There are several types of semiconductor devices used for emitting light. LEDs and laser diodes are very commonly used flashlights, medical devices, traffic signals, etc. but the main difference between these two devices lies in the working principle. The nature of the light emitted by these devices is also different and hence has different applications.
LED vs Laser Diode
The main difference between LED and laser diode is that LED’s working principle is based on electroluminescence such that the charges recombine at the junction and emit energy in the form of photons. On the other hand, the working principle of a laser diode is based on stimulated emission.
LED emits light energy when the majority and minority charges (electrons and holes) recombine in the forward bias p-n junction. The electrons and holes are at different energy levels so when the former jumps from the conduction band to the valance band, some amount of energy is released and it is used for emitting light.
Laser diodes are extensively used in telecommunication and the main parts in this device are photodiode, laser, glass lens at the front, and fiber. Laser diodes work on the principle of stimulated emission and the concentration of charge carriers is very high in laser diodes.
Comparison Table Between LED and Laser Diode
| Parameters of Comparison | LED | Laser Diode |
| Definition | LEDs are semiconductor materials that emit light when an electric current passes through them. | Laser diodes are a type of semiconductor device that uses a p-n junction to emit coherent light beans. |
| Full-Form | The full form of LED is Light Emitting Diode. | The full form of laser is light amplification by stimulated emission of radiation. |
| Working Principle | The main working principle of a LED is based on electro-luminance. | The main working principle of a laser diode is stimulated emission. |
| Response Time | Response times of LEDs are much slower than laser diodes. | Response time of laser diode is much faster than LEDs. |
| Current | The driving current ranges from 50mA to 100mA. | The driving current ranges from 5mA to 40mA. |
| Nature | The light emitted by LED is incoherent and comprises of various colors. | The light emitted by the laser diode is coherent and monochromatic. |
What is LED?
An LED device is best described as a p-n junction diode from where light emits when current passes through it. In the junction area, the electrons from the n side combine with the holes from the p side and emit enough energy in the form of light (and heat also). The light energy that is formed is radiated through the junction of the diode. Single LEDs are used for making decimal points whereas several LEDs are used together to form a line segment. To understand the working of an LED, one needs to understand quantum theory because it is related to the movement of electrons from higher to lower levels of energy.
During the construction of an LED, it is connected in the forward bias so that the current flows in the forward direction. The electrons move in the opposite direction. Since there is an energy gap between the conduction band and the valence band, the difference in this energy is equal to the energy of the photons.
There are several advantages of using LED in electronic displays. For example, the intensity of the LED lights can be controlled very smoothly and unlike laser diode, they emit various colors such as green, red, yellow, etc. They are also very economical for both domestic and industrial purposes.
What is Laser Diode?
Laser diodes are extensively used especially when it comes to scientific and medical purposes. The light that is emitted from a laser diode forms a narrow beam and hence can be easily launched from an optical fiber. Monochromaticity is one of the main characteristics of the light emitted by laser diodes. Because they contain only a single color, they have larges medical applications. The light beams emitted by the laser diodes are also coherent meaning that there is only a single wavelength present. There are two classes of laser diodes, one that can emit light by itself and another one is that uses an external source.
Laser has a very big advantage that the light can travel very long distance. Apart from the fact that it can travel long distances, there are other advantages of using laser diodes. For example, laser diodes consume low power, they can operate for long hours, the manufacturing cost of this equipment is also low, and due to their small size, they are easily portable.
Among several advantages, laser diodes also have a few disadvantages. The most significant disadvantage is that the light emitted by the laser is harmful to our eyes and the performance of the device varies because of the rise in temperature (vulnerable to high temperature).
Main Differences Between LED and Laser Diode
- The working principle of LED and laser diode is different. While the former works on electro-luminance the latter works on stimulated emission.
- The driving current for LED is more than that of laser diodes.
- LED lies in a very broad bandwidth range (10THz to 50THz) whereas laser diodes lie in a very narrow bandwidth range (1MHz to 2MHz).
- In LED the concentration of the charge carriers is much lower than that of the laser diodes.
- LED has a wider junction area and hence light passes through a very wide space whereas laser diodes have a very narrow junction area.
Conclusion
Both LEDs and laser diodes have various applications in different fields. LED televisions are very common are these days and hence it is of great importance in the electronic appliances market. LEDs are used for various dynamic operations because the switching time in LEDs (on and off time) takes less than even one nanosecond. The big advantage of LEDs over laser diodes is that LEDs are highly economical whereas lasers are comparatively much expensive. This is why the scientific instruments and also those used by medical professionals are very costly. But laser diodes are not suitable for high-power operations.
References
- https://ieeexplore.ieee.org/abstract/document/999188/
- https://www.nature.com/articles/nphoton.2014.326?draft\\u003djournal