Semiconductors and Diodes

The p-terminal at -28V and n-terminal at -29V means the p-side is at a higher potential (less negative) than the n-side. This creates a forward bias condition of +1V across the diode, allowing current to flow through the p-n junction.

Peak Inverse Voltage (PIV) is the maximum reverse voltage a diode can withstand without breakdown. Breakdown Voltage is the voltage AT which breakdown occurs, not the maximum safe voltage. PIV is a critical rating that limits reverse-bias operation.

Knee Voltage (or cut-in voltage) is the minimum forward voltage at which a diode starts conducting heavily. Below this voltage, current is negligible. For silicon it's about 0.7V, for germanium about 0.3V.

Zener diodes can operate via two breakdown mechanisms: Zener breakdown (dominates below 5V) and avalanche multiplication (dominates above 5V). In the transition region (3-5V), both mechanisms occur simultaneously, not exclusively.

A PIN diode has advantages over a normal p-n junction diode in both speed and current handling. The intrinsic region allows it to switch faster than regular diodes and handle higher current ratings due to its structure. This makes PIN diodes suitable for high-frequency applications like RF switches and attenuators.

A tunnel or Esaki diode is much more heavily doped than a normal p-n junction diode - typically about 1000 times higher doping concentration. This heavy doping creates a very narrow depletion region that allows electrons to tunnel through, creating the negative resistance characteristic that makes tunnel diodes useful in high-frequency oscillator circuits.

Zener diodes, varactor diodes, and photodiodes all operate in reverse bias for their intended applications (voltage regulation, capacitance tuning, and light detection respectively). However, tunnel diodes are unique in that they typically operate in forward bias where they exhibit negative resistance, making them useful for high-frequency oscillators and switching circuits.

BJTs (Bipolar Junction Transistors) are generally better than MOSFETs for amplification purposes because they have higher transconductance, better linearity, and typically higher gain. NMOS transistors are more commonly used as switches in digital logic due to their efficiency, not for analog amplification.

MOS (Metal Oxide Semiconductor) transistors conduct current through majority carriers only - electrons in NMOS (n-channel) and holes in PMOS (p-channel). Unlike BJTs which use both majority and minority carriers, MOSFETs are unipolar devices, making them faster and less susceptible to temperature effects.

MOS transistors are indeed classified into two main types: Enhancement type and Depletion type. Enhancement type transistors have no channel initially and require gate voltage to create one. Depletion type transistors have a pre-existing channel that can be depleted. Both types are fundamental to MOSFET technology.

Tunnel diodes exhibit negative resistance where current decreases as voltage increases over a specific range, due to quantum tunneling effect. This makes them useful in high-frequency oscillators. Varactor diodes are voltage-variable capacitors. Schottky diodes have low forward voltage drop. LEDs emit light.

Schottky diodes have a metal-semiconductor junction, unlike regular p-n junction diodes. This gives them faster switching speeds and lower forward voltage drop. Zener, Tunnel, and LEDs all use p-n semiconductor junctions. The metal-semiconductor junction is key to Schottky diode operation.

MOSFETs are superior to BJTs in switching applications due to lower switching losses, faster switching speeds, and simpler drive requirements. MOSFETs are voltage-controlled devices needing negligible gate current. BJTs are current-controlled requiring continuous base current. MOSFETs also have better thermal stability and easier paralleling.

Zener diodes are specifically designed for voltage regulation due to their sharp breakdown characteristic at a precisely controlled voltage. In reverse breakdown, they maintain nearly constant voltage across varying current. Schottky diodes are for fast switching. Tunnel diodes are for oscillators. LEDs emit light.