Low dislocation density benefits laser diode developments and ultra bright LEDs
Chinese company Suzhou Nanowin is announcing the mass production of high quality 2inch GaN substrates with a dislocation density lower than 1 x105 cm-2, making them suitable for blue and green laser diode production and also ultra high brightness LEDs.
According to Nanowin, the new GaN substrates offer several advantages for making blue InGaN laser diodes. These include improved lifetimes and better yields. Smooth facets, for example, can be obtained by cleaving along the m-plane, which helps to reduce the threshold current density and improve yield. Also vertical laser diode structures can be made by depositing the n-electrode on the N-face of the GaN substrate, which eliminates the current crowding effect that exists in lateral laser diode structures, thus reducing operation voltage.
By using Nanowin’s ultra-high quality GaN substrates, Suzhou Institute of Nano-tech and Nano-bionics has obtained blue laser diodes with a low threshold current, low voltage, and high slope efficiency. At 650mA, light output power was 500mW and voltage 5.8V, which means a wall-plug efficiency of 13 percent.
Green laser diode structures with excellent luminescence homogeneity have also been made using Nanowin’s new GaN substrates. The threshold current at room temperature was 400 mA under pulse operation with 300ns pulse width and 10 kHz repetition frequency. These results have recently been published in Applied Physics Express [Appl. Phys. Express 7, 111001 (2014)].
The company says that the cost of an ultra high brightness LED chip made using GaN-on-GaN techniques with its new substrates is comparable to using GaN on Sapphire ($0.07 versus $0.045), but with far better light efficiency.