Hello,world.
Let's continue.I will talk about that why led light will be emitted by diode when running through current.
A semiconductor with extra electrons is called N-type material, since it has extra negatively charged particles. In N-type material, free electrons move
from a negatively charged area to a positively charged area.
A semiconductor with extra holes is called P-type material, since it effectively has extra positively charged particles. Electrons can jump from hole to
hole, moving from a negatively charged area to a positively charged area. As a result, the holes themselves appear to move from a positively charged area to
a negatively charged area.
A diode consists of a section of N-type material bonded to a section of P-type material, with electrodes on each end. This arrangement conducts electricity
in only one direction. When no voltage is applied to the diode, electrons from the N-type material fill holes from the P-type material along the junction
between the layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original insulating state -- all of the
holes are filled, so there are no free electrons or empty spaces for electrons, and charge can't flow.

When the negative end of the circuit is hooked up to the N-type layer and the positive end is hooked up to P-type layer, electrons and holes start moving and the depletion zone disappears.

To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-type area and holes moving in the reverse direction. To do
this, you connect the N-type side of the diode to the negative end of a circuit and the P-type side to the positive end. The free electrons in the N-type
material are repelled by the negative electrode and drawn to the positive electrode. The holes in the P-type material move the other way. When the voltage difference between the electrodes is high enough, the electrons in the depletion zone are boosted out of their holes and begin moving freely again. The depletion zone disappears, and charge moves across the diode.
If you try to run current the other way, with the P-type side connected to the negative end of the circuit and the N-type side connected to the positive
end, current will not flow. The negative electrons in the N-type material are attracted to the positive electrode. The positive holes in the P-type material
are attracted to the negative electrode. No current flows across the junction because the holes and the electrons are each moving in the wrong direction.
The depletion zone increases.

When the positive end of the circuit is hooked up to the N-type layer and the negative end is hooked up to the P-type layer, free electrons collect on one end of the diode and holes collect on the other. The depletion zone gets bigger.

The interaction between electrons and holes in this setup has an interesting side effect -- it generates light! In the next section, we'll find out exactly why this is.