# How do we account for the hole current?

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#### nandinichakrab

##### Newbie level 5
hole is a theoritical concept given by the scientists which has no actual existance. so how do we account for the hole current? can something which has no actual existance produce current?

what is hole current

MY DEAR FRIEND HOLE IS JUST ABSENCE OF ELECTRON.
THE CURRENT CARRIED BY ELECTRON WHEN IT IS IN VALANCE BAND IS NOTHING BUT HOLE CURRENT .AS IT JUMPS FROM ONE ATOM BOND TO ANOTHER IT SEEMS THAT THE EMPTY PLACE IS MOVING OPPOSITE THAT CONTRIBUTES FOR HOLE CURRENT AND U CAN REFFER FOR HALL EFFECT IN DETAIL WHICH GARRANTEES HOLE EXISTANCE .........................

### nandinichakrab

Points: 2
what is an hole current

Hi,

An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice.

The electron hole was introduced into calculations for the following two situations:

1)If an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconductors).

2)In crystals, band structure calculations lead to an effective mass for the charge carriers, which can be negative. Inspired by the Hall effect, Newton's law is used to attach the negative sign onto the charge.

In solid state physics, a hole is the absence of an electron from the otherwise full valence band. A full (or nearly full) valence band is present in semiconductors and insulators. The concept of a hole is essentially a simple way to analyze the electronic transitions within the valence band.

The hole is delocalized and spans an area in the crystal lattice covering many hundreds of unit cells. Instead of analyzing the movement of an empty state in the valence band as the movement of billions of separate electrons, physicists propose a single imaginary particle called a "hole". In an applied electric field, all the electrons move one way, so the hole moves the other way. If a hole associates itself with a neutral atom, that atom loses an electron and becomes positive. The physicists therefore say that the hole must have positive charge—in fact, they assign a charge of +e, precisely the opposite of the electron charge.

Rather big explaination...but I hope u r clear now.. ### nandinichakrab

Points: 2
who introduced concept of electron holes

Hi Infinytus,
I confussed with your reply, what is the difference between the hole and positive ion

Regards

physical concept of electron-hole picture

A hole is not a physical particle like electron but is assumed to exist in the position where there is a lack of electron. It is complementary to electron and is assumed to have charge opposite to electron i.e positive charge.

A positive ion is a single atom minus atleast 1 electron. An ion consists of a nucleus at the core surrounded by electron cloud. An atom which is neutral becomes a positive ion when atleat 1 electron is removed or knocked out of the atom
So its quite evident that the mass of the positive ion is more than that of a hole.

### nandinichakrab

Points: 2
simple concept of electron-hole picture

good xplanation Infinytus

concept of current flow

everything is fine Infinytus, but here u hav urself said that hole is just a concept to xplain the movement of electron in valence band.how can a current be associated with a concept?that means there is no current called hole current, bcoz holes r hypothetical.

hole is really exist semiconductor

Hi

Any semiconductor(intrinsic/extrinsic) consists of both holes and electrons.

How electrons are formed ?
The electrons in a semi-conductor are nothing but the valence electrons of the element forming the semi-conductor(here silicon). They are loosely attached to their nucleus core and are therefore allowed to move freely inside.

How holes are formed ?
In an intrinsic semiconductor like silicon at temperatures above absolute zero, there will be some electrons which are excited across the band gap into the conduction band and which can produce current. When the electron in pure silicon crosses the gap, it leaves behind an electron vacancy or "hole" in the regular silicon lattice. In other words, there is a finite probability that an electron in the lattice will be knocked loose from its position, leaving behind an electron deficiency called a "hole".

Current in semi-conductor
Under the influence of an external voltage, both the electron and the hole can move across the material.The current which will flow in an intrinsic semiconductor consists of both electron and hole current. The free valence electrons form the electron current which flow opposite to the direction of the voltage applied.

The electrons which have been freed from their lattice positions into the conduction band can hop between lattice positions to fill the vacancies left by the freed electrons. This additional mechanism is called hole conduction because it is as if the holes are migrating across the material in the direction opposite to the free electron movement.

As u can see in the image that the direction of the hole current is same as that of the positive current or the conventional current flow. ### nandinichakrab

Points: 2
compare electron current and hole current

Here Infinitus has compared the mass of a Hole which is actually nothing but the absence of an Electron. So if hole really has some mass then we can say that with the generation of an Electron Hole pair, mass of a semi-conductor should increase, because new mass is getting generated. But is this really feasible?? In some places i have seen that hole has mass and charge of the same magnitude as that of an electron but opposite in sign. But can mass be considered negative??If it so then during recombination of a electron hole pair, what would happen to the mass of the material???

Re: hole current concept

I am also puzzled to think that the mobility of hole is different from that of an electron. If the real entity which is giving the current flow (both electron and hole current) is the electron, then why is the mobility of hole different from that of electron.

Re: hole current concept

The mobility of holes is less than that of electrons due to more vacancy in the conduction band, where electrons are supposed to 'move', and much less in the valence band , where the holes do. Intuitively, the movement of a hole requires two conditions: 1) the movement of the corresponding electron to cover up the vacancy in a covalence bond and 2) the existence of that vacancy in the crystal lattice, while the electron just 'moves around'. The first case (hole movement) is somewhat less probable and that is expressed mathematically by a lesser mobility for holes. It would be most helpful to refer to a textbook that covers basic concepts of semiconductor devices' physics like the classic: Physics of Semiconductor Devices by S.M. Sze

Added after 1 hours 23 minutes:

Also, here is an interesting/fun video related to the previous discussion:

Re: hole current concept

Interesting topic. But I think the situation is even more complicated.
For example, read this excerpt from
Scott Hamilton: An analog electronics companion.

Quote:
"The drift velocity...... Vd=74*1E-6 m/second, a very small velocity indeed (about 3 h to travel 1m). So currents, or charges, do not flow at the speed of light, but the electromagnetic field does.....A Mexican wave travels around a stadium very much more rapidly than a person could. The individual electrons do move at high velocity , but since they are randomly scattered very frequently, it is only the average drift velocity which matters.....The electrons are only accelerated by the electric field E for an average about 2.4*1E-14 seconds before suffering a collision, so it is not surprising that the drift velocity is so low".

hole current concept

You could think of it like a partially filled tube of water. The air is the holes and the water electrons. If you tilt the tube, the water flows. The amount of air flowing up is equal to the amount of water flowing down

If the tube is completely full, i.e. no holes, the water does not flow when the tube is tilted

Light falls on one end of a long open-circuited n-type semiconductor bar for low level injection the hole current is predominantly to :

Drift
Both drift and diffusion
Diffusion
Length of bar