It is said that this is the first time that a 565nm yellow InGaN/GaNMQWLED has been successfully fabricated on a silicon substrate, and the LOP of the 505nm LED is much higher than that of the conventional silicon LED device. In addition to improving material quality, researchers at the agency believe that nanorods can also enhance light extraction scattering effects.
On 2-inch silicon, the researchers used metal organic vapor phase deposition (MOCVD) to create the initial template, which was nucleated by aluminum nitride (AlN) and 8 pairs of aluminum nitride/gallium nitride (AlN/GaN). The layers are composed to create a superlattice (SL) (used as a stress-balanced interlayer) and a 2Î¼m GaN buffer layer.
The researchers first precipitated the SiO2 layer and the indium tin oxide (ITO) layer, etched the ITO with a hydrogen chloride (HCL) acid solution, and finally formed a silicon dioxide (SiO2) nanorod using plasma etching. The nanorods have a density of 2x109/cm2 and a surface coverage of 35%. As a GaN regrown mask, they reduce the dislocation density and improve the crystal quality.
Subsequently, an LED structure was generated by MOCVD technology, and 800 nm of GaN was regenerated around nanorods, AlN/GaNSL interlayer, 2 Î¼m N-type GaN, 5-cycle multiple quantum well (MQW), and 200 nm p-GaN. The regenerated GaN dislocation density is 8x108/cm2, which is called "the lowest silicon substrate GaN dislocation density".
The researchers then prepared materials suitable for emitting yellow (565 nm) and green (505 and 530 nm) light to make 300 Î¼m x 300 Î¼m LED chips. As expected, as the wavelength increases, the light output power (LOP) gradually decreases. At 20 mA, the output power at 505 nm is 1.18 mW, and the output power at 530 nm and 565 nm is 0.30 mW and 74 Î¼W, respectively. For 505 nm, 530 nm, and 565 nm devices, the optical output power is saturated at 7.60 mW (200 mA), 2.72 mW (180 mA), and 0.52 mW (160 mA), respectively.
In theory, the use of silicon as a substrate can reduce material costs and achieve economies of scale in mass production of large wafer diameter products, but compared to traditional, more expensive stand-alone GaN, sapphire or silicon carbide (SiC) substrates. Nitrogen semiconductors on silicon substrates can cause larger lattice mismatches.
Researchers say that producing larger wavelength nitrogen semiconductor LEDs is challenging because it is difficult to produce indium gallium nitride (InGaN) products of superior quality and higher indium concentrations. Although the silicon substrate process in the field of semiconductor transistors is very mature, similar growth methods have recently been applied to LED device materials.
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