Point Contact vs. Hot Carrier Diode: Key Differences

This article compares the point contact diode and the hot carrier diode (Schottky diode), highlighting their differences, advantages, and disadvantages. Various diode types are designed for specific applications, including GUNN diodes, PIN diodes, varactor diodes, tunnel diodes, standard P-N junction diodes, Zener diodes, Schottky diodes, Impatt diodes, Trapatt diodes, baritt diodes, point contact diodes, and hot carrier diodes.

For a deeper understanding, refer to the diode tutorial and the links provided below.

Point Contact Diode

• Construction: A point contact diode consists of a piece of semiconductor material with a fine wire making contact. Historically, germanium was used as the semiconductor material. Nowadays, a P-type semiconductor typically serves as the anode, while a fine tungsten wire acts as the cathode.
• Capacitance: Due to the small contact area between the wire and the semiconductor, the diode exhibits very low capacitance, hence the name “Point Contact Diode.”
• Function: Current flows easily from the cathode (fine wire) to the anode (semiconductor). However, current flow from anode to cathode is significantly restricted.

Advantages of Point Contact Diodes

• Ideal for low signal applications.
• Extremely low capacitance.
• Widely used in microwave mixers and detectors.

Disadvantages of Point Contact Diodes

• Delicate and susceptible to damage from shock and vibration.
• Cannot withstand high power levels.

Hot Carrier Diode (Schottky Diode)

• Construction: A hot carrier diode consists of N-type silicon with a thin metal layer deposited on top. The semiconductor acts as the cathode, while the metal serves as the anode. Common metals used include nickel chromium, aluminum, and gold. It is also known as a Schottky diode.
• Capacitance: Possesses a tiny junction capacitance due to its small size.
• Bias Voltage: Requires a lower bias voltage compared to other diode types.

Advantages of Hot Carrier Diodes (Schottky Diodes)

• Ideal for mixing and signal detection applications. Extensively used in mixers and modulator circuits.
• Used in switches at microwave frequencies due to their very high-frequency response.

Difference Between Point Contact Diode and Hot Carrier Diode

Here’s a breakdown of the key differences:

• RF Mixer Performance: In RF mixers, point contact diodes perform better at low Local Oscillator (LO) levels, while Schottky diodes are more suitable for high LO levels.
• Detector Performance: Point contact diodes offer superior performance as detectors, while hot carrier diodes perform about 30 dB worse in comparison.
• Voltage Output: Point contact diodes exhibit high voltage output at low levels, whereas hot carrier diodes have low voltage output at low levels.
• Saturation Level: Point contact diodes have a lower saturation level, while hot carrier diodes have a higher saturation level.