on what principle does a semiconductor laser works?

5 months ago


Answers : (1)

The semiconductor materials have valence band V and conduction band C, the energy level of conduction band is Eg (Eg>0) higher than that of valence band. To make things simple, we start our analysis supposing the temperature to be 0 K. It can be proved that the conclusions we draw under 0 K applies to normal temperatures.
Under this assumption for non-degenerate semiconductor, initially the conduction band is completely empty and the valence band is completely filled. Now we excite some electrons from valence band to conduction band, after about 1 ps, electrons in the conduction band drop to the lowest unoccupied levels of this band, we name the upper boundary of the electron energy levels in the conduction band the quasi-Fermi level Efc. Meanwhile holes appear in the valence band and electrons near the top of the valence band drop to the lowest energy levels of the unoccupied valence energy levels, leave on the top of the valence band an empty part. We call the new upper boundary energy level of the valence band quasi-Fermi level Efv. When electrons in the conduction band run into the valence band, they will combine with the holes, in the same time they emit photons. This is the recombination radiation. Our task is to make this recombination radiation to lase. Then several conditions must be met.
First for the radiation to be amplified, the light energy hnmust satisfy:
Efc- Efv³hn³Eg
From this relation we have Efc- Efv³Eg. This decides the critical condition. The value of Efcand Efvis influenced by the pumping process, i.e., by the intensity (N) of the electrons being raised to the conduction band. When N is increased, Efcincreases and Efvdecreases. The N satisfies Efc- Efv= Eg is named Ntr. We inject carriers into the semiconductor material to make the free electron intensity to be larger than Nth, then the semiconductor exhibits a net gain. We put this active medium in a suitable cavity, laser action occurs when this net gain overcome losses. The pumping of semiconductor lasers can be realized by the beam of another laser, or by an electron beam, but the most convenient way is by using electrical current that flows through the semiconductor junctions. This uses the semiconductor laser in the form of diode.
Thanks and Regards
Apoorva Arora
IIT Roorkee
askIITians Faculty
one month ago

Post Your Answer

More Questions On General Physics

Ask Experts

Have any Question? Ask Experts
Post Question
Answer ‘n’ Earn
Attractive Gift
To Win!!!
Click Here for details
A block of mass m, attached to a spring of spring constant k, oscillates on a smooth horizontal table. The other end of the spring is fixed to a wall. If it has a speed v when the spring is...
Consider the block + the spring as the system. The external forces acting on the system are (a) the force of gravity, (b) the normal force by the table and © the force by the wall. None...
Apoorva Arora 8 days ago
Two balls of same mass are thrown horizontally from top of a tower in the opposite direction with velocities 3 and 4m/s. the dis. b/w walls when their velocities are mutually prependicular...
Hello Student, v1=3i-gtj v2=-4i-gtj v1.v2=0 for 90 deg =>-12+g^2t^2=0 =>gt=root12 =>t=root(12) /10 =>dis = 7 *root(12)/10 Thanks & Regards Arun Kumar Btech, IIT Delhi...
Arun Kumar 22 days ago
can we follow physics every day.how?
yes.......baaga gaali veestunappudu kobbari chettu kinda undu appudu telustundi newton 3rd law............jaffaaaga
sampath ramaraju 6 months ago
Daily nuvvu song paadutunte memu paaripovadame PHYSICS.
GADDAM MAHESH 4 months ago
BALAKRISHNA 4 months ago
eq. resistance in parallel
mohit yadav 11 months ago
for derivation http://answers.yahoo.com/question/index?qid=20080812112655AAQ7JDg for example http://www.wikihow.com/Calculate-Series-and-Parallel-Resistance
Keerthi Raj 11 months ago
what is entropy
It is the measure of the disorder of a system where disorder refers to the number of states a system can be in, having a fixed composition, volume,energy,pressure and temperature. Thanks...
Ruchi Shaw 5 months ago
a partical droped from the heighest place of a building. in the final second the particle moved half height of the bulding . what is the height of the building?
distance travelled in n seconds, s = 5n^2 v= 10(n-1) s’= 10(n-1)+ 5 (n-1)^2 s-s’= s/2= 5n^2- 10n+10-5n^2+10n-5= 5= s/2 s=10
Sher Mohammad 16 days ago
View all Questions »