Effect of temperatures on semiconductor parameter

 

in this post we will discuss about effect of temperatures over different types of semiconductor parameters, this topic is very important for many competitive exams. if you have any doubt regarding this post then comment below, for video lectures on electronics devices and circuit subscribe our you tube channel, all links given below.

 

 

Effect of temperatures over different types of semiconductor parameters 

 

In this topic we will discuss effect of temperature on different parameters of semiconductor, such as

  1.   Effect of temperature on intrinsic concentration (ni)
  2.   Mobility (μ)
  3.   Conductivity (σ)

 

effect of temperature on intrinsic concentration (\({ n }_{ i }\)) 

 

\({ n }_{ i }=\sqrt { { A }_{ 0 } } \quad { T }^{ \frac { 3 }{ 2 }  }\quad { e }^{ -\frac { { E }_{ GO } }{ 2KT }  }\)

 

Where,  \(\sqrt { { A }_{ 0 } } \)  is  constant that depends on material

T is temperature

\({ E }_{ GO }\) is energy gap

 

NOTE –  Energy gap \({ E }_{ GO }\) at 0k = 1.21 ev for Si

= 0.785 ev for Ge

K = Boltzmann constant = \(1.38\times { 10 }^{ -23 }\quad j/kelvin\)

 

Having seen above relation we have come to know that intrinsic concentration is heavily depends upon the temperature. that means if we increase temperature then intrinsic concentration also increased and  if we decrease temperature then intrinsic concentration also decreased.

 

 

Energy Gap

 

\(Energy\quad gap\quad =\quad { E }_{ GO }-\beta T\)

 

Where,

β is constant and very small

NOTE- Energy gap decreases with respect to temperature

 

 

Mobility 

 

\(\mu =\frac { V }{ E } \)

 

where,

V = drift velocity

E = Electric Field

 

NOTE – mobility is inversely proportional to temperature i.e. when temperature increase then mobility decreases and vice versa also valid, because drift velocity in certain direction decreases when temperature increases.

 

 

Conductivity 

 

(1) for intrinsic semiconductor

 

\({ \sigma  }_{ i }={ n }_{ i }q({ \mu  }_{ e }+{ \mu  }_{ h })\)

 

As we already discuss intrinsic concentration is directly proportional to temperature and mobility is inversely proportional to temperature that means if we increases temperature then intrinsic concentration will increase and mobility will decrease, but the rate of decrement  is very small comparison to increment, so when temperature increase then conductivity of intrinsic semiconductor is also increases.

so we can say conductivity of intrinsic semiconductor is directly proportional to temperature.

 

 

For extrinsic semiconductor

N-type    \({ \sigma  }_{ n }={ n }q{ \mu  }_{ e }\)

P-type   \({ \sigma  }_{ p }={ n }q{ \mu  }_{ h }\)

 

NOTE – there is a little impact of the temperature over the majority charge carrier but in extrinsic semiconductor the mobility of charge carrier decreases heavily, hence we see that conductivity of extrinsic semiconductor decreases with respect to temperature.

 

 

 

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June 18, 2018

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