Effect of temperature on Semiconductor

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

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