Consider a semiconductor described schematically by the figure below. The conven
ID: 2072414 • Letter: C
Question
Consider a semiconductor described schematically by the figure below. The conventional diffusion current for electrons in the conduction band will be either in the +8 or -8 direction. Determine this direction and explain the reasons for your choice of direction. The conventional diffusion current for holes will be in either the +x or -x direction, " Choose the appropriate direction and explain why the conventional diffusion current for holes is in your choice of direction. Explain why there is no conventional drift current for electrons or holes for this semiconductor. Based on the diagram, is this semiconductor n-type or p-type? Explain your answer.Explanation / Answer
a. The graph indicates that the concentration of electrons is decreasing as we go in the +ve X direction ( towards right ). DIffusion of charge carriers happens from region of higher concentration to region of lower concentration. So, the electrons would diffuse to the right or in the +ve X direction. Since the sign of the conventional current for electrons ( -ve charge carriers ) is opposite to the direction of the movement of the electrons, we can say the diffusion current caused by electrons is in -X direction.
b. The graph indicates that the concentration of holes is decreasing as we go in the +ve X direction ( towards right ). DIffusion of charge carriers happens from region of higher concentration to region of lower concentration. So, the holes would diffuse to the right or in the +ve X direction. Since the sign of the conventional current for holes ( +ve charge carriers ) is in the direction of the movement of the holes, we can say the diffusion current caused by holes is in +X direction.
c. In this semiconductor, there is no conventional drift current for electrons or holes because there is no electric field present. And drift current needs electric field.
d. As per the graph, the concentration of holes is more than the concentration of the electrons ( the graph of p(x) is above the graph of n(x) ). If the concentration of holes is more than that of electrons, then it is a 'p' type semiconductor.