Chapter 6, Basic semiconductor physics Video Solutions, Solar Energy: The Physics and Engineering of Photovoltaic Conversion, Technologies and Systems

Problem 1

Which statement is not true about a semiconductor at room temperature and in the dark?
(a) The band gap of the semiconductor is within a range of $0.5 \mathrm{eV}$ to $3 \mathrm{eV}$.
(b) In a semiconductor only a few electrons fill the conduction band.
(c) In a semiconductor electrons almost fully fill the valence band.
(d) In a semiconductor the valence band is fully filled with electrons.

Aman Kumar

Numerade Educator

01:35

Problem 2

What are the 'free' carriers in the different electronic bands of a semiconductor?
(a) Electrons in conduction band and holes in valence band.
(b) Holes in conduction band and electrons in valence band.
(c) Both electrons and holes in conduction band when an electric field is applied.
(d) Both electrons and holes in valence band when an electric field is applied.

Ajay Singhal

Numerade Educator

00:58

Problem 3

What is the maximum number of electrons that can occupy the 3p energy state in an atom?
(a) 2 electrons.
(b) 6 electrons.
(c) Only 1 electron can occupy this state according to the Pauli exclusion principle.
(d) 8 electrons.

Lottie Adams

Numerade Educator

01:44

Problem 4

According to the molecular description of the band gap, which of the following statements are true?
(a) The anti-bonding level is a lower energy state than the bonding level.
(b) The anti-bonding level is a higher energy state than the bonding level.
(c) The closer the two neighbouring atoms making a molecular orbital are together, the smaller the energy splitting between the bonding and anti-bonding levels.
(d) The bonding state of a molecular orbital represents the conduction band.

David Collins

Numerade Educator

01:59

Problem 5

In case of $p$-doping of Si, the energy of the acceptor state...
(a) $\ldots$ is located in the Si bandgap, relatively close to the conduction band.
(b) $\ldots$ is located out of the Si bandgap, relatively close to the conduction band edge.
(c) $\ldots$ is located in the Si bandgap, relatively close to the valence band.
(d) $\ldots$ is located out of the Si bandgap, relatively close to the valence band edge.

Ajay Singhal

Numerade Educator

01:56

Problem 6

Considering Si as the bulk material, which of the dopant materials below can be used in order to achieve $n$ doping?
(a) Ge.
(b) In.
(c) Ga.
(d) As.

Marissa Turner

Numerade Educator

01:35

Problem 7

A photon with energy $E_{\mathrm{ph}}=1.35 \mathrm{eV}$ is absorbed in a semiconductor creating one electronhole pair. At the same
time, the energy lost due to thermal relaxation of the electron and hole is $0.27 \mathrm{eV}$. What is the bandgap of the semiconductor?

Anand Jangid

Numerade Educator

02:06

Problem 8

Silicon is doped with $10^{16}$ arsenic atoms per $\mathrm{cm}^{3}$. Assume intrinsic carrier concentration equal to $1.5 \times 10^{10} \mathrm{~cm}$ $-3$ at room temperature. What is the minority carrier concentration at room temperature $(T=300 \mathrm{~K}) ?$

Chai Santi

Numerade Educator

01:21

Problem 9

Which of the following statements is false regarding diffusion of charge carriers in semiconductors?
(a) Diffusion occurs only in the presence of an electric field.
(b) During diffusion, net flow of carriers takes place from high concentration to low concentration regions.
(c) Over time, carriers will diffuse randomly throughout the cell, until concentrations of different regions are uniform.
(d) Diffusion occurs faster at higher temperatures.

Tate Hilken

Numerade Educator

01:35

Problem 10

Which of the following statements is false regarding the drift of charge carriers?
(a) It is the dominant carrier transport mechanism when an electric field is applied in the semiconductor.
(b) Holes move in the direction opposite to that of the applied field.
(c) During drift, the carrier transport is characterized by their respective electron/hole mobilities.
(d) During drift, electrons and holes move in opposite directions.

Ajay Singhal

Numerade Educator

01:01

Problem 11

An isolated piece of a $p$-type ...
(a) $\ldots$ is positively charged, due to a hole excess.
(b) $\ldots$ maintains charge neutrality.
(c) $\ldots$ is negatively charged, due to an electron excess.

Varsha Aggarwal

Numerade Educator

04:15

Problem 12

What is the electron configuration of phosphorus (atomic number 15) in its ground state?
(a) $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{0} 3 p^{5} .$
(b) $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1} 3 p^{4}$.
(c) $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{3}$.
(d) $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{3} 3 p^{2}$

Edward Zhang

Numerade Educator

01:47

Problem 13

If we assume there is no light absorption, then the conductivity of an intrinsic semiconductor...
(a) ... decreases when temperature increases.
(b) $\ldots$ is zero at $T=0 \mathrm{~K}$.
(c) $\ldots$ is generally lower than the conductivity of an insulator.
(d) $\ldots$ is not affected in case of doping.

Ajay Singhal

Numerade Educator

00:58

Problem 14

The diffusion coefficient of electrons in silicon is $D_{n}=36 \mathrm{~cm}^{2} \mathrm{~s}^{-1}$. In a silicon layer, the electron density drops linearly from $n=2.7 \times 10^{16} \mathrm{~cm}^{-3}$ down to $n=10^{15} \mathrm{~cm}^{-3}$ over a distance of $2 \mu \mathrm{m}$. What is the electron diffusion current density $J_{n}$, diff induced by such a density gradient?

Chai Santi

Numerade Educator

02:08

Problem 15

From the previous data, what electric field over the gradient zone of $2 \mu \mathrm{m}$ would be required to compensate the electron diffusion flux with an electron drift flux? The electron mobility in silicon is $\mu_{n}=1,350 \mathrm{~cm}^{2} \mathrm{~V}^{-1} \mathrm{~s}^{-1}$ and the direction of drift to compensate diffusion flux is directed from lower density to higher density.

Chai Santi

Numerade Educator