Semiconductor Devices and the P-N Junction:
- Basis of most Semiconductors - PN Junction.
|Energy band diagrams for conductors, insulators, and semiconductors.|
- The above shown EG diagrams are fundamentally correct. But, in order to understand the depth, we use the diagram shown below (example - introducing the concept of direct/indirect bandgap S/Cs).
- Properties are based on the Valence shell.
- Example of a poor conductor - Rubber.
- But, we are interested in the Semiconductors.
- 4 valence shell electrons.
- N-Type S/C (abbreviated for Semiconductor): Pentavalent Dopant (shown below).
- Dopant has 5 electrons in the valence shell (P).
- Doping: Vaporize P with heat and diffuse it over pure Si - You can control it with pressure, temperature, and so forth . . .
- Similarly, we dope for P-Type S/C.
The P-N Junction:
When Sandwiched at the atomic level, the charge interface region called the depletion region (acts like energy barrier).
Forward Biasing the P-N Junction:
|PN Junction at equilibrium.|
- Reverse Biasing the P-N Junction:
- The Diode: A device that allows current to flow only in one direction.
- Forward bias is usually in the range of 0.3V for Germanium-based diodes and 0.7V for Silicon-based diodes to initiate conduction.
|Diode Circuit with forward bias.|
- Diode Characteristics - Example:
Instantaneous Forward Voltage of a Diode: Forward Characteristics.
- Tip: to know more about the particular diode, check out the datasheet of the respective diode for its characteristics.
|Various diode packages and types.|
- Other types - Schottky diode (symbol: similar to Zener diode): Have very low forward voltages (turns on/off very quickly).
- LEDs: 1.7V(Red side) - 3.1V (Blue side).
- Black or White stripe on one side of the diode body indicates the Cathode.
- Bridge rectifier: has FOUR diodes in it (AC <> DC).
Example Part Numbers (Diodes):
|1N4006: Silicon Rectifier diode.|
|1N4001: White bar - Cathode.|
|1N4001 (different manufacturer).|
|1N4001 - Glass Passivated.|
|STPS 2L60 (702): Schottky Diode - used in power systems to steer power.|
|1N4739A (9.1V Zener diode)|
|1N751 fairchild: Zener diode (5.1V).|
- The Schottky diode on power rails - rectification.
Example 2: Forward V-drop vs Forward I (STPS2L60).
- Silicon Rectifier Diode or simply Rectifier Diode: 1N4001
|Forward Biased Rectifier Diode.|
|After reverse biasing the diode, we can read small amount of current (literally small values). You can see the multimeter on the right reading the leakage current (~0.1uA). But, in the forward direction, we can get up to 2A of current flow! Interesting isn't it? 😃|
*For ratings and features, check the datasheet(s) online.
**Wire guage (AWG Size) - lower the number => higher diameter.
***Read more about diodes and their modeling equations on Wikipedia (click here).
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