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     

Tantalum nitride-p-silicon high-voltage Schottky diodes

Rectifying contacts between TaN and p-silicon with very high reverse breakdown voltage (V_BR >700 V) without using any guard ring have been realized. Barrier heights of TaN to both p-type silicon and n-type silicon have been measured at 0.68 and 0.48 eV, respectively. The breakdown voltage V_BR of TaN to p-silicon diodes, as deposited, is ~400 V and decreases to less than 200 V after annealing in hydrogen at 450°C for 30 min. On the other hand, annealing in a nitrogen ambient at 450°C for 30 min. increases the V_BR of these diodes to more than 700 V. An explanation for the difference in V_BR is sought in terms of the structural/chemical changes introduced at the interface by the annealing process. The high forward drop of TaN to p-silicon diodes (>1 V at 10 mA) results from the high substrate resistance and the probe contact resistance, and it is being optimized     

I-V characteristics of high-voltage 4H-SiC diodes with a 1.1-eV Schottky barrier

The I-V characteristics of high-voltage 4H-SiC diodes with a Schottky barrier ∼1.1 eV in height are measured and analyzed. The forward I-V characteristics proved to be close to “ideal” in the temperature range of 295–470 K. The reverse I-V characteristics are adequately described by the model of thermionic emission at the voltages to 2 kV in the temperature range of 361–470 K if, additionally, a barrier lowering with an increase in the band bending in the semiconductor is taken into account.     

Thermally oxidized mesa Schottky barrier diodes

Schottky barriers with a thermally oxidized mesa structure have been fabricated. The fabrication process is described. The mesa structure averts electric field crowding at the barrier periphery. The reverse diode characteristic shows a sharp breakdown at the voltage expected for an ideal, abrupt diode of semi-infinite extent and identical doping concentration.     

Low-frequency noise in Schottky barrier diodes

The low-frequency excess noise in Schottky barrier diodes has been investigated. In the ideal case where the saturation current is completely determined by thermionic emission of electrons, no 1/? noise will be produced in the barrier. The presence of trap states in the depletion region can lead to generation-recombination noise. At sufficient high forward currents 1/? noise can be generated in the series resistance of the Schottky diode. Deviations from the ideal diode, for example as a result of edge effects, produce 1/? noise and increase at the same time the ideality factor. It is empirically found that the 1/? noise level decreases very rapidly if the ideality factor tends to unity.     

AuSiC Schottky barrier diodes

Results of the experimental study of Au n-type SiC Schottky barrier diodes at room temperature are presented. The diodes are fabricated by vacuum-evaporating gold on chemically etched n-type hexagonal (6H) SiC surfaces and exhibit excellent forward current vs voltage characteristics with the exponential factor n of about 1·07±0·02 for voltages between 0·35 and 0·85 V. The linear part of the characteristic, in a semi-logarithmic plot, extends over seven orders of magnitude in current. The forward current-voltage characteristics are found to agree quantitatively with the theory based on thermionic emission with the barrier height modified by image force lowering. The Schottky barrier height is determined from three independent techniques: differential capacitance vs voltage, photoresponse, and forward current vs voltage methods. The barrier height deduced from the three methods is about 1·40±0·05 V.     

Gallium arsenide dual Schottky barrier diodes

Gallium arsenide diodes were made which had Schottky-barriers for both contacts. Devices which were too thick for space change reach-through to occur at breakdown showed microwave oscillations, while thin diodes did not oscillate. Additionally, the structures could be distinguished on the basis of the noise accompanying breakdown. The performance was analysed in terms of transistor theory in which there is avalanche multiplication in the collector space charge region. It was concluded that there is a smooth transition between the reachthrough breakdown characteristic of the BARITT and true avalanche breakdown. The nature of the breakdown depends on the base width and the emitter efficiency.     

Current transport in large-area Schottky barrier diodes

The conventional method used to determine the mechanism of current transport in a Schottky barrier diode can lead to erroneous inferences if a fluctuation of parameters, such as that which would occur in a large area diode, is present. This has been illustrated by taking a Gaussian variation of a parameter in case of diodes showing T0anomaly.     

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     

Design considerations for planar Schottky barrier diodes

The cut-off frequency of the simplest planar Schottky diode on a uniformly doped n-layer of GaAs is derived. The theoretical results are given as functions of doping concentration and layer thickness with the specific contact resistance as parameter. An improved planar diode structure is presented with several short Schottky contact fingers connected in parallel. Experimental values ranging from 100 to 300 GHz agree with the calculated values when parasitic capacitances are taken into account.     

Shot noise in silicon Schottky barrier diodes

Noise measurements have been performed on forward and reverse-biased silicon Schottky barrier diodes. Measurements were performed in the frequency range of 100 Hz to 50 kHz. Apart from excess noise observed for some diodes in a portion of this frequency range, the noise for the diodes was found to be in excellent agreement with shot-noise theory. Some refinements of the shot-noise theory have been considered, but the difference between the refined and the simple theories was not resolvable in our measurements. A useful noise-measurement technique is described.     

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     

Computer study on GaAs Schottky barrier IMPATT diodes

Oscillation characteristics of GaAs Schottky barrier IMPATT diodes are studied by computer simulation. For a Schottky barrier-n-n⁺ structure, the Read condition and the just-punch-through condition are found to be optimum with respect to the efficiency and power at 30 GHz. In order to improve the efficiency, a superabrupt doping profile is proposed and a high efficiency of 32 per cent is predicted. Calculation of the frequency dependence of the efficiency shows that GaAs IMPATT diodes still have the potentiality of high efficiency oscillator at 100 GHz and they are a promising microwave source in mm-wave region.     

Correlation between current-voltage and capacitance-voltagecharacteristics of Schottky barrier diodes

A correlation between the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics of Schottky barrier diodes (SBDs) is revealed and claimed to be a general property of SBDs for the first time. Analytical expressions explaining the correlation based on the electric field dependence of the Schottky barrier height are derived, yielding novel approaches to evaluate Schottky barrier height lowering and to model the device behaviors     

On the current-voltage characteristics of epitaxial Schottky barrier diodes

The J-V characteristics of epitaxial Schottky barrier diodes are analyzed. Based on the assumption of negligible recombination in the epitaxial layer, formal solution from which the J-V characteristics can be calculated is derived. The solution is valid for all injection levels and reduces to the form I = I_s[exp (q(V?IR)/kT) ? 1], where R is the series resistance of the epitaxial layer, under C12 C12V low-injection conditions. The analysis is justified by very close correspondence with exact numerical calculations using the Finite Element Device Analysis Program (FIELDAY) in which thermionic emission boundary conditions are implemented for both electrons and holes. It is shown that for low barrier Schottky diodes the minority carrier injection is negligible and the expression I = I_s[exp (q(V?IR)/kT) ? 1] describes the I-V characteristics over large bias range. For high barrier C12 C12 V Schottky diodes the exact solution must be used as minority carriers are injected and the series resistance is decreased due to conductivity modulation effect.