Nichia, a Japanese LED manufacturer, uses a GaN substrate for blue lasers to improve the process and structure to produce a continuous-wave green laser diode with a wavelength of 515 nm, breaking the previous electrically excited indium gallium nitride (InGaN) laser. Maintaining the longest wavelength record of 500nm, and is moving toward the goal of a life cycle of hundreds of hours.
Nichia, a leader in GaN series research, does not provide reliability data for 515nm lasers, but they also produce another 510-513nm laser diode that can operate for 500 hours without being electrically charged; more than 500 hours. After that, the laser performance will gradually decrease. Nichia's researchers defined the laser's useful life by increasing the operating current by 30 compared to the initial value. It is estimated that the laser can be used for up to 5,000 hours.
The Nichia team used the diodes of the separate confinement heterostructure (SCH) to generate lasers, almost identical to the designs they published in 2001. The deposition of AlInGaN thin films on a free-stadium dc c-plane GaN substrate through an optimized MOCVD process is the key to producing green light in high indium content materials.
The Nichia team said that they improved the epitaxial layer, especially the multiple quantum well layer (MQW) growth conditions, while also improving the crystal quality of the high indium-rich InGaN active layer, but did not further publish details about the optimization conditions. Nichia has previously published an InGaN laser diode with a wavelength of 488 nm, but the non-radiative region is generated due to poor crystal quality, and a dark region is exhibited under photoluminescence (PL) analysis. Nichia's Takashi Mukai et al. pointed out that these areas have been eliminated in the design of new devices.
At room temperature, the current and current density thresholds of the 515 nm laser diode are 53 mA and 4.4 kA/cm2, respectively. The output power is 5 mW under the conditions of an operating current of 88 mA and a voltage of 5.5 V. The laser diode operating at 510 ° C 513 nm has a maximum wavelength shift of 0.022 nm / K due to temperature changes at room temperature, which is much smaller than the recently launched green laser diodes of Osram and Rohm.
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