Review of Bipolar Junction Transistors and Semiconductor Physics

A series of flashcards designed to help students understand and recall key concepts related to semiconductors, diodes, and transistors in preparation for their exam.

What is a semiconductor?

A semiconductor is a material whose conductivity lies between that of conductors (like copper) and insulators (like glass).

What are intrinsic semiconductors?

Intrinsic semiconductors are pure materials that have not been doped, such as silicon and germanium.

How many valence electrons does a silicon atom have?

A silicon atom has four valence electrons.

What happens to silicon's conductivity at low temperatures?

At low temperatures, all covalent bonds are intact and no free electrons are available for conduction, resulting in zero conductivity.

What is thermal generation in semiconductors?

Thermal generation is the process by which free electrons and holes are created due to thermal energy, allowing for some conductivity at higher temperatures.

What is doping in semiconductors?

Doping is the intentional introduction of impurities into an extremely pure (intrinsic) semiconductor to change carrier concentrations.

What is a p-type semiconductor?

A p-type semiconductor is created when silicon is doped with an element that has a valence of 3, increasing the concentration of holes (p). An example is boron.

What is an n-type semiconductor?

An n-type semiconductor is formed when silicon is doped with an element that has a valence of 5, increasing the concentration of free electrons (n). An example is phosphorus.

What does the term 'electronic mobility' refer to?

Mobility describes how strongly the motion of an electron is influenced by an applied electric field.

What is the Hall effect?

The Hall effect is the production of a voltage difference across an electrical conductor when a magnetic field is applied perpendicular to the current.

What is the built-in voltage (V0) of a pn-junction?

The built-in voltage of a pn-junction is the equilibrium value of barrier voltage, typically between 0.6V and 0.9V for silicon at room temperature.

What is meant by reverse bias in a diode?

Reverse bias occurs when a positive voltage is applied to the n-type region and a negative voltage to the p-type region, preventing current from flowing.

What happens during forward bias of a pn-junction?

During forward bias, an external voltage reduces the barrier voltage, allowing current to flow as majority carriers move towards the junction.

What is the difference between soft and hard limiter circuits?

Soft limiters gradually reduce output voltage upon reaching the limit, while hard limiters abruptly block signals beyond the threshold.

Describe how a half-wave rectifier works.

A half-wave rectifier utilizes only one half of the input AC waveform, allowing current to pass through the diode only during one half of the cycle.

What is a full-wave rectifier?

A full-wave rectifier utilizes both halves of the input AC waveform, providing better efficiency and output.

What is the significant feature of Zener diodes?

Zener diodes are designed to operate in reverse breakdown without damage, providing a stable output voltage.

What is the main purpose of using filter capacitors in rectifiers?

Filter capacitors are used to smooth out the ripple in the output DC voltage, creating a more stable power supply.

What is a transistor's active mode?

The active mode of a transistor is where it amplifies current; it is achieved by properly biasing the emitter-base and collector-base junctions.

How does an npn transistor operate in active mode?

In active mode, a small current flowing into the base controls a larger current flowing from collector to emitter.