Structure of Schottky Barrier Diodes

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Fabricating Schottky Diodes

A PhD candidate requested a quote for the following.

My lab is researching MEMS and semiconductor fabrication. I looked up on your website and found that you deal with the various kinds of wafers and depositions.

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  2. We need the p+ doping concentration in the wafers of around 1.9x10^20 cm^-3 to 2.1x10^20 cm^-3.
  3. The p- doping concentration should be in between 1.7x10^15 cm^-3 to 1.9x10^15 cm^-3.
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Reference #278949 for specs and pricing.

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What are Structure of Schottky Barrier diodes?

A Schottky barrier diode is a metal–semiconductor junction device rather than a p–n junction diode. Its structure is intentionally simple to achieve fast switching, low forward voltage drop, and low power loss.

Schottky barrier diode structure showing metal–semiconductor junction, epitaxial layer, substrate, and edge termination

1. Basic Physical Structure

A Schottky diode consists of:

A. Metal Contact (Schottky Metal)

Common metals:

  • Platinum (Pt)

  • Nickel (Ni)

  • Molybdenum (Mo)

  • Titanium (Ti)

  • Aluminum (Al)
    These metals form a rectifying (Schottky) barrier when deposited on an n-type semiconductor.

The choice of metal affects:

  • Barrier height (Φ_B)

  • Reverse leakage current

  • Forward voltage drop

B. Semiconductor Layer

Usually n-type silicon, but can also be:

Why n-type?

The semiconductor stack often includes:

  • Lightly doped epitaxial layer (controls breakdown voltage)

  • Highly doped substrate (reduces series resistance)

C. Ohmic Contact (Backside Metal)

The backside (bottom) of the semiconductor has a low-resistance ohmic metal contact, often:

  • Au/Ni

  • Ti/Al

  • Ni/Ag
    Its purpose is to allow easy current flow without rectification.

D. Passivation & Guard Ring (for high-voltage SBDs)

To reduce surface leakage and edge breakdown, many SBDs include:

These improve:

  • schottky-barrier-diode-structure.html

    Breakdown voltage

  • Reliability under high reverse bias

2. Cross-Sectional Structure

A simplified cross-section:

Metal (Schottky Contact) ------------------------ Lightly Doped n- Epitaxial Layer ------------------------ Heavily Doped n+ Substrate ------------------------ Ohmic Contact (Back Metal)

Edge termination (for high-voltage devices):

Metal Contact | Field Plate -------------|------------   Guard Ring / Junction Termination Extension (JTE)

3. How the Structure Creates the "Schottky Barrier"

When the metal touches the n-type semiconductor, electrons cannot freely flow because of:

  • Work function difference between metal and semiconductor

  • Formation of a depletion region at the interface

This creates:

  • Forward conduction through majority carriers (electrons)

  • No charge storage → fast switching

  • Low forward voltage (~0.2–0.4 V)

Energy band diagram:

4. Variations in Schottky Diode Structures

A. Planar Schottky Diode

  • Metal deposited on the planar surface

  • Used for low- and medium-voltage devices

B. Trench Schottky (Super Barrier / TMBS)

  • Metal fills trenches etched into the semiconductor

  • Better electric field distribution

  • Higher breakdown voltage

  • Lower leakage

C. GaN and SiC Schottky Diodes

High-power applications use wide-bandgap semiconductors:

  • SiC SBDs (common in EVs, power supplies)

  • GaN SBDs / HEMTs for RF and high-efficiency power devices

These offer:

  • High breakdown voltage

  • Fast recovery

  • Extreme temperature performance

5. Key Structural Advantages

Feature Structural Reason
Fast switching No minority carrier storage (metal–semiconductor junction)
Low forward voltage drop Low Schottky barrier height (depends on metal)
High-speed power electronics Simple structure with majority carriers
Low reverse recovery time No charge storage region like p–n diodes

Summary

A Schottky diode is built from:

  1. Metal Schottky contact

  2. Lightly doped n-type epitaxial layer

  3. Heavily doped n+ substrate

  4. Backside ohmic contact

  5. (Optional) Guard rings, field plates, trench structures

This structure creates a metal-semiconductor rectifying junction that allows ultra-fast switching and low forward voltage.