Optoelectronic Devices

Optoelectronic devices are semiconductor devices which use light to generate electricity or vice versa. The efficiency in their function is highly dependent on light absorption by the semiconductor material to convert into electrical signals.

Light is comprised of photons. When incident on a semiconductor material, photons with an energy equivalent or more than the energy band gap of the material clash with atoms to produce free electron- hole pairs. These electron – hole pairs recombine to produce photons. (Nptel.ac.in. 2018). It is the minority carrier characteristics, in particular the minority carrier lifetime, diffusion coefficient and mobility, which determine the rate of recombination of electron- hole pairs. This consequently impacts the function and efficiency of optoelectronic devices.

An example of this is the light emitting diode. Since electron – hole pairs recombine to produce photons, the rate of electron- hole recombination determines the intensity of light emitted by an LED. The shorter the minority carrier lifetime, the less time required for recombination of electron- hole pairs to occur, resulting in a higher efficiency LED.

Another example of an optoelectronic device dependent on minority carrier parameters is the solar cell. In a solar cell, light is converted to electricity through the production of electron – hole pairs in a p-n junction. Electrons produced are filtered through an external circuit to recombine with holes in the p-type material. As it travels through the wire, this generates an electric current. Solar cells made from wafers with long minority carrier lifetimes are usually more efficient than those with shorter lifetimes as carriers need to travel to their point of generation to be collected.