| Parameter | PN Junction Diode | Schottky Diode | Varactor (Varicap) Diode | Tunnel Diode |
|---|---|---|---|---|
| Construction | P-type + N-type semiconductor | Metal + N-type semiconductor | Special PN junction operated in reverse bias | Heavily doped PN junction |
| Operating Bias | Forward & Reverse | Mainly Forward Bias | Reverse Bias Only | Forward Bias (Negative Resistance Region) |
| Forward Voltage Drop | 0.7 V (Si), 0.3 V (Ge) | 0.2–0.4 V | Not used in forward bias | Very low |
| Switching Speed | Moderate | Very High | High | Extremely High |
| Reverse Recovery Time | Higher | Almost Zero | Very Low | Very Low |
| Junction Capacitance | Normal | Low | Variable (Main Feature) | Very Low |
| Negative Resistance | No | No | No | Yes |
| Power Consumption | Moderate | Low | Very Low | Very Low |
| Frequency Range | Low to Medium | High Frequency | RF & Microwave | Microwave Frequency |
| Current Flow Mechanism | Majority & Minority carriers | Majority carriers only | Capacitance variation | Quantum Tunneling |
| Special Property | Rectification | Fast switching | Variable capacitance | Negative resistance |
| Main Application | Rectifier circuits | SMPS, High-speed switching | Tuning circuits, VCO, PLL | Oscillators, High-speed switches |
| Symbol Feature | Normal diode symbol | Diode with bent cathode line | Capacitor-like plates at junction | Diode with extra line |
"P-N = Power Rectification"
→ Converts AC to DC.
"Schottky = Speed King"
→ Fastest switching, low voltage drop.
"Varactor = Variable Capacitor"
→ Used in tuning circuits.
"Tunnel = Tunneling + Negative Resistance"
→ Used in microwave oscillators.