Feature
The Green Laser Diode: Completing the Rainbow
Traditionally, green laser diodes have been difficult to construct due to the characteristics of the quantum wells that serve as their gain region. Now, however, several companies and research groups have found ways to fill this “green gap,” by mastering the epitaxy of high-indium-containing quantum wells, balancing strain and defect formation against the quantum-confined Stark effect and using optimized waveguides. Their work is driving new applications in consumer electronics, biophotonics and other areas.
The latest addition to the family of semiconductor laser diodes is the green laser, which is based on the material system (Al,In)GaN. In 1996, this system enabled the first laser diode on the short wavelength side of the visible spectrum—405 nm, the “sweet spot” for light emitters based on InGaN quantum wells (QWs). Since then, researchers have found it extremely difficult to push toward longer wavelengths. Due to the physical and material properties of the InGaN QWs, efficiency drops drastically as diodes move towards green. And, unfortunately, this spectral region cannot be reached with other III-V materials, such as AlGaAs or InGaAlP from the long wavelength side.
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