EFFECT OF TEMPERATURE ON SEMICONDUCTOR
In case of semiconductors, by increasing the temperature forbidden energy gap of semiconductor will decrease and conductivity of semiconductor will increase that means due to thermal agitation Covalent bonds break and new electron hole pairs ( EHP) generate
Forbidden energy gap for a semiconductor shown in figure below→
Forbidden energy gap Vs Temperature T curve →
For Si→ Variation of forbidden energy gap with respect to temperature T
(T) = 1.21–3.6×
T eV
Here Temperature T represented in Kelvin (K)
Q1. Find forbidden energy gap for Si at K ?
Answer : We know that for Si
(T) = 1.21–3.6×
T eV
At T= K
(
) = 1.21 eV
So for Si at K forbidden energy gap will be 1.21 eV
Q2. Find forbidden energy gap for Si at room temperature T= C?
Answer : Temperature in K = 273+25 =K
We know that for Si
(T) = 1.21–3.6×
T eV
Put T= 298 in above equation
(298) = 1.21-3.6×
×298
= 1.1 eV
So for Si at room temperature, forbidden energy gap will be 1.1eV
Q3. Find forbidden energy gap for Si at temperature C?
Answer : Temperature in K = 273+107 =380 K
We know that for Si
(T) = 1.21–3.6×
T eV
Put T= 380 in above equation
= 1.21–3.6×
= 1.07 eV
For Ge → Variation of forbidden energy gap with respect to temperature T(K)
=
eV
Here Temperature T represented in Kelvin (K)
Q4. Find forbidden energy gap for Ge at
K ?
Answer: We know that for Ge
=
eV
At T= K
=0.785 eV
So for Ge at K forbidden energy gap will be 0.785 eV
Q5. Find forbidden energy gap for Ge at room temperature T= ?
Answer: Temperature in K = 273+25 = 298
We know that for Ge
=
eV
Put T= 298 in above equation
= 0.72 eV
So for Ge at room temperature, forbidden energy gap will be 0.72 eV
NOTE:
- From above calculation it is clear that for a particular temperature T ( K), it may be possible that forbidden energy will become zero
- At any temperature forbidden energy gap
of Ge is less than forbidden energy gap
of Si
- conductivity of Ge will be more than the conductivity of Si because as forbidden energy gap
decrease ,conductivity will increase
- At room temperature forbidden energy gap
of Ge is less than the forbidden energy gap
of Si
- At room temperature conductivity of Ge is greater than conductivity of Si