How the depletion layer and potential barrier of a p-n junction form

This type of question, asked 2 times: 2 May 2023 S2, 4 May 2023 S2. All 2 questions below, oldest first.

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Question 1
2 May 2023 S2
14 $The potential barrier in p-n junction diode is due to$
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Question 2
4 May 2023 S2
41 $The depletion layer in p-n junction region is caused by$
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