Opto electronic devices

Optoelectronics is the communication between optics and electronics which includes the study, design and manufacture of a hardware device that converts electrical energy into light and light into energy through semiconductors. This device is made from solid crystalline materials which are lighter than metals and heavier than insulators. Optoelectronics device is basically an electronic device involving light. This device can be found in many optoelectronics applications like military services, telecommunications, automatic access control systems and medical equipments.

1. Opto electronic devices A.Vivetha Assistant Professor of Physics Bon secours College for Women

2. photons A photon is the smallest discrete amount or quantum of electromagnetic radiation. It is the basic unit of all light. Photons are always in motion and, in a vacuum, travel at a constant speed to all observers of 2.998 x 10 8  m/s. This is commonly referred to as the speed of light, denoted by the letter  c. 

3. Optoelectronics devices Optoelectronics device is basically an electronic device involving light. This device converts electrical energy into light and light into energy through semiconductors.

4. The photoelectric effect The photoelectric effect is the emission of electrons or other free carriers when electromagnetic radiation, like light, hits a material. Electrons emitted in this manner can be called photoelectrons. This process is called extrinsic photoelectric effect.

5. Intrinsic photo electric effect When light incident on a semiconductor, electron – hole pairs are generated. This increases the electrical conductivity. This is called intrinsic photo electric effect.

6. Classification of photonic devices

7. electroluminescence Electroluminescence is the generation of light by an electric current passing through a material under an applied electric field. it is differ from thermal radiation. It contains narrow range of wavelength.

8. Radioactive luminescence luminescence is the emission of optical radiation ( UV,Visible or IR) as a result of electronic excitation of a material. this luminescent radiation is a cold radiation.

9. The luminescence properties exhibited by semiconductors are due to the transition of electrons from the valence band or from the impurity levels to the conduction band.

10. Classification of luminescent radiation: It is based on electronic excitation classified into four types.

11. Types of transitions The quantum transitions are divided into two types. radioactive and non radioactive In the radioactive transition the emitted radiations are called recombination emission. In non radioactive transitions the liberated energy is expended on heating the crystal lattice. This may occur either may impurity level or defect level.

12. Method of excitations

13. A powder of semiconductor is suspended in a dielectric medium It will emit lught only by applying an alternating voltage. Its efficiency is less than 1%. This is mainly caused by field emission of electrons from trapping centres Intrinsic excitation

14. Avalanche excitation For the avalanche excitation a p-n junction is reverse biased. when the reverse voltage is in the avalanche break down, electron -hole pairs produced due to ionization.it may result in emission of light.

15. Tunneling excittion Electro luminescence may be excited by tunnelling process. Wnen a large rverse bias is given to a metal semiconductor barrier, holes at the metal fermilevel can tunnel into the valence band. It makes a radioactive recombination with electrons that have tunneled from the valence band to the conduction band.

16. Injection process In which the radiation originates recombination of electros in the p region. Here the pn junction is in the forward direction. The recombination luminescence produced in higher intensity.