The Depletion Layer in Thermal Equilibrium

[physics0]

Homework Statement

question: b,c,d,e

Homework Equations

possion's equation

The Attempt at a Solution

I try to solve the problem 1 of Chap.29 on the text:
Solid State Physics,Ascroft & Mermin

but when I cannot solve after quesion (a).

so, anyone, pls help me or give some hints about question b,c,d,e.

thank you

 

[physics0]

pls see the attachments about the problem