Semiconductor Physics and Optoelectronics: Key Concepts and Principles

In an intrinsic semiconductor, are free electrons more abundant than holes?

No, in an intrinsic semiconductor, the number of free electrons is equal to the number of holes.

How does the effective mass of a carrier in a parabolic energy band with sharp curvature compare to a band with less pronounced curvature?

The effective mass is smaller in a band with sharp curvature compared to a band with less pronounced curvature.

How does the concentration of electrons in the conduction band of an intrinsic semiconductor depend on temperature?

The concentration of electrons in the conduction band increases with temperature.

What is the probability of finding an electron at the Fermi energy level in an intrinsic semiconductor?

The probability of finding an electron at the Fermi energy level is low, as it is typically located near the middle of the bandgap.

What happens to the bandgap energy when the lattice parameter of a semiconductor contracts?

The bandgap energy increases when the lattice parameter contracts.

What is the probability of finding an electron with energy corresponding to the Fermi energy in a conductor at room temperature?

The probability is approximately 50% for a conductor at room temperature.

What is the position of the Fermi energy level in an intrinsic semiconductor at room temperature with respect to the band edges?

The Fermi energy level is positioned near the midpoint between the valence band edge ($E_v$) and the conduction band edge ($E_c$).

In a semiconductor doped with donor impurities, how do the densities of electrons and holes compare?

Electrons in the conduction band are more abundant than holes in the valence band.

What is the position of the Fermi energy level in a p-type semiconductor at room temperature?

The Fermi energy level is closer to the valence band edge ($E_v$) in a p-type semiconductor.

What is the equation for the Law of Mass Action governing electron and hole concentration?

The Law of Mass Action states that the product of the electron concentration ($n$) and hole concentration ($p$) is constant: $np = n_i^2$, where $n_i$ is the intrinsic carrier concentration.

In an n-type semiconductor subjected to an electric field in the positive x-direction, what is the direction of the resulting electrical current?

The resulting electrical current flows in the positive x-direction.

What happens to the measured transmitted power when a tunable laser beam is tuned to longer wavelengths at constant power?

The measured transmitted power decreases as the laser is tuned to longer wavelengths.

What is the main difference in spectral bandwidth between the photoluminescence (PL) spectrum and the absorption spectrum of a direct bandgap semiconductor?

The PL spectrum typically has a narrower spectral bandwidth compared to the absorption spectrum.

What does an indirect bandgap mean in terms of the E-K band diagram?

An indirect bandgap means that the maximum of the valence band and the minimum of the conduction band occur at different values of momentum (k).

What other process/particle is involved for absorption to take place in an indirect bandgap semiconductor?

A phonon is involved in the absorption process in an indirect bandgap semiconductor.

Between an 800 nm (IR) laser and a 530 nm (Green) laser of equal power, which will produce higher photoluminescence intensity for a semiconductor with a bandgap of 1.653 eV?

The 530 nm (Green) laser will produce higher photoluminescence intensity because its energy is closer to the bandgap energy.

What prevents electrons and holes from continuing to diffuse across a PN junction indefinitely?

The built-in electric field created by the charge separation at the junction prevents further diffusion.

If the p-side concentration is larger than the n-side concentration, where is the depletion layer mostly located?

The depletion layer is mostly located on the n-side.

If Semiconductor A has a larger bandgap than Semiconductor B, how would their built-in voltages ($V_{bi}$) differ?

Semiconductor A would have a larger built-in voltage ($V_{bi}$) than Semiconductor B.

What happens to the magnitude of the potential barrier when a PN junction is forward biased?

The magnitude of the potential barrier decreases when a PN junction is forward biased.

In a forward-biased diode, far from the depletion region on the n-side, is the current mostly due to electrons, holes, or equal amounts?

The current is mostly due to electrons in the forward-biased diode.

What happens to the potential barrier when a PN junction is reverse biased?

The potential barrier increases when a PN junction is reverse biased.

What happens to the width of the depletion region when a PN junction is reverse biased?

The width of the depletion region increases when a PN junction is reverse biased.

Is the depletion layer thickness for a PIN diode larger or smaller than that of a standard PN diode?

The depletion layer thickness for a PIN diode is larger than that of a standard PN diode.

In a heterojunction, is it easier or harder for electrons vs. holes to overcome the built-in barrier?

It is easier for holes to overcome the built-in barrier than for electrons.

What is one major problem of the homojunction LED that does not exist in the heterojunction LED?

One major problem is the inefficiency due to poor carrier confinement in the homojunction LED.

What is the relationship between the Quasi-Fermi levels and the applied voltage in a homojunction LED?

In a homojunction LED, the Quasi-Fermi levels separate as the applied voltage increases.

Why is it disadvantageous to make an LED with a very thin top semiconductor layer?

A very thin top semiconductor layer can lead to increased surface recombination and reduced efficiency.

In a Double Heterojunction (DH) LED ($E_{gA} > E_{gB}$), what is the approximate energy of the emitted photons?

The emitted photon energy is approximately equal to the bandgap energy of the smaller bandgap material ($E_{gB}$).

What is the biggest challenge to achieving high external quantum efficiency in a bare heterojunction LED?

The biggest challenge is managing the non-radiative recombination losses.

What are two optical processes in semiconductors that are the exact opposite of each other?

Absorption and emission (photoluminescence) are two optical processes that are opposite.

What must happen to the Quasi-Fermi levels for a semiconductor to exhibit optical gain instead of loss?

The Quasi-Fermi levels must be separated, indicating a population inversion for optical gain.

What are the minimum and maximum photon energies for which a semiconductor can exhibit gain?

The minimum photon energy is equal to the bandgap energy, and the maximum photon energy is determined by the energy states available in the semiconductor.

What happens to the optical gain bandwidth when the injection current is increased?

The optical gain bandwidth typically increases with higher injection current.

What happens to the peak energy of the gain spectrum as the injection current is increased?

The peak energy of the gain spectrum shifts to higher energies as the injection current increases.