The structure of semiconductor light emitting diode (LED) varies according to the application and material doping. LED used for visible light indication and display shall be optimized in structure to obtain high efficiency; LED used for optical communication needs high radiation to couple the maximum power into the fiber, and also hopes to have greater modulation capability. The basic structure of LEDs used as indicators and displays.

LED

The emission wavelength of the optical communication LED must be in the window area of the optical fiber with low loss. 0.8-0.9 μ m GaAlAs GaAs LED and 1.3-1.6 μ m InGaAsP InP LED, their wavelengths fall on the first and second transparent windows of the quartz fiber, respectively. In order to couple with the fiber, light can be extracted from one side or one side of the LED.

Requirements for LED

① To improve the internal quantum efficiency, it is required to minimize crystal defects and harmful impurities;

② To improve external quantum efficiency, the structure should be convenient for light collection, extraction and emission;

③ The output current carrying information can be used to directly modulate the optical output at a high rate;

④ The structure shall be conducive to heat dissipation and reduce the decrease of optical power caused by junction temperature rise;

⑤ For high emissivity, direct band gap semiconductors and structures capable of driving at high current densities must be used.

Characteristics of LED

Working under low voltage (less than 2 volts) and low current (tens of milliamperes to 200 milliamperes), it has small power consumption, small size and can be directly connected with solid circuits; Stable, reliable and long service life (105~106 hours); Easy to modulate, light output is modulated by modulating LED current; The response speed of optical output is relatively fast (1~100 MHz); cheapness. Application LED can be used as indicator light, text digital display, optocoupler, light source of optical communication system, etc.