22 June 2012

Sumitomo and Sony claim first 100mW true-green 530nm laser diode

Tokyo-based compound semiconductor materials provider Sumitomo Electric Industries Ltd (SEI) and Sony Corp say that, by using a semi-polar gallium nitride (GaN) substrate and improving the production techniques, they have developed what is claimed to be the first semiconductor laser diode with an optical output power exceeding 100mW in the true-green region of the spectrum at a wavelength of 530nm.

The new laser diode features twice the luminosity compared with conventional GaN-based green laser diodes (emitting 60mW or less at a wavelength of 520nm or less), and a color gamut broadened by 182% based on the NTSC standard (CIE 1976 color gamut). As a result, it is reckoned that the laser diodes can significantly improve the performance of laser projectors and other display devices, allowing the reproduction of vibrant video and images.

Picture: True-green laser emission.

Of the primary red-green-blue (RGB) colors, red and blue laser diodes have been commercially available for some time, but there has been great need for high output green laser diodes to enable the development of high-performance laser projectors and display devices. Currently, green lasers are created by converting the wavelength of light from an infrared laser light source by using optical materials. However, such a green laser light source is large and expensive.

In addition, conventional GaN-based green diode lasers have difficulties achieving sufficient luminosity, as luminous efficiency declines in the green spectral region due to the internal field effects resulting from distortion in the crystal structure and the resultant internal polarization. Performance is limited to an output power of several tens of milliwatt at a wavelength of 520nm or less. It is possible to suppress the internal field effects by adopting semi-polar GaN substrates. This enables the sustainable production of homogenous indium-based active layers, allowing the growth of a high-quality light-emitting layer. However, for practical use of the laser, it is necessary to optimize the entire laser production process.

Graphic: Schematic illustration of true-green laser diode and structural device.

Sumitomo Electric and Sony therefore collaborated on developing a true-green semiconductor laser by drawing on Sumitomo Electric’s semi-polar GaN substrate oriented in the {20-21} plane (tilted 75 degrees compared with the conventional GaN crystal c-plane), its crystal growth, and its wafer processing technologies, together with Sony’s GaN-based laser technology (acquired through its Blu-ray development).

By introducing new techniques and improving the entire semiconductor laser production process (including structural design, crystal growth, wafer processing, and electrode configuration), Sumitomo Electric and Sony have hence been able to develop a true green laser with an optical output power of more than 100mW at a wavelength of 530nm. In addition, through optimization of the laser structure, impurity control in the crystal, and the minimization of electrode resistance, the firms have reduced the operating current and voltage. The laser is also highly reliable, with a wall-plug efficiency of more than 8%.

Graphic: Internal polarization.

The development of a true-green laser diode completes the three basic colors for RGB laser light sources. Sumitomo Electric and Sony anticipate a wide variety of applications for the technology, such as incorporation into advanced laser projectors with high luminosity and broad color gamut, as well as compact, light, energy-efficient laser projectors.

The firms say that they will continue to jointly develop true-green laser diodes, aiming to achieve higher output power, efficiency, and laser quality.

Tags: Sumitomo Electric Sony 530nm Green laser diode GaN GaN substrate

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