Laser diodes: from violet to blue

For quite some time, laser diodes emitting at a wavelength of 405 nm are commercially available primarily due to their wide use in BluRay players. Other lasers with an emission in the violet and blue spectral range are either not offered by manufacturers or only available for a few selected wavelengths such as 450 nm. Yet there is much interest of users in numerous other wavelengths, e. g. for applications in atomic spectroscopy. Together with Technische Universität Berlin and eagleyard Photonics, FBH jointly works on the realization of wavelength stabilized laser diodes based on GaN with an emission at 436 nm. With these devices FBH aims at extending its spectrum of GaN laser diodes which so far has been limited to wavelengths below 420 nm [1].

To increase the emission wavelength was mainly challenging with regard to epitaxial growth of the wafers. The AlGaN/GaN waveguide structure for instance had to be revised, and the active region consisting of InGaN quantum films was completely modified in terms of its layer design and its epitaxial growth conditions. Only by this means, a sufficiently low transparency threshold [2] and a satisfying uniformity of the wafers [3] could be achieved.

After successfully optimizing these device details, FBH recently succeeded in realizing laser diodes with emission wavelengths in the blue spectral range > 430 nm. Fig. 1 shows the characteristics of a broad area laser diode in pulsed operation. The FBH thus features the technology to fabricate laser diodes in the wavelength range from 397 to 436 nm (compare Fig. 2). The current work focuses on ridge waveguide laser structures which should allow for a continuous-wave operation of the laser diodes in this spectral range.

Publications:

[1] Van Look et al., IEEE Phot. Technol. Lett. 22, 416 (2010)

[2] V. Hoffmann et al., J. Cryst. Growth 312, 3428 (2010)

[3] V. Hoffmann et al., J. Cryst. Growth, doi:10.1016/j.jcrysgro.2010.09.048 (2010)

FBH research: 18.11.2010