Laser Diodes

Diode lasers are essential to many of the exploding technologies we have witnessed in the last decade, including CD, DVD, laser printing, scanners, data transfer and telecommunications. Diode lasers continue to represent the largest share of the worldwide laser market, even as competing technology such as LEDs and VCSELs continue to evolve.

Williams Products Used

Williams products are used throughout the manufacturing of photo and laser diodes. Gold sputtering targets featuring SFG™ technology and gold evaporation materials featuring EVAPro™ technology are used for metallization of the contact surface. SiO₂ targets are also used for insulating layers in the diode. Williams also offers a full array of backing plate designs and internal services including the ability to replace, refurbish, repair and design backing plates using CAD/CAM. With target bonding facilities throughout the world, industry leading bonding services and minimized shipping logistics are assured.

What are Photo and Laser Diodes?

All laser diodes are based on light-emitting diodes (LEDs). As with the photodiode, the underlying structure is a p-n junction, the only difference is the direction of the applied voltage or bias. The p-n junctions consist of a semiconductor layer (silicon in most photodiodes) doped with atoms carrying extra valence electrons (n-type semiconductors) under a layer doped with atoms carrying one valence electron less than silicon (p-type semiconductor). Charge migration creates a depletion region with an electric field directed toward the p region, allowing current to flow in only one direction. In a photodiode, a reverse bias potential is applied across the diode, preventing current from flowing in the absence of light. With exposure to light, electron-hole pairs are created, generating a current. In a laser diode or a LED, the process is exactly reverse. A positive bias is applied, causing current to flow. As the electrons form the n-type semiconductor flow into the p-type semiconductor, they combine with the holes, releasing energy in the form of light.

Diode lasers differ, in that light is generated by stimulated rather than spontaneous emission, resulting in much higher generation efficiency. A second difference between diode lasers and LEDs is that lasers require a higher current. With higher current, the excited states become more populated than the relaxed states— the condition known as a population inversion. Laser amplification now occurs because each photon on average produces more than one stimulated photon before leaving the laser or being absorbed. Once this laser amplification occurs, the quantum efficiency in converting additional electrical energy into light jumps to values much higher than those for LEDs.

Schematic Diagram

Figure 1: Schematic diagram of an edge emitting laser diode