Hi Everyone! There are some things about semiconductors that have always puzzled me,and I think it's high time I got them cleared up! Here are my four questions...please help. 1. When an impurity atom (dopant) is added to an intrinsic semiconductor,(say germanium),is the band structure of germanium atoms modified or is it the dopant atom's band structure that is modified? 2. A hole is simply an electron vacancy...then why does a hole have a different mobility and mass than the electron?. 3. Again,a hole is simply a vacancy of an electron,so a movement made by an electron is equivalent to a movement by a hole...then why do we add the currents due to the hole-movement and electron movement together to calculate total current?...aren't the two just different aspects of the same electron movement? 4. In an n-type semiconductor,the minority carriers are the holes. Now,when these holes do move,they also cause electrons to move in the opposite way.....so really,it's all the same, so why do we differentiate between majority and minority carriers?