Difference between Normal diode and LASER,LED Diode's

 Hi friends, every one who knows about electronics devices will be familiar with diode and optical sources like LASER and LED. The optical sources are also diodes. By knowing this every one may think that why a normal diode could not emit light where as a LASER and LED does?

The answer to this question lies in developing of these normal and optical diodes.

The major differences between normal and LASER and LED type of diodes is

“Semiconductor materials used for making”

Due to this we have variation in formation of junction between P and N region and differences in band gap energies also plays a role to not emit light(radiate) in case of normal diode

*As we know that Normal diode is made from semiconductor materials of group 4 like Si and Ge. These are doped with either group 3 or group 5 elements to form  P and N type materials respectively and when this doping is done on single semiconductor material, a diode is formed.

*In this case we will see a non heterojunction formed between P and N regions of a diode, this is called depletion layer(or)region  which is increased or decreased  by biasing.

*We have used single semiconductor material for making, so indirect band gap exists between conduction and valence band. On baising  electrons  and holes recombine across the band gap and third particle generated in this process will conserve the momentum which is the reason for normal diode to not emit the light.

 *LASER and LED diode cant be developed with single semiconductor element, as these need direct band gap materials. These are made from compounds of a group 3(Al,Ga,In) and group 5(P,As,Sb). These are suitable for developing optical sources like LASER and LED.

*In case of laser and led diodes hetrojunction is formed between two adjoining materials with different band gap energies.

*In direct band gap semiconductor, electrons and holes can recombine directly across the band gap without needing a third particle to conserve momentum. In this radiative recombination is sufficiently high to produce an adequate level of optical emission.

Why Si and Ge are widely used as semiconductor materials?

It is known that inert gases like Ne(10),Ar(18),Kr(36) contain stable electronic configuration. These atoms have no tendency to combine with other atoms as they have stable electronic configuration. Elements like fluorine(9) and chlorine(17) are very reactive as they are one short of stable electronic configuration. Electronic configuration is defined as systematic arrangement of electrons in the atomic orbits. The maximum number of electrons present in each orbit is generally given by 2(n*n),where n=number of orbit.

1^st orbit =2,2^nd orbit=8,3rd orbit=18….Electrons present in the last orbit of an atom is called "valence electrons".

Si,Ge belong to group 4 of periodic table and they have 4 valence electrons at T>0k,neither have  stable electronic configuration nor they are too far to attain stable electronic configuration like nonmetals. This is reason why group 4 is treated as semiconductor metals. In this we also have carbon which is non metal so we will not consider it, remaining are Sn,Pb,Fl which are post transistion metals (poor metals) and these have lower melting and boiling points which make them to not consider as semiconductor metals. So Si and Ge are widely used as semiconductor metals.