Optoelectronics is the communication of optics and electronics which involves the study, design and manufacturing of hardware device which converts electrical energy into light and light into energy through semiconductors.
Made up of semiconductor materials.
Used in Military services, telecommunications,automatic access control systems and medical equipments.

Types of Optoelectronic devices

Light Emitting Diode(LED)

When sufficient voltage is applied to the leads of the LED, electrons move in one direction across the junction between the p and n regions.
The electrons recombine with the holes within the device.
Release energy in the form of photons.
This effect is called electroluminescence.

Light sensor made up of semiconductor materials
When light falls on the junction, voltage or current is generated
PN- Junction diode, operated in reverse bais
When a photon(light) strikes a semiconductor, electron- hole pairs are generated through band-band optical absorption
Electric field is produced when the electron diffuse into the junction
This electric field across the depletion region is equal to the negative voltage across the unbaised diode. This is known as inner photoelectric effect

Optical energy(light) is converted to electrical energy(current/voltage) through optical receivers.
Refered to as O/E Converter.
Photodector is the fundamental element of optical receivers.

Similar to bipolar junction transistor(BJT)
Only difference is that base current is produced and controlled by light except voltage source
Converts light energy to electrical signal
Light sensitive
Have collector, base and emitter

Light sensitive collector base pn junction controls current flow between emitter and collector
Resistance decreases as intensity increases, creating more emitter-base current
The small base current controls the larger emitter-collector current