GATE EC 2015 Set 1 — Question 45
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Electronic Devices → P-N Junction & Diodes → Diode Equation & Resistance
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Question
For a silicon diode with long P and N regions, the accepter and donor impurity concentrations are and , respectively. The lifetimes of electrons in P region and holes in N region are both 100 . The electron and hole diffusion coefficients are 49 and 36 , respectively. Assume = 26 mV, the intrinsic carrier concentration is , and C. When a forward voltage of 208 mV is applied across the diode, the hole current density (in ) injected from P region to N region is _____.
Correct answer
28 to 30
Solution
The hole current density injected from the P region to the N region () is given by:
Where:
C (charge of an electron)
= 36 (hole diffusion coefficient)
= equilibrium hole concentration in the N-region
= hole diffusion length in the N-region
= 208 mV = 0.208 V (applied forward voltage)
= = 26 mV = 0.026 V (thermal voltage)First, calculate :
Given and (donor concentration in N-region).
Next, calculate :
Given = 100 s (lifetime of holes in N-region).
Now, substitute these values into the equation:
Convert to :
Rounding to the nearest integer, the value is approximately 29 . This falls within the range of 28 to 30.
Where:
C (charge of an electron)
= 36 (hole diffusion coefficient)
= equilibrium hole concentration in the N-region
= hole diffusion length in the N-region
= 208 mV = 0.208 V (applied forward voltage)
= = 26 mV = 0.026 V (thermal voltage)First, calculate :
Given and (donor concentration in N-region).
Next, calculate :
Given = 100 s (lifetime of holes in N-region).
Now, substitute these values into the equation:
Convert to :
Rounding to the nearest integer, the value is approximately 29 . This falls within the range of 28 to 30.
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