Solid State Devices Flashcards (61 cards)

What defines a semiconductor’s electrical conductivity relative to conductors and insulators?

It lies between that of conductors and insulators.

Which electron-energy range is filled at 0 K?

The valence band.

What band-gap size characterizes insulators?

About 6 eV or greater than 5 eV.

What are the band gaps of silicon and germanium?

Silicon has a gap of 1.1 eV; germanium has a gap of 0.66 eV.

What band structure characterizes conductors?

Their valence and conduction bands overlap, giving an approximately zero gap.

What distinguishes an intrinsic semiconductor from an extrinsic semiconductor?

An intrinsic semiconductor is pure; an extrinsic semiconductor is doped with impurities to control conductivity.

What type of impurities dope an N-type semiconductor?

Donor impurities, usually group V elements.

Which carriers are the majority in an N-type semiconductor?

Electrons.

Which carriers are the minority in an N-type semiconductor?

Holes.

At absolute zero, what is the electron occupancy probability at the Fermi level?

One-half.

What does the Fermi level determine about electrons?

Their distribution across energy states.

What does the Fermi–Dirac function calculate?

The occupancy probability of an energy state.

In the Fermi–Dirac function, what does $E_F$ represent?

The Fermi level.

At finite temperature, what is the occupancy probability at the Fermi level?

One-half.

Where does the Fermi level lie in intrinsic material?

Near the middle of the band gap.

For an intrinsic semiconductor, how are electron and hole concentrations related?

$n_i=p_i$

What relation does the mass action law give at thermal equilibrium?

$np=n_i^2$

For N-type material with $N_D\gg n_i$, what is the approximate majority electron concentration?

$n\approx N_D$

For N-type material with $N_D\gg n_i$, what is the minority hole concentration?

$p=\frac{n_i^2}{N_D}$

What happens to intrinsic carrier concentration as semiconductor temperature rises?

It increases strongly.

Why does intrinsic carrier concentration increase with temperature?

The exponential factor $\exp(-E_g/2kT)$ increases.

Which regions does a semiconductor pass through as temperature rises?

Freeze-out, the extrinsic region, and the intrinsic region.

What characterizes the freeze-out region in a semiconductor?

Dopants are not sufficiently ionized.

What characterizes the extrinsic region in a semiconductor?

Dopants are mostly ionized.

What characterizes the intrinsic region in a semiconductor?

Thermal carrier generation dominates.

What is the semiconductor conductivity formula?

$\sigma=q(n\mu_n+p\mu_p)$

What causes carrier drift in a semiconductor?

An electric field.

What causes carrier diffusion in a semiconductor?

A concentration gradient drives carriers from high to low concentration.

What does a perpendicular magnetic field do to charge carriers in the Hall effect?

It deflects them sideways, separating charge across the sample and producing a transverse Hall voltage.

What is the Hall voltage for a sample of thickness $d$?

$V_H=\frac{IB}{nqd}$

What material type does a positive Hall coefficient indicate?

P-type material.

What material type does a negative Hall coefficient indicate?

N-type material.

What is the Shockley diode equation?

$I_D=I_S\left(e^{V_D/(nV_T)}-1\right)$

What does $I_S$ represent in the Shockley diode equation?

Saturation current.

How does an ideal diode behave when forward- and reverse-biased?

It acts as a short circuit when forward-biased and blocks current when reverse-biased.

What is the load-line equation for a diode in series with supply $V_S$ and resistor $R$?

$V_D=V_S-I_DR$

What does a diode’s Q-point represent on its I–V characteristic and load line?

Their intersection gives the diode’s steady-state voltage and current.

Which materials are common semiconductors?

Silicon, germanium, and gallium arsenide.

What is an energy band in a solid?

A range of allowed electron energies.

What is the forbidden gap between the valence and conduction bands?

The energy interval with no electron states.

Which impurities are examples of donors in N-type semiconductors?

Phosphorus, arsenic, and antimony.

Which impurities are examples of acceptors in P-type semiconductors?

Boron, gallium, and indium.

What happens when donor atoms are added to a semiconductor?

They donate extra electrons to the conduction band.

What happens when acceptor atoms are added to a semiconductor?

They accept valence-band electrons and leave holes behind.

At 0 K, what is the occupancy of states below the Fermi level?

They are filled.

At 0 K, what is the occupancy of states above the Fermi level?

They are empty.

What is the formula for the effective density of states in the conduction band?

$N_C=2\left(\frac{2\pi m_n^*kT}{h^2}\right)^{3/2}$

What is the formula for the effective density of states in the valence band?

$N_V=2\left(\frac{2\pi m_p^*kT}{h^2}\right)^{3/2}$

How is intrinsic electron concentration related to the conduction-band edge?

$n_i=N_C\exp\left(-\frac{E_C-E_F}{kT}\right)$

How is intrinsic hole concentration related to the valence-band edge?

$p_i=N_V\exp\left(-\frac{E_F-E_V}{kT}\right)$

What is the carrier state of a semiconductor at 0 K?

Impurities are frozen out, and no free carriers exist.

What is the drift current density formula?

$J_{drift}=q(n\mu_n+p\mu_p)E$

What is the diffusion current density formula?

$J_{diff}=q(D_n\nabla n-D_p\nabla p)$

What is the Einstein relation for electrons and holes?

$\frac{D_n}{\mu_n}=\frac{D_p}{\mu_p}=\frac{kT}{q}$

What is the total current density formula?

$J=q(n\mu_n+p\mu_p)E+qD_n\nabla n-qD_p\nabla p$

What is the Hall coefficient in terms of Hall voltage and carrier concentration?

$R_H=\frac{V_Hd}{IB}=\frac{1}{nq}$

How is carrier concentration calculated from the Hall coefficient?

$n=\frac{1}{R_Hq}$

What are Hall-effect applications?

Hall sensors, current sensing, determining material properties, and controlling electronic behavior.

What is the approximate thermal voltage at room temperature?

Approximately 26 mV.

What is the piecewise-linear model for a conducting diode?

$V_D=V_\gamma+I_Dr_D$ for $I_D>0$.

What is the small-signal resistance of a diode at forward current $I_D$?

$r_d=\frac{nV_T}{I_D}$.