3-6. Maximum rated reverse voltage (VR)

VR is the maximum rated reverse voltage that can be applied across an SBD.
When an SBD is reverse-biased, it is applied across the depletion region that extends from the junction into the semiconductor. The width of the depletion region depends on the dopant concentration; the higher the dopant concentration, the narrower the depletion region. Increasing or decreasing the reverse bias causes the depletion region to expand or shrink.
Figure 3-10 shows the relationship between the depletion region width and the electric field. The area of the triangle formed by the depletion region width and the electric field represents the reverse bias voltage applied.
As the reverse bias is increased, the electric field increases. When the electric field exceeds a certain value (the maximum electric breakdown field of silicon), an SBD is destroyed by the resulting excessive current. VR is defined as the maximum reverse bias that does not cause the electric breakdown field to be exceeded.
Therefore, the less heavily an SBD is doped, the higher its rated VR.

Figure 3-10 Relationship of reverse bias, depletion region width, and electric field
Figure 3-10 Relationship of reverse bias, depletion region width, and electric field

The dopant concentration also affects the series resistance of a diode directly. The more heavily doped a diode is, the smaller its series resistance becomes. In the case of pn junction diodes, excessive carriers due to the conductivity modulation effect described above reduce the effect of the dopant concentration. However, SBDs do not have the conductivity modulation effect since they are unipolar devices.

Figure 3-11 compares the IF-VF curves of the SBDs with a VR of 30 V and 40 V. (CBS10S30 and CBS10S40). In the low-current region, both the CBS10S30 and CBS10S40 exhibit the same IF-VF curve. As the forward current approaches the maximum rated current (1 A), the CBS10S40 with a higher VR conducts less forward current than the CBS10S30 at the same forward voltage.
This is because the CBS10S40 is less heavily doped and thus has a higher series resistance than the CBS10S30. This tendency becomes more marked as the VR is increased. It is therefore difficult to increase the maximum rated reverse voltage (VR) of silicon SBDs.

Figure 3-11 Forward characteristics of SBDs with different maximum rated reverse voltages
Figure 3-11 Forward characteristics of SBDs with different maximum rated reverse voltages

Chapter3 Basics of Schottky Barrier Diodes

3-1. Classification of diodes
Details
3-2. Comparison between SBDs and pn junction diodes
Details
3-3. Applications of SBDs
Details
3-4. Forward voltage
Details
3-5. Reverse recovery time
Details
3-7. Leakage current
Details

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