GATE 2021 PH – Question 14
Two metal–semiconductor junctions are formed between an n-type semiconductor S and metal M as shown. Their work functions are $\phi_S$ and $\phi_M$, with $\phi_M>\phi_S$. Which graph best represents the current–voltage characteristics on a linear scale?
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Correct answer: (A) Figure (A)
Explanation
For an n-type semiconductor, the higher-work-function metal produces a depletion barrier. The two identical contacts face opposite directions, so reversing the voltage interchanges their roles. The overall characteristic must therefore reverse its current when the voltage reverses and must pass through the origin. The official key selects A, the symmetric nonlinear characteristic with increasing high-bias current. Its precise shape depends on the junction transport and breakdown regime; a simple ideal back-to-back diode model alone does not fix that high-bias shape.