How to distinguish between LED and LD

- 2021-08-24-

I think everyone is silly and confused about LED and LD. Although it is only missing an E, it is actually the essential difference. Today I will introduce you to the difference between LED and LD. What is the difference?

1.LED is Abbreviation for Light Emitting Diode. It is widely seen in daily life, such as the indicator lights of household appliances and the rear anti-fog lights of automobiles. The most notable feature of LED is long service life and high photoelectric conversion efficiency. The reason is that in the PN junction of some semiconductor materials, when the injected minority carriers and the majority carriers recombine, the excess energy will be released in the form of light, thereby directly converting electrical energy into light energy. With reverse voltage applied to the PN junction, it is difficult to inject minority carriers, so it does not emit light. This kind of diode made by injection electroluminescence principle is called light-emitting diode, commonly known as LED. 

2. LD is the English abbreviation of laser diode. The physical structure of laser diode is to place a layer of light-active semiconductor between the junctions of light-emitting diodes, and its end surface has a partial reflection function after being polished, thus forming an optical resonant cavity. In the case of forward bias, the LED junction emits light and interacts with the optical cavity, thereby further stimulating the emission of single-wavelength light from the junction. The physical properties of this light are related to the material. The working principle of a conductor laser diode is theoretically the same as that of a gas laser. Laser diodes have been widely used in low-power optoelectronic devices such as optical disc drives on computers and print heads in laser printers.

3. The difference between the two in principle, structure, and efficiency. 1. The difference in working principle: LED uses the spontaneous emission of carriers injected into the active area to recombine light, while LD is recombined light-emitting by stimulated radiation. 2. The difference in architecture: LD has an optical resonant cavity to make the generated photons oscillate and amplify in the cavity, while LED does not have a resonant cavity. 3. The difference in efficiency: LED has no critical value characteristics, the spectral density is several orders of magnitude higher than that of LD, the output light power of LED is small, and the divergence angle is large. In summary, compared to LD, LED has its own characteristics: no critical value characteristics, no configuration noise, stable operation and no need for temperature control, long working life, high yield, and low price.