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What distinguishes the I-V characteristics of a resistor from those of a PN junction?
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A resistor shows a linear I-V relationship according to Ohm's Law, while a PN junction exhibits a non-linear, exponential I-V characteristic in forward bias and minimal current in reverse bias.
What is the significance of the depletion region in a PN junction?
The depletion region is crucial as it creates an electric field that affects the movement of charge carriers, playing a key role in determining the junction's electrical characteristics.
In what way do the properties of majority carriers differ between N-type and P-type semiconductors?
In N-type semiconductors, the majority carriers are electrons, while in P-type semiconductors, the majority carriers are holes.
How do charge carriers redistribute themselves at the P-N interface?
Charge carriers diffuse from regions of high concentration to low concentration, leaving behind immobile ions that create an electric field and a depletion region at the interface.
What is Einstein's relation in semiconductor physics?
Einstein's relation connects the mobility (μ) and diffusivity (D) of carriers with the equation D/μ = kT/q, where k is Boltzmann's constant, T is temperature, and q is the charge of an electron.
Describe diffusion current in the context of carrier transport.
Diffusion current arises from the movement of carriers from high concentration regions to low concentration regions, driven by concentration gradients rather than electric fields.
How does doping with acceptor atoms like boron affect pure silicon?
It creates a P-type semiconductor by increasing the number of holes, leading to decreased free electron density.
What is the effect of adding donor atoms like phosphorus to pure silicon?
It creates an N-type semiconductor by increasing the number of free electrons, thereby improving conductivity.
What happens to the current through a PN junction in reverse bias?
In reverse bias, the current through a PN junction is minimal because the built-in electric field prevents the movement of majority carriers across the junction.
What is the relation between drift current and carrier density in a semiconductor?
The total drift current is given by the product of carrier velocity, cross-sectional area, carrier density, and charge.
Explain the formation of the depletion region in a PN junction.
The depletion region forms as electrons from the N-region and holes from the P-region diffuse across the junction, leaving behind charged ions and creating an electric field that opposes further diffusion.
How does the PN junction behave under forward bias?
Under forward bias, the potential barrier is reduced, allowing majority carriers to cross the junction and resulting in an exponential increase in current.
What are the units for diffusivity (D) in semiconductor physics?
The units for diffusivity (D) are cm²/s.
Define drift current in a semiconductor.
Drift current is the flow of charge carriers due to an applied electric field, causing the carriers to move with a velocity proportional to their mobility and the electric field.
Provide the equations for diffusion current density for electrons and holes.
For electrons: J_n = q * D_n * (dn/dx). For holes: J_p = q * D_p * (dp/dx).
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