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**: $ ho_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.