Everything Science Grade 11

20.4 CHAPTER 20. ELECTRONIC PROPERTIES OF MATTER

valence band

conduction band

intrinsic semiconductor

valence band

conduction band

n-type semiconductor

donor atom

valence band

conduction band

p-type semiconductor

Energy acceptor atom

The energy level of thedonor atom is close to the conduction band andit is relatively easy for

electrons to enter the conduction band. The energy level of the acceptoratom is close to the valence

band and it is relativelyeasy for electrons to leave the valence band andenter the vacancies.

Exercise 20 - 2

1. Explain the process of doping using detaileddiagrams for p-type andn-type semiconductors.


2. Draw a diagram showing a Ge crystal doped with As. What type of semiconductor is this?


3. Draw a diagram showing a Ge crystal doped with B. What type of semiconductor is this?


4. Explain how dopingimproves the conductivity of semi-conductors.


5. Would the followingelements make good p-type dopants or good n-type dopants?

(a) B

(b) P

(c) Ga

(d) As

(e) In

(f) Bi

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20.4 The p-n junction

Differences between p- and n-type semi-

conductors

ESBIY

We have seen that the addition of specific elements to semiconductor materials turns them into p-type

semiconductors or n-type semiconductors. The differences between n- and p-type semiconductors are

summarised in Table ??.