Electrical conductivity in solids
Again, we are eventually interested in determining the current-voltage characteristics
of semiconductor devices. We will need to consider electrical conduction in
solids as it relates to the band theory we have just developed. Let us begin by considering
the motion of electrons in the various allowed energy hands
The Energy Band and the Bond Model
we discussed the covalent bonding of silicon. Figure 3.12 shows a twodimensional
representation of the covalent bonding in a single-crystal silicon lattice.
This figure represents silicon at T = 0 Kin which each silicon atom is surrounded by
eight valence electrons that are in their lowest energy state and are directly involved
in the covalent bonding. Figure 3.4b represented the splitting of the discrete silicon
energy states into bands of allowed energies as the silicon crystal is formed. At
T = 0 K, the 4N states in the lower band, the valence band, are tilled with the valence
electrons. All of the valence electrons schen~aticallys hown in Figure 3.12 are
in the valence band. The upper energy band, the conduction band, is completely
empty at T = 0 K.
As the temperature increases above 0 K, a few valence band electrons may gain
enough thermal energy to break the covalent bond and jump into the conduction
band. Figure 3.13a shows a two-dimensional representation of this bond-breaking
effect and Figure 3.13b. a simple line representation of the energy-band model,
shows the same effect.
The semiconductor is neutrally charged. This means that, as the negatively
charged electron breaks away from its covalent bonding position, a positively
charged "empty state" is created in the original covalent bonding position in the valence
band. As the temperature further increases, more covalent bonds are broken,
more electrons jump to the conduction hand, and more positive "empty states" are
created in the valence band.
We can also relate this hond breaking to the E versus k energy bands.
Figure 3.14a shows the E versus k diagram of the conduction and valence bands at
T = 0 K. The energy states in the valence band are completely full and the states in
the conduction band are empty. Figure 3.14b shows these same bands for T > 0 K,
in which some electrons have gained enough energy to jump to the conduction band
and have left empty states in the valence hand. We are assuming at this point that no
external forces are applied so the electron and "empty state" distributions are symmetrical
with k
|
of semiconductor devices. We will need to consider electrical conduction in
solids as it relates to the band theory we have just developed. Let us begin by considering
the motion of electrons in the various allowed energy hands
The Energy Band and the Bond Model
we discussed the covalent bonding of silicon. Figure 3.12 shows a twodimensional
representation of the covalent bonding in a single-crystal silicon lattice.
This figure represents silicon at T = 0 Kin which each silicon atom is surrounded by
eight valence electrons that are in their lowest energy state and are directly involved
in the covalent bonding. Figure 3.4b represented the splitting of the discrete silicon
energy states into bands of allowed energies as the silicon crystal is formed. At
T = 0 K, the 4N states in the lower band, the valence band, are tilled with the valence
electrons. All of the valence electrons schen~aticallys hown in Figure 3.12 are
in the valence band. The upper energy band, the conduction band, is completely
empty at T = 0 K.
enough thermal energy to break the covalent bond and jump into the conduction
band. Figure 3.13a shows a two-dimensional representation of this bond-breaking
effect and Figure 3.13b. a simple line representation of the energy-band model,
shows the same effect.
The semiconductor is neutrally charged. This means that, as the negatively
charged electron breaks away from its covalent bonding position, a positively
charged "empty state" is created in the original covalent bonding position in the valence
band. As the temperature further increases, more covalent bonds are broken,
more electrons jump to the conduction hand, and more positive "empty states" are
created in the valence band.
We can also relate this hond breaking to the E versus k energy bands.
Figure 3.14a shows the E versus k diagram of the conduction and valence bands at
the conduction band are empty. Figure 3.14b shows these same bands for T > 0 K,
in which some electrons have gained enough energy to jump to the conduction band
and have left empty states in the valence hand. We are assuming at this point that no
external forces are applied so the electron and "empty state" distributions are symmetrical
with k
|
This is great post.
Thanks for your response