Even though small second-harmonic-generation (SHG)-based external-cavity green lasers are readily available, the advantages of pure semiconductor laser diodes—such as miniature size, high stability, and high efficiency—make them better candidates for red-green-blue (RGB) displays. Unfortunately, electrically injected semiconductor laser diodes have only been developed with wavelengths as long as 515 nm—blue-green lasers not quite able to reach the green spectrum. But that was before researchers at Sumitomo Electric Industries (Hyogo, Japan) found a way to combat quantum-well effects that limit the lasing wavelength. Now, Sumitomo has demonstrated the first electrically pumped “true green” laser diode, operating at 531 nm–more than suitable for compact RGB applications.
For conventional indium gallium nitride (InGaN)-based laser diodes on crystalline-plane (0001) GaN substrates, radiative recombination probabilities are reduced within the device quantum wells due to large electric fields caused by both spontaneous and piezoelectric polarization effects, as well as to defects in the quantum-well layers. The Sumitomo researchers instead used an alternate semipolar (2021) plane that produces highly homogeneous (in both composition and quantum-well thickness) InGaN quantum wells. This structure produces electroluminescence at a longer lasing wavelength (531 nm) with a very narrow full-width-half-maximum compared to what results from using other crystalline planes. Contact Yohei Enya at [email protected].