Emitter devices

1.2. Emitter

 These are devices used to convert electricity into light.

These are LED, IR and LASER

LED

     These are semiconductor devices in which light is emotion When an electric current flow through.

It is forward biased PN-Junction.

                                                                           

                          

          

Theory           fig show that

1.                  It is a forward biased PN-Junction device in which light emit are activated.

2.                  As discussed emitter charge carrier recombination takes place when electron from N-side cross the junction and recombine with the holes in P-side. During charger combination release in the form of heat and light photon.

3.                  For semiconductor material SI and GE greater percentage of energy is released in the form of heat.

4.                  For other type of materials Gallium Arsenide (GaAs), Glum phosphide (Gap) gallium Arsenide phosphide (Gasp), energy released in the form of light.

5.                  If semiconductor materials are translucent (crystal which is transparent and light can easily pass from it), light is emitted and Junction becomes energy source i.e.

6.                  The color of emitted light depends upon the types of materials given below: -

(i)                 GaAs IR.

(ii)               Gap                                                    Blue or green.

(iii)             GaAP                                                  Blue and Yellow.

Construction

7.          Electron are N-side and holes are in p-side.

 N layer is grow substrate and P-layer is deposited on it by diffusion.    

Since carrier combination occur in P-side and it is kept upper most.

Mattel anode connection are placed at the outer edge of P-side.

Mattel cathode are at the bottom edge of N-side.       

Used/ Application of LED

(i)                 Burglar alarm system.

(ii)               These are used for numeric display in pocket calculator.

(iii)             It is used for image sensing circuit in picture phone.        

1.3 Photo diode

The devices in which we used reverse biased junction.

   These are junction type photoconductive devices.

IT HAS FOLLOWING TYPES: -

(i)     P-N junction photodiode

(ii)   PIN photodiode

(iii) Avalanche photodiode

A.             P-N junction photodiode

It has two terminal devices which is operated 1^st reverse biased junction and then illuminated it.

In reverse biased junction amount of current is so small due to thermally generated electron hole pair.

Basic diagram is:

    

             

The diameter of these devices is 2.5 mm and they mounted to-5-pakages with a window to allow minimum light

ü  A photo diode cantor’s current on and off in Nano second

ü  These devices are fast photo detector.

Uses

(i)     These are used to detecting visible and invisible light.

(ii)   Characteristic recognition

(iii) Optical communication equipment’s.

(iv) These are used in logic circuit where high speed required.

(v)   Encoder

(vi) Switching.

(vii)                        Demodulation.

B.      PIN photodiode

It is three region PN-junction device.

1.          These are fast response then PN-junction photo diode.

2.      These are ultrafast device having switching speed of nanosecond. These devices generate low noise.

3.      These devices are capable of processing very weak signal

4.      So these are widely used in electronic circuits

C.        Avalanche photodiode     

1.                      It is a PN-junction device which operated in avalanche break down region.

2.                      It is ultrafast device like PIN Photodiode

3.                      And can be operated at a frequently Geo Giga Hertz