Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne What is Doping?
Name: Nathan P.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: Thursday, June 06, 2002


Question:
What is electron doping?


Replies:
Nathan,

I have heard the term "electron doping" used in two different ways. One definition involves making something negatively charged. One involves semiconductors as used in diodes and transistors.

Electron doping can be adding electrons to a material to give it a negative charge. This can apply to something such as a capacitor. It is often done to produce an electric field that extends out for a significant distance.

Electron doping can also be a procedure that makes semiconductors such as silicon and germanium ready for diodes and transistors. Semiconductors in their undoped form are actually electrical insulators that don't insulate very well. They form a crystal pattern where every electron has a definite place. Most semiconductor materials have four valence electrons, four electrons in the outer shell. By putting one or two percent of atoms with five valence electrons such as arsenic in with a four valence electron semiconductor such as silicon, something interesting happens. There are not enough arsenic atoms to affect the overall crystal structure. Four of the five electrons are used in the same pattern as for silicon. The fifth atom doesn't fit well in the structure. It still prefers to hang near the arsenic atom, but it is not held tightly. It is very easy to knock it loose and send it on its way through the material. A doped semiconductor is much more like a conductor than an undoped semiconductor. You can also dope a semiconductor with a three-electron atom such as aluminum. The aluminum fits into the crystal structure, but now the structure is missing an electron. This is called a hole. Making a neighboring electron move into the hole is sort of like making the hole move. Putting an electron-doped semiconductor (n-type) with a hole-doped semiconductor (p-type) creates a diode. Other combinations create devices such as transistors.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory