Effect of temperature on Semiconductor

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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→

diode 17

 

Forbidden energy gap  Vs Temperature T curve →

 

ice screenshot 20160407 023618

 

For Si  Variation of forbidden energy gap  with respect to temperature T

                chart?cht=tx&chl=E %7B%7BG%7D%7D(T) = 1.21–3.6×chart?cht=tx&chl=%2010%5E%7B%7B 4%7D%7D T   eV

                Here Temperature T represented in Kelvin (K)

Q1. Find forbidden energy gap   for Si at  chart?cht=tx&chl=0%5E%7Bo%7DK ?

Answer :  We know that for Si

                chart?cht=tx&chl=E %7B%7BG%7D%7D(T) = 1.21–3.6×chart?cht=tx&chl=%2010%5E%7B%7B 4%7D%7D T   eV

                At T=  chart?cht=tx&chl=%200%5E%7B%7Bo%7D%7DK

               chart?cht=tx&chl=E %7BG%7D (chart?cht=tx&chl=%200%5E%7B%7B%7D%7D) = 1.21 eV

               So for Si at chart?cht=tx&chl=%200%5E%7B%7Bo%7D%7DK forbidden energy gap  will be 1.21 eV

Q2. Find forbidden energy gap for Si at room temperature T= chart?cht=tx&chl=%2025%5E%7B%7Bo%7D%7D C? 

Answer : Temperature in K = 273+25 =chart?cht=tx&chl=%20298%5E%7B%7Bo%7D%7DK

                  We know that for Si

                 chart?cht=tx&chl=E %7B%7BG%7D%7D(T) = 1.21–3.6×chart?cht=tx&chl=%2010%5E%7B%7B 4%7D%7D T   eV

                  Put T= 298 in above equation

                chart?cht=tx&chl=E %7B%7BG%7D%7D(298)  = 1.21-3.6×chart?cht=tx&chl=%2010%5E%7B%7B 4%7D%7D×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 chart?cht=tx&chl=%20107%5E%7B%7Bo%7D%7D C?

Answer : Temperature in K = 273+107 =380 K

                  We know that for Si  

                 chart?cht=tx&chl=E %7B%7BG%7D%7D(T) = 1.21–3.6×chart?cht=tx&chl=%2010%5E%7B%7B 4%7D%7D T   eV

                  Put T= 380 in above equation

                  chart?cht=tx&chl=%20E %7BG%7D(380)  = 1.21–3.6× chart?cht=tx&chl=%2010%5E%7B%7B 4%7D%7D%5Ctimes380 

                                      = 1.07 eV

For Ge → Variation of forbidden energy gap  with respect to temperature T(K)

                   chart?cht=tx&chl=E %7B%7BG%7D%7D(T) = chart?cht=tx&chl=0.785 2 eV

                 Here Temperature T represented in Kelvin (K)

Q4. Find forbidden energy gap chart?cht=tx&chl=E %7B%7BG%7D%7D  for Ge at  chart?cht=tx&chl=%200%5E%7Bo%7D K ?

Answer:  We know that for Ge

                 chart?cht=tx&chl=E %7B%7BG%7D%7D(T) = chart?cht=tx&chl=0.785 2 eV

                   At T= chart?cht=tx&chl=%200%5E%7Bo%7D K   

                  chart?cht=tx&chl=%20E %7BG%7D%7D(0) =0.785 eV

                  So for Ge at chart?cht=tx&chl=%200%5E%7B%7Bo%7D%7DK forbidden energy gap  will be 0.785 eV

Q5. Find forbidden energy gap for Ge at room temperature T=  chart?cht=tx&chl=%2025%5E%7B%7Bo%7D%7DC

 Answer: Temperature in K = 273+25 = 298

                 We know that for Ge

                 chart?cht=tx&chl=E %7B%7BG%7D%7D(T) = chart?cht=tx&chl=0.785 2 eV

                  Put T= 298 in above equation

                  chart?cht=tx&chl=%20E %7B%7BG%7D%7D(298)%20%3D%200.785 2

                                   = 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 chart?cht=tx&chl=E %7B%7BG%7D%7D of Ge is less than forbidden energy gap chart?cht=tx&chl=E %7B%7BG%7D%7D of Si
  • conductivity  of Ge will be more than the conductivity of Si because as forbidden energy gap        chart?cht=tx&chl=E %7B%7BG%7D%7D decrease ,conductivity will increase
  • At room temperature forbidden energy gap chart?cht=tx&chl=E %7B%7BG%7D%7D of Ge is less than the forbidden energy gap chart?cht=tx&chl=E %7B%7BG%7D%7D of  Si
  • At room temperature conductivity of Ge is greater than conductivity of Si
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