resistance is decreased.In this paper we report results from one-dimensional numerical calculations as well as experimental results of high barrier Schottky diodes. We discuss the voltage drop at high forward currents for different substrate resistivity and thickness, as well as values of the high barrier.     

Ni，Ti/4H-SiC肖特基势垒二极管

采用本实验室生长的4H-SiC外延片,分别用高真空电子束蒸Ni和Ti做肖特基接触金属,Ni合金作欧姆接触,SiO_2绝缘环隔离减小高压电场集边效应等技术,制作出4H-SiC肖特基势垒二极管(SBD)。该器件在室温下反向击穿电压大于600 V,对应的漏电流为2.00×10~(-6)A。对实验结果分析显示,采用Ni和Ti作肖特基势垒的器件的理想因子分别为1.18和1.52,肖特基势垒高度为1.54 eV和1.00 eV。实验表明,该器件具有较好的正向整流特性。     

Schottky barriers on atomically clean cleaved GaAs

We report here the first systematic study of the electronic properties of Al, Au, Ag and Cu Schottky barrier diodes on n-type GaAs. These diodes were formed on cleaved (110) surfaces in ultra-high vacuum (UHV) using similar conditions and evaporation rates during the initial stages of Schottky barrier formation as in the photoemission spectroscopy (PES) studies. Barrier height determinations using device measuring techniques (current-voltage (I–V), capacitive-voltage (C–-V) and internal photoemission) are compared with the results from the PES studies. Essentially identical barrier heights are found from PES and the electrical measurements for the noble metals. The barrier height of the noble metal: n-GaAs system (0.9 eV) is larger than any simple metal on n-type GaAs previously reported. This is examined in light of recent work by Zur, McGill and Smith [22] and a model is suggested to explain it. Results of this study are found to be consistent with the unified defect model which has hypothesized that the barrier height is established by the energy levels of structural defects formed at the surface during the metal deposition.     

Sprayed zinc-cadmium sulfide films for Cu2S/ZnxCd1-xS heterojunction solar cells

Cu2S/ZnxCd1-xS solar cells with stable open-circuit voltages up to 0.784 V were formed on zinc-cadmium sulfide films deposited by spray pyrolysis. x was varied between zero and 0.7 by varying the spray solution composition. ZnxCd1-xS films formed Schottky diodes with evaporated chromium contacts; depletion layer width (in light) in the films increased with x, from 0.16 to 3.1 microns. Resistivity of the films increased exponentially with x. Optical band gap increased with x from 2.41 eV at x = 0 to 2.82 eV at x = 0.6.     

Avalanche phenomena in 4H-SiC p-n diodes fabricated by aluminum orboron implantation

Characteristics of p-n junction fabricated by aluminum-ion (Al⁺) or boron-ion (B⁺) implantation and high-dose Al⁺-implantation into 4H-SiC (0001) have been investigated. By the combination of high-dose (4×10¹⁵ cm^-2) Al⁺ implantation at 500°C and subsequent annealing at 1700°C, a minimum sheet resistance of 3.6 kΩ/□ (p-type) has been obtained. Three types of diodes with planar structure were fabricated by employing Al+ or B+ implantation. B ⁺-implanted diodes have shown higher breakdown voltages than Al⁺-implanted diodes. A SiC p-n diode fabricated by deep B+ implantation has exhibited a high breakdown voltage of 2900 V with a low on-resistance of 8.0 mΩcm² at room temperature. The diodes fabricated in this study showed positive temperature coefficients of breakdown voltage, meaning avalanche breakdown. The avalanche breakdown is discussed with observation of luminescence     

Dual metal SiC Schottky rectifiers with low power dissipation

Nickel and titanium are the most commonly used metals for Schottky barrier diodes on silicon carbide (SiC). Ti has a low Schottky barrier height (i.e. 0.8 eV on 6H-SiC), whilst Ni has a higher barrier (i.e. 1.25 eV). Therefore, the first metal allows to achieve a low forward voltage drop V_F but leads to a high leakage current. On the other hand, the second one presents the advantage of a lower reverse leakage current but has also a high value of V_F. In this work, dual-metal-planar (DMP) Schottky diodes on silicon carbide are reported. The rectifying barrier was formed by using an array of micrometric Ti and Ni₂Si (nickel silicide) stripes. This low/high Schottky barrier allowed to combine the advantages of the two metals, i.e. to fabricate diodes with a forward voltage drop close to that of a Ti diode and with a level of reverse current comparable to that of a Ni₂Si diode. Under the application point of view, using this kind of barrier can lead to a reduction of the device power dissipation and an increase of the maximum operating temperature.     

Carrier Transportation Mechanism of the $hbox{TaN}/ hbox{HfO}_{2}/hbox{IL}/hbox{Si}$ Structure With Silicon Surface Fluorine Implantation

In this paper, the current transportation mechanism of HfO₂ gate dielectrics with a TaN metal gate and silicon surface fluorine implantation is investigated. Based on the experimental results of the temperature dependence of gate leakage current and Fowler-Nordheim tunneling characteristics at 77 K, we have extracted the current transport mechanisms and energy band diagrams for TaN/HfO₂/IL/Si structures with fluorine incorporation, respectively. In particular, we have obtained the following physical quantities: 1) fluorinated and as-deposited interfacial layer (IL)/Si barrier heights (or conduction band offsets) at 3.2 and 2.7 eV; 2) TaN/fluorinated and as-deposited HfO₂ barrier heights at 2.6 and 1.9 eV; and 3) effective trapping levels at 1.25 eV (under both gate and substrate injections) below the HfOF conduction band and at 1.04 eV (under gate injection) and 1.11 eV (under substrate injection) below the HfO₂ conduction band, which contributes to Frenkel-Poole conduction.     

Silicon-carbide high-voltage (400 V) Schottky barrier diodes

The authors describe the fabrication and characteristics of the first high-voltage (400-V) silicon-carbide (6H-SiC) Schottky barrier diodes. Measurements of the forward I-V characteristics of these diodes demonstrate a low forward voltage drop of ~1.1 V at an on-state current density of 100 A/cm² for a temperature range of 25 to 200°C. The reverse I-V characteristics of these devices exhibit a sharp breakdown, with breakdown voltages exceeding 400 V at 25°C. In addition, these diodes are shown to have superior reverse recovery characteristics when compared with high-speed silicon P-i-N rectifiers