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Blue-Violet Laser Diode Uses GaN Substrate

Tokyo, Japan: Featuring a wavelength of 405nm, Renesas Electronics Corp.’s first blue-violet semiconductor laser diode integrates a new inner-stripe structure incorporating an optical waveguide into the semiconductor device. The NV4A61MF laser diode is suitable for Blu-ray disc recording and playback.

The optical waveguide substantially influences the quality of the laser diode. It’s fabricated on a gallium-nitride (GaN) substrate, which Renesas says provides approximately 10X improved accuracy and 20% increased heat dissipation compared to the conventional devices.

Specific device features include optical power output of 350mW, which suits 8X Blu-ray disc recording at temperatures of up to 85°C. Current and optical output characteristics deliver excellent linearity from the low-output range through the high-temperature, high-output range. Also, laser noise (output fluctuation) that occurs during playback is reduced to less than one-third of the company’s existing devices—a 5-dB/Hz improvement.

Most existing blue-violet semiconductor laser diodes adopt a ridge-waveguide structure. For this configuration, a dry etching process is used on the semiconductor surface to fabricate an optical waveguide, a path that guides laser light, and current confinement to the light emitting layer in a ridge formation. In a laser device, the thickness of the cladding layer formed immediately above the light-emission layer directly determines the device performance. However, the conventional dry etching process makes it difficult to control the cladding-layer thickness due to lack of suitable material for etching stopper, which sometimes resulted in inconsistent laser performance.

Renesas’ new inner-stripe structure reduces performance inconsistency while providing good power output and low noise. The epitaxial growth technology, which can control the layer thickness at 1-nm level (same as that of an atomic layer), improves accuracy of the cladding-layer fabrication by 10X compared to the conventional dry etching process. In addition, to efficiently concentrate current in the light-emitting layer, the new laser adopts aluminum nitride (AlN) as the material to form the current blocking layer directly above the cladding layer.

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