GATE 2025 EC – Question 63

Electronic Devices · P-N Junction and Semiconductor Devices · 2 marks · Numerical answer

An ideal p-n junction germanium diode has a reverse saturation current of 10 μA at 300 K.

The voltage (in Volts, rounded off to two decimal places) to be applied across the junction to get a forward bias current of 100 mA at 300 K is _____.

(Consider the Boltzmann constant $k_B=1.38\times10^{-23}$ J/K and the charge of an electron $e=1.6\times10^{-19}$ C.)

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Correct answer: 0.23 to 0.25

Explanation

$V_T=k_BT/e=1.38\times10^{-23}\times300/1.6\times10^{-19}=25.875$ mV. From $I=I_s(e^{V/V_T}-1)$: $V=V_T\ln\!\left(\dfrac{I}{I_s}+1\right)=0.025875\times\ln(10001)=0.025875\times9.2104=0.238$ V $\approx0.24$ V.