The Science Behind LED Technology and Semiconductor Architecture

The core of an LED is a semiconductor chip manufactured with processes similar to those used for integrated circuits. The chip consists of multiple ultrathin layers deposited in sequence on a supporting substrate, typically silicon or doped gallium. The device’s light output arises from the physical properties of a p-n junction: an initial semiconductor layer is doped to create an excess of electrons, forming n-type material, and a second, electron-deficient layer is deposited on top to form p-type material. The interface between the two layers is known as the active layer.

When voltage is applied to the diode, holes from the p-type region and electrons from the n-type region meet in the active layer and recombine, releasing photons. The wavelength of the emitted light depends on the chemical composition of the doped semiconductor materials and their relative energy levels. By adjusting the dopant composition, LEDs can be made to emit across all primary colors of the visible spectrum and into the infrared range.

Common semiconductor materials include aluminum, arsenic, gallium, indium, phosphorus and nitrogen in nitride form. Different proportions and doping levels of these elements determine the color of the light produced.

The semiconductor chip is mounted in a reflective cup connected to a lead frame and is linked to the anode and cathode by fine bonding wires. The assembly is encapsulated in an epoxy dome lens that focuses the light in a chosen direction. The lens design directly affects the beam distribution.

• Diffusion control: Tiny glass particles embedded in the lens can scatter light and broaden the beam.
• Color indication: The lens may be dyed to indicate operating status, but the emission color is determined fundamentally by the semiconductor material, not by the lens dye.
• Beam angle adjustment: Changing the lens shape, the reflective-cup geometry and the distance between the chip and the top of the lens can precisely control the beam angle.

Representative wavelengths for common LED colors are listed below.

Because a single LED chip typically produces monochromatic light at a specific wavelength, white LEDs require a special mechanism. The most common method adds a phosphor to the reflective cup. High-energy blue light emitted by the chip excites the phosphor, producing secondary radiation that covers the visible spectrum and combines to form white light.