• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Why are holes formed only in semiconductors?

Status
Not open for further replies.

suhasm

New Member
Why are holes found only in semiconductors?
Here is what i have understood by my own logic :

A hole is the absence of an electron in the valence band. It behaves like a positive charge.
In a metal , there is practically no difference between a valence electron and free electron. ie. Every valance electron is also free to participate in conduction
as the valence and conduction bands overlap.
So , Holes are not formed.

Is this correct?:confused:

But what about insulators? For example , air.
Suppose we apply a very large voltage , the valence electrons in the air molecules will gain sufficient energy to become free electrons and air will become ionized.
When this happens , will holes be formed at the places where the valence electrons previously existed?:confused:
 

Papabravo

Well-Known Member
It is a consequence of the energy required to remove an electron from a valence band. In a metel, the single outer electron is loosely bound. In an insulator the electrons of the outer shell are tightly bound. In an intrinsic semiconductor the electrons of the outer shell are in between. The application of a forward bias changes everything. It allows the semiconductor to behave like a conductor, except the property is directional. The potential barrier to current flow is lowered in one direction.
 

Ratchit

Well-Known Member
suhasm,

Why are holes found only in semiconductors?
Because semiconductors contains a scarcity of electrons such that they cannot readily fill a hole. That is why they are called a semiconductors. They do not conduct all that well. Conductive metals contain a vast sea of free and loose electrons. A hole would not last very long in such an environment. It would be very quickly filled and disappear.

But what about insulators? For example , air.
Suppose we apply a very large voltage , the valence electrons in the air molecules will gain sufficient energy to become free electrons and air will become ionized.
When this happens , will holes be formed at the places where the valence electrons previously existed?
The positive ions of the air molecules will be deficient an electron, of course. But as a gas, they can travel to the negative terminal and pick up a electron. The ions in a semiconductor are fixed in a crystal lattice and cannot move.

Ratch
 

Dean Huster

Well-Known Member
A play was written about this stuff decades ago: Arsenic and Hole Lace.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top