IV.16 - Blue-Green-Violet Laser Diodes?

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Application Note: Driving Blue Laser Diodes

Blue lasers are a very hot topic right now - but they aren't quite yet ready for commercialization. There is huge interest in developing blue lasers for two reasons:

• To complete the Red-Green-Blue combination needed to provide realistic color displays
• Blue diode lasers have very short wavelengths, which means that they can be used to pack data more densely than red lasers, in storage media such as CDs.

At the moment, a fierce battle is raging between the proponents of II-VI and III-V compound material systems. (II-VI compounds have one element from the IIA or IIB columns and one element from the VIA or VIB columns of the periodic table, and similarly III-V compounds have one element from the IIIA or IIIB columns and one element from the VA or VB columns of the periodic table.)

Research originally started out in the II-VI compounds. Some of these compounds are shown in the figure below:

The first blue semiconductor laser to be demonstrated was developed by 3M, in 1991. This diode was a quantum well structure fabricated from ZnSe (a II-VI compound), that operated at liquid nitrogen temperatures (77K, or -196 C) and emitted light at 490 nm wavelengths. Prior to this date, no method had been found to produce p-type ZnSe doping, which made it all but impossible to make a diode. The quantum well was made of Zn_1-xCd_xSe, and the optically guiding cladding layers were ZnSe. These layers, plus additional ones, were grown by molecular beam epitaxy (MBE) on a GaAs substrate (wafer). 

The latest results from this line of research are given in the table below, for the most recent 3M device: