ROHM has recently established a crystalline growth technology of non-polar gallium nitride, and succeeded in the trial production of a blue-violet laser diode. In this development, ROHM's unique technology completely solved difficulty in the crystalline growth of non-polar gallium nitride and realized the continuous-wave operation of the laser diode at room temperature. Moreover, the application of this technology will make it possible to develop a green laser diode, which means ROHM made great progress toward the realization of laser diode in three all primary colors (i.e., red, green, and blue).

<General explanation of technology>
When a non-polar plane is used, efficient light emission is enabled at a constant wavelength regardless of current injection changes.
Furthermore, the unique property of the polarized light emission ensures the more efficient laser operation.

<Conventional technology and present situation (background)>
Presently, GaN-based blue-violet laser diodes with a wavelength of 405 nm are put in practical use as a pickup light source for high-definition media, such as the next-generation DVDs.

<Existing technology>
The device structure of these laser diodes is formed by the crystalline growth under a high-temperature environment. The crystals are grown in the plane direction called "c-plane" conventionally.

<New technology>
ROHM succeeded in eliminating stacking faults in the m-plane crystalline growth. By applying this technology, ROHM achieved the continuous-wave operation of a 404 nm laser diode at room temperature. The laser diode that ROHM manufactured on a trial basis is of typical type with a waveguide width of 1.5μm and a waveguide length of 600μm. The laser diode attained a threshold current for lasing of 28 mA before the mirror coating. This performance is already equivalent to or higher than that of blue-violet laser diodes by the c-plane.
The waveguide is formed to make maximum use of polarized light. The trial product is of easy-to-laser-operation device structure, which enables a reduction in power consumption as well.

<Technical ripple effect>
ROHM is presently manufacturing a laser diode in a blue region (460 nm) on a trial basis. By the end of this year, ROHM will aim at the development of a 532-nm green laser diode. So far, the longest wavelength of GaN-based laser diode is 470 nm with the conventional technology applied. If red, green, and blue laser light sources are applied, large-screen, high-definition display with a color range 1.5 to 1.7 times as high as the conventional NTSC is possible. If the green laser diode is manufactured, subminiature projectors will be available and expected to be included in mobile phones. In future, ROHM will further develop optical devices by using the novel material, non-polar m-plane Gallium Nitride.

<Supplement>
ROHM exhibited blue LEDs that used the m-plane GaN in the Combined Exhibition of Advanced Technologies (CEATEC) 2006 and demonstrated polarized light. The spread of compact and efficient liquid-crystal-display backlights are expected owing to this unique character of the polarized emission. Moreover, ROHM already manufactured green LEDs on a trial basis and confirmed that the wavelength is not changed with an increase in the current injection, and thinks that this shows a possibility of the realization of the green laser diode.