Counter-doped SiC Schottky Diode Leakage Reduction
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Solution Overview
Problem
Silicon carbide Schottky Barrier Diodes (SBDs) face high reverse leakage current issues due to elevated electric fields, which limits their high-voltage operation and increases off-state power dissipation, and previous attempts to reduce this through Junction-Barrier Schottky (JBS) diodes with P+N junctions increase specific on-resistance and capacitance.
Innovation Solution
The implementation of a counter-doped Schottky diode structure with shallow, fully depleted P-type layers at the semiconductor surface, reducing the surface electric field and leakage current without impacting forward bias performance, and incorporating counter-doping in JBS diodes to further minimize reverse bias leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If SiC SBDs are used to reduce switching losses and increase switching speed, then switching performance is improved, but reverse leakage current increases due to higher electric fields
Solution Approach 1:
The patent introduces a shallow P-type layer only at the surface region where the metal contact is formed, creating a localized counter-doping region. This local modification reduces the electric field at the metal-semiconductor interface without affecting the bulk N-type drift region, thereby reducing reverse leakage current while preserving the high switching speed characteristics of SiC SBDs
Solution Approach 2:
The patent changes the doping concentration and depth parameters of the P-type layer to optimize its effectiveness. By controlling the P-type doping concentration (1E16 to 1E18 atoms/cm³) and depth (10 nm to 500 nm), the electric field at the surface is reduced, which exponentially reduces the reverse leakage current through thermionic-field emission while maintaining low forward voltage drop
2Object-generated harmful factors
If P+N junctions are inserted to reduce surface electric field and leakage current, then reverse leakage is reduced, but specific on-resistance and capacitance increase
Solution Approach 1:
Instead of using heavily doped P+ junctions that create high electric fields at the junction interface, the patent inverts the approach by using lightly doped P-type layers with very shallow depth. This inversion of doping strategy reduces the electric field at the metal-semiconductor interface without creating the harmful effects of deep P+ junctions, thereby reducing reverse leakage while maintaining low on-resistance
Solution Approach 2:
The patent applies partial counter-doping only in the regions directly beneath the metal contact where the electric field is highest. By limiting the P-type layer to shallow depth (10-500 nm) and specific lateral regions, the solution provides sufficient field reduction to lower leakage current while minimizing the impact on forward conduction paths, thus avoiding significant increases in on-resistance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The counter-doped diodes exhibit significantly reduced reverse bias leakage current while maintaining low forward bias resistance, effectively addressing the limitations of conventional SBDs and JBS diodes in high-voltage applications.
Implementation Method 1
The leakage is due to electrons that enter the semiconductor material from the metal by thermionic-field emission (TFE) under reverse bias
Implementation Method 2
The electric field is given by the slope of the conduction band at the surface
Data Source
AI summary
A Schottky diode includes an upper region having a first doping concentration of a first conductivity type, the upper region disposed above the SiC substrate and extending up to a top planar surface. First and second layers of a second conductivity type are disposed in the upper region adjoining the top planar surface and extending downward to a depth. Each of the first and second layers has a second doping concentration, the depth, first doping concentration, and second doping concentration being selected such that the first and second layers are depleted of carriers at a zero bias condition of the Schottky diode. A top metal layer disposed along the top planar surface in direct contact with the upper region and the first and second layers is the anode, and bottom metal layer disposed beneath the SiC substrate is the cathode, of the Schottky diode.