Ohmic Contact

Ohmic Contact is a metal-semiconductor junction that exhibits linear (ohmic) I-V characteristics — passing current equally in both directions without rectification, achieved when the Schottky barrier is thin enough for electrons to tunnel through freely.

What Makes a Contact Ohmic?

• High Doping: Doping the semiconductor heavily (>$10^{20}$ cm$^{-3}$) makes the depletion width so thin (~1 nm) that electrons tunnel through the barrier regardless of its height.
• Low Barrier: If $Phi_B \approx 0$, the contact is inherently ohmic (rare in practice due to Fermi level pinning).
• Silicide: Forming a silicide (NiSi, CoSi₂) at the interface provides a smooth, low-resistance junction.

Why It Matters

• Transistor Performance: Every MOSFET needs ohmic contacts at source and drain. Non-ohmic contacts add series resistance that degrades $I_{on}$.
• Specific Resistivity Target: $\rho_c < 10^{-8}$ $Omega cdot$cm² is needed at sub-7nm nodes.
• Contact Engineering: The art of making reliable, low-resistance ohmic contacts is one of the core challenges in semiconductor manufacturing.

Ohmic Contact is the invisible doorway — a junction so well-engineered that electrons pass through without even noticing the transition from metal to semiconductor.